solar panels

The power of photovoltiac cells is measured in Wp ('peak Watts'), which means the amount of electricity (in Watts) that can be produced by a cell in ideal (or peak) sunlight conditions. A standard 9 cm diameter cell produces about 0.5 to 0.7 Wp and a output voltage of 0.5V. This is too low to power electrical equipment.

To increase the power output, solar cells are wired together:

• To increase the voltage output, photovoltiac cells are wired in series. This is the same principle as putting batteries together: positive-to-negative. For example 24 cells wired in series have the output voltage 24 x 0.5V = 12V.

• To increase the amperage output, photovoltiac cells are wired in parallel. This means that each plus-pole wired together and each minus-pole wired together.

• A photovoltiac module (solar panel) is a combination of photovoltiac cells wired together in series and parallel with the purpose of generating a specific current and voltage at a given level of irradiance. For example, a module composed of 9 cells wired in series/parallel (three in series / three in parallel) has the treefold voltage output, the threefold amperage output and the ninefold power output. Photovoltiac modules may contain thirty or more cells. For protection the modules of cells are encapsulated in glass or transparent plastic. An average panel produces 50 Wp (12V).

• A photovoltiac array is composed of two or more photovoltiac modules.

The more solar panels that are used, the more electricity can be generated. A single solar panel can produce enough electicity to power a computer. Forty solar panels can power a house.

Modules which are installed on buildings, are wired into the mains electricity system and produce electricity for use directly in the building, or wired up to batteries, where the electricity can be stored for the night. The electricity produced by solar panels is direct current (DC) and therefore non-battery systems need to have an inverter to convert the current to alternating current (AC).

Solar panels produce electricity all year round. They work best when the sun is at its brightest (power output is directly proportional to light intensity), but also produce electricity on cloudy days, in the winter, in the snow and even when it is raining.

1. http://www.greenpeace.org/uk/solar/faq2.html
2. http://www.greenpeace.org/uk/solar/brief2.html
3. http://www.hammock.ifas.ufl.edu/txt/fairs/3734
4. http://www.solarelectric.com/ses/product.html
5. centre for Alternative Technology, Machynlleth, Powys SY20 9AZ, 0654 702400

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