When you buy solar panels you have a lot to consider.
Firstly you have to consider what type of solar panel you want to buy and secondly what brand of solar panel you wish to buy.
The first question is usually a choice between a poly-crystalline solar panel and a mono-crystalline solar panel. Poly solar panels normally offer the advantage of a lower temperature co-efficient and mono crystalline panels are often favoured because theoretically mono-crystalline cells can be slightly more efficient. However, the truth is that if you have two solar panels, one is a 250 watt poly and one a 250 watt mono then this means in normal test conditions they both produce the same amount of power. Why? Because when they decide if a panel is going to be rated at a certain number of watts they shine 1000 megajoules per sqm of irradiation at the panel at 25 degrees and measure the output. If both are rated at 250 then this says both produced 250 watts with that level of irradiation. As such the cell type is of little real importance when you buy solar panels.
The next question to ask is what brand should I buy. I think the thing to consider here is trust, do you trust that either you, or the solar company you are buying from has a good enough relationship with the manufacturer such that this manufacturer will not sell them dodgy solar panels.
We certainly feel we have this relationship with Canadian Solar, who are high quality manufacturers. We have a great deal of trust based in our history of dealing with them.
Probably the more important decision when you buy solar panels is not the choice of panels themselves but the choice of inverter that you pair with the solar panels. In our experience all tier 1 brands of solar panels we have dealt with and sold have been fine but there has been a great discrepancy between the quality of inverter brands. We have found the SMA Sunny Boy and Fronius are far more reliable than any other brand.