PHOTOVOLTAIC SOLAR ENERGY OVERVIEW What is photovoltaic solar energy The sun is the source of life and the origin of the different forms of energy used by mankind since its very first steps on Earth. Initially, the energy from the sun can meet all the primary needs of society in terms of energy. Indeed, the daily solar energy reaching the earth s surface is roughly equivalent to 15,000 times the primary daily energy currently used worldwide. In addition to the direct use of solar energy through the natural processes, it can be used through artificial conversion into thermal and electric energy to meet daily needs, similar to the energy produced by most popular sources, i.e. oil, gas, coal, hydropower or nuclear energy. The two key characteristics of solar energy are: a) it is virtually inexhaustible, and b) it is not polluting. In addition, as a source of energy it is available, to a greater or lesser extent, almost anywhere on Earth (see Figure 1), and it can be collected and transformed where it is used 1. Watts por metro cuadrado por día Figure 1: Average daily solar radiation incident on the earth s surface It must be noted that the solar radiation reaching the earth s surface has low energy density, and it is intermittently supplied (day-night cycles). Therefore, it must be captured on relatively large surfaces capable of accumulating the energy required, or supplement it with other sources of energy to make it available at night or in periods with less sunshine as the winter time. 1 The latter can offer significant economic benefits, particularly in remote and isolated areas where the transportation cost of conventional fuels (oil products and gas) or the distribution of electricity can be very high. 1
Historical review From 1958 until the first crisis of 1973, solar cells have been mainly applied to the space and military industries. The oil crisis of 1970s promoted the development of photovoltaic (PV) technology for terrestrial use. By mid 1990s, the activities in the PV field gained momentum as a result of the increasing environmental demands of society, and a reduction in the cost of systems. How it works The required surface vs. demand To understand the extension required to meet a given demand of solar energy, the following example illustrates the electric energy scenario in Argentina. The average annual incident solar radiation in the national territory, North of the Colorado river, covering a surface of 2 million km2, is 4.6 kwh/(m2.day). Since in 2010, the annual energy consumption was 115 x 10 9 kwh, considering a conversion efficiency of solar energy into electricity in the order of 15% (average efficiency of a solar panel), and a floor occupation factor of 50%, an area of approximately 900 km2 would be required to produce this amount of energy. The extension would be similar to the water surface of Chocón hydroelectric dam, but capable of producing 25 times more electricity. This is a clear example of the feasibility to obtain sufficient solar energy to meet human consumption. The massive use of solar energy will depend on the relative cost of use at an integrated level, including the cost of storage and transportation, and distribution if necessary, and on the policies to promote development. The global analysis should include the environmental care associated to the production of energy. Photovoltaic conversion The direct conversion of solar energy into electricity is obtained through photovoltaic (PV) devices. The main component of the PV industry is the crystalline silicon solar cell (c-si). The technology supporting this semiconductor is highly developed, as it is the basis of the electronic industry. While there has been considerable progress in the development of the new PV cells, it is expected that the c-si technology, that governed the photovoltaic market during the last 30 years, continues to do so over at least the following 10 years. Modules or photovoltaic panels, a group of PV cells connected in series with each other (Figure3), is the building block of the PV system. They can generate DC and their main feature is the power (W peak or Wp) they can deliver when lighted through a solar radiation of 1 kw/m2 (typical value at noon on a clear sky). There are commercial PV modules within a relatively wide range of power, typically between 80 Wp and 300 Wp, with 12 V to 48 V standard operating voltage. 2
Typical photovoltaic (PV) system Figure 3: Photovoltaic modules for illustrative purposes. A typical PV system includes modules, batteries (if required), a power control and conditioning system, a DC-to-AC converter (if required), and a mounting structure. Systems can be classified in two major categories: stand-alone (isolated) or connected to the power line. The following uses apply to both categories: Stand-alone systems: space; rural electrification; water pumping; communications (repeaters, radiotelephony, etc.); remote monitoring (climatic, seismic, etc.); navigation buoys; cathodic protection to avoid corrosion; consumer goods (watches, calculators, etc.); battery chargers; solar cars. Systems connected to the power line: integrated to buildings ( PV in buildings ); power plants. Figure 4: stand-alone systems (school located in the North-West area of Argentina) and systems connected to the power line (www.kinsolar.es) Special applications PV energy also plays a key role in spatial applications. Solar panels deliver electric power to satellites, and are responsible for the ongoing operation of equipments. In this sense, the Department of Solar Energy (DSE), an agency of the National Atomic Energy Commission, develops photovoltaic devices for spatial applications as part of the National Space Plan. One of its most recent advances is the Argentine SAC-D/Aquarius satellite, a joint development of the National Commission of Spatial Activities (NCSA) and the US NASA space administration, 3
