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Solar Power and Chemical Systems Implementing Agreement of the International Energy Agency

Solar from Concentrated Sunlight 2 Solar Fuels from Concentrated Sunlight Solar Fuels from Concentrated Sunlight 3

Contents

4 Executive Summary

6 Intermittent – Need for Storage 6 Why solar fuels? 8 Why solar ? 9 Solar fuels production

10 In Focus – Solar Concentrating Technologies 10 Solar tower facilities 12 Concentrating solar research facilities

Photos 16 Solar Hydrogen – Future 1 CESA 1 Solar Tower, CIEMAT- PSA, Almería, (DLR) 16 Solar production of hydrogen 2 CESA 1 Solar Tower, CIEMAT- 18 H2 from H2O by solar thermolysis PSA, Almería, Spain (DLR/Steur) 7 Blue Sky (PSI) 18 H2 from H2O by solar thermochemical cycles 11 SSPS Solar Tower, CIEMAT-PSA, 21 H2 by decarbonization of fossil fuels Almería, Spain (DLR) 17 SEDC Solar 23 H2 from H2S by solar thermolysis Center, Rotem, (BrightSource Energy/Eilon Paz) 24 Solar Hydrogen – At Competitive Costs! 25 Solar Two, Barstow, USA (Sandia National Laboratories) 26 Boosting Solar Fuels – Need for Worldwide R&D 27 DLR , Cologne, (DLR) 31 WIS Solar Tower, Rehovot, 30 Transition to Solar Fuels – Recommended Strategy

Israel (WIS) 30 R&D strategy for solar H2 production 35 , CIEMAT-PSA, Almería, Spain (DLR/Steur) 33 R&D needs for solar H2 production 36 PS10 & PS20, Sanlúcar La Mayor, Spain (Abengoa Solar) 34 Bright Future for Solar Fuels – Outlook 4 Solar Fuels from Concentrated Sunlight

Executive Summary

Sunlight is by far the most abundant carbon- later stage, the emerging solar technologies neutral energy resource on . However, so- will be based on processes that are completely lar energy is intermittent and does not neces- independent of any resources. sarily match the variations in demand. If it is The main vector for this transformation will be to become a major contributor to our energy the production of hydrogen, a potentially clean supply, some form of storage is necessary. alternative to fossil fuels, especially for use in Conversion of solar energy into chemical fuels transport. Today, however, more than 90% of is an attractive method of solar energy stor- hydrogen is produced by using high tempera- age. Solar fuels, such as hydrogen, can be used ture processes from fossil resources, mainly for upgrading fossil fuels, burned to generate natural gas. If hydrogen is generated from solar heat, further processed into electrical or me- energy, it is a completely clean technology; no chanical by turbines and generators or hazardous wastes or climate changing byprod- internal combustion engines, or used directly ucts are formed and only sunshine and water to generate in fuel cells and batteries are required as inputs to the process. This is the to meet energy demands whenever and wher- vision outlined in the European Commission’s ever required by the customers. The challenge ‘European hydrogen and roadmap’, is to produce large amounts of chemical fuels which runs up to 2050. directly from sunlight in robust, cost-effective ways while minimizing the adverse effects on the environment. Solar fuels production The success of solar thermal power genera- There are basically three routes, alone or in tion – known as ‘concentrating ’ combination, for producing storable and trans- (CSP) – is already moving towards sustainable, portable fuels from solar energy. The electro- large scale fuel production: concentrating so- chemical route uses solar electricity made from photovoltaic or concentrating solar thermal high temperature process heat for driving ef- systems followed by an electrolytic process; lar radiation with re�lecting provides the photochemical/photobiological route makes technical feasibility of various technologies has direct use of solar energy for photo- �icient thermochemical processes. Although the been demonstrated, commercialization of these chemical and photobiological processes; the processes has been hindered by the economics. thermochemical route uses solar heat at high Nevertheless, solar fuels are among the most temperatures followed by an endothermic ther- promising technologies to curb the growing mochemical process. demand for fossil fuels and to mitigate the ef- The thermochemical route offers some intrigu- fects of climate change. To achieve this it is rec- ing thermodynamic advantages with direct eco- ommended that commercial implementation nomic implications. steadily evolves, starting from the current state- of-the-art fossil fuel production technologies. To facilitate the introduction of new solar fuels Concentrating solar technologies production processes, the existing know-how The state-of-the-art CSP technology capable from both the fuel production industry and the of achieving high process temperatures is the

CSP research institutes should be merged. At a ‘solar tower’ con�iguration, where a �ield of Solar Fuels from Concentrated Sunlight 5

(tracking mirrors) focuses the - radiation as the source of high temperature gies must be further developed and proven to rays onto a solar receiver mounted on top of a process heat. be technically feasible and economical. Second- centrally located tower. Such solar concentrat- ly, a worldwide consensus on the most prom- ing systems already operate in large-scale pi- ising future energy carriers – both renewable lot and commercial plants, such as the 11 MWel Economic solar hydrogen electricity and hydrogen – needs to be reached. PS10 plant near Seville in Spain, in operation The economical competitiveness of The arguments in favor of a future hydrogen since 2007 to deliver solar generated electric- production is closely related to two factors: the economy are excellent, and the political com- ity to the grid. They make use of a heat transfer cost of fossil fuels and the necessity to control mitment to move in this direction has been

the world climate by drastically reducing CO2 manifested in many initiatives. What is urgently sodium, or molten salt) that is heated by solar emissions. needed now is a clear decision to start the tran- �luid (typically air, water, synthetic oil, helium, energy and then used in traditional steam or gas Both the US Department of Energy and the Eu- sition from fossil to renewable and turbines. The typical land area required for a 50 ropean Commission have a clear vision of the from gasoline to hydrogen. 2 MWth plant is about 300,000 m . We encourage politicians and policy-makers, Solar thermochemical applications, although gen production costs. The US target for 2017 , with �irm targets for hydro- not as far advanced as solar thermal electricity is 3 $/gge (gasoline gallon equivalent; 1 gge is nies, development banks and private investors energy of�icials and regulators, utility compa- generation, employ similar solar concentrat- about 1 kg H2), and the EU target for 2020 is ing technologies. However, high-temperature 3.50 €/kg H2. lar fuels – primarily hydrogen – by taking con- to �irmly support the massive production of so- thermochemical processes require higher solar The economics of large scale solar hydrogen crete steps to enable future infrastructure and concentration than CSP plants, which has an production has been assessed in numerous market development without delay. studies, which indicate that the solar thermo- We have only a short time window of opportu- eration. chemical production of hydrogen can be com- nity to tackle and solve the critical problems of impact on heliostat �ield layout and plant op- petitive compared with the of water gas emission and climate change. tion technologies, in particular solar hydrogen, using solar-generated electricity. It can even Solar fuels are part of the solution – they have For ef�icient development of solar fuels produc- dedicated concentrating research facilities – become competitive with conventional fossil- the capacity to help satisfy the energy needs of solar furnaces and solar simulators – are em- fuel-based processes at current fuel prices, es- the world without destroying it. ployed. The largest solar furnaces currently pecially if credits for CO2 mitigation and pollu- operating in and Uzbekistan have a ther- tion avoidance are applied. mal power of 1 MW. Further R&D and large-scale demonstrations

are therefore justi�ied. This would have positive Solar hydrogen ment cost reduction for materials and compo- effects on achievable ef�iciencies and invest- Clean will be based on water and energy from renewable sources. Re- installation of commercial solar thermal power nents. An important factor will be the massive placing fossil fuels with will plants, in particular power towers, since helio- shift the balance between electricity and fuels. stats will be one of the most expensive compo- For many applications, electricity will be used nents of a solar thermal hydrogen production instead of fuels, but two major applications will plant. require a massive production of solar hydrogen. Firstly, renewable energy must be stored for balanced use, and secondly, mobility will prob- Recommended strategy ably be based on fuels rather than electricity. The ’s World Energy Technol- way, with the ultimate goal of developing tech- A range of research activities are already under ogy Outlook scenario predicts a hydrogen de- nically and economically viable technologies for mand equivalent to about 1 billion tons of oil solar thermochemical processes that can pro- in 2050. duce solar fuels, particularly hydrogen. Imple- Solar electricity generated by CSP technology, mentation should start immediately to acceler- and followed by electrolysis of water, is a viable ate the transition from today’s fossil-fuel-based technical route for producing hydrogen. It can economy to tomorrow’s solar driven hydrogen be considered as a benchmark for other routes, economy. such as solar-driven water-splitting thermo- chemical cycles that offer the potential of en- has already developed a roadmap, which shows The EU-FP6 project INNOHYP-CA (2004-2006) the pathway to implementing thermochemical gen. The projected costs of hydrogen produced processes for massive hydrogen production. ergy ef�icient large-scale production of hydro- by CSP and electrolysis, assuming solar thermal electricity costs of 0.08 $/kWhel, range from

0.15-0.20 $/kWh, or 6-8 $/kg H2. The future for solar fuels There are also a range of thermochemical Solar energy is free, abundant and inexhaust- ible, but at least two crucial steps are necessary these involve energy consuming (endothermic) for a successful market introduction of solar fu- routes to solar production of hydrogen. All of reactions that make use of concentrated solar els. Firstly, production technolo- 6 Solar Fuels from Concentrated Sunlight

