The widget above shows how much energy we produce as world and how much alternative energy we produce.
How do we get the solar energy into an electricity?
Solar energy can be convert into electricity in two ways: Photovoltaic (PV devices) ,or "solar cells", and Solar Thermal/Electric Power Plants. (1)
Solar cells produce electricity by absorbing the energy in sunlight and causing electrons to flow. The diagram above shows that after material absorb enough energy, electrons leave their position, creating a hole. Then, the electrons travel toward surface of the solar cell, which creates the difference of the charge between the cell's front and back surfaces. An energy like positive and negative of the battery form from the difference. Electricity flows after you connect the two surfaces with an external load. (1)
The picture above is from http://www.basinandrangewatch.org/CrescentDune.html. It is a picture of solar power tower which is one type of solar thermal plant.
Solar Thermal/Electric Power Plants convert into electricity by concentrating solar energy to heat a fluid to very high temperatures. The fluid circulate through a pipe to trasfer its heat to water so it'll create steam. Then the steam turns the turbine, creating mechanical energy and the generator that is connected to turbine creates electricity. There is three main types of solar thermal power system: Parabolic Trough, Solar Dish, and Solar Power Tower. (1)
Parabolic Trough has a reflector that is in shape of half circle that will focus the sunlight to the receiver tube in the middle. As the sun moves from east to west, it will turn itself by drive motor so they are always focused on the sun.
A heat transfer fluid goes through receiver tube, heating the fluid. Then, it'll go through heat exchanger to transfer the heat of fluid to water, which will create high-pressured, superheated steam. (After the fluid goes through the heat exchanger, it'll cool down and go through the receiver tube to heat up again.) The steam will go through turbine and generator to create electricity. (1)
Solar dish. or engine system, uses concentrating solar collector that track the sun, so they are always pointing straight at the sun. They concentrate the solar energy at the focal point of the dish.
Solar power tower, or central receiver, creates electricity from sunlight by focusing concentrated solar energy on a heat exchanger that is mounted on a tower.
Solar energy is being directly transferred by reflecting the sunlight to a single receiver panel that has fluid inside to collect the heat. Then, the fluid transfer heat to water to create steam that will turn the turbine and create electricity by generator like parabolic trough. (1)
How do we use solar energy as heat?
For solar water heating, water goes through the black pipes in the glass panel, so they get heated by sunlight when it shines on the pipe. The water comes from bottom so convention helps the flow of the hot water out through the top. For some solar water heating system, you have to drain the water from pipe so the panels won't freeze in winter. (4)
There is two types of solar space heating, passive or active.
Passive space heating heats up the inside of a building. The air is circulated past a solar heat surface and through the building by convetion. This doesn't require mechanical equipment. The picture above shows how the air moves as sunlight heats the air. It's from http://www.iklimnet.com/save/passive_solar_heating.html.
Active heating system need some kind of collector that absorb and collect radiation. They also need a fans to circulate a heated air. Most of the times, they have some type of energy storage system.
