At the core of all Solar panel systems is the array of photovoltaic modules. Almost all PV modules are made from crystalline silicon. It´s important for you to know that there can be variations in the performance of different brands. In order to make an educated choice you must consider 4 important factors:
1) Performance labels: Real performance (PTC) vs. commercial labeling (STC). The solar panel manufacturing plants do their testing at a 78 degree standard (standard test conditions). In the real world panels absorb light and heat and their temperature can go up to 150 degrees. High temperature affects the performance of solar panels. So it´s very important that you skip the commercial labeling and look for the PTC, PV USA or CEC ratings that will give you more real life performance information.
2) Watts per square feet: After gathering information about the real performance of different brands you must also know the watts produced per square foot. Sometimes the space where the panels can be installed is reduced or you just simply want the highest yield per square foot. In those cases you may decide to invest more on your panels to get a product with higher efficiency.
3) The temperature factor: Modules perform better at cooler temperatures: They lose watt production when it gets hot, some more than others depending on materials and the technology used to make them. Be sure to check those metrics before you make a decision.
4) Performance “tolerance”: Another important factor for you to know is that modules are priced on a “per watt basis” and are tested after they come out of the manufacturing line to measure the actual wattage production. Some (not all) manufacturers give themselves a tolerance percentage. For example when a module does not perform to the number it was intended to, the manufacturer might label it as a “250 watt” module with a 5% tolerance. But will most certainly charge you for a 250 watt module.