Solar Energy
Sharbanee Bhattacharyya
Product Manager || Accelerating AI/ML Adoption in Renewable Energy Sector
Solar energy is readily harnessed for low temperature heat, and in many places domestic hot water units (with storage) routinely utilise it. It is also used simply by sensible design of buildings and in many ways that are taken for granted. Industrially, probably the main use is in solar salt production – some 1000 PJ per year in Australia alone (equivalent to two-thirds of the nation's oil use). It is increasingly used in utility-scale plants, mostly photovoltaic (PV). Domestic-scale PV is widespread.
IRENA 2017 statistics had 296 GWe of solar capacity in 2016 (up from 225 GWe in 2015), which produced 256 GWh – so an average capacity factor of 13%. Of the 2016 total, 291 GWe (98%) was solar PV.
Three methods of converting the Sun's radiant energy to electricity are the focus of attention.
Photovoltaic (PV) systems
The best-known method utilises light, ideally sunlight, acting on photovoltaic cells to produce electricity. Flat plate versions of these can readily be mounted on buildings without any aesthetic intrusion or requiring special support structures. Solar photovoltaic (PV) has for some years had application for certain signaling and communication equipment, such as remote area telecommunications equipment in Australia or simply where mains connection is inconvenient. Sales of solar PV modules are increasing strongly as their efficiency increases and price falls, coupled with financial subsidies and incentives. In 2012 world installed PV capacity reached the 100 GWe milestone, with 30.5 GWe installed that year, and it reached 291 GWe at the end of 2016. Utility-scale solar PV achieved a global weighted average LCOE of about $135/MWh (13.5 c/kWh) for projects completed in 2015. In the World Energy Outlook 2017 New Policies scenario, 2067 GWe of solar PV capacity (and a lot less CSP) would be operational in 2040, producing 3162 TWh (17.5% capacity factor). In the Sustainable Development scenario, solar PV capacity would reach 3246 GWe, producing 5265 TWh.
In Germany, 1.5 million solar PV installations in 2015 had a combined capacity of 40 GWe and delivered 38.7 TWh of electricity – an 11% capacity factor. Capacity in 2016 was 41 GWe. On summer weekdays, solar irradiation covers up to 35% of German grid requirements, and nearly 50% on weekends. Italy is more sunny and in 2015 had 18.9 GWe installed which delivered 22.9 TWh – 13.8% capacity factor. Capacity in 2016 increased to 19.2 GWe.
In east Asia, China in 2015 had 44 GWe installed which delivered 39.7 TWh – a 10.3% capacity factor. Capacity in 2016 increased dramatically to 78 GWe. Japan in 2015 had 33 GWe installed which delivered 37.9 TWh – 13.1% capacity factor. Capacity in 2016 increased to 41.6 GWe.
The USA in 2015 had 24.4 GWe installed which delivered 31.2 TWh – 14.6% capacity factor. Capacity in 2016 increased to 33 GWe. (all IRENA data)
Many solar PV power plants are connected to electricity grids in Europe and USA, and now China.
More efficiency can be gained using concentrating solar PV (CPV), where some kind of parabolic mirror tracks the sun and increases the intensity of the solar radiation up to 1000-fold. Modules are typically 35-50 kW. In Australia a 2 MWe demonstration plant followed by a 102 MWe dense-array CPV power station was planned by Silex SolarSystems for Mildura in Victoria, with A$ 125 million government support promised. Anticipated cost of power is under 15c/kWh. Silex claimed 34.5% conversion efficiency, with a target of 50%. This project was abandoned in 2015 due to failure to find investment capital.
In the USA Boeing has licensed its XR700 high-concentration PV (HCPV) technology to Stirling Energy Systems with a view to commercializing it for plants under 50 MWe from 2012. The HCPV cells in 2009 achieved a world record for terrestrial concentrator solar cell efficiency, at 41.6%. CPV can also be used with heliostat configuration, with a tower among a field of mirrors.
In 2011 several Californian plants planned for solar thermal changed plans to solar PV – see mention of Blythe, Imperial Valley and Calico below.
China's 200 MWe Golmud solar park was commissioned in 2011 and is claimed to produce 317 GWh/yr (18% capacity factor). The Longyangxia Dam solar park on the eastern Tibetan Plateau in China has grown to 850 MWe and has a 20% capacity factor.
