Solar Energy

Solar energy is the light and radiant heat from the Sun that drives the Earth's climate, plant, marine and terrestrial life and cycles. Humans have tried since ancient times to harness solar energy using a range of ever-evolving technologies. From cultivating food using the seasonal cycles to using direct sunlight to dry food for storage to the use of photovoltaic cells to generate electricity and now giant mirrors to generate concentrated radiant heat, has been a non-stop quest to capture this practically unlimited source. Solar energy is also a perishable commodity. Direct solar energy is neither geographically nor temporally available at points of use in adequate quantities.

Solar radiation, along with secondary solar resources such as wind and tidal power or wave power, gravity driven river flows and biomass, accounts for most of the available renewable energy on Earth. Once this energy is captured in the form of heat or electricity, it is like any other energy source and can be put to all the uses that human ingenuity can devise. Of all the renewable energy resources only bio-mass, once created, is a natural storehouse of energy. This is a property it shares with fossil fuels. Most of the cost and operational problems associated with alternative energy sources arise from the fact that once the energy is converted to heat or electricity, it has to be used right away or stored at enormous cost and trouble. Even for hydro-electricity, the water has to be stored using barriers built at enormous cost and risk. Also the timing cycles of the water needs of down-stream farmers often clash with the power needs of the rest.

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.[1] Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.[2] The absorbed solar light heats the land surface, oceans and atmosphere. The warm air containing evaporated water from the oceans rises, driving atmospheric circulation or convection. When this air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the earth's surface, completing the water cycle.

The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as cyclones and anti-cyclones. Wind is a manifestation of the atmospheric circulation driven by solar energy.[3] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.[4] The conversion of solar energy into chemical energy via photosynthesis produces food, wood and the biomass from which fossil fuels are derived