DIRECTORATE FOR FUEL AND ENERGY SECTOR
Development of Solar Technology in the World
General Information on Solar Energy Solar energy is a renewable and inexhaustible source of energy that is used for production of heat and electricity. Moreover, solar energy is an ecologically clean product that does not produce dangerous emissions Solar energy is a relatively new way of producing electricity. The rapid development of the industry began in the mid-2000s and was caused mainly by the policies in developed countries (primarily EU countries) to reduce dependence on hydrocarbons in the power industry and the desire to achieve the goals of reducing gas emissions. In addition, the rapid development of the industry contributed to the decline of production costs of solar panels and the increase of their efficiency. Natural conditions for the development of solar energy are: • • •
availability of long daylight hours; clear predominant (sunny) weather in the daytime; high angle of incidence of sunlight, which is determined by the latitude of the territory – the closer it is to the equator, the greater the angle of incidence of sunlight is.
Socio-economic factors for development of solar energy are: • • • •
high level of economic development and sustainable development; desire to reduce dependence on traditional fuel energy resources (primarily oil and coal) and the reduction of their imports; development of energy efficiency through the release of traditional fuel resources from electricity production by using solar energy and other renewable energy sources; promotion of solar energy by the state by providing lower taxes for both producers and consumers of electricity generated by solar power plants.
Taking into account the natural factors, the most favorable regions for solar energy development are the countries in tropical and subtropical climatic zones, with long daylight hours throughout the year and insolation (incoming solar rays). In temperate latitudes, the most favorable conditions are observed during the summer season, and a negative factor in the equatorial zone is the cloudiness in the middle of sunny days.
Development of solar technology in the world
Development indicators of solar energy in the world Global solar power stations consist of photovoltaic (conversion of solar energy directly into electricity) and solar thermal stations (which produce both heat and electricity). According to BP, in 2012, the world's installed capacity of solar photovoltaic power plants amounted 100.1 GW – which is less than 2% of the total electric power indicator throughout the world (this share increased from 0.2% in 2007). The main increase of the capacity of photovoltaic plants occurred in the last 5 years, when their volume increased by 10 times (Figure 1). Figure 1
Development of Photovoltaic Industry in the World (left) and the leading global operators of Photovoltaic Plants (right)
Source – International Energy Agency, BP Statistical Review of World Energy, June 2013
Still the photovoltaic power plants have a lower role in the production of electricity, which, primarily, is due to their relatively low ratio (about 30%) in utilization capacity, as compared with other types of power plants (TEP, APP, HEP, etc.). Thus, according to the IEA, in 2011, the world's solar power plants produced 61.2 billion kW of electricity, or 0.28% of the total global electricity production. For comparison, this volume is twice less than the production of the electric power by HEP in Russia.
The main power photovoltaic plants in the world are located in a small number of leading countries: in 2012, the top 7 countries had 80% of total capacity. The greatest development of photovoltaic industry was in Europe, where 68% of the world's installed capacity is located. The sole leader in the region is Germany, which accounts for about 33% of world capacity, followed by Italy, Spain and France. Of non-European countries in 2012, plants of solar energy with 7–10 GW capacity were located in China, the U.S.A. and Japan. In recent years, especially rapid development of solar energy has been observed in China, where the total capacity of photovoltaic power plants has grown 10 times in 2 years – from 0.8 GW in 2010 to 8.3 GW in 2012. According to the Renewable Energy Policy Network for the 21st Century (REN21), in 2012 the world's installed capacity of solar thermal power was 255 GW of thermal power (most came from China).The structure is dominated by power stations, aimed at heating the air and water. Solar power in Russia has only started to develop. The first photovoltaic power plant of 100 kW was commissioned in 2010 in the Belgorod Oblast. Polycrystalline solar panels for the station were bought from Ryazan Metal Ceramics Instrumentation Plant. Currently a variety of projects are being analyzed in this sphere, including in the Stavropol and Primorsky Territories, and Chelyabinsk Oblast.
Cost of solar-generated electricity The cost of electricity from solar power is one of the highest among the alternative generation methods (Table 1). According to public data of OpenEI Transparent Cost Database, the cost of electricity production from photovoltaic plants is far greater to other sources of generation: higher by an average of one third – over solar thermal power generation, 2 times – over continental wind and 4–5 times – over all other methods. However, in the last few years, there has seen a reduction of the cost of electricity produced directly from solar energy using photovoltaic converters (photovoltaics). Thus, in 2008-2012, the minimum cost decreased from 0.21 to 0.14 USD / KW/h.
