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Photovoltaics or solar electricity

Photovoltaics (PV), or solar electricity, is the simplest form of battery charging available. A photovoltaic module is used to convert the sun's energy into electricity. There are no moving parts in photovoltaic modules and little maintenance is required. Solar electric systems are modular, allowing you to start with a small system. As your power requirements grow, you can add more modules.

PV Module Construction
Most PV modules are constructed of a series of silicon cells. Each cell has a positive and negative side. A group of these cells are wired together to form a PV module. Electric current is generated when sunlight strikes the positive side of the silicon cell and the photons activate electrons contained in the silicon.

There are three types of silicon used to construct PV modules: single crystal, multicrystalline and amorphous silicon. Single crystal silicon cells are extremely thin wafers of silicon cut from a single silicon crystal. These are the most efficient silicon cells and have a life expectancy exceeding 25 years. The cells are fragile so they must be mounted in a rigid frame. Multicrystalline silicon cells are also extremely thin wafers of silicon but are cut from multiple crystals grown together in an ingot. They are similar to single crystal cells in life expectancy and fragility. However, they are slightly less efficient than single crystal cells and require more surface area to produce a given amount of electricity. Amorphous silicon cells are made by depositing a micro thin layer of silicon directly onto a sheet of glass or other substrate. They can also be mounted on a flexible backing, making them ideal for portable use.

Sunshine and Shading
PV modules produce electricity in proportion to the amount of sunlight falling on them. In full overhead or 'peak' sun (1000 watts/m2) they will produce their rated power. Reduced sunlight caused by clouds or location will diminish the amount of electricity generated. Modules will produce electricity even when there is no direct sunlight. A cloudy sky with an occasional blue patch will often be equivalent to approximately 50% peak sun. A cloudy day with rain in the forecast will be about 10 to 20% peak sun.

It is very important to note that shading even one cell of a module will reduce the output of the entire module. The only exception to his is the Uni-Solar modules which have built in diodes between the cells to reduce this effect, but it is better to mount the solar modules so shading is avoided.

It is a common misconception that heat is required for PV modules to produce electricity. High temperatures actually increase resistance and reduce the voltage within the silicon cells. Warmer climates require PV modules with a higher maximum voltage than those used in cold climates. Cold temperatures decrease resistance and increase voltage. Modules with a low voltage rating are ideal in colder climates such as Canada because more of the power produced is available as charging current, rather than voltage.

Power Rating
PV modules from the main manufacturers are similar quality and should provide years of reliable power. Most people base their buying decision on the cost of the module and its power output. However, power ratings for PV modules can be misleading and this can lead to disappointing performance. Each of our products have watts, amps and voltage listed in the product tables. PV modules are rated at their peak power point. This is measured on a curve showing voltage and current. It is the point where the panel will produce the maximum power in watts. PV modules seldom operate at their peak power point.

For example: the peak power point of the Solec SQ-75 is at 16.5 volts and the panel will produce 4.6 amps at this voltage. Since volts x amps = watts, the rated power for the SQ-75 is 75 watts (16.5 volts x 4.6 amps).

Rated power is a measurement of ideal performance. However, it is important to note that a panel may produce less than its rated power when charging a battery. Battery voltage averages about 13.5 volts when charging.


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