Intermittent Solar Energy – Need for Storage

CSP Sunlight is by far the most abundant carbon- usage of solar energy will be constrained until plants produce neutral energy resource on earth. More energy reliable and low-cost technologies for storing electric power by converting the sun’s from the sun strikes the earth’s surface in one radiative energy into high-temperature heat hour than is consumed annually by all of the fos- scheme must result in using various configurations. solar energy become readily available. A viable sil fuels. However, solar energy is intermittent and does not necessarily match the variable ratio for the production of stored fuels and must a 10–50 fold decrease in the cost-to-ef�iciency daily and seasonable demands for energy. If so- be stable and robust for a 20–30 year period. lar energy is to become a major contributor to our , some form of is necessary for use during times when there is Why solar fuels? little or no sunlight. The growth in worldwide Conversion of solar energy into chemical fuels is an attractive method of solar energy storage

used for upgrading fossil fuels, burned to gen- (�igure 1). Solar fuels, such as hydrogen, can be How it works – solar energy storage erate heat, further processed into electrical or mechanical work by turbines and generators or internal combustion engines, or used directly to generate electricity in fuel cells and batteries to meet energy demands whenever and wherever required by the customers. The challenge is to produce large amounts of chemical fuels direct- ly from sunlight in robust, cost-effective ways to deal with growing energy demands while mini- mizing the adverse effects on the economy and environment. Sustainable, large scale fuel production relies on the success of solar thermal power genera- tion (→CSP) 1: concentrating the incident solar

vides high temperature process heat for driving radiation (�igure 2) with re�lecting mirrors pro-

Source: PSI ef�icient thermochemical processes in compact centralized plants. Although the technical feasi- Figure 1: Energy conversion into solar fuels – Concentrated solar radiation is used as the energy source 1 Concentrating Solar Thermal Power – Now! of high-temperature process heat for driving thermochemical reactions towards the production of storable and transportable fuels. Brochure published by Greenpeace, ESTIA, IEA SolarPACES, 2005. Solar Fuels from Concentrated Sunlight 7 8 Solar Fuels from Concentrated Sunlight

GHG Greenhouse gas emissions result in global Solar Potential warming, climate change and connected extreme weather events. CO is the most 2 2 Annual (kWh/m /a) prominent GHG but others like have much higher impact.

Solar thermochemical process Any endothermic chemical process that uses concentrated solar energy as the source of high-temperature process heat.

Solar cavity receiver A well-insulated enclosure – with a small opening to let in concentrated solar energy – approaching a blackbody absorber in its ability to capture solar energy.

Exergy efficiency Efficiency for converting solar energy into <1000 1000 1500 2000 2500 3000 (kWh/m2/a) , given by the ratio of the maximum work that may be extracted from a solar fuel to the solar energy Source: Krieth & Krieger, Principles of Solar Engineering, Mc Graw Hill, 1978 input for producing such a fuel by a solar thermochemical process. Figure 2: Annual solar irradiance on Earth – The square of 1000 x 1000 km2 plotted in the middle of the Atlantic Ocean stands for the land area required for supplying the world’s energy needs with Carnot efficiency concentrated solar energy. Maximum efficiency of a cyclic process for converting heat from a high-temperature thermal reservoir at TH into work and rejecting heat to a low-temperature thermal bility of various technologies has been demon- reservoir at TL, given by ηCarnot = 1-TL/TH. strated in the past, commercialization of these Hydrogen Economy – political initiatives processes had been hindered – predominantly • International Partnership for the Hydrogen due to economical reasons. Economy (IPHE) Nevertheless, solar fuels are among the most • Hydrogen Implementing Agreement of the International Energy Agency (IEA-HIA) promising technologies to curb the growing • Hydrogen program of the US DOE demand for fossil fuels – associated with soar- • European Hydrogen and fuel Cell Platform ing prices for diminishing fossil fuel resources (HFP) – and to mitigate the effects of climate change. • European Hydrogen and Fuel Cell Joint Their rapid implementation will create new Technology Initiative (JTI). markets for developing countries and increase the , due to greater independ- ence in fuel production and a larger number of lization, as manifested in a number of political countries supplying solar fuels. initiatives. One striking vision is outlined in the It is recommended that commercial implemen- tation steadily evolves, starting from the current ure 3), which runs up to 2050.2 European hydrogen and fuel cell roadmap (�ig- state-of-the-art fossil fuel production technolo- 2 is widely accepted as the energy gies. To facilitate the introduction of new solar Although H fuels production processes, the existing know- quirements of a economy, carrier of the future, it must still ful�ill the re- how from both the fuel production industry and i.e. it must be produced from unlimited energy sources, without →GHG emission, at an afford- a later stage, the emerging solar fuel technolo- able price. the CSP research institutes should be merged. At gies will be based on processes that are com- Today, more than 90% of the H2 is produced pletely independent of any fossil fuel resources. from fossil resources, mainly natural gas (NG). Half of the annual production of more than 100 million tons is used for producing fertilizers Why solar hydrogen? Many believe that over the next several decades, The latter application alone will drastically rise and about 45% for petro-chemical processes. there will be a shift away from today’s fossil in the next years because an increasing amount

fuel economy toward a much cleaner hydrogen of H2 future. The enormous problems accompanied is needed for re�ining heavy oils. 2 European Commission, EUR 20719 EN – Hydro- environmental advantages of the Hydrogen with a fossil fuel economy and the signi�icant Economy (see box) are strong drivers toward Europeangen Energy Communities, and Fuel Cells 2003 – A vision – 36 pp., of ourISBN future, 92- clean hydrogen (H2) production, supply and uti- Luxembourg: Of�ice for Of�icial Publications of the

894-5589-6. Solar Fuels from Concentrated Sunlight 9

European hydrogen and fuel cell roadmap – a challenging vision

H2 production Hydrogen- & distribution oriented economy

Direct H2 production from renewables 2050 FC become dominant technology De-carbonized H2 society in transport, in distributed power generation,

Increasing decarbonization of H2 production and in micro-applications Renewables, fossil fuel with sequestration, new nuclear 2040

Widespread H2 pipeline infrastructure H2 prime fuel choice for FC vehicles 2030

Significant H2 production from renewables Public rewardcommercialization and private benefits Hydrogen and Fuel Cell large-scaleFC vehicles competitive for passenger cars H2 produced from fossil fuels with C sequestration 2020 Increasing market penetration Atmospheric and hybrid SOFC systems commercial (< 10 MW) H2 production by reforming and electrolysis at local refueling station 2010 FC vehicles series production for fleets H2 produced by Stationary low-temperature FC systems NG reforming (PEM; < 300 kW) 2000 2) and Fuel Cell (FC) fundamental and electrolysis Public incentive and private effort Stationary high-temperature FC systems (MCFC/SOFC; < 500 kW) Hydrogenand applied(HRTD, field research; test, nichedemonstration fleets

Fossil fuel-based FC & H2 systems economy development & deployment

Source: Adapted from European Commission2

Figure 3: From fossil fuel-based to hydrogen-oriented economy – Today, H2 is produced by reforming of natural gas and electrolysis. In 2020, a significant amount of H2 will be produced from renewables, and increasing decarbonization of H2 production is expected for 2040. In a decarbonized H2 society around 2050, H2 will be directly produced from renewables.

Figure 4: Exergy efficiency high temperature processes, which are able How it works – exergy efficiency – Variation of the ideal These demands can potentially be ful�illed by exergy efficiency as a to provide large amounts of H2 in centralized function of the process plants. Many think that H2 produced using solar E xergy Efficiency operating temperature energy will provide the long-term solution for 100% 1 Carnot for a blackbody cavity- solar energy storage. In fact, if H2 is generated 0.9 receiver converting Toptimum from solar energy, it is a completely clean tech- concentrated solar en- 0.8 nology; no hazardous wastes or climate chang- ergy into chemical energy. 40000 ing byproducts are formed and only sunshine 0.7 The mean solar flux concentration is the and water are required. 0.6 20000 parameter (given in units 50% 0.5 of 1 sun = 1 kW/m2): 1000; around the world, because solar H2 seems to 10000 5000; …; 40,000 . Also A lot of research is currently being undertaken 0.4 have the highest technical and economical po- 5000 plotted are the →Carnot 0.3 efficiency and the locus tential for successful market introduction. How- 1000 of the optimum cavity ever, since other technologies for energy storage 0.2 temperature Toptimum. are available – such as (CO2) or 0.1 metal – the pros and cons of all of those 0% 0 alternatives should be carefully evaluated. 0 500 1000 1500 2000 2500 3000 3500 4000 Temperature [K]

Solar fuels production Source: Fletcher & Moen, Hydrogen and from Water, Science, 1977 The conversion of solar energy into solar fuels opens up numerous possibilities. There are ba- sically three routes that can be used alone or in The thermochemical route offers some intrigu- combination for producing storable and trans- ing thermodynamic advantages with direct eco- (�igure 4). The thermochemical route offers the portable fuels from solar energy: nomic implications. Irrespective of the type of ing 50%, higher than those obtained by all alter- potential of reaching exergy ef�iciencies exceed- Electrochemical: solar electricity made from fuel produced, higher reaction temperatures photovoltaic or concentrating solar thermal the lower the required power (solar collection • native routes. The higher the exergy ef�iciency, systems followed by an electrolytic process; However, higher temperatures also lead to area) for producing a given amount of solar fuel yield higher energy conversion ef�iciencies. Photochemical/Photobiological: direct use greater losses by re-radiation from the →solar and, consequently, lower costs for the solar con- of solar photon energy for photochemical and cavity-receiver. centrating system, which usually correspond to • photobiological processes; half of the total investments of the entire solar Thermochemical: solar heat at high temper- Exergy ef�iciency – The measure of how well atures followed by an endothermic →ther- solar energy is converted into chemical energy imply favorable economic competitiveness. • chemical plant. Thus, high exergy ef�iciencies mochemical process. stored in solar fuels is called →

exergy ef�iciency 10 Solar Fuels from Concentrated Sunlight

In Focus – Solar Concentrating Technologies

Solar concentration ratio Solar tower facilities Non-dimensional ratio of the solar flux The state-of-the-art solar concentrating tech- ferred to as central receiver systems – may have tower. Solar tower systems (�igure 5) – also re- intensity – e.g., given in “suns” nology for large-scale solar energy collection at (1 sun = 1 kW/m2) – achieved after high →solar concentration ratio is based on the tered receiver on top of the tower, as in the case concentration to the normal insolation either a circular �ield of heliostats with a can- of incident beam. of (a) the Solar Two power plant at Barstow,

solar tower optical con�iguration using a �ield mirrors) that focus the sun rays onto a solar ing test facilites at (b) the Plataforma Solar de of heliostats (two-axis tracking parabolic or �lat USA, or an asymmetric �ield, like the south fac- receiver mounted on top of a centrally located

Almería (PSA), Spain, and (c) Targassonne, Solar tower facilities – state of the art

(a) 60 MWth solar tower, Barstow, USA (Solar Two) (b) 7 MWth solar tower, PSA, Almería, Spain (CESA 1) (c) 4.5 MWth solar tower, Targassonne, France (THEMIS)

Figure 5: Solar towers – Examples of concentrating solar research facilities based on the tower concept.

