Photovoltaic Cells as a power option for larger systems
Solar cells are the only direct conversion of light into electricity.
The basic solar cell is a semiconductor device of silicon 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.
Photovoltaic Cell Ratings
Solar cells are rated as the amount of watts available under standard conditions.
maximum power point
This is defined as: the current and voltage combination at which the cells produce maximum power, as measured at 25 degrees c.
is defined as: 1000watts/m square
are rated as: outputs are rated in peak watts (Wp) and are available in panels up to about 280Wp
If you choose to have photovoltaic panels as part of your over all alternate energy system, shop around as prices vary. There are several top brands available, some with 10-20 year warranties. Remember than in planning any alternate energy system, you must first practice energy management and energy efficiency. You can also forget about powering electric stoves and other energy hungry "resistive heating" appliances. These are usually powered by prophane or natural gas. PV power is simply too expensive to be used with these devices. However, using a hybrid system (PV and another source i.e. wind)to power a computer, a few lights, a microwave, tv etc. is a good first step to aim for. Get a realistic over view of your true electrical needs first, get yourself a good battery bank and a properly sized generator and you have made the first step. Sizing a PV system depends on a number of factors. The number of average hours of sun in your area, the load requirements, battery storage capacity needed and other calculations need to be made to size the system properly. While the price of PV panels has come down in recent years, they are still quite expensive if they are considered as the only source of charge for the battery bank. The PV panels would have to cover a larger area and the system will be much more costly than a hybrid system. A generator is essential in any alternate energy system. It will be activated when the battery charge controller shows that the load required is exceeding the recharging capabilities of the PV Panels. A generator will handle heavy loads such as washers, motors etc and will provide an equalization charge to the battery bank. Equalization of the battery bank is a controlled overcharging of the batteries. This is performed once a month(sometimes more often) to equalize charges between individual cells in the battery bank.
Practice energy efficiency and energy management. Get a realistic view of your true energy needs. Set up your properly sized battery bank, generator, charge control. Investigate wind turbines and other sources of alternate energy that you may have available. Combining sources such as PV and wind energy, an energy efficient home and appliances can go along way in reducing your overall energy bills and lower the initial cost of your system too.
author - Keith Anderson
© copyright 2002