AGENZIA NAZIONALE PER LE NUOVE TECNOLOGIE, L’ENERGIA E LO SVILUPPO ECONOMICO SOSTENIBILE CONCENTRATING SOLAR POWER IN ITALY Ing. Giorgio SIMBOLOTTI Head Strategies and Project Management ENERGY, TRANSPORT AND SUSTAINABILITY Hannover Messe – April the 10th, 2013 Abstract Among variable renewable technologies such as solar and wind, concentrating solar power (CSP) offers the potential for integrated, efficient energy storage. This enables electricity generation even under cloudy skies or after sunset, and increases significantly the plant capacity factor and dispatchability of CSP electricity. While CSP is economically affordable only in regions with high direct solar irradiation – so- called sun-belt regions - it holds the potential for contributing significantly to meeting global energy demand in a near future. Since 2001, the Italian Agency for New Technologies, Energy and Sustainable Development (ENEA) has been developing a new concept of CSP technology aimed to achieve a better exploitation of the energy storage potential of CSP plants. This new technology is currently being demonstrated at the Archimede 5-MWe power plant, which was built by ENEL at Priolo (Sicily) and started the operation in July 2010. This short paper offers an overview of the current status of CSP, as well as the innovations introduced by ENEA in the CSP technology, and current prospects for research and commercial deployment of CSP. Keywords : Concentrating solar power, CSP, renewable energy, electricity generation, energy storage. 1 An overview of today’s CSP technology Concentrating Solar Power (CSP) plants use mirrors to concentrate the sunlight and produce heat and steam to generate electricity via a conventional thermodynamic cycle. Unlike solar photovoltaics (PV), CSP uses only the direct component (DNI) of sunlight and can provide heat and power only in the so- called sun-belt regions with high DNI, i.e. Southern Europe, South-Western United States, North Africa and Middle East, and large areas of China, India and Latin America. CSP plants can be equipped with a heat storage system to generate electricity even under cloudy skies or after sunset. Thermal storage can significantly increase the CSP capacity factor and dispatchability of CSP electricity compared with PV and wind power. It can also facilitate grid integration and competitiveness. Further advantages of CSP include: easy integration in conventional power plants using same thermodynamic cycle and components (steam generator, turbines); combined production of electricity and high-temperature heat for industrial and residential use (e.g. water desalination in arid regions); potential for small-scale, multi- purpose applications; and the profitable use of vast, arid land. Fostered by policies to reduce the CO2 emissions, the global installed CSP capacity has been growing rapidly in the past years. At the end of 2012, the global capacity was about 1.9 GW, compared to about 1.3 GW in 2010, with an additional 20 GW under construction or planned. The United States, Spain and – most recently – Saudi Arabia and United Arab Emirates are leading countries in terms of CSP installations and deployment plans. Other countries such as Germany and Italy contribute significantly the development of CSP technology. The CSP technology includes four variants, namely Parabolic Trough (PT), Fresnel Reflector (FR), Solar Tower (ST) and Solar Dish (SD), see Figure 1. While PT and FR plants concentrate the sun’s rays on a focal line and reach maximum operating temperatures between 300 and 550°C, ST and SD plants focus the sunlight on a single focal point and can reach higher temperatures. PT is currently the most mature and dominant CSP technology accounting for some 90% of the installed capacity. Most commercial PT plants use synthetic oil to transfer the solar heat to a steam generator, and have capacities between 14 and 80 MWe. They reach a maximum operating temperature of 390°C, which is limited by the thermal degradation of the synthetic oil. Their efficiency (i.e. the ratio of electricity to solar energy) is about 14-16% and the capacity factor is on the order of 25%, depending on the location. Some plants have a molten-salt thermal storage system with a storage capacity of about 6-8 hours, which can increase the plant capacity factors more than 35% on a seasonal basis. Two demonstration plants (i.e. a 5-MW PT plant in Italy and a 20-MW 2 Figure 1 - CSP technology variants: 1) Solar Dish; 2) Solar Tower; 3) Parabolic Trough; 4) Fresnel Reflector ST plant in Spain) are currently testing the use of high-temperature (550°C) molten salt for either heat transfer and thermal storage. This option is expected to improve significantly the CSP performance and storage capacity. While CSP still needs policy incentives to compete economically with conventional power technologies, in the years to come the technology is expected to become more economically attractive thanks to larger deployment and the associated reduction of industrial costs. At present, recent (2012) estimates by the International Renewable Energy Agency (IRENA, 2020) suggest upfront investment costs of between USD 5,500 and 8,000 per kW for PT plants with no storage and between USD 7,500-8,500 per kW for PT plants with 6h storage. The current levelized cost of electricity (LCOE) ranges from USD200/MWh (i.e. typically, plants with 6h storage and high DNI) to USD330/MWh (i.e. with no storage and low DNI). Typically, the investment costs account for about 85% of the LCOE, the rest being operation and maintenance costs. Investment cost and LCOE are expected to decline by 10-20% by 2015 and by 30-50% by 2020 due to technology learning and economies of scale following an increasing deployment of CSP power. The increasing value of carbon-free energy should also contribute the CSP’s competitiveness. CSP offers a considerable potential in terms of energy production. In principle, assuming a land-use of 2 ha/MWe, the North African potential could meet several times the combined electricity demands of Europe, the Middle East and North Africa. The International Energy Agency in its CSP Roadmap (IEA, 2010) suggests that the technology could become economically competitive for intermediate and peak loads within the current decade and the global installed capacity could reach 100 GW by 2020, with an average capacity factor of 32%. Between 2020 and 2030, CSP could become economically 3 competitive with conventional base-load power due to reduced CSP costs and the increasing prices of fossil fuels and CO2. The United States, North Africa and the Middle East are seen as the major producers of CSP electricity. At present, many countries (e.g. Algeria, Australia, China, Egypt, India, Italy, Morocco, South Africa, Spain, United Arab Emirates, Saudi Arabia and the United States) have policies in place and/or plans to support CSP deployment. CSP in Italy Between 2001 and 2010, the Italian Agency for New Technologies, Energy and Sustainable Development (ENEA) has developed a novel variant of CSP parabolic trough technology aimed to fully exploit the CSP energy storage potential. The main objective of the research programme was to increase the capacity factor and the electricity generation in the CSP plants, thus reducing the cost, and improving the dispatchability of CSP electricity. Figure 2 - Thermal storage optimization in CSP power plants The ENEA technology innovation consists of using high-temperature (550°C) molten salt as either heat-transfer and heat-storage fluid, thus replacing synthetic oil at 390°C, which is currently used in CSP plants. The use of high-temperature molten salt for both heat transfer and storage purposes enables a significant improvement of the heat storage capacity and cost reduction of the storage system, which can provide heat for electricity generation for several hours (up to 10-12 h) under cloudy skies or after sunset. This allows a significant increase of the capacity factor of the CSP plant on a seasonal basis, as well as increased electricity production and reduced cost of electricity. The use of high-capacity storage systems also improves the flexibility of CSP plants, which can provide either dispatchable electricity and high-temperature heat for industrial or residential use. Moreover, molten salt (a 60-40% 4 mix of KNO3-NaNO3) is safer (non-flammable), cheaper and environmentally more friendly than synthetic oil. However, a trade-off exists between the economic benefit from an increased electricity production and the incremental investment cost due to the storage system and the associated oversizing of the solar field. The analysis suggests that the theoretical optimal is between 9 and 12 h of thermal storage (Figure 2). As a drawback, the use of molten salt requires electrical heating for operation start-up, and the use of thermal storage increases to a certain extent the complexity of the plant. The actual optimization depends on a number of technical and commercial factors such as the local DNI and the power plant target service. The use of higher operation temperature also required the development of new technologies for the key components of the CSP plant such as heat receivers, solar collectors, and the heat storage system. New components and systems working at 550°C have been developed, patented and tested by ENEA at the full-scale CSP test facility (Figure 3), which was built since 2004 and operated now for more than 15,000 hours. Plant operation ENEA Casaccia National Labs, Rome Start-up April 2004 Tests and qualification of the basic concept & components More than 15,000 hr operation Figure 3 - CSP Test Facility . ENEA National Labs – Rome Italy Of particular relevance is the development of a high-temperature heat receiver working under vacuum at 550°C, with a special coating, which maximises heat absorption and minimises losses (Figure 4). Italian and European companies have contributed the R&D programme since the very beginning, and some of them currently produce key components such as heat receiver and solar collectors under ENEA license.