This is a question that plagues many people who are just starting out and planning their renewable energy setup. What size (wattage) solar panels should you buy? Solar panels come in many shapes and sizes although there are a couple pointers I have for you that will help you make the best decision.
Cost per Watt
This is probably the best indicator of what size of solar panels you should buy. You will notice that the larger the solar panel is the cheaper price per watt you get. For example, a 100 watt solar panel usually runs you $2.50 per watt all the way up to $3.50 per watt; however, a 220 watt panel can run as little as $1.25 per watt which means for the same amount of money you’re getting twice the output!
These sizes of solar panels are generally the cheapest (with the 220 watt solar panels being the cheapest I’ve found.
Warranty
The nice thing about solar panels is that there are no moving parts that need maintenance or that can break like they do in a wind generator; however, sometimes there was a defect in that panel and suddenly it stops working.
If the seller doesn’t list a warranty make sure you inquire. Most panels have a warranty through the manufacturer so make sure it’s a trusted manufacturer like Evergreen or Schott and not a knock off Chinese brand. With a brand name panel you’ll get a 25 year warranty on the panels and although you probably won’t use it it’s best to have it just in case.
New vs. Used
Like building your own solar panels buying used panels can be a big money saver. If you shop around, you can probably find prices comparable to building your own.
There are a couple things that you’re going to want to look out for though. First off, why are they selling their panels? Solar panels are expensive so make sure that they have a REALLY good reason for wanting to get rid of them.
Always make sure that you closely inspect each panel and test it (or make sure there is a return policy) before you do anything with it. The glass shouldn’t be cracked or scratched. It should generate it’s rated amount of power (make sure you test both volts and amps!). It’s a little difficult to test rated output power so a good rule of thumb is in full sunlight it should be able to get up to 90% of what it’s rated for. Remember that larger used solar panels will probably be cheaper per watt as well (since they were cheaper per watt in the first place).
My recommendation is to buy new 200 watt plus solar panels. You get a great price per watt and you’ve got a good warranty if anything goes wrong.