The principle of photovoltaic cells PVs

PVs are devices which convert light directly into electricity. At present most PVs consist of two thin layers of a semi-conducting material, each layer having different electrical characteristics. In most common PV cells both layers are made from silicon but with different, finely calculated amounts of impurities: p-type and n-type. The introduction of impurities is known as 'doping'. As a result of the doping one layer of silicon is negatively charged (n-type) and has a surplus of electrons. The other layer is given a positive charge (p-type) and an electron deficit. These two neighbouring regions generate an electrical field. When light falls on a PV cell electrons are liberated by the radiative energy from the sun and able to migrate from one side to the other. Some of the electrons are captured as useful energy and directed to an external circuit (Figure 7.2).

Cells with different characteristics and efficiencies can be created by using different base and doping materials. The output is direct current (DC) which must be changed to alternating current (AC) by means of an inverter if it is to be fed to the grid. Converting to AC current involves a power loss.

The capacity of cells to convert light into electricity is defined by watts peak (Wp). This is based on a bench test and is the power generated by a PV under light intensity of 1000 watts per square metre, equivalent to bright sun. The efficiency of a cell is a function of both peak output and area. This is a laboratory measurement and does not necessarily give a true indication of energy yield.

Principle Photovoltaic Power

Figure 7.2 At the time of writing the most efficient PVs are monocrystalline

Photovoltaic cell structure and silicon consisting of wafers of a pure crystal of silicon. They achieve a function peak output of about 15 per cent. That means that 15 per cent of day light is converted to electricity when daylight is at its maximum intensity. Due to the production processes involved these cells are expensive.

The solar cell size of around 10 cm X 10 cm has a peak output of about 1.5 watts. To realise a usable amount of electricity cells are wired into modules which, in turn, are electrically connected to form a string. One or more strings form an array of modules.

The cells are sandwiched between an upper layer of toughened glass and a bottom layer of various materials including glass, Tedlar or aluminium. It must be remembered that a number of linked cells produces a significant amount of current, therefore during installation solar cells should be covered whilst all the electrical connections are made.

Figure 7.2 At the time of writing the most efficient PVs are monocrystalline

Photovoltaic cell structure and silicon consisting of wafers of a pure crystal of silicon. They achieve a function peak output of about 15 per cent. That means that 15 per cent of day light is converted to electricity when daylight is at its maximum intensity. Due to the production processes involved these cells are expensive.

The solar cell size of around 10 cm X 10 cm has a peak output of about 1.5 watts. To realise a usable amount of electricity cells are wired into modules which, in turn, are electrically connected to form a string. One or more strings form an array of modules.

The cells are sandwiched between an upper layer of toughened glass and a bottom layer of various materials including glass, Tedlar or aluminium. It must be remembered that a number of linked cells produces a significant amount of current, therefore during installation solar cells should be covered whilst all the electrical connections are made.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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