What Every New Solar Owner Should Know
How do you interpret your new utility bill and your overall system output once you get solar? You might think you know, but read through these tips to make sure.
NET-METERING and your bill
1. Once you have your net-meter installed in place of your regular meter, the utility company will begin recording “delivered” and received” kilowatt-hours (kwh). Until this point they could only measure “delivered” kwh to you.
2. Your new “net-meter” will show delivered (which is reduced now with your solar power system), and received (which is the EXCESS kwh you generated that you didn’t use at the time you generated them).
3. Your net-meter does not record your solar power production. Only your inverter can do this. Your net-meter shows your consumption MINUS your solar power production.
4. When you get your utility bill you will see these two numbers, “delivered” and “received”. The utility will subtract the received from what they delivered and bill you on that amount of kwh.
5. If you were to turn your house off for the entire billing period then the “received” kwh number would match your inverter kwh number of generated power, and delivered would be zero.
SYSTEM OUTPUT and reading your inverter output
*** (Your inverter has the solar power generated available on the local display screen – SMA inverters show daily and total on the main screen, Outback shows this information on the MATE screen or the charge controller)
1. Your solar power system will generate power proportional to the sunlight that strikes it with certain modifiers. These modifiers decrease (derate) your output and are estimated with the program called PVWATTS.
2. A copy of your PVWATTS calculation was provided for you in your customer information packet. If you misplaced your PVWATTS sheet (needed