whereby the NCSA DSE was responsible for the development and integration of the solar power panels (Figure 2). MARKET The evolution of photovoltaic solar energy Figure 2: SAC-D/Aquarius satellite The current state policies implemented in different developed and emerging countries in Europe, or in Japan, China, India, Korea, USA etc., are aimed at achieving a change of scale in the PV market. These policies have laid stronger emphasis on the systems connected to the power line, through various government support programs and promotion policies. In recent years, the photovoltaic industry saw a major boost as a result of which the power installed between 2005 and 2010 was multiplied by more than 7, reaching approximately 40 GW. Of all the renewable sources of energy, solar PV shows the most significant growth in the 2005-2010 period, with an average annual rate of 49% that rises to 72% if we only consider the year 2010. Taking into account only the systems connected to the power line, these rates reach 60% and 81% respectively. In comparison, the average growth rate of wind energy was 27%, thermal solar energy 25%, biodiesel production 38%, and hydroelectric power 3%. While the rate of electricity production from renewable energy sources at a global level is 19.4%, almost half of 194 GW installed globally in 2010 was from renewable sources. While wind power installed capacity in 2010 was 39 GW, and hydro power contributed 30 GW, solar PV contributed 17 GW, an amount that should not be at all disregarded in the context of renewable energies. In the case of the European Union, more than half of new renewable energy installations were solar PV. Operating capacity In terms of the solar PV operating capacity by country, Germany still holds a leading position with 44% operating capacity by 2010, followed by Spain with 10%, Italy and Japan with 9%, the US with 6%, and the remarkable example of the Czech Republic that achieved 5% with 2 GW in 4
2010, in a country where by 2008 there were virtually no installations. Other countries, in the same order, are France with 3%, and China, Belgium and South Korea with 2%. Figure 5 shows the operating power of the most significant renewable energies in different regions, excluding large-scale hydroelectric generation. The total worldwide operating capacity is approximately 6800 GW. The PV technology indicator includes only the installations connected to the power line. While as shown in Figure 5, PV technology is currently less developed than other renewable sources of energy, it must be noted that showing a growth rate higher than other renewable energies may lead us to assume that its significance will grow over time. Otras Geotérmica Solar FV Biomasa Eólica Total Mundial Países en Desarrollo Estados Unidos Alemania España Figure 5: Operating capacity to generate electricity from renewable energy by 2010, in different regions and major countries Production cost The improvements in PV technology have been steady, while the cost of PV electric generation has decreased as the production volume has increased. After a period of stagnation in the price of PV modules as a result of the insufficient silicon production vis-à-vis the growth of the PV industry, investments in the sector boosted an increase in the supply of such base material, with the resulting reduction in PV modules prices that by 2010 reached values from USD 1,30 to 1,80 per Watt. This downward trend continued in 2011. The most widely used technology Today, the crystalline silicon technology still dominates the PV market, while the so-called thinfilm technologies based on cadmium telluride and amorphous silicon, have 13% market share. Emerging technologies such as compounds of copper indium gallium selenide (CIGS), dyesensitized cells (DSSC), organic cells, and cells based on III-V semiconductors such as gallium arsenide using optical concentration of solar radiation, are even at the experimental stage. However, there are 20 MW of the latter already connected to the power line, while contracts have been entered into in California (US) for the installation of 300 MW based on the use of this technology. 5
Future development The growth of the PV market has put a lot of expectations in this technology, due to the technological improvements and a predictable increase in the operating costs of traditional energy sources based on fossil fuels. According to field experts, in a few years the cost of unsubsidized PV-based electric energy for end-users will be equivalent to that produced by fossil fuels or other sources in different markets. It must be noted that this is already a fact in Italy, Spain and Portugal, markets that have in common relatively high levels of sunshine, high electricity costs, and regulatory price regimes that encourage the growth of renewable energies. This will be the expected scenario for the next 10 years in the vast majority of countries, including Argentina. The photovoltaic market in Argentina In Argentina, there are facilities aimed at generating power from technologies based on wind, biomass and solar energy that up to now have had low impact in terms of the operating power. In the case of solar PV, it must be noted that the first 1.2 MW PV power plant built under the Solar San Juan Project of the province of San Juan, has started to inject energy to the Argentine Interconnection System. Moreover, although there is a high rate of rural areas supplied with electricity, there are many rural populations without electricity across the Argentine territory. In addition, there are many schools and other public services in rural areas that do not have electricity. In most of these cases, renewable sources of energy and especially solar PV are the best alternative in terms of energy. The Argentine PV market can be divided into three major demand groups: rural, industrial and institutional. The total domestic demand of PV modules had a sustained annual growth of 20% to 50% until 1999, when it reached a value of approximately 1,000 kwp / year. Since then and particularly after the devaluation of the AR$, the demand for PV systems suffered a sharp decline that could only be reversed in 2003, with a further drop in 2007. Figure 6 illustrates the evolution of the market between 1997 and 2008, differentiating between sales in Argentina (local use) and exports. The rural demand includes the requirements of livestock and farming establishments, or of rural populations. The most highly required types of equipment are, among others, PV modules to charge batteries at the health posts of the border police, lighting systems, and power supply for small water pumps to replace traditional windmills. 6
