How to Use the PVWatts Calculator
Now you’re ready to use the actual calculator and get your numbers for monthly solar radiation, AC energy in kWh your solar panels will produce, and energy cost savings at your location.
You should see the following screen, which is the only page you have to complete:
On this screen, the NREL has entered default values for all these fields. We’re going to take you through each one to help you understand what they mean, and how to fill it in.
DC System Size
This will play the greatest role in the numbers you get from the calculator. Most residential systems will be less than 10kW. Commercial systems and large farms can be quite a bit larger, even into the megaWatts range (1 MW = 1000 kW).
How do you know how big your solar power system should be? Eventually you’ll need to talk with an expert. But if you look at your power bill, you can see how many kilowatt-hours you’re using each month.
A 1 kW solar energy system means it produces 1 kilowatt of energy per hour – of direct sunlight. So in southeastern states like Georgia, South Carolina, Florida, and Mississippi, you get a lot of sunlight. If you average 8 hours of direct sunlight per day, then a 1 KW solar system will produce 8 kWh of energy per day. Multiply that by 30 and you get your kWh per month.
Here’s a simple formula you can use:
x KW system * hours of sunlight per day * 30 = approximate kWh per month
See how much sunlight Georgia averages per day
If you look at your current bills, you might want to do this in reverse to find out how many total kWh you need to produce. If you want to produce 300 kWh of solar energy per month, then divide that by 30 to get your kWh per day. Then divide that by the average hours of sunlight per day. That tells you about how large a solar power system you’ll need to get free electricity.
Here, you have just thr