[caption id="attachment_685" align="alignleft" width="300" caption="Solar Map"] 

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The first thing to do when trying to decide if  Solar PV or Thermal will work for you is to never listen to what politicians say.  Do your own research!  The map at left is a good start to gauge how well a solar system will perform on your house.

If you live in the south-west, then your solar resources are pretty great.  The south-east looks pretty good (FL is currently the site of the largest Solar PV array installed by FPL) and the north-east is ok.  Surprisingly, one of the states with the highest incentives to do solar is New Jersey!  So just because you may not live in AZ doesn't mean solar wont work for you.

After getting a rough idea from the map above on your State's suitability for Solar you should go to NREL PVWatts to get some numbers.  Once on the site click on, "The PV Watt Photovoltaic Solar System Performance Calculator" and then  "PVWatts Version 1 Calculator".  Alternatively, if you live in a city in the U.S. that does not come up in the version 1 calculator, you can use the version 2 calculator to select your location by zip code.

PVWatts is developed by the National Renewable Energy Laboratory (NREL), the same people who did the map above, so they obviously have some great tools.  The online Calculator they have produced is meant only for grid-tied solar systems; basically systems that put the energy they produce on the electricity grid and not in a battery bank.

When you get to the Calculator there are two main things you will need to enter:  the size of the system you are interested in (which will be 3 - 5 kW for most residential systems) and the DC to AC derate factor.  This derate factor encompasses the efficiency of the panels and inverters, losses due to connections and wiring, any shade present, the age of the system, etc.  Basically, the derate factor encompasses any inefficiencies in the system because no energy producing system is 100% efficient (2nd law of thermodynamics).

The standard derate factor PVWatts fills in is .77.  Since some panels are more efficient than others this derate factor will change depending on the panel you decide to use for your house.  For instance, Sunpower, which currenlty has the highest efficieny panels on the market suggests using .833 as the derate factor.

Once you hit calculate the most important value you get is in the bottom right hand corner.  This is found under the column "AC Energy (kWh)" and you want the yearly value.  Once you have this value, you have to multiply it by the amount that your utility will pay you for solar energy under the net-metering agreement between you and the utility.  The Calculator asks you for what you pay for electricity, but this is not always the rate your utility will pay for your Solar power!

For instance, I pay almost 10 cents/kWh for electricity from my utility, Georgia Power, but they will credit me 17.7 cents/kWh for any solar power a system I install produces!  They do this because they use it for their "Green Energy" program.  And utilities usually don't cut you a check, they just credit your bill for the amount you use.  You can see the results of a calculation I ran below.

After completing these steps, you will have an excellent estimate of annual amount of money your solar panels will generate for you!

PVWatts Calc Output