(d) 500 kWth solar tower, CSIRO, Newcastle, (e) 3 MWth solar tower with “beam down” optics, WIS, Australia Rehovot, Israel Solar Fuels from Concentrated Sunlight 11 12 Solar Fuels from Concentrated Sunlight

CPC France, or (d) CSIRO’s north facing test facility Compound Parabolic Concentrator, First commercial solar tower a secondary optical element intended to ration – called “beam-down” – developed at (e) power plants augment the concentration of incoming in Newcastle, Australia. A novel optical con�igu- solar radiation, e.g. on top of a solar tower WIS in Israel for the tower system makes use of a facility. re-direct sunlight to a secondary concentrator hyperboloidal re�lector at the top of the tower to Solar furnace and a receiver-reactor located at ground level. Two main configurations are used: (a) On-axis: heliostat, parabolic concen- Secondary concentrators trator, and experimental platform are positioned in one line. centration ratio typically obtained by solar tower – The solar �lux con- (b) Off-axis: facetted mirrors with varying systems is between 1000–1500 suns (1 sun = focal lengths reflect the solar radiation 1 kW/m2). In principle, such concentrating so- to the side, where the solar receiver- lar devices can reach temperatures exceeding reactor is mounted in the focal plane. 1700°C, with optimal cavity temperatures of Source: Abengoa Solar HFSS Figure 7: Commercial electricity production using so- High-Flux Solar Simulators (HFSS) in lar tower concept – The 11 MW PS10 plant (back) operation: around 1000°C (�igure 4). To some extent, the el is in operation since 2007, and the 20 MWel PS20 (a) 150 kWel HFSS consisting of 10 Xenon �lux concentration can be further augmented 6), such as a compound parabolic concentrator plant (front) is in operation since 2009, both at arc lamps with common focus at with the help of a secondary concentrator (�igure Sanlúcar La Mayor near Seville, Spain. Paul Scherrer Institute (PSI), Villigen, (→CPC), which is positioned in tandem with the . primary parabolic concentrating system. Higher

(b) 60 kWel HFSS using 10 IR radiators tics is that their smaller acceptance angle – which at German Aerospace Center (DLR), heat losses from smaller aperture areas and high- �lux concentrations have the advantage of lower Cologne, Germany. er attainable temperatures in the cavity receiver. – results in optimum temperatures closer to requires a longer and less ef�icient heliostat �ield The disadvantage of such solar concentrating op- erating a solar tower system on an annual basis. 1000°C rather than to 2000°C for ef�iciently op- The solar concentrating systems have proven to Secondary concentrator (CPC) be technically feasible in large-scale pilot and commercial plants aimed at producing elec-

tricity (�igure 7). They make use of a working sodium, or molten salt) that is heated by solar �luid (typically air, water, synthetic oil, helium, energy and then used in traditional steam or gas turbines. The typical land area required for a 50 2 MWth solar tower plant is about 300,000 m ,

tive mirror area). with a land use factor of 0.25 (fraction of re�lec- Solar thermochemical applications, although

a Source: DLR not as far advanced as solar thermal electricity generation, employ the same solar concentrat-

layout may look different since high-temper- ing technologies. However, the heliostat �ield ature thermochemical processes require a higher performance in solar concentration than solar thermal power plants. This also has an im- pact on investment costs for the concentrating solar facilities and their operational strategies.

Concentrating solar research facilities

All over the world, research groups are develop- large scale production of solar fuels, in particu- ing the scienti�ic and engineering know-how for lar solar hydrogen. For these state-of-the-art R&D efforts, dedicated concentrating research facilities – solar furnaces and solar simulators – b Source: WIS

Figure 6: CPC – a) Multiple CPC mounted in front are employed (�igure 8). Solar furnace – Solar furnaces receive the solar of a solar receiver on the CESA 1 solar tower at PSA, Spain; b) CPC for “beam down” application radiation by one or more heliostats like solar at WIS, Israel. towers. But instead of a tower with a central re- Solar Fuels from Concentrated Sunlight 13

Solar research infrastructure worldwide – state of the art

50 kWth HFSS at PSI, Villigen (CH) 20 kWth HFSS at DLR, Cologne (D)

25 kWth off-axis solar furnace at DLR, Cologne (D)

40 kWth on-axis solar furnace at PSI, Villigen (CH)

1 MWth solar furnace at CNRS-PROMES, Odeillo (F)

40 kWth on-axis solar furnace at KIER, Daejeon (KOR)

60 kWth on-axis solar furnace at Plataforma Solar de Almería (E)

25 kWth off-axis solar furnace 500 kW solar tower at NREL, Golden, CO (USA) th at CSIRO, Newcastle (AUS)

3 MWth solar tower with “beam down” optics at WIS, Rehovot (IL) 16 kWth on-axis solar furnace at Sandia, Albuquerque, NM (USA)

1 MWth solar furnace at Parkent (Uzbekistan)

Figure 8: Concentrating solar research facilities – High-flux solar furnaces (HFSF) and simulators (HFSS), and solar towers. 14 Solar Fuels from Concentrated Sunlight

ceiver, a parabolic mirror is used as a secondary ‘off-axis’ concept has the advantage of easier optical component to concentrate the sunlight operation but is more complex and, therefore, up to 20,000 times. The parabolic mirror may more expensive. be facetted because single mirrors are restrict- ed in their size. The largest solar furnaces in Solar simulator – In contrast to solar furnaces, Odeillo, France, and Parkent, Uzbekistan, have a which depend on varying weather conditions thermal power of 1 MW and a size equivalent to and deal with problems of intermittent so- a 12-story building. The standard geometrical lar irradiation and a moving radiation source, →solar furnace consists of →HFSS) offer more a heliostat, parabolic concentrator, and experi- stable and reproducible operating conditions con�iguration of a high-�lux solar simulators ( mental platform in one line and, therefore, is tions can be performed easily without the prob- (�igure 10). Experiments requiring long dura- is mounted on a platform and then raised up called ‘on-axis’ (�igure 9). Usually, the reactor to the focus of the parabolic mirror, thereby, velopment of solar fuel production processes, lem of daytime-only operation. For ef�icient de- shadowing part of the concentrator. To avoid however, both concentrating research facilities shadowing of the concentrator, facetted mirrors are extremely important and, because of their different characteristics, neither one can be the solar radiation to the side. This so-called substituted for the other. with varying focal lengths can be used to re�lect

How it works – solar furnace

Source: PSI

Figure 9: Solar furnace – PSI’s High-Flux Solar Furnace (HFSF) consists of a 120 m² sun-tracking fl at heliostat on-axis with an 8.5 m-diameter paraboloidal con- centrator. It delivers up to 40 kW at peak concentration ratios exceeding 5000 suns. The solar fl ux intensity can be further augmented to up to 10,000 suns by using CPC secondary concentrators. A Venetian blind type shutter located between the heliostat and the concentrator controls the power input to the reactor. Solar Fuels from Concentrated Sunlight 15

How it works – solar simulator

lamp array

Lambertian target

Radiation flux measurement Radiation flux measurement

(4) data processing (3) CCD camera, (4) data processing (3)optical CCD filter camera, optical filter image chemical reactor reflector array acquisitionimage acquisition in focus IO

IO (5) intensity (5)distribution intensity distribution experimental platform

(2) Lambertian target (1) concentrated (2) Lambertian target (1) concentrated(sun-) Source: PSI (sun-) light

Figure 10: Solar simulator – PSI’s High-Flux Solar Simulator (HFSS) comprises an array of ten 15 kWel high-pressure Xenon arcs, each closed-coupled with truncated ellipsoidal specular refl ectors of common focus. Each Xe-arc can be switched on and off individually, allowing for adjustment of the radiative power input into the chemical reactor. The radiation fl ux distribution in the focal plane is measured optically by recording the image on a Lambertian target, acquired by a fast CCD camera equipped with optical fi lters. This facility is able to deliver a total radiative power of 50 kW with a peak radiative fl ux exceed- ing 10,000 suns. The total radiative power intercepted by a 6-cm diameter circular target – representing the reactor’s aperture – is 20 kW, and the average radiative power fl ux over this aperture is more than 7,000 suns. Such high radiation fl uxes correspond to stagnation blackbody temperatures exceeding 3300 K. Further coupling with a tandem 3D-CPC may augment the power fl ux concentration by approximately 90%. Thus, PSI’s HFSS features the world’s highest performance level of combined radiative power and power fl ux. 16 Solar Fuels from Concentrated Sunlight

Solar Hydrogen – Future Energy Carrier

Electrolysis of water Hydrogen is envisioned as a future energy carri- Decomposition of water (H2O) into oxygen er. The production routes require chemical and Hydrogen – future energy carrier (O2) and hydrogen gas (H2) due to an energy sources that are truly sustainable only electric current being passed through the 5000 if they offer closed material cycles that do not Coal, Lignite water. 4500 Oil produce CO2. Clean H2 production from water 4000 Gas Electricity 3500 Electrolyzer (H2O) and energy from renewable sources will Hydrogen 3000 An apparatus to separate chemically become the paradigm of the hydrogen economy 2500 bonded elements and compounds by concept. Replacing fossil fuels with renewable 2000 passing an electric current through them. energy will shift the balance between electricity 1500 1000 LHV and fuels. For many applications, electricity will 500

