PHOTOVOLTAIC CELLS COME IN MANY SIZES AND SHAPES

Photovoltaic cells come in many sizes and shapes—from smaller than a postage stamp to several inches across. Each cell is capable of producing one to two watts of power. Although this is not enough to power most appliances, cells can be linked together in modules. Modules store photovoltaic cells in a weatherproof container and may be up to several feet long and a few feet wide. 

Depending on how much energy is needed, the modules can also be linked together to provide higher voltages. Photovoltaic power plants use a few thousand modules to generate electricity for household or business uses. Because photovoltaic systems come in small and large sizes and shapes, they are able to meet almost any electric power need, whether in a small house or in a large community of homes. 

The modules, in turn, can be combined and connected to form photovoltaic arrays of diff erent sizes and power output. These kinds of arrays can be seen on the Nellis Air Force Base and on large solar farms.  

Power of a Solar Array 

Electrical power is measured in watts. A watt is a measurement of total electrical power: Volts x Amps = Watts. For electrical power, one watt is equal to one ampere of current per second. 

The power output of a single solar cell or an array of solar cells can be measured in watts, watt-hours, kilowatt-hours, kilowatt-hours per day, or even megawatts. A megawatt will produce electricity for 400–900 homes per year. Utility power plants usually measure their output in megawatts. Th e megawatt is equal to one million watts. 

 SOLAR STORAGE 

The biggest problem of solar power technologies is how to store the power generated for those times when sunlight is unavailable. Currently, most solar power plants do not have the capability to store excess energy from sunny days to be used on cloudy days. One option is to use a storage battery bank that will collect and store power anytime the system is producing more energy than is needed.  

Photovoltaic to Battery Storage 

A storage battery is an excellent system for supplying electricity when and where it is needed on non-sunny days when solar power is not available. Photovoltaic systems with a backup battery storage unit are used to provide electricity for power tools, lights, home appliances, telephones, and televisions. Photovoltaic/battery systems work well in remote areas where utility power is unavailable or at a distance that is so far away that it would be too costly to install utility transmission lines to a building. 


Although batteries make photovoltaic systems more useful, they also require some maintenance. The batteries used in photovoltaic systems are referred to as deep-cycling batteries, the kinds that are used on many golf carts. Th e batteries are bigger than the typical car battery. These kinds of batteries allow more stored energy for use each day. 

Batteries designed for photovoltaic projects need to be handled with care. Th e fl uid needs to be checked in unsealed batteries periodically. 


John F. Mongillo
A Student Guide to Energy 
Copyright 2011
Greenwood Publishing Group
Volume 2 Solar Energy and Hydrogen Fuel Cells