Tips on how to choose solar (photovoltaic) panels, solar pumps and solar lighting
First of all if you are really interested in getting a lot of power out of the sun, then you need something pretty efficient and panels that will actually give you power on a dull day. Rather than looking for a kit, buy a seperate solar panel to suit the job you have in mind for it. In our case it will be to run a 12volt pump. Once you have the power require by the pump, sourcing the panel should be easy.
For methods of measuring and evaluating what power you need from a photovoltaic panel : www.wholesalesolar.com/
When shopping for a solar electric system, always check the PTC rating (a PVUsa Test Conditions Rating) and the warranted minimum power rating of the solar panels that are used in the system. This very often differs quite considerably from the STC rating (Standard Conditions Rating), which is very often what a manufacturer will advertise as the power produced by that panel. Here's a link showing you a comparison of several 170 watt solar panels that are currently listed on the state of California’s website. http://www.partsonsale.com/mitsucomparison.html
Solar panels are manufactured in batches or lots with each solar panel varying in performance from the next one. So it seems prudent to assume that a manufacturer would send only the best panel from a production lot to be evaluated for it's PTC rating.
When shopping for a solar electric system, always look for the solar panels that have the longest factory warranties possible. 25 years should be the minimum. And beware of dealers that offer their own warranties beyond the manufacturers warranty. A 30 solar panel warranty may sound good at first glance, but do you really believe for a moment that the dealer will be around 30 years from now!
The part the system depends upon the most is the inverter that converts the D/C from the photovoltaic cells to A/C, which is the type of current your pump is likely to run on. Make sure this has a good long guarantee. The dealer is not doing you any favors by offering you a 5year inverter warranty because in the States it is a legal requirement. Always ask for at least a 10year warranty on the system's inverter.
For big solar panels, make sure you have professionally engineered racks to support them otherwise they will just buckle under the first storm.