Solar energy collected on Earth is the energy of the stream of electromagnetic radiation coming from the Sun to Earth. We will continue to receive this stream of energy until the nuclear reaction on the Sun runs out of fuel, about 5 billion years from now.
This energy can be obtained directly through the photoelectric effect, which converts the solar photons energy into electricity, as in the solar cell. The energy of the photons can also be absorbed to heat objects, i.e. convert to heat, used for solar water heaters, or boil water in the solar tower's thermoelectric machines, or heat systems such as solar air conditioners.
The energy of the photons can be absorbed and converted into energy in the chemical bonds of photochemical reactions.
A natural photochemical reaction is photosynthesis. This process is thought to have stored solar energy in non-renewable fossil fuel sources that the industries of the nineteenth to twenty-first centuries had been making use of. It is also the process that energizes all natural biological activities, for livestock traction and firewood, traditional renewable bioenergy sources. In the future, this process could help create renewable energy sources in biofuels, such as liquid fuels (biodiesel, vegetable oil fuel), gas (biogas) or solid. .
Solar energy is also absorbed by the Earth's hydrosphere and Earth's atmosphere to produce meteorological phenomena containing exploitable forms of energy reserves. The Earth, in this energy model, resembles the water heater of the early heat engines, converting the heat absorbed from the Sun's photons into the kinetic energy of the currents of water, steam and air. , and alter the chemical and physical properties of these flows.
The potential of rainwater can be stored in dams and run the generator of hydroelectric plants. One form of making use of the energy from rivers and streams that existed before hydroelectricity was the water mill. The currents of the sea can also move the generator of a power plant using the currents of the sea.
The flow of the air, or wind, can generate electricity by turning a wind turbine. Before wind power generators were introduced, windmills were used to grind grain. Wind energy also causes wave motion across the sea surface. This movement can be utilized in power plants using waves.
Oceans on Earth have a greater specific heat than air and therefore change temperature more slowly than air when absorbing the same heat of the Sun. The ocean is hotter than air at night and colder than air during the day. This difference in temperature can be exploited to run heat engines in power plants that use the heat of the sea.
When the absorbed heat from the Sun's photons evaporates the seawater, some of that energy is stored in separating the salt from the salt water of the sea. The power plant uses the reaction of fresh water - salt water reclaim this energy when it brings fresh water from the river back to the sea.