The lower heating value of a fuel is be used instead of fuels, but two major applica- Oil Equivalent (mtoe) Million Tons 0 1990 2001 2010 2020 2030 2050 defined as the amount of heat released by tions will require a massive production of solar combusting a specified quantity (initially Source: WETO-H , 2006 H2. Firstly, renewable energy must be stored for 2 at 25°C) and returning the temperature of the combustion products to 150°C, which balanced use, and, secondly, mobility will prob- Figure 11: Global energy carrier demand – The WETO assumes the latent heat of vaporization ably be based on fuels rather than electricity. (World Outlook) study1 by of water in the reaction products is not Therefore even in rather conservative studies, the European Union is a projection of the world recovered. the drastic increase in demand for electricity in 2050 with emphasis on the will be coupled with a rising demand for H2. hydrogen economy. After 2030, the increasing This development is starting slowly now, but demand for electricity will be coupled with a rising demand for H2. various scenarios indicate that H2 will become

more important after 2030. The WETO-H2 sce- 1 nario predicts a H2 demand equivalent to about and 20%, respectively, and →electrolyzers at

1 billion tons of oil in 2050 (�igure 11). 80% ef�iciency, the overall solar-to-hydrogen 12% and 16%. Projected costs of H2, assuming energy conversion ef�iciency ranges between Solar production of hydrogen solar thermal electricity costs of 0.08 $/kWhel,

Solar electricity – generated via range from 0.15–0.20 $/kWh (→LHV of H2),

(PV) or concentrating thermal power (CSP) i.e. from 6–8 $/kg H2. For PV electricity, costs – followed by →electrolysis of water, is a vi- are expected to be twice as high. The electric-

able technical route for producing H2. Today, it can be considered as a benchmark for other reduced if the electrolysis of water proceeds at ity demand for electrolysis can be signi�icantly routes such as solar-driven water-splitting thermochemical cycles that offer the potential 1 World Energy Technology Outlook – 2050,

the European Communities, 2006, H2 Luxembourg: Of�ice for Of�icial Publications of of energy ef�icient large-scale production of ISBN 92-79-01636-9, online: http://ec.europa.eu/ research/energy/pdf/weto-h2_en.pdf (�igure 12). With solar electricity from PV and solar thermal at ef�iciencies of around 15% Solar Fuels from Concentrated Sunlight 17 18 Solar Fuels from Concentrated Sunlight

SOEC A Solid Electrolyzer Cell is able to How it works – thermochemical routes for the production of split water at high temperatures up to 900°C with a higher efficiency than solar fuels (H2, syngas) conventional steam (alkaline) electrolysis near room temperature. This technology H2O-splitting Decarbonization currently under development is one Concentrated Solar Energy promising candidate for efficient high temperature hydrogen production. H2O Fossil Fuels (NG, oil, coal) Effusion Flow of gas through an orifice whose diameter is small as compared with the distance between molecules of the gas.

Quench Solar Solar Solar Electricity Solar Solar Solar Rapid cooling – for example used as Thermochemical Thermolysis Cycle + Reforming Cracking Gasification gas separation technique to prevent Electrolysis recombination of product gases.

VHTR The Very High Temperature Reactor is one of six designs under discussion for the next generation of nuclear reactors. Optional CO2/C Recently, a pebble bed nuclear reactor was Sequestration demonstrated at the research center Jülich, Source: PSI Solar Fuels (Hydrogen, Syngas) Germany.

Sulfur-iodine cycle Figure 12: Thermochemical routes for solar hydrogen production – Indicated is the chemical source of H2:

3-step cycle based on the thermal decom- H2O for the solar thermolysis and the solar thermochemical cycles; fossil fuels for the solar cracking, position of sulfuric (H2SO4) at 850°C. and a combination of fossil fuels and H2O for the solar reforming and solar gasification. For the

Mainly developed by General Atomics (GA) solar decarbonization processes, optional CO2/C sequestration is considered. All of those routes and demonstrated as an electrically heated involve energy consuming (endothermic) reactions that make use of concentrated solar radiation as laboratory plant at Japan Atomic Energy the energy source of high-temperature process heat. Agency in 2004.

UT-3 cycle 4-step cycle based on the hydrolysis of cal- higher temperatures (800–1000°C) via Solid atures required by the thermodynamics of the cium and bromide (CaBr and FeBr ) at 2 2 Oxide Electrolyzer Cells (→SOEC). Concentrat- 750°C and 600°C, respectively. University ed solar energy can be applied to provide the mospheric pressure) pose severe material limi- of Tokyo (UT), Japan. process (e.g. 2725°C for 64% dissociation at at- high-temperature process heat. reaction tations and can lead to signi�icant re-radiation Reduction/oxidation reactions describe all chemical reactions in which atoms have from the reactor, thereby lowering the ef�iciency. H2 from H2O by solar thermolysis their oxidation number (oxidation state) H from H O by solar thermochemical cycles changed. The single-step thermal dissociation of H2O to 2 2 H2 and O2 Water-splitting thermochemical cycles by- Aerosol-flow reactor though conceptually simple, its realization is pass the separation problem and further allow is known as water thermolysis. Al- The aerosol flow reactor method is a simple very challenging since it needs a high-temper- operation at moderately high temperatures. and efficient one-step process that can ature heat source above 2200°C for achieving Previous studies performed on thermochemi- directly produce particles within a desirable particle size range with consistent and a reasonable degree of dissociation, and an ef- cal cycles were mostly characterized by using controlled properties. fective technique for separating H2 and O2 to process heat at temperatures below 950°C, which are expected to be available in the future

proposed for separating H2 from the products from very high temperature nuclear reactors avoid an explosive mixture. Among the ideas are →effusion separation and electrolytic sepa- (→VHTR). These cycles required three or more ration. Membranes based on ceramics like zir- steps (two steps in the case of conia and other high-temperature materials the hybrid sulfuric acid cycle incorporating one have been tested above this temperature, but electrolysis step) and are challenging because they usually fail to withstand the severe ther- mal shocks that often occur when working un- cies associated with heat transfer and product of material problems and inherent inef�icien- separation at each step. The leading candidates Rapid →quench by injecting a cold gas, expan- for multi-step thermochemical cycles include der high-�lux solar irradiation. sion in a nozzle, or submerging a solar-irradiat- mainly a three-step → iodine cycle based ed target in liquid water, is simple and workable, on the thermal decomposition of sulfuric acid at 850°C and a four-step →UT-3 cycle based on the hydrolysis of calcium and iron bromide at but the quench introduces a signi�icant drop in gas mixture. Furthermore, the very high temper- 750°C and 600°C, respectively. the exergy ef�iciency and produces an explosive Solar Fuels from Concentrated Sunlight 19

Figure 14: Rotary solar made in the development of optical systems Rotary solar cavity reactor reactor for the thermal In recent years, signi�icant progress has been for large-scale solar concentrators capable of dissociation of oxide rotary water/gas to zinc and oxygen at achieving mean solar concentration ratios that ceramic feeder joint inlets/outlets insulation above 1700°C – The ZnO concept features allow temperatures above 1200°C, which are cavity - a windowed rotating ½ Zn + O 2 exceed 5,000 suns. Such high radiation �luxes receiver cavity-receiver lined chemical cycles using metal oxide →redox reac- with ZnO particles that needed for the more ef�icient two-step thermo- quartz are held by centrifugal window force. With this arrange- tions (�igure 13). ment, ZnO is directly exposed to high-flux How it works – metal oxide cycles solar irradiation and concentrated serves simultaneously solar radiation the functions of radi- Concentrated ant absorber, thermal Solar Energy insulator, and chemical reactant. SOLAR ½ M O O2 x y REACTOR Source: PSI

MxOy = xM + y/2 O2 M

HYDROLYSIS Rotary solar reactor H2 H O REACTOR 2 xM + yH2O = MxOy + yH2

recycle MxOy

Source: PSI

Figure 13: Thermochemical route based on metal oxide redox reactions – The first step of the cycle is the solar thermal release of O2 from the metal oxide (MxOy). This step requires very high temperatures. The second step is the reaction of the metal (M) with H2O to form H2 and the cor- responding MxOy. This step proceeds at lower temperatures and does not require additional heating in some cases. Since H2 and O2 are Source: CNRS-PROMES formed in different steps, the need for high-tem- perature gas separation is thereby eliminated. Figure 15: Lab-scale solar reactor for the reduction of tin oxide (SnO2) at 1500°C – The rotary reactor can This cycle was originally proposed for an iron operate continuously by particle injection and at reduced nitrogen pressure in order to decrease the oxide redox system. decomposition temperature.

Zn/ZnO cycle – One of the most researched seconds and was resistant to thermal shocks. sible application of this cycle is to use the energy metal oxide redox pairs for the two-step cycle is In 2010, the solar chemical reactor concept for carrier Zn directly in Zn-air batteries. This tech- based on zinc (Zn) and zinc oxide (ZnO). Since the thermal dissociation of ZnO will be demon- nology is already commercially available, and the products of the solar high temperature ZnO strated in a 100 kWth pilot plant at a large solar some companies are pursuing a fuel-cell ana- decomposition – gaseous Zn and oxygen (O2) – research facility. logue with ‘mechanically-rechargeable’ Zn-air rapidly recombine, a quenching process is nec- For the H2 production step (Zn + H2O → ZnO batteries for stationary or mobile applications.

