The sun shines approximately 1,000 watts of energy per square meter. If we could collect all of that energy we could easily power our homes and offices for free.

Unfortunately only 5 – 17 percent of solar energy can be converted to useful electricity. To understand this and help in selecting the solar cells for your application it helps to understand a little about how solar works

Types of Solar panels

1.	Crystalline Silicon PV Module: There are 2 types of crystalline silicon (c-Si) are used PV modules. Mono crystalline and poly crystalline. Conversion efficiencies of crystalline pv modules averages about 10-15%. Downside is  poor effeicieny in low light conditions and are not shadow reststant. Dust and dirt deposits reduces efficiency considerably.
2.	Amorphous Silicon PV Module: Amorphous silicon (a-Si) PV module or thin-film silicon PV module absorbs light more effectively than crystalline silicon PV module, so it can be made thinner. However it’s efficiency is low at between 6 – 8%. Production cost is lower. Amorphous panels are usually twice the size of crystalline panels for the same wattage. Because of it’s higher efficiency in low light and being shadow resistant actual power production is higher than crystalline panels.
3.	Hybrid Silicon PV Module: This combines the advantages of the above two types of panels (c-SI) and (a-SI). By surrounding mono crystalline silicon with thin layers of amorphous silicon we increase the mono crystalline panels to lower light levels and indirect light. Hybrid silicon PV module has highest conversion efficiency at around 17%.

Which Solar Panel

Mono Crystalline	Poly Crystalline	Amorphous

For most people price is always the single most crucial factor.

Amorphous panels are cheaper to manufacture and to compemsate for lower efficiency the panels are twice the size of similar capacity multi-crystalline panels but half the price.

If space is a problem such as on boats and caravans then mono-crystalline panels are the way to go.

If not then amorphous panels should be the choice as the same 20 year warranty is offered.

Advantages of Amorphous Panels

Amorphous panels are reputed to work in low light. The reason for this is clear when you consider that the BS40 amorphous panel has peak operating voltage of 62 volts. As voltage drops in low light it is still above 13.5 volt charging voltage of your 12 volt battery bank.

With a multi-crystalline panel it’s operating voltage is from 14 – 18 volts. If the voltage falls below 13.5 volts the battery cannot be charged. Energy produced will be dissipated by the controller.

Amorphous panels are shadow resistant meaning that power production is not cut-off if a shadow falls over the panel.

The glass surface is smooth. Dirt and grime forming are easily washed off. Bird droppings will not cut-off power production.

As amorphous panels work well in indirect light it’s efficiency could be increased with reflected light.

MPPT Controllers

These are essentially Dc to Dc converters. If a solar panel produces 2 amps at 20 volts ie 40 watts feeding this current directly into the battery results in only 2 amps X 12 volts  that is 24 watts. 16 watts is “lost”, An MPPT controller converts the current to 3.3 amps at 12 volts (40 watts) before feeding it into the battery.