Solar Energy

Photovoltaic (PV) systems

Solar energy is readily harnessed for low temperature heat, and in many places domestic hot water units (with storage) routinely utilize 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), and by mid-2013 some 15 GWe of utility-scale solar power was installed, 3.1 GWe of this in China, and 2.9 GWe in each of Germany and USA. Domestic-scale PV is widespread.

According to Worldwatch Inst., over 39 GWe of solar capacity was installed at the end of 2013, and delivered 124.8 TWh that year, suggesting 36% capacity factor. That source quotes PV module spot prices as $630/kW, though in Melbourne the price is $1400-1800/kW installed, net of certificates sale.

The best-known method utilizes 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. In the World Energy Outlook 2011 New Policies Scenario, 553 GWe of new solar PV capacity (and 81 GWe of CSP) would be added by 2035.

Thin-film PV modules using silicon or cadmium telluride are at least 20% less costly than crystalline silicon-based ones, but are less efficient. Even working on 1 kilowatt per square meter in the main part of a sunny day, intensity of incoming radiation and converting this to high-grade electricity is still relatively inefficient – typically 10% in commercial equipment or up to 30% in more expensive units. But the cost per unit of electricity – at least ten times that of conventional sources – limits its unsubsidized potential to supplementary applications on buildings where its maximum supply coincides with peak demand.

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 2011 several Californian plants planned for solar thermal changed plans to solar PV – see mention of Blythe, Imperial Valley and Calico below.

The 550 MWe Desert Sunlight solar farm in the Mojave Desert opened Q1 of 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%.

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.

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.11