+ H2) laboratory studies and preliminary tests cycle is 35% without heat recovery from the with a novel concept of a hydrolyser (hydrolysis SnO/SnO2 cycle – essary. The estimated exergy ef�iciency of this reactor) indicate that the water-splitting reac- oxide cycle is based on tin oxide (redox pair Another promising metal methods for in-situ separation of gaseous Zn SnO/SnO2 quench process. Alternatively, electro-thermal and O2 at high temperatures have been experi- This was experimentally demonstrated using a this redox pair are 30% and 36% respectively. tion works at reasonable rates above 425°C. ). Exergy and energy ef�iciencies of mentally demonstrated in small-scale reactors. so-called →

High-temperature separation further enables mation and hydrolysis of Zn nano-particles. In ments showed that the SnO2 reduction can be aerosol-�low reactor for in-situ for- Atmospheric and reduced pressure experi- recovery of the sensible and latent heats of the principle, the heat liberated by the exothermic reaction could be used to melt Zn and produce performed ef�iciently at 1500°C and the SnO perature solar chemical reactor concept was de- 2 production plant totype was successfully tested for continuous products to enhance the ef�iciency. A high-tem- hydrolysis at 550°C. A 1 kW solar reactor pro- was located next to the solar plant, molten Zn steam. Alternatively, if the H carried out at PSI’s solar furnace, Switzerland, veloped for this process (�igure 14). Solar tests operation at Odeillo, France (�igure 15). with a 10 kW reactor prototype subjected to a could be fed directly to the hydrolyser. On the Mixed iron oxide cycle – Other metal ox- from the quencher unit at 425°C (or higher) other hand, transportation of solid Zn to the site ides such as manganese oxide or cobalt oxide, the low thermal inertia of the reactor system – where H2 as well as mixed oxides redox pairs – mainly peak solar concentration of 4000 suns revealed the surface temperature reached 1700°C in two storage and transportation of H2 based on iron – have also been considered. The is �inally used eliminates the need for . Another pos- 20 Solar Fuels from Concentrated Sunlight

Nano-material Consists of nano-sized particles hav- Monolithic solar reactor ing diameters of less than 1 microm- four-way to mass eter. valve N2 spectrometer steam ducts for feed inlet for feed N (O ) gases Reducing agent 2 2 gases H2 Donates to a chemical com- steam pound, e.g. de-oxidizes a metal.

four-way Syngas valve

Synthesis gas is a mixture of H2 and CO double tube produced by reacting natural gas with for feed gas steam at 850°C and high pressure. The preheating name comes from its role as an important cylindrical sealing SiC housing starting substance for chemical synthesis. quartz windows

Source: DLR coated honeycomb structure Sequestration Term mainly used for permanent storage Figure 16: Monolithic dual chamber solar receiver-reactor for continuous H2 production – The concept of CO2, either in gaseous form in deep features a closed receiver-reactor constructed from ceramic multi-channeled monoliths (left). geological formations, in liquid form in the Cyclic operation of the water-splitting and regeneration steps is established in two reaction ocean, or in solid form in mineral carbon- chambers. Their individual temperature levels are controlled by focusing and defocusing heliostats ates. during thermal tests at PSA, Spain (right).

Fischer-Tropsch A process developed in 1925 by Franz mixed iron oxide cycle was demonstrated at Continuation within the EU’s award-winning Fischer and Hans Tropsch to convert syn- the 10 kWth level within the EU’s R&D project P&D project HYDROSOL 2 (2005-2009) is di- gas into liquid hydrocarbons, e.g. fuels like HYDROSOL (2002–2005). The model for the rected at testing a 100 kWth dual chamber pi- gasoline or diesel.

Watergas shift reaction ure 16) was the catalytic converter used for monolithic solar thermochemical reactor (�ig- lot reactor at the Plataforma Solar de Almería Chemical reaction in which CO reacts with exhaust treatment in automobiles. The reactor (PSA), Spain. water to form CO2 and H2. contains no moving parts and is constructed Carbothermal reduction of metal oxides from ceramic multi-channeled monoliths that – The carbothermal reduction of metal ox- Pressure swing adsorption Technology used to separate some gas absorb the solar radiation. The monolith chan- ides using coke, natural gas (NG), and other species from a mixture of gases under nels are coated with mixed iron oxide →nano- carbonaceous materials as →reducing agents pressure at near-ambient tempera- materials, which are activated by heating to brings about reduction of the oxides at even tures. 2, they are capable lower temperatures. Carbothermal reductions of splitting water vapor passing through the of metal oxides like iron oxide, manganese ox- 1250°C. After releasing the O reactor by trapping the O2 and leaving H2 as ide, and zinc oxide with carbon and natural gas to produce the metals and →syngas have been Thus, no explosive gas mixtures are produced. demonstrated in solar furnaces. Such a solar the product in the ef�luent gas stream at 800°C. Cyclic operation is established on a single, chemical reactor concept – PSI’s ‘two-cavity’

uous H2 irradiation of ZnO and carbon (C) for producing closed receiver-reactor system. A quasi-contin- solar reactor (�igure 17) based on the indirect of two or more reaction chambers. Zn and (CO) – was scaled up �low is produced by alternate operation

Figure 17: Two-cavity solar Two-cavity solar reactor reactor concept for the carbo- thermal reduction of ZnO – 300 kW The upper cavity (absorber) concentrated solar serves as the solar receiver upper cavity power (absorber) and radiant emitter. The quartz lower cavity is a well-insu- window carrier gas lated enclosure containing a inlet ZnO/C packed bed. It serves as the reaction chamber and is subjected to thermal radiation from the upper lower cavity cavity. With this arrange- (reaction chamber) ment, the upper cavity protects the quartz window against particles and con- ZnO/C gaseous densable gases coming from packed- bed products the reaction chamber.

Source: PSI Solar Fuels from Concentrated Sunlight 21

within the EU’s R&D project SOL ZINC (2001– process can be CO2-neutral if charcoal is used forming process developed within the EU’s R&D

2005). Testing of the 300 kWth solar chemical for reducing ZnO. project SOLREF

up to power levels of 300–500 kWth and tested (2004–2009) has been scaled- facility of WIS, in Israel, at temperatures rang- at 850°C and 8–10 bars in a solar tower using reactor (�igure 18) at the solar tower research ing from 1000–1200°C yielded up to 50 kg/h H2 by decarbonization of fossil fuels two solar reforming reactor concepts: indirect- of 95%-purity Zn and an energy conversion Three solar thermochemical processes for H2 irradiation and direct-irradiation (see box). SOLZINC proc- production using fossil fuels as the chemical The indirect-irradiated solar reforming reactor source are considered: cracking, reforming, (not shown here) consists of a cavity receiver ef�iciency of around 30%. The for storing and transporting solar energy. The ess provides an ef�icient thermochemical route route refers to the thermal decomposition of set of vertical tubes externally exposed to the and gasi�ication (�igure 19). The solar cracking insulated with ceramic �ibers that contains a NG, oil, and other hydrocarbon into H2 and car- bon. The carbonaceous solid product can either is installed at the windowless cavity →aperture concentrated solar radiation. A matching CPC be →sequestered (see box) without CO2 release for capturing radiation spillage, augmenting the or used as material commodity or reducing

agent under less severe CO2 restraints. uniform heating of the tubes. Similar to the indi- average solar �lux concentration, and providing Steam-reforming of NG, oil, and other hydrocar- rect-irradiated reactor, a CPC is installed at the aperture of the direct-irradiated solar reactor – solid carbonaceous materials yield syngas, the also referred to as the volumetric solar reactor bons, and steam-gasi�ication of coal and other building block for a wide variety of synthetic fuels including →Fischer-Tropsch type chemi- Source: PSI (�igure 20). cals, H2, , and methanol. The quality

is determined mainly by the ratios between H2, Figure 18: 300 kWth solar chemical pilot plant devel- CO, and CO2. The CO content in the syngas can Volumetric solar reactor oped and tested in the EU’s R&D project SOLZINC – The two-cavity reactor (1.4 m inner diameter) for be shifted to H2 via a catalytic reaction with CPC Window Reactants inlet the carbothermal reduction of ZnO is specifically steam – the so called →watergas shift reaction. designed for beam-down incident radiation, as The product, CO2, can be separated from H2, e.g. obtained at the solar tower research facility at by using the →pressure swing adsorption tech- WIS, Israel. nique.

Solar reforming – Solar reforming of NG, using

How it works – decarbonization either steam or CO2, has been extensively stud- processes ied in solar concentrating facilities with small- Catalytic absorber Products outlet Concentrated scale solar reactor prototypes. The solar re- Source: DLR Solar Energy

Figure 20: Volumetric solar reactor concept for the Fossil Fuels Solar Cracking (NG, oil) Rea ctor reforming of NG – The main component is the How it works – carbon sequestration porous ceramic absorber, coated with Rhodium From the point of view of carbon sequestration, catalyst, which is directly exposed to the H 2 C Sequestration O2 it is easier to separate, handle, transport, and concentrated solar radiation. A concave quartz

store solid carbon than gaseous CO2. Further- window, mounted at the aperture, minimizes Fuel cell Work Output more, while the /gasification reflection losses and permits operation at method requires additional steps for shifting CO elevated pressures.

and for separating CO2, the thermal cracking accomplishes the removal and separation of Concentrated Solar Energy carbon in a single step. Solar reactor – direct vs. indirect irradiation Fossil Fuels In contrast, the major drawback of the thermal (coal, NG, oil) Solar Gas ./Ref. Reactor decomposition method is the energy loss Direct-irradiation reactor – Provides efficient ra- associated with the sequestration of carbon. diation heat transfer to the reaction site where H 2O Thus, the solar cracking may be the preferred the energy is needed, by-passing the limitations CO H 2 O imposed by indirect heat transport via heat H 2 option for NG and other hydrocarbons with high H2/C ratio. For coal and other solid carbona- exchangers. The major drawback when work- ceous materials, the solar gasification has the ing with reducing or inert atmospheres is the Shift CO 2 Reactor Separation H 2 additional benefit of converting a solid fuel requirement for a transparent window, which is traditionally used for combustion to generate a critical and troublesome component in high- electricity into a cleaner fluid fuel – cleaner only pressure and severe gas environments. O2 H 2 CO 2 when using solar process heat – that can be Sequestration Indirect-irradiation reactor – Eliminates the used in highly efficient fuel cells. need for a transparent window. The disadvan- Fuel cell Work Output For the solar NG cracking and the solar coal tages are linked to the limitations imposed by Source: PSI gasification without CO2 sequestration, specific the materials of construction of the reactor

