Science – photocells and solar panels Part 1-How a photocell generates electricity?(from bitesize) –The Sun provides a stable source of heat and light energy. Photocells transfer light into electricity, and glass can provide passive heating for buildings. Wind turbines transfer kinetic energy in the wind into electricity.
Photocells - The Sun is a stable source of energy that is transferred to the Earth as light energy and heat energy. We can use this energy.
Photocells are devices that transfer light energy directly into electrical energy. They produce DC - direct current - electricity. This is electricity in which the current moves in the same direction all the time.
Photocells have no moving parts, and can work in remote locations. For example, they are used to power the lights for some road signs.
The output of photocells depends on the surface area that is exposed to light. For a given light intensity, the larger the area, the greater the power output.

The Hubble Space Telescope uses photocells to generate the electricity it needs - image courtesy of NASA
You may have seen photocells in pocket calculators. Very large panels of photocells are used to power satellites in orbit around Earth.
Photocells produce no power in bad weather, or at night. But sunlight is a renewable energy resource and photocells do not produce polluting waste while they are in use. Here are some other advantages to photocells: * no fuel is needed * no power cables are needed * they have a long life and are rugged - little maintenance is required

Solar heating - Glass windows provide passive solar heating for buildings. Sunlight passes through the glass and is absorbed by surfaces in the building. It is transferred into heat energy, which is emitted as infrared radiation. This is reflected back into the building by the glass.
Solar panels - Solar panels do not generate electricity - rather they heat up water. They are often located on the roofs of buildings, where they can receive energy from the Sun. The diagram outlines how they work:

Solar panel
A pump pushes cold water from the storage tank through pipes in the solar panel. The water is heated by energy from the Sun and returns to the tank. In some systems, a conventional boiler is used to increase the temperature of the water.
Solar collectors - Solar collectors use mirrors to focus the Sun’s rays onto a small area. In some parts of the world, this idea is used to make simple solar ovens to cook food without using fuel. More complex solar collectors use curved mirrors to reflect the Sun’s rays onto a focus point. Motors are used so that the collector moves to track the position of the Sun in the sky.
Wind - Wind is produced as a result of giant convection currents in the Earth's atmosphere, which are driven by heat energy from the Sun. This means the kinetic energy in wind is a renewable energy resource: so long as the Sun exists, wind will too.
Wind turbines - Wind turbines have huge blades mounted on a tall tower. The blades are connected to a nacelle, or housing, that contains gears linked to a generator. As the wind blows, it transfers some of its kinetic energy to the blades, which turn and drive the generator.
Several wind turbines may be grouped together in windy locations to form wind farms.
Photocells and wind turbines – higher – Photocells - Photocells consist of two types of silicon crystal. When light energy is absorbed by the silicon: * negatively charged electrons are knocked loose from the silicon atoms * the electrons flow freely, creating an electric current

Positive 'holes' are also formed, which move in the opposite direction to the electrons
The power output of a photocell increases as: * the light intensity increases * the exposed surface area increases
Wind turbines - Some advantages and disadvantages of wind turbines advantage | disadvantage | uses a renewable energy resource - wind | may not look nice |