Write a summary of the article Solar Will Supply Half of Electrical Energy.
The sun provides an effectively unlimited supply of energy that we can use to generate electricity and heat. At the moment, solar energy technology contributes only 0.02 per cent of our total energy supply, but this proportion is growing fast. In the Ecofys scenario, solar energy supplies around half of our total electricity, half of our building heating and 15 per cent of our industrial heat and fuel by 2050, requiring an average annual growth rate much lower than the one currently sustained year on year.
Solar energy provides light, heat and electricity. Photovoltaic (PV) cells, which convert sunlight directly into electricity, can be integrated into devices (solar-powered calculators have been around since the 1970s) or buildings, or installed on exposed areas such as roofs. Concentrating solar power (CSP) uses mirrors or lenses to focus the sun's rays onto a small area where the heat can be collected-for example to heat water, which can be used to generate electricity via a steam turbine or for direct heat. The same principle can be used on a small scale to cook food or boil water. Solar thermal collectors absorb heat from the sun and provide hot water. Combined with improved insulation and window architecture, direct sunshine can also be used to heat buildings.
For developing countries, many of which are in region that receive the most sunlight, solar power is an especially important resource. Solar energy can generate power in rural areas, on islands, and other remote places "off-grid".
One obvious drawback of solar power is that the supply varies. Photovoltaic cells don't function after dark-although most electricity is consumed in daylight hours when sunshine also peaks-and are less effective on cloudy days. But energy storage is improving: CSP systems that can store energy in the form of heat-which can then be used to generate electricity-for up to 15 hours, are now at the design stage. This issue of variability can also be addressed by combining solar electricity with other renewable electricity sources.