CO2 emissions amount to 0.53-0.56 kg CO2/ walls: constraints in maximum operating tem-

Figure 19: Solar thermochemical routes for H2 pro- kWhel, about half as much as the specific emis- perature, thermal conductivity, radiant absorb- duction using fossil fuels and H2O as the chemical sions discharged by conventional coal-fired ance, inertness, resistance to thermal shocks, source – Solar cracking (top), and solar reforming power plants. and suitability for transient operation. and gasification (bottom). 22 Solar Fuels from Concentrated Sunlight

Aperture Dry reforming of methane (CH ) with CO2 was later time and place, the reaction products of Opening of a solar cavity-receiver for ac- performed in an aerosol solar4 reactor similar H2 and nitrogen (N2) react in an energy releas- cepting incoming solar radiation. ing (exothermic) reaction to re-synthesize am-

Catalyst below). Operating with residence times around to the one used for NG cracking (see �igure 24 2 Catalysis is the process in which the rate 10 milliseconds and temperatures of approxi- monia. An industrial demonstration plant has of a chemical reaction is increased by mately 1700°C, methane and CO2 conversions →parabolic dishes. been announced using four of ANU’s 400 m means of a chemical substance known as of 70% and 65%, respectively, were achieved in a catalyst. the absence of →catalysts. Solar steam gasi�ication –

The solar dry reforming of CH with CO2 can tion of carbonaceous materials and related re- Rankine cycle The steam-gasi�ica- Thermodynamic cycle that converts heat also be used in a closed-loop chemical4 heat pipe actions has been performed using concentrated into work. The heat is supplied externally to solar energy in early exploratory studies with a closed loop, which usually uses water as tion is syngas which can be stored at ambient (�igure 21). The product of this reversible reac- the working fluid. temperatures and transported to sites requir- coal and oil shale. A conceptual design of a solar ing energy. Stored solar energy is released by Parabolic dish reactor for the gasi�ication of carbonaceous ma- A 3-dimensional parabola-shaped reflective the reverse exothermic reaction in the form of rect the solar radiation into the reaction cham- terials was performed using optical �ibers to di- device (e.g. faceted mirror) used to collect heat, which can be used for generating electric- ber. In the framework of the industrial project and focus solar energy. ity via a →Rankine cycle. The products of this SYNPET (2003–2009), the solar chemical tech- reverse reaction are again recycled to the solar →petcoke Petcoke reactor to complete the cycle. particles was developed. For this process, a 10 Petroleum coke (often abbreviated petcoke) nology for the steam-gasi�ication of is a carbonaceous solid by-product Similarly, the dissociation/synthesis of ammo- kWth solar reactor was designed that featured derived from oil refinery coker units or other nia (NH3) can be applied in a chemical heat pipe a continuous gas-particle → cracking processes. for storage and transportation of solar energy. vortex �low con- Vortex flow �ined to a cavity receiver and directly exposed th Motion of a spinning, often turbulent flow of In this system developed by the Australian Na- to concentrated solar radiation. A scale-up of fluid swirling rapidly around a center. ed in an energy storing (endothermic) chemical tional University (ANU), ammonia is dissociat- the vortex solar reactor (�igure 22) to 500 kW progressing within the timeframe of the project. Claus process and testing at the Plataforma Solar de Almería is Chemical process originally developed to reactor as it absorbs solar . At a produce sulfur from H2 sulfide, which Figure 21: Solar chemical is being formed as by-product in the How it works – chemical heat pipe heat pipe for the storage and formation of coke from coal or the desul- transportation of solar energy furization of crude oil. – High-temperature solar process heat is used to drive the endothermic reversible reaction A–B. The product B may be stored and trans- ported to the site where the energy is needed. At that site, the exothermic reverse reaction B–A is effected and yields high temperature proc- ess heat in an amount equal to the stored solar energy. The chemical product A of the

Source: PSI reverse reaction is returned to the solar reactor for reuse.

Figure 22: Vortex solar reactor Vortex solar reactor for the steam-gasification of petcoke – This configura- petcoke + H2O slurry tion features a continuous quartz window ceramic cavity gas-particle vortex flow vortex flow confined to a cavity receiver and directly exposed to concentrated solar radiation. The reactants are injected concentrated as liquid slurry of petcoke solar particles and water. radiation

syngas (H 2 + CO)

H2O nozzle

Source: ETH/PSI/CIEMAT/PDVSA Solar Fuels from Concentrated Sunlight 23

Tubular solar reactor Aerosol solar reactor

particle feed

H2 sweep feed NG

porous C(gr) tube

solid C(gr)

quartz envelope

H2, C, CHx

Source: CNRS-PROMES Source: NREL

Figure 23: Tubular solar reactor for NG cracking – Methane (CH4) and argon (Ar), are indirectly heated Figure 24: Aerosol solar reactor for thermal cracking inside graphite tubes (top). Test campaign with a 10 kWth solar reactor prototype for NG cracking at of NG – This configuration features two con- the focus of the 1 MW solar furnace, Odeillo, France (bottom). centric graphite tubular reactors: the outer solid tube serves as the solar absorber and the inner porous tube contains the reacting flow consist- ing of fine carbon black particles suspended in a Solar cracking – Cracking of CH or NG is a serve simultaneously as radiant absorbers and CH4 feed gas stream. nonconventional route for potentially4 cost-ef- nucleation sites for the heterogeneous decom- fective H2 production and carbon nano-mate- position reaction. rial synthesis with concentrated solar energy. The process thermally decomposes NG in a high temperature solar chemical reactor, yield- H2 from H2S by solar thermolysis ing two valuable products: a H2-rich gas and a 2 marketable high-value nano-material called (H2S), a toxic industrial byproduct derived from An optional source of H is hydrogen sul�ide ‘Carbon Black’ (CB). Thus, both H2 and CB are NG, petroleum, and coal processing. Current produced by renewable energy, resulting in po- industrial practice uses the →Claus process to tential CO2 2 recover sulfur from H2S, but H2 is wasted by and energy saving of 277 MJ per kg H2 com- oxidizing it to H2 2S can be emission reduction of 14 kg of CO pared to conventional NG steam reforming and thermally decomposed above 1500°C to pro- O. Alternatively, H standard CB processing. duce H2 and sulfur (S), which, after quenching,

th naturally separate due to phase change. Solar was successfully tested at a temperature range experiments indicate high degrees of chemical A novel 10 kW tubular solar reactor (�igure 23) conversion. of 1430–1800°C at the solar furnace of CNRS- of 98% was achieved with a 90% H2 PROMES in Odeillo, France. A high dissociation advanced 50 kWth solar reactor prototype is yield. An being developed in the framework of the EU’s R&D project SOLHYCARB

(2006–2010). Also, at NREL in Golden, Colorado, where methane a tubular aerosol reactor (�igure 24) was tested conversion of up to 90% was obtained. Fur- ther studies are being performed at ETH Zurich, Switzerland, in a so-called vortex solar reactor con�iguration (�igure 22), which was tested in a methane �low laden with carbon particles that 24 Solar Fuels from Concentrated Sunlight

Solar Hydrogen – At Competitive Costs!

The economical competitiveness of solar fuel The weaknesses of these economic assessments production is closely related to two factors: the are primarily related to the uncertainties in the 2.3 300m 2.1 cost of fossil fuels and the necessity to control 1.9 1.7 the world climate by drastically reducing CO2 various solar components due to their early 1300m viable ef�iciencies and investment costs of the 1.5 200m emissions. Transition processes like the solar stage of development and their economy of 1.3 1000m 400m steam reforming of NG will be economically scale. Therefore, further development and large- 1.1 0.9 1800m competitive at a NG price of 11 $/MMBtu or scale demonstrations are warranted. This would 0.7 3; for comparison, the NG price for Relative HPC (best case =1) 0.5 0 100 200 300 400 500 600 long-term contracts was 8-9 $/MMBtu, and the and investment cost reduction for materials and Thermal Power [MW] 0.42 $/Nm 1 have positive effects on achievable ef�iciencies components. In this respect, an important factor Source: HYTHEC Both the US Department of Energy and the Eu- will be the massive installation of commercial spot price was 14-16 $/MMBtu (DOE, 2008). ropean Commission have a clear vision of the solar thermal power plants, in particular power Figure 26: Comparison of H2 production costs (HPC) for solar, nuclear, and hybrid powered H production 2 pro- towers, since heliostats will be one of the most 2 plants based on the hybrid sulfuric acid cycle – The expensive components of a solar thermal H2 hydrogen economy with �irm targets for H EU-FP6 project HYTHEC (2004–2007) has evalu- is 3 $/gge (gasoline gallon equivalent; 1 gge is production plant. duction costs: the US target (�igure 25) for 2017 ated 26 scenarios for large-scale H2 production about 1 kg H2), and the EU target for 2020 is based on the hybrid sulfuric acid thermochemi- 3.50 €/kg H2. DOE’s → cal cycle using either solar, nuclear, or hybrid developed the tools necessary to conduct rig- (combined solar and nuclear) sources of high H2A Analysis Group has Massive hydrogen production – orous and consistent analyses of a wide range temperature process heat. Interestingly enough, economics H2 production cost would be lower for solar of H2 technologies and the transition to a H2 thermal plants than for nuclear plants in a power Characteristics Units 2006 2012 2017 economy. Predicted solar thermal hydrogen range up to 250 MWth, whereas hybrid operation Target Target Target would be the cheapest solution at power levels thermochemical cycles. Solar thermo- $/gge 10 6 3 above 300 MWth. These findings are in good production cost are 2–4 $/kg for ef�icient solar chemical H2 cost H2 agreement with conceptual studies presented by The economics of massive solar H2 production General Atomics (GA) in the early 1980s where Installed helio- $/m2 180 140 80 stat capital cost the high temperature step of sulfur-based ther- studies, which indicate that the solar thermo- mochemical cycles was assumed being carried (�igure 26) has been assessed in numerous Process energy % 25 30 >35 chemical production of H2 can be competitive out in a solar reactor. efficiency compared with the electrolysis of H2O using Source: STCH it can even become competitive with conven- Figure 25: Technical and economic targets of the US solar-generated electricity. As described above, tional fossil-fuel-based processes at current DOE hydrogen program – Cost improvements by technical innovations (process energy efficien- fuel prices, especially if credits for CO2 mitiga- tion and pollution avoidance are applied. cy), scaling up the solar chemical plant, and increasing the production volume are expected for the STCH project (Solar-driven high tempe- 1 US DOE, February 2008, rature Thermo Chemical Hydrogen production) http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp endorsed by the IPHE. Solar Fuels from Concentrated Sunlight 25 26 Solar Fuels from Concentrated Sunlight

