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Solar energy is energy from the Sun in the form of heat and light. This energy drives the climate and weather and supports virtually all life on Earth. Heat and light from the Sun, along with secondary solar resources such as wind and wave power, hydroelectricity and biomass, account for over 99.9% of the available flow of renewable energy on Earth.[2][3]
Solar energy technologies harness the sun's heat and light for practical ends such as heating, lighting and electricity. These technologies date from the time of the early Greeks, Native Americans and Chinese, who warmed their buildings by orienting them toward the sun.[4][5]
Solar power is used synonymously with solar energy or more specifically to refer to the conversion of sunlight into electricity. This can be done with photovoltaics, concentrating solar thermal devices and various experimental technologies.
Urban heat islands (UHI) are metropolitan areas with higher temperatures than the surrounding environment. These higher temperatures are the result of urban materials such as asphalt and concrete that have lower albedos and higher heat capacities than the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and plant trees. A hypothetical "cool communities" program in Los Angeles has projected that urban temperatures could be reduced by approximately 3 °C after planting ten million trees, reroofing five million homes, and painting one-quarter of the roads.