Solar cells are connected together and encapsulated to form solar modules. The solar cells are generally sandwiched between a toughened glass front and a poly vinyl back sheet surrounded by an aluminium frame. While solar modules have traditionally been sized to suit lead acid batteries, with outputs of 12 volts, new grid connect modules tend to be larger.
What are the different types of solar modules?
There are two main types of solar modules available. These are stand alone modules, or traditional solar modules, and grid connect modules which have been developed especially for grid connect applications.
Traditionally solar power has been used in remote areas in conjunction with battery backup systems. These systems have voltages of 12 volts for smaller systems and multiples of 12 volts for larger systems. This lead to the vast majority of solar modules been made with a nominal voltage of 12 volts.
What should I look for in a solar module?
As a minimum you should ensure that any solar panel that you are considering is certified to the IEC (European) or UL (American) standards. These standards are developed to ensure a minimum level quality and safety in solar modules and any rebate application will require that the solar panels to be used are certified to one of these standards.
Solar modules are rated to a certain power which is the power that they should produce under standard test conditions (STC). They will also have a tolerance rating, typically ±10% of the rated power which shows the power range that the module will lie in. For example a 100W module with a tolerance of ±10% will have a power output of somewhere between 90W and 110W at STC. Another 100W module with a tolerance rating of -5% to +15% will have a power output of between 95W and 115W at STC. Generally, lower tolerances are preferable as they mean that all panels of a certain model will have similar power outputs which is important in high voltage systems.
The quality of the raw polysilicon silicon feedstock used to make crystalline solar cells has a strong impact on the actual power output of the finished module (as opposed to the 'rated' power).
There is currently a world shortage of the polysilicon feedstock that is used to make solar cells due to the rapidly growing solar industry outstripping supply. The larger solar cell manufacturers have typically responded by entering into long term supply contracts with the major polysilicon feed stock manufacturers, ensuring both availability and quality of their raw materials. Smaller cell manufacturers, especially new entrants to the market don't have the long term certainty to do this however and tend to buy silicon feedstock on the spot market, buying what they can get within their acceptable price range. This means that they are using highly variable raw materials, often of lower quality, which in turn affects the power output of these modules.
Although you can't check the quality of the raw materials by looking at a finished solar module, you can ensure against low quality products by using products manufactured by reputable manufacturers with a track record in the solar industry.
Virtually all solar modules carry a warranty of at least 10 years, with most reputable manufacturers offering warranties of 20 or 25 years in Australia . With such long warranty periods, it is important to consider the ability of the manufacturer, or importer in the case of an overseas manufacturer, to honour their warranty. In particular, a 25 year warranty is worthless if the company offering it goes broke or disappears in 5 years time.
Most solar modules have an anodised aluminium frame to give them strength. Unframed modules break much more easily when hit by hail or other impacts. Furthermore, different manufactures use different types of frames. The better modules, such as Kyocera's KC series, have a double wall containing a boxed section that gives the frame much more strength than a single walled frame.