Boosting Solar Fuels – Need for Worldwide R&D

H2A Most activities on solar fuel production are fund- ogy Initiative (JTI)2 and the hydrogen program of US Department of Energy (DOE) standard ed by national or international research programs the US DOE3 format and list of parameters for reporting like the Framework Programs of the European ally carried out by international consortia from realistic economic and technology-based 1 (�igure 27). The projects are gener- analysis results for central production, Union , the Hydrogen and Fuel Cell Joint Technol- distributed production, and delivery of H . 2 R&D, industry and academia (see �igure 28). 2 JTI: https://www.hfpeurope.org/hfp/jti 1 EU FP7: http://cordis.europa.eu/fp7/ 3 US DOE: www.hydrogen.energy.gov/

Networking – benefits from synergy

European JTI European HFP Hydrogen & Fuel Cell Hydrogen & Fuel Cell Joint Technology Initiative Technology Platform EU-FP6 Projects IEA HCG HYTHEC, INNOHYP-CA Hydrogen Coordination Group EU-FP7 Projects HYCYCLES IEA SHC Solar Heating and Cooling Network US DOE / Japan GEN IV Projects IEA HIA Other Hydrogen US DOE Technology Agreements Hydrogen + Other Nat & Int’l Projects IEA HIA IEA SolarPACES Task 25 Task II High Temperature Solar Chemistry Processes (HTP) Research

Expert Groups Hydrogen Production Processes

IPHE STCH – Solar high temperature Thermo Chemical production of Hydrogen SOLREF – Solar Hydrogen from Reforming of Methane HYTHEC – HYdrogen THErmochemical Cycles

Source: DLR and PSI

Figure 27: Network for solar fuels – Linking pertinent research activities for the production of solar hydrogen and other fuels under the umbrella of international organizations such as IEA or IPHE. Solar Fuels from Concentrated Sunlight 27 28 Solar Fuels from Concentrated Sunlight

International networking – The global rel- evance of solar fuels makes it necessary to Solar projects – endorsement by IPHE link the pertinent research activities under the umbrella of organizations such as the Interna- STCH – Solar Thermo Chemical production of H2 (IEA) and the Interna- • Within this project, the most promising thermochemical cycles for H2 production will tional Partnership for the Hydrogen4 Economy be identified, and one or two cycles will be tional Energy5 Agency (IPHE) . down-selected for demonstration. • Lower cost solar concentrating technology International Energy Agency – The main net- will be developed, as well as solar receiver and thermochemical reactor technology to demonstrate a fully integrated thermochemi- Solar Chemistry Research of the IEA Solar- work for solar fuels (�igure 27) is Task II on cal process on-sun. PACES 6. Task 25 on

High Temperature Hydrogen Production of the SOLREF – Solar H2 from Reforming of Methane Implementing Agreement (IEA- • The project aims at designing, testing, and HIA)7 creates a link between solar, nuclear, and demonstrating a unique, low temperature, IEA Hydrogen Implementing Agreement steam reforming reactor using concentrated conventional H production technologies. 2 solar energy. • A world-class solar facility for international

International Partnership for the Hydrogen collaboration in H2 production from solar Economy – The IPHE was established in 2003 sources will be built to integrate the system. as an international institution to accelerate the HYTHEC – HYdrogen THErmochemical Cycles transition to a global hydrogen economy. This • Within the former EU-FP6 project HYTHEC

key organization is supported by the govern- (2004–2007), the potential for massive H2 ments of the member states. The purpose of the production by the sulfur-iodine (S-I) cycle was IPHE is to provide a mechanism for partners to investigated and compared to the hybrid sul- organize, coordinate and implement effective, furic acid cycle. The work is being continued in the EU-FP7 project HyCycleS (2008–2010). • The emphasis is on the suitability of materials development, demonstration and commercial and the reliability of components of a scalable ef�icient and focused international research, utilization activities related to H2 and fuel cell reactor. Of particular interest is the potential use of solar sources for the thermochemical projects for the massive pro- decomposition of sulfuric acid. technologies. A number of high-quality solar duction of H2 are endorsed by the IPHE (see box).

5 4 IPHE: http://www.iphe.net/ 6 IEA: http://www.iea.org/index.asp org/Tasks/Task2/task_ii.htm 7 IEA-SolarPACES Task II: http://www.solarpaces. php?s=static&p=task25 IEA-HIA Task 25: http://www.ieahia.org/page. Solar Fuels from Concentrated Sunlight 29

Solar fuels production – worldwide activities (national and international research programs)

Topic of R&D Participating Entity Remarks

Solar Decarbonization • CIEMAT (E) + ETH/PSI (CH) Petcoke gasification; + PDVSA (Venezuela) Industrial project SYNPET

• ETH/PSI (CH) Gasification of carbonaceous material

• CNRS-PROMES (F) + ETH/PSI (CH) NG cracking; + TIMCAL (B) + ABENGOA (E) EU-FP6 project SOLHYCARB + N-GHY (F) + CREED (F) + APTL (GR) + WIS (IL) + DLR (D) • Florida Solar Energy Center (USA) • CIEMAT (E)

• DLR (D) + WIS (IL) + ETH (CH) NG reforming; • CSIRO (Australia) EU-FP6 project SOLREF • Tokyo Institute/Niigata U. (Japan)

Solar Thermochemical Cycles • APTL (GR) + DLR (D) Fe-based cycle; + Johnson Matthey (UK) EU-FP5 project HYDROSOL, + StobbeTech (DK) + CIEMAT (E) EU-FP6 project HYDROSOL 2

• PSI/ETH (CH) + U. of Minnesota (USA) ZnO/Zn cycle

• PSI/ETH (CH) + WIS (IL) ZnO+C reaction; + CNRS-PROMES (F) + ScanArc (S) EU-FP5 project SOLZINC

• CNRS-PROMES (F) SnO2/SnO cycle and comparison with ZnO/Zn cycle; Ce-based mixed oxide cycles; Fe-based cycles

• Sandia + NREL + U. of Colorado ZnO cycle; Fe-based cycle; SI cycle; + Pinnacle West (USA) DOE project

• Tokyo Institute / Niigata U. (Japan) Fe-based cycle

• ENEA (I) UT3-cycle

• CEA (F) + DLR (D) + ProSim (F) SI cycle; hybrid sulfuric acid cycle; + U. of Sheffield (UK) + DIMI (I) EU-FP6 project HYTHEC + Empresarios Agrupados (E)

• DLR (D) + CEA (France) + ETH (CH) SI cycle, materials, components; + U. of Sheffield (UK) + BoosTec (F) EU-FP7 project HyCycleS + Empresarios Agrupados (E) + APTL (GR) + JRC (EU) + ENEA (I) + General Atomics (USA) + Westinghouse (USA) + JAEA (Japan) + CSIRO (Australia)

Figure 28: Solar fuels production – Overview on research institutes active in national and international research programs for producing solar hydrogen and other fuels. 30 Solar Fuels from Concentrated Sunlight

Transition to Solar Fuels – Recommended Strategy

The ultimate goal of all research activities de- scribed above is to develop technically and development. Some of the proposed processes were thought to bene�it from synergies in their economically viable technologies for solar can be operated by both energy sources sepa- thermochemical processes that can produce so- rately or in hybrid installations. However, the

lar fuels, particularly H2. The implementation nuclear option is impeded in many countries should start immediately to accelerate the tran- due to political opposition, and the processes sition from today’s fossil-fuel-based economy driven by future VHTR are limited to 950°C. In to tomorrow’s solar driven hydrogen economy particular, the processes with highest exergy ef-

solar systems. (�igure 29). �iciency can only be attained by concentrating

R&D strategy for solar H2 production Processes and timeframe – Since the various The EU-FP6 project INNOHYP-CA ( solar fuel production technologies under con- has developed a roadmap to implement thermo- sideration are at diverse stages of maturity, the 2004–2006) chemical processes for massive H2 production INNOHYP-CA project proposes three phases and a staggered timeframe for their individual both solar and nuclear sources of process heat development and commercial demonstration. (�igure 30). Within this project, processes with

Figure 29: Strategy for substitu- How it works – transition to solar fuels tion of fossil fuels with solar H2 involving research on two paths

– The long-term approach

via H2O-splitting thermo- chemical cycles brings us to the complete substitution of Fossil & Solar Energy Mix fossil fuels with solar H2. The short-to-mid term approach via decarbonization of fossil Solar Decarbonization of Fossil Fuels fuels creates a link between PRESENT TRANSITION FUTURE today’s fossil-fuel-based technology and tomorrow’s Fossil Fuels Solar Fuels solar chemical technology. (Oil, Coal, Natural Gas) (Hydrogen)

H2O-Splitting Thermochemical Cycles

Source: PSI Solar Fuels from Concentrated Sunlight 31 32 Solar Fuels from Concentrated Sunlight

First phase Second phase – The second phase lasts un- and is devoted to the pilot demonstration of til 2020 and investigates the most promising – The �irst phase lasts until 2015 transition processes like solar steam reforming nominally CO2-free thermochemical processes of NG (SOLREF) such as the iodine sulfur (IS) cycle, the hybrid (SYNPET), or solar carbothermal reduction of sulfuric acid cycle (WH), the mixed iron oxide , solar gasi�ication of petcoke ZnO (SOLZINC). The further development of cycle (Ferrites), as well as the high temperature

the zero CO2 emission technologies will need steam electrolysis (HTSE) and will be demon- strated at pilot scale. Their chances for success- work should be dedicated to studying alterna- ful commercialization will then be assessed. more time for market introduction. Additional tive processes, which in the long term offer a high potential but also a high risk of failure.

