Solar photovoltaic cells are small, square shaped panel semiconductors manufactured in thin film layers from silicon and other conductive materials. When sunlight strikes the PV cell, chemical reactions release electrons, generating electric current. The photovoltaic cells connected in series or parallel. When the cells are connected in series, the total voltage is the sum of the voltages from each individual cell. The output current in this configuration will remain the same as that produced from a single cell. When the cells are connected in parallel, the total current is the sum of the currents from the individual cells and the output voltage is the same as that produced from a single cell.

Typically, cells are arranged in a module to produce voltages in increments of 12. Hence, most modules in the marketplace are 12 volts, 24 volts, and even 36 volts. The trend is to higher voltage modules.

Like photovoltaic cells, solar modules can also be arranged to produce a specific current and voltage. By connecting solar panels in certain configurations (called a solar array), one can dictate the current and voltage of the array, thus dictating the electricity the system produces.

The size of your photovoltaic system will be dictated by the amount of daily energy required and the amount of energy available at your location.

Module Types
Modules are available in different power outputs, frame types, cell technology, life expectancy and efficiency. These factors will determine the best panel to suit your needs.

Module Colors
Modules can be produced in various colors. This is typically associated with the need to create a distinctive look either for security reasons or for architectural reasons.

Efficiency Ranges for Various Module Types
Cell Type Efficiency Range
- Monocrystalline cells about 13 %
- Polycrystalline cells 11 to 12%
- CIS, thin film cells about 6 to 8 %

PVs do generate electricity in cloudy weather although their output is diminished. In general, the output varies linearly down to about 10% of the normal full sun intensity. Since flat plate PVs respond to a 180-degree window, they do not need direct sun and can even generate 50-70% of their rated output under a bright overcast. A dark overcast might correspond to only 5-10% of full sun intensity, so output could be diminished proportionately. Indoor light levels, even in a bright office are dramatically lower than outdoor light levels, typically by a factor of several hundred or more. PVs designed for outdoor use will generally not produce useful power at these light levels since they are optimized for much higher intensities. On the other hand, PVs designed for lower light levels like the cells found on calculators are optimized for those conditions and perform poorly in full sunlight.

There are two primary PV markets. Off-grid systems are used where the cost of a PV system is cheaper than stringing electrical power lines long distances from the local utility. Grid-connected PV systems usually cannot compete directly with the cost of utility-produced power. However, with the changing deregulated marketplace, many people are considering grid-connected PV systems. If the PV system provides more power than the home or business uses, additional electricity is fed back into the grid for other people to use. This effectively spins an electricity meter backward.

Stand alone PV system can be as simple as a module and a load (such as a direct driven water pumps), most PV systems include batteries to store the energy generated by the PV array. Systems with batteries also need electronic devices to control their charging or limit the discharging of the batteries.

In general, the PV modules are the longest lived component of a PV system. Top quality modules such as Siemens/Shell series are designed to last at least 30-50 years and carry a 25 year warranty. They are designed to withstand all of the rigors of the environment including arctic cold, desert heat, tropical humidity

Warranty, 80% of their original minimum power rating for 25 years.