Development of solar technology in the world
Себестоимость производства электроэнергии в зависимости от источника, на основе данных за 2009-2012 годы, долл./кВт·ч
Source of electric power
Solar thermal power plant
Note — the cost of electricity is provided, including return on the initial investment and operating costs Source — OpenEI Transparent Cost Database
Technology in Solar Energy Solar energy is converted into thermal or electrical energy (Figure 2). The generation of the electricity can be carried out via an intermediate thermal process and directly – with the help of photovoltaic converters. Photovoltaic power plants supply electricity directly to the network or serve as a source of autonomous power in the enterprise, household, etc. Thermal solar stations mainly focus on obtaining heat energy through the heating of various kinds of coolants, including water and air. Table 2
Main System Scheme of Transforming the Solar Energy
Solar Technology Using Thermal Process Solar collector Efficiency = 45–75% Solar thermal collector – installation, which uses solar radiation to heat the heat-absorbing material, for example, water or air. The efficiency of such plants (percentage of the released energy (produced) to the energy received in the form of solar radiation) ranges from 45–75%. Heated by solar thermal power plants, water can be used directly in the heating system of buildings or in the household. As a source of heat, the air can be used, which is heated by circulating it through the cavity, exposed to direct sunlight. Solar pond (salt water) Efficiency = 10% Salt lakes have a specific vertical structure, which allow the use the heated water. In such lakes, there are three salinity layers: on the surface, the layer of low salinity is situated, at the bottom, the layer with a high salinity is situated. Between them is an insulating layer that keeps the heat, is placed. Under sunlight, water temperature at the bottom of the lake rises to 90–100 °C. Salinity gradient (increasing with depth) causes a density gradient (increasing with depth) and it counteracts the temperature gradient, thereby enabling the heat (hot water) to move to the upper layers due to convection. This means that the temperature at the bottom of the reservoir is greater than 90 °C, while the temperature at the top of the pond is generally 30 °C. Heat, which is retained in the bottom layer of the pond, may be utilized for the production of electricity through the use of various mechanisms, including an organic Rankine cycle (Organic Rankine Cycle – ORC) and a Stirling engine. Both of these technologies involve the conversion of heat into electricity without the use of steam, they do not require temperatures above 100 °C. Concentrating solar collectors (CSP) In CSP-systems, to achieve higher temperatures focused sunlight is used. Solar energy is reflected onto the surface of a large reservoir with a smaller surface area, which is there converted instantly into heat. Due to the concentration of energy in a smaller area, its greater heat is achieved and less heat is lost by radiation and convection. Most of these collectors can be oriented towards the rays coming directly from the disk of the sun (direct radiation), and must follow the sun in its motion across the sky. There are four types of solar concentrators: parabolic reflectors in the form of troughs, parabolic mirrors, plates, central receiver system of energy and Fresnel lens (Figure 3).
Development of solar technology in the world
Parabolic trough focuses the incoming solar radiation in a line extending over the entire length of the trough. On this line is the tube (receiver), filled with a liquid heat-absorber, focusing the solar energy heats the fluid. Reflectors must be rotated around one axis. Since the surface area of the tube receiver is small, compared with the area of the reflector, the temperature can reach 400 °C, and it is achieved without significant heat loss. Parabolic dish focuses the solar radiation onto a point. Hermetic chambers, containing the heat transfer device, are situated in the focus of the radiation concentration. Parabolic plates must be rotated around two axes. The central receiver system consists of a large number of movable flat mirrors (heliostats) and a receiver located in the upper part of the tower. Each heliostat, during the day, moves along two axes, positioning the reflection of sunlight onto a receiver at the top of the tower. Receiver – is a system of vertical conduits, which heat the reflection of sunlight from multiple mirrors, thereby heating the fluid passing through the conduit. Figure 3
Methods of solar energy focusing
Fresnel lenses to focus solar energy into a point use refraction rather than reflection. Typically molded from inexpensive plastic, these lenses are used in photovoltaic panels. They are not designed for increasing temperature, but for focusing the light onto a small photovoltaic cell, thereby increasing its efficiency. As parabolic dishes, Fresnel collectors must track the sun on two axes.
Photovoltaic converters Most effective in terms of energy, semiconductor photovoltaic converters (PVC) are devices for converting solar energy into electricity. They represent a direct, one-step transfer of energy. Efficiency of the photovoltaic converters, produced on an industrial scale, is 16%, the best models reach 25%. In laboratory conditions, in the summer of 2013, Sharp achieved the efficiency of PV converters that reached 44.4%, and in September, German scientists from Institute of Solar Energy of Fraunhofer Society and Helmholtz Berlin Center of Materials and Energy announced the creation of the most efficient solar cell in the world, the efficiency of which is 44.7%. Depending on the material, construction and method of manufacturing of solar converters, there are three generations of PVC: • • •
First-generation solar converters based on crystalline silicon wafers; Second-generation solar converters based on thin films; Third generation solar converters based on organic and inorganic materials.
To improve the efficiency of solar energy conversion, some solar converters are developed on the basis of cascade multilayer structures. PVC of first generation First-generation solar converters based on crystalline wafers are mostly used today. In recent years, producers have managed to repeatedly reduce the production cost of solar converters, which ensures the strengthening of their position in the global market. Types of PVC of the first generation: • Monocrystalline silicon (me-Si); • Polycrystalline silicon (m-Si); • based on GaAs; • ribbon-technology (EFG, S-web); • thin-film silicon (Apex). The largest producers of solar converters of the first generation are Chinese companies Suntech Power, JA Solar, Yingli Green Solar, Solarfun Power, and Trina Solar. PVC of the second generation Technology of thin-film solar converters of the second generation involves using the layering vacuum method. Vacuum technology, in comparison with the production technology of crystalline solar converters, is less energy intensive and
Development of solar technology in the world
it is also characterized by a smaller volume of capital investments. It allows producing cheap flexible large-area solar converters; however, the conversion factor of elements is lower than the first-generation solar converters. Types of second-generation solar converters: • Amorphous silicon (a-Si); • micro-and nano-silicon (μc -Si/nc-Si); • silicon on glass (CSG); • admium telluride (CdTe); • (Di) selenide copper (indium) gallium (CI(G)S). Third-generation solar converters The idea of creating the third-generation solar converters was further directing to the reduction of the cost of solar converters, eliminating the use of expensive and toxic materials in favor of cheap and recyclable polymers and electrolytes. An important difference is also the possibility of applying layers using printing methods, for example, the technology “rollto-roll” (R2R). Currently the bulk of projects in the field of third-generation solar converters are under investigation. Types of third generation solar converters: • • •
photosensitized dye (DSC); organic (OPV); inorganic (CTZSS).