Figure 30: INNOHYP-CA road- INNOHYP-CA – roadmap for thermochemical hydrogen production map – An important aspect is the continuous evalua- tion and benchmarking of 2004 2007 2010 2013 2016 2019 2022 the processes (marked by SSMR – Solar Steam Methane Reforming triangles) to avoid time con- suming dead ends. Since the Transition processes Processes Solzinc – Carbothermic ZnO Decomposition Transition solar process prototype pilot plant -– 2015 2015 various solar fuel production SynPet – Solar Steam Gasification of Petcoke with lower CO2 emissions technologies under consid- eration are at diverse stages IS – Iodine Sulfur Cycle Nuclear & solar IS pilot plants of maturity, three phases and Nominal WH – Westinghouse Cycle () Nuclear & solar WH pilot plants a staggered timeframe are FreeCO2- COFree2 processes Processes proposed for their individual FeO/Fe2O3 – Ferrite Cycle Solar FeO/Fe2O3 pilot plants development. pilot plant - – 2020 2020 HTSE – High Temperature Steam Electrolysis Nuclear & solar HTSE pilot plants

Zn/ZnO – Zinc Oxide Cycle Alternative Alternative CuCl – Copper Chloride Cycle Free CO processes CO - Free2 Processes 2 CeCl – Cerium Chloride Cycle Hypothetic pilot plant - hypothetic CeO – Cerium Oxide Cycle 2025 pilot plant – 2025 Others

Figure 31: INNOHYP-CA R&D INNOHYP-CA – roadmap for R&D infrastructure for massive hydrogen production roadmap – Cross-cutting actions are proposed to develop high-temperature 2004 2007 2010 2013 2016 2019 2022 materials and infrastructure Catalysts – Performances & technologies components. The foundation of a worldwide alliance of re- Ceramics for electrolyzer cells – HTSE & hybrid search facilities is envisaged

GenericGeneric Materials Low cost metallic materials & coatings / corrosion to exploit synergies and to SupportSupport provide access to experi- SiC family – Corrosion & mechanical behavior mental platforms. The reali- zation of these far-reaching SiC family – Shaping & assembling technologies initiatives can be fostered by IEA’s SolarPACES, while or- Heat exchangers (including heat source coupling) ganizations like the IPHE or the European JTI also work Chemical components technologies Generic Components in this direction. Support Membranes

Electrolyzer technologies (hybrid cycles)

1-10 MW HT solar facilities dedicated to H2 production 1-10 MW Scale Test 1-10 MW European HT experimental Facilities facilities infrastructure 1-10 MW simulated nuclear facilities development Dedicated EU projects Open shared Experimental & qualification exploitation European Platform Solar Fuels from Concentrated Sunlight 33

R&D needs for solar H2 production Materials and process R&D – In parallel, a development of the high tempera- ate materials for the proposed chemical reac- (�igure 32) that combines R&D of appropri- tool box ture technologies for massive H2 production, tor components with adequate manufacturing the INNOHYP-CA project, proposes a roadmap processes, e.g. shaping, brazing and welding. Manufacturing for further improving the existing R&D infra- It is imperative to know the limitations of ma- Processes terials and manufacturing technologies before designing and constructing industrial solar Components Materials structure, mainly for the ef�icient use of concen- Tool Box R&D also addresses material and component devel- trating solar facilities (�igure 31). The roadmap size of a single chemical reactor may be limited chemical plants (�igure 33). For example, the ning thermochemical processes for the produc- to less than 50 MWth solar power input, mean- Process Solar Hydrogen opments required for safely and ef�iciently run- R&D Production Plants tion of solar fuels, in particular solar H2. ing that a cyclic process coupled to a 500 MWth Future national and international research pro- solar tower plant would be realized in at least grams will need to focus on further evaluating ten modular units. Source: INNOHYP-CA and improving the proposed thermochemical processes, since adequate technical data and search and test infrastructure for large-scale A vital factor is the availability of adequate re- Figure 32: Integration of components tool box information on production cost and GHG emis- solar testing of thermochemical cycles. It is and process R&D – The components tool box sion are still missing. In addition, important indispensable to build such demonstration combines materials and components develop- ments required for safely and efficiently running cross-cutting actions are required to develop plants in an international context by pooling thermochemical processes for massive H2 high-temperature materials and infrastructure R&D budgets to achieve a maximum impact of production. components. the huge investments. This development proc- ess can be facilitated by founding strategic al- materials are available that can withstand the liances of research institutes such as SOLLAB At present, hardly any reliable reactor wall severe operating conditions of the various so- Third phase – The third phase lasts until 2025 lar fuel production processes. For many lower Thermal Concentrating Systems)1 or virtual in- (Alliance of European Laboratories on Solar and will be committed to improving the nomi- temperature processes, e.g. the sulfur based stitutes like vICERP (virtual Institute of Central 2 nally CO2-free technologies (see second phase), thermochemical cycles, the major problem is Receiver Power Plants). as well as the demonstration of alternative CO2- corrosion. For very high temperature metal ox- free technologies, provided their technical and ide cycles, the challenge is the thermal shock re- economical feasibility can be shown. Empha- and chemically stable ceramic materials will be sistance of the materials. As soon as thermally step thermochemical cycles (in particular the available, the next challenge is to manufacture sis is given to potentially highly ef�icient two- Zn/ZnO cycle) for solar application, and low complete components that can be safely inte- temperature thermochemical cycles (like the hybrid copper chloride cycle) for nuclear ap- ple is the gas-tight connection of ceramic ma- grated into the solar chemical plants. An exam- plication. terials to metals at temperatures above 900°C.

For this purpose, the INNOHYP-CA project 1 suggests the creation of a components tool box 2 vICERP http://vicerp.com/ SOLLAB: www.sollab.eu

Figure 33: Design concepts Industrial solar chemical plant for massive hydrogen production – design concepts for large-scale solar tower plants – a) Example of a circular heliostat field layout showing largest distances of 733 m from central tower [%] 52 54 and annual efficiencies of 56 each heliostat (color code). 58 b) Conceptual design of 60 62 multi-eye tower for multiple 64 solar thermochemical 66 reactor operation. 68 70 72 74 76 78 80 82 84 86 88 90 92 a b

Source: DLR 34 Solar Fuels from Concentrated Sunlight

Bright Future for Solar Fuels – Outlook

Acknowledgements Solar thermal power plants have paved the way We encourage politicians and policy-makers, for solar fuels production plants. Similar to con- Contributions to this brochure are centrating solar power (CSP) plants emerging nies, development banks and private investors extracted in part from the literature energy of�icials and regulators, utility compa- cited below: as an alternative for large scale power genera- tion, concentrating solar chemical plants will solar fuels – primarily H2 – by taking concrete to �irmly support the massive production of Steinfeld A. and Meier A. (2004) presumably become the salient option for sus- steps to enable future infrastructure and mar- Solar Fuels and Materials. tainable production. ket development without delay. In Encyclopedia of Energy, Elsevier, Solar energy is free, abundant and inexhaust- We have only a short time window of opportu- Vol. 5, 623-637. ible, but at least two crucial steps are necessary nity to tackle and solve the critical problems of Steinfeld A. (2005) for a successful market introduction of solar fu- greenhouse gas emission and climate change. Solar Thermochemical Production els. Firstly, the solar chemical production tech- Solar fuels are part of the solution – they have of Hydrogen – A Review. nologies must be further developed and prov- the capacity to contribute to the energy sup- Solar Energy 78, 603-615. en to be technically feasible and economical. ply and security and to help satisfy the energy

Steinfeld A. (2002) Secondly, a worldwide consensus on the most needs of the world without destroying it.

Solar H2 production via a 2-step promising future energy carriers – both renew- water-splitting able electricity and H2 – needs to be reached. based on Zn/ZnO redox reactions. The arguments in favor of a future hydrogen Int. J. Hydrogen Energy 27, 611-619. litical commitment to move in this direction has economy (�igure 34) are excellent, and the po- Suggestions for Further Reading been manifested in many initiatives. What is ur- gently needed now is a clear decision to start Fletcher, E. A. (2001) the transition from fossil to renewable energies Solarthermal Processing: A review. and from gasoline to H2. J. Solar 123, 63-74.

Abanades S., Charvin P., Flamant G., Figure 34: Benefi ts of the Neveu P. (2006) hydrogen economy – H is a Screening of water-splitting thermo- Hydrogen Economy – beneficial effects 2 superb fuel for road trans- chemical cycles potentially attractive for port, distributed heat and hydrogen production by concentrated solar power generation, and energy, Energy 31, 2469-2486. Hydrogen Economy for energy storage. It is widely considered to have Ecology Economy Policy a strong potential for use Energy diversity Energy security Energy acceptance in future energy systems, Environmental viability Economic competitiveness Public awareness meeting climate change, Clean technology Market & job opportunities Social integration air quality, resource use goals, and securing Source: DLR and PSI energy supply. Solar Fuels from Concentrated Sunlight 35 Solar Power and Chemical Energy Systems Implementing Agreement of the International Energy Agency

IEA SolarPACES Implementing Agreement

Plataforma Solar de Almería Authors Apartado 39 Dr. Anton Meier (PSI) 04200 Tabernas Dr. Christian Sattler (DLR) Spain Design and layout Tel: +34 950 27 14 86 Paul Scherrer Institut (PSI), Switzerland Fax: +34 950 36 53 13 E-mail: [email protected] Print Internet: http://www.solarpaces.org Burger Druck GmbH, Germany

Chairman: Dr. Thomas Mancini Copyright Executive Secretary: Dr. Christoph Richter SolarPACES, August 2009