Concentrated Photovoltaic Energy
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August 2015 Exchange Issue19 Concentrated Photovoltaic Energy Guest Author: Mr. Santiago Martínez Ceballos Manager of Termosolar Borges; [email protected] 1 Introduction Renewable energy has been used by humans since Concentrated Solar Energy to generate the beginning of times. With the Industrial Revolution electricity and the low price of fossil fuels these resources were virtually abandoned. But currently, due to the high costs of fossil fuels and the serious environmental There are two basic streams used for electricity problems that we are facing, this type of energy is re- generation based on concentrated solar power, emerging. Climate Change mitigation relies on photovoltaic (CPV) and thermoelectric (CSP). replacing conventional energy with renewable and sustainable energy. Solar energy, wind energy and Both of which generate electricity through the hydropower are growing strongly, to become the concentration of the solar radiation in a point or area. main sources for energy generation. The difference is set by the type of energy Several technologies could be used to generate concentrated: Concentrated Photovoltaics (Figure 1) energy (i.e. thermal and electricity) from solar concentrate solar light (photon) and directly generate radiation. This publication aims to provide an overview electricity; while thermoelectric (Figure 2) uses on Concentrated Photovoltaic Energy (CPV) as one concentrated solar radiation to heat a transfer fluid of the technologies that uses solar radiation to and generate electricity mechanically by transforming produce energy and which may contribute to the thermal energy into mechanical energy through energy mix to reach the 12% of energy from moving a generator. renewables by 2020 as set by the Government of Lebanon. Furthermore, while CSP requires an installed power of at least 25 MW to offset the investment costs of Page2 the power block (turbine, steam train…); the minimum system with coolers for controlling the steam process; capacity for a CPV power plant is in order of 10-25 such systems increase the internal power kW ,(depending on the model and manufacturer). consumption of the installation. It is important to properly select the location of the Local water resources should also be considered power plant depending on the technology and as part when selecting the adequate technology. Lebanon is of the investment. Opting for one or another a coastal country, and has a river like the Nahr al- technology depends on the operating costs and Litani crossing the country before reaching the resources required. Solar thermal requires a Mediterranean, thus the water resource for cooling is significant amount of cooling water or a refrigeration present in some areas of the country. Figure 1: CSP Hub of Termosolar Borges (Lleida-Spain) Figure 2: CPV collector at Solmir (Lleida-Spain) Page3 Concentrated photovoltaic (CPV) of a photoelectric cell is shown in Figure 3. technology Between the layers of the semiconductor material an electric field is created through the impact of the Photovoltaic phenomena sunlight photons. Thus, photosensitive material is crucial for this technology. The photovoltaic solar energy is based on semiconductor materials which collect sunlight and Electrical energy is created in direct current (DC), convert it into electricity. The initial operating scheme which is then transformed to alternating current (AC). Figure 3: PV cell Why Concentrated? installed in the same . PV power plants with high electricity generation When lower surface of photosensitive material is require large ground availability for the distribution of required, more efficient material can be used. Albeit the PV modules. The price of PV has decreased but more expensive initially, the high electricity production the main cost is still the silicon. during its lifetime offsets the investment costs. CPV aims to reduce the price of conventional PV CPV cells have an average efficiency between 39% electricity by using less amount of photosensitive and 41% (and have reached up to 43.5 % in the material. The objective is achieved by concentrating lab), while the average performance of conventional the sunlight received through elements such as silicon photovoltaic cells remain between 13% and mirrors and lenses which are cheaper; in addition to 21%. reducing the total collection area and more power is Figure 4: CPV cell Page4 Figure 5: GEN2 ISOFOTON Cell Figure 6: Sunsensor Siemens in Termosolar Borges GEN2 CPV model from ISOFOTON, has a rated CPV system components power of 95 W per cell (0.38m2), and has a 41% of performance in service (257W/m2). The CPV systems have the following elements: PV commercial models are: • ATERSA A320M 161W/m2 Concentrators. The most commonly used are • ISOFOTON IS-230 137W/m2 concentric mirrors or lenses with magnifying effect • SUNTECH STP175S 137 W/m2 that concentrate the sunlight in the photovoltaic cell As it can be seen, the area can be reduced up to 50% (Figure 8). The