Potencia (kwp) Mercado Argentino 2000 1800 1600 1400 1200 1000 800 600 400 200 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Año Ventas en Argentina Exportación Figure 6: total domestic demand of PV modules in Argentina The industrial sector includes the requirements of some companies, such as the telephone providers that are the most representative in terms of the volume of modules purchased. Applications are aimed at providing energy to communication systems, telemetry, markings, signs, highway emergency systems and cathodic protection to avoid corrosion. The institutional sector includes social assistance programs, energy regulators, foundations and provincial energy companies aimed at providing small amounts of electricity to rural communities that are far from the distribution lines. The demand has shown significant growth since the launch of the Renewable Energy Project for Rural Electricity Markets (Proyecto de Energías Renovables para Mercados Eléctricos Rurales -PERMER) agreed with the World Bank by the end of 1999. On a first stage, the service was provided to almost 87,000 users and 2,000 public institutions especially for lighting and social communication purposes. More than 500 rural schools in different provinces benefited from the installation of photovoltaic systems to serve their basic needs for electric power. The alternative energies have recently gained new momentum with public tenders (ENARSA and San Juan) for the installation of plants for the production of PV connected to the power line. While the plant bid on by San Juan (1.2 MWp) is already operating, the tenders carried out by ENARSA will provide for the installation of a total of 20 MW connected to the power line in the short term. The realization of these initiatives and the reactivation of the PERMER initiative that projects the installation of approximately 2 MWp between 2010 and 2011, are leading to a change of scale in the local market with respect to the operating power. Other incentives are the benefit of AR$ 0.90 per kwh produced by solar energy as per law 26190/06 currently in force, and the 2011 call by the National Agency for the Promotion of Science and Technology (Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT) under the Ministry of Science, Technology and Productive Innovation (Ministerio de Ciencia, Tecnología, e Innovación Productiva - MINCyT), encouraging projects that reflect the introduction of new technologies in Argentina, in order to produce solar-based electricity 7
connected to the power line. As a result, there are encouraging signs related to the adoption of state policies that significantly add PV technology to the country, promoting a domestic market to fuel the industrial development of the sector and, therefore, the diversification of power generation through the addition of renewable sources of energy. REFERENCES The author Department of Solar Energy (Departamento Energía Solar -DES) under the national Commission of Atomic Energy (Comisión Nacional de Energía Atómica -CNEA): started his academic activities in the year 1976. His early works dealt with photothermal conversion (conversion of solar radiation into heat) through the use of radiation concentrators suitable for the production of hot fluids for industrial use or power generation. In the mid 1980s, the research and development work on photovoltaic conversion of solar energy (direct conversion of sunlight into electricity) started to develop. In 1986, there was the startup of the silicon crystal growth process using the Czochralski technique. Since 1992, the activity was focused on the design, development and measurement of silicon solar cells After 1995, DES key efforts were focused on the development of solar cells and panels for artificial satellites, within the framework of a cooperation agreement with the National Commission on Space Activities (Comisión Nacional de Actividades Espaciales -CONAE). This led to the first experiment with Argentine solar cells in space that was performed in the SAC-A Argentine satellite that was put into orbit by the end of1998. After the successful experience with SAC-A and in order to provide solar panels for future satellite missions under the National Space Plan, in March 2001 CONAE and CNEA signed a cooperation agreement with the final purpose of providing flight solar panels to SAOCOM observation satellites. This agreement, framed in Law No. 23,877 of technological innovation, led to the initiation of the Solar Panels Subproject that was part of the SAOCOM Project at the Constituyentes Atomic Center (CAC). The implementation of the subproject in the country led to the development of design tools and techniques to manufacture, characterize, qualify and test solar panels for space applications. In subsequent contracts, the collaboration with CONAE was expanded to include the development of solar panels for the Aquarius / SAC-D mission and of environmental tests on solar cells and other components for satellite applications. 8
The Aquarius / SAC-D satellite mission is a joint venture between CONAE and NASA space agency, whereby CNEA is responsible to develop solar panels for the satellite. Under the relevant contract, in 2008 the qualification and testing campaign for the Qualification Model ("Engineering Qualification Model ") of the solar panels for the mission was successfully completed. The production of flight solar panels based on the technology developed by CENEA has been recently completed. Currently, DES continues working on the development of solar panels for SAOCOM missions that will be part of the Italian-Argentine Satellite System for Emergency Management (Sistema Italo Argentino de Satélites para la Gestión de Emergencias - SIASGE). In recent years, low cost PV cell-based solar radiation meters were developed for terrestrial applications. Several radiometer prototypes were tested and calibrated at the National Weather Service, and some of them are being used by weather stations in different provinces. In 2011, two grants were approved to support the "Interconnection of PV systems to the power line in urban environments", for projects which involve not only the feasibility study, but also the installation of pilot systems in agencies and social households. One remarkable aspect is the engagement of 5 private companies in the creation of a public-private consortium with UNSAM and CNEA. DES promotes and participates in setting national standards for systems that use solar energy, under the Argentine Standardization Institute (Instituto Argentino de Normalización - IRAM). It also advises public and private agencies on matters related to the development and application of photovoltaic technology in the country. In addition, DES performs significant activities related to train human resources in this field through lab work, and Major s, Master s and PHD Thesis. The team members give conferences, seminars, and extension and training courses to students and professionals of different specialties on a regular basis, as well as to general audiences. 9
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