India’s 214 MWe Gujarat Solar Park was commissioned in 2012 and aims for eventual 1000 MWe capacity. Adani’s 648 MWe Kamuthi solar PV plant in Tamil Nadu was completed in September 2016. The Indian government announced the 4 GWe Sambhar project in Rajasthan in 2013, expected to produce 6.4 TWh/yr, i.e. capacity factor of 18% from almost 80 sq km. The initial 1 GWe is expected to operate from 2016, costing Rs 7,500 crore ($1.2 billion).
The 100 MWe Perovo solar park in Ukraine was commissioned in 2011 also, with 15% capacity factor claimed. EdF has built the 115 MWe Toul-Rosieres thin-film PV plant in eastern France. There is a 97 MWe Sarnia plant in Canada. In Italy, SunEdison plans to build a 72 MWe solar PV plant near Rovigo, for $342 million.
In Australia the 102 MWe Nyngan solar PV array cost A$290 million and is expected to produce 230 GWh/yr from 2015, i.e. 26% capacity factor.
In the USA, the 550 MWe Desert Sunlight solar farm in the Mojave Desert opened early in 2015, using cadmium telluride thin film technology and financed with a $1.46 billion federal loan guarantee. MidAmerican’s Antelope Valley plants in California comprise a 579 MWe development with Sunpower as EPC contractor and due to be complete at the end of 2015. Its panels will track the sun, giving 25% more power. MidAmerican Solar owns the 550 MWe Topaz Solar Farms in San Luis Obispo County, Calif., and has a 49% interest in the 290 MWe Agua Caliente thin-film PV project commissioned in 2014 by First Solar in Yuma County, Arizona. Many PV plants are over 20 MWe, and quoted capacity factors range from 11% to 27%.
A South Korean consortium has commissioned 42 MWe PV capacity at two plants in Bulgaria, which are expected to produce 61 GWh/yr (16.5% capacity factor), their cost being €154 million (€3667/kW). Research continues into ways to make the actual solar collecting cells less expensive and more efficient. In some systems there is provision for feeding surplus PV power from domestic systems into the grid as contra to normal supply from it, which enhances the economics. The 2000 MWe Ordos thin-film solar PV plant is planned in Inner Mongolia, China, with four phases – 30, 100, 870, 1000 MWe – to be complete in 2020. Over 30 others planned are over 100 MWe, most in India, China, USA and Australia. A 230 MWe solar PV plant is planned at Setouchi in Japan, with GE taking a major stake in the JPY 80 billion project expected on line in 2018. Serbia plans a 1 GWe solar PV project costing €1.3 billion which is expected to deliver 1.15 TWh/yr to Enerxia Energy from 2015, a 13% capacity factor, without any feed-in tariff. (That output at €50/MWh would return €57.5 million pa. After €20 million pa maintenance, it is less than 3% pa return on capital.)
In recent years there has been high investment in solar PV, due to favourable subsidies and incentives. In 2011 Italy saw 9000 MWe of solar PV installed, and Germany 7500 MWe of solar. In Germany, solar PV capacity reached 32.4 GWe at end of 2012 (7.6 GWe installed during the year) and generated 28 billion kWh, increasing 45% over 2011, but apparently only 11% capacity factor. In Italy, feed-in tariffs range from 15-27 euro cents/kWh, depending on size, giving a 2011 cost to consumers of nearly €6 billion. In the World Energy Outlook 2011 New Policies Scenario, 553 GWe of new solar PV and 81 GWe of CSP capacity would be added by 2035. Solar PV capacity at the end of 2011 was 67 GWe.
In Nigeria, the federal government and Delta state have set up a $5 billion public-private partnership with SkyPower FAS Energy to build 3 GWe of utility-scale solar PV capacity, with the first units coming on line in 2015. A feed-in tariff regime will support this.
A serious grid integration problem with solar PV is that cloud cover can reduce output by 70% in the space of one minute. Various battery and other means are being developed to slow this to 10% per minute, which is more manageable. The particular battery system required is designed specifically to control the rate of ramp up and ramp down. System life is ten years, compared with twice that for most renewable sources.
The manufacturing and recycling of PV modules raises a number of questions regarding both scarce commodities, and health and environmental issues. Copper indium gallium selenide (CIGS) solar cells are a particular concern, both for manufacturing and recycling. Silicon-based PV modules require high energy input in manufacture, though the silicon itself is abundant.
IRENA in 2016 estimated that there was about 250,000 tonnes of solar PV waste, and that the total could reach 78 million tonnes by 2050. Recycling solar PV panels is generally not economic, and there is concern about cadmium leaching from discarded panels.