concentration factors that can be for the same amount of power. achieved by these elements range from 500 units up to 1,000 or even 2,000. Figure 8: Fresnel concentrator scheme The photovoltaic cell is situated in the focal axis of Solar tracking system. The module should be the reflective or of the lens and is responsible for perpendicular to the sun, Therefore, the panels require transforming sunlight into electricity. The PV cell is solar tracking systems that follow the sun’s path. The composed of two or three layers of different materials systems typically used have two axes of movement (e.g. GaInP / GaInAs / Ge) each part optimized to (Figure 10), one to follow the sun from east to west convert all the electromagnetic spectrum of sunlight (azimuthal movement) and another to follow the sun into electricity (Figure 9). from sky to ground (zenithal movement). However, there are some examples of tracking systems which Dispersant warmth. The high concentration of solar have only a vertical axis (azimuthal movement). radiation produces very high temperatures. Although the CPV cells energy production is not affected by Inverters. Inverters are another key component that high temperatures any more than conventional impacts the plant cost, design and performance. silicon PV, the excess heat is to be evacuated. The Inverters electronically convert the electrical PV cell is coupled to copper and aluminum foils for characteristics of a DC power source to AC to be the heat dissipation. injected into the distribution grid. In many cases inverters are part of the monitoring system. Page5 Figure 9: Each of the materials exploits a part of the electromagnetic spectrum of the sun). The end result is the sum of the efficiency of each of the layers separately Figure 10: 2-Axes movement system Energy performance and applicability Although the PV cells work with indirect radiation, the presence of these materials in a CPV panel is CPV technology requires a climate with high direct dramatically reduced that the amount of electricity radiation and clear sky. In geographic areas with produced could be minimal. annual rates below 1,500 kWh/m2/year the use of conventional PV is more favorable than CPV. Optimal The following table (Table I) shows a comparison of areas for CPV are tropical deserts, like the Sahara or various types of solar energy generators. Currently the Middle East, or other regions such as California, the CPV is relatively more expensive than PV, but in southern Europe and northern and southern Africa. areas like Lebanon, where direct radiation exceeds For cloudy and humid climates with low radiation, 1,500 kWh/m2/year, the electricity produced offsets CPV is inefficient given that the reflection can only the initial costs over the power plant’s life. be done with direct light and not with diffuse light. Table I: Comparative energy solar generators Page6 Installation and operating costs translated into an increase of energy generated per area (kWh/m2), given the advances in solar If we eliminate the environmental variables, the main concentrators and the high efficiency of the solar reason for the construction of PV plants is its financial cells. and economic benefit, or rather the ratio of $ per kW installed. Today, there are no studies about the evolution of CPV costs. Figure 11 shows conventional PV total The evolution from conventional PV to CPV is installed watt price is in the range of 2.5$/W. Figure 11: Projected solar PV system deployment cost (2010-2020). Source: IRENA (2014c) CPV installation companies estimate the installation • Suntech Power (China) cost at approximately $ 4-6 per watt installed. Follow- • Sharp (Japan) ing the evolutionary trend of the PV, in 2020, costs • Q-Celis (Germany) could be of the order of the current costs of convec- • Yingli Green Energy (China) tional PV (2.5$/W). • JA Solar (China) • Kyocera (Japan) • Trina solar (China) Current Global Situation • SunPower (US) • Gintech (Taiwan) Photovoltaic panels manufacturers As it can be seen Figure 12, the manufacture of The world›s leading manufacturers of PV and CPV PV-CPV modules has been shifting to Asia. In other cells are: countries or in the rest of the world (ROW) PV-CPV modules manufactures are minor. • First Solar (U.S) Page7 Figure 12: Photovoltaic Modules production. Navigant Consulting ISE Photovoltaic Report 2014 CPV status worldwide companies that have installed prototypes but still not high capacity CPV power generation plants. Solfocus, Abengoa and Solar Zhenit are some Figure 14: Solfocus Panel Figure 13: Abengoa Pernanbuco University In 2013, Soitec built a 1.5 MW plant in California. 30-50 MW installations are becoming more common; Nowadays, the Atacama Desert in Chile is the area currently there are not many projects in service, were most CPV projects can be found with mines but many prototypes and project developers have in the desert as their main customers. Abantia has information for each particular project, which leads to recently completed the construction of a 36 MW a general lack of information.