After researching the regulations and finding what types of incentives are available, it’s time to find out how much energy you currently use. Dig into your file cabinet…ugh, I mean download your online utility statements for the last year. (preferably the last whole calendar year, Jan – Dec. if you intend to deeply analyze things) Add up how many kWh’s (killowatt hours) you used for the year & divide by 12. That will give you the average kWh’s used per month. According to the US Energy Information Administration the average US household uses 940 kWh per month. (fyi – 1 KWH = 1000 watts for 1 hour) Your 12 month average will be a factor in what watt size solar panels you should get, and how many. If you’re going with a backup solar power system, these numbers will also play a role in buying batteries and inverter size.
If your original goal is just to save some money on your utility bill (from Step 1), then precise usage calculations are not really absolutely necessary. But, if you are looking to live mostly off grid or make a profit selling energy back, then you should try to calculate and estimate as much as you can prior to purchasing anything. Either way, there are free tools online to simplify the research.
The National Renewable Energy Laboratory offers PVWatts which calculates hour-by-hour performance simulations that provide estimated monthly and annual energy production in kilowatts based on your location. It’s pretty cool and not nearly as complicated as it sounds. Just plug in some numbers (or hypothetical’s) and it will spit out useful information. If you want to get all kinds of nerdy with it, download the Homer Energy hybrid modeling simulation software. The program is a fully functional 2 week demo, or you can use the previous version free for six months. Below I’ve included a PV (photo voltaic) solar map for the US which shows how many kWh of energy are typically available for your location. Additional solar maps, for your visual stimulation, can be found here. A very helpful resource in doing your solar site survey in a more traditional way can be read at Build it Solar. (recommended) If you need to make conversions (Watts, Kilowatts, Amps, Volts, etc.) the users at this forum OnlineConversions.com seem to know everything!
Anyway, keeping your goal in mind, determine how much energy you use & how much you want to produce as it will be a primary factor in what solar hardware you buy.
On a related topic, prior to installing a home solar power system you should make your home as energy efficient as possible. There are allot of simple things you can do like The Over 100 Ways to Save on Your Energy Bill. A free and simple energy savings estimator is also available online. If you are really serious about conserving energy and money, you should consider getting a home energy audit. The money would be better spent on energy efficiency in the home, than using expensive solar equipment to support the exaggerated need. (Example: Rather than getting up to close the front door all the way in the dead of winter…just turning up the heat until you don’t notice the cold draft.) I’ve included a video below that shows some of what’s involved in an energy audit.