photovoltaic cells

Solar cells are the only direct conversion of sunlight to electricity. The basic solar cell is a semiconductor properly ?doped? to obtain a p-n junction. The n silicon has free electrons and the p silicon has free moving positive charges called holes. at the p-n junction the charges neutralize and with no incidental light, there is no charge motion. As light rays strike the thin n silicon layer, it permits a penetration of photons to the junction. the light energy forces electrons out of the crystal structure. This motion of charges produces an output current when a load is connected between the positive p silicon terminal and the negative n silicon terminal.

Solar panels are rated as the amount of watts available under standard conditions. the ? maximum power point? is used and can be defined as the current and voltage combination at which they produce maximum power under peak sunlight, measured at 25 degrees celsius. Peak sunlight is defined as 1000 watts/square meter. modules with outputs up to around 320 peak watts are available.

If you choose to have pv panels as part of your system it is a good idea to shop around as prices vary. if you are adventurous you can assemble cells into panels yourself.

Individual cells are wired in to panels and then to increase power they are assembled into arrays.

the output of the array is connected to a voltage regulator if necessary, but in most cases this is not needed unless the array output is much greater in relation to the battery capacity. If the panels are capable of delivering a rate of charge larger than 10% of the battery capacity expressed in ampere hours then a regulator should be used, especially if the systems battery is not used often.

[if a regulator is needed, an inexpensive one can be constructed by you . Complete details and schematics of suitable pv regulators will be featured here in future articles.] at night and at low light levels, the batteries provide power on a continuing basis. The array and the battery capacity must be greater than the actual peak demand.

An important component of the solar panel is the blocking diode. In darkness and at low light levels the battery voltage can exceed the panel voltage. Without the blocking diode the battery can discharge into the array.

There are other factors that must be considered in a pv system. peak sun hours have to be calculated for your particular area. The average peak sun hours and the daily load in ampere hours can be used to find the total current in amperes that has to be supplied by the array.

Check your monthly or bimonthly electricity bill and note the kilowatt hour consumption. To find out your daily consumption divide by 30 or the number of billing days. If you start practicing energy efficiency and energy management techniques, your daily consumption will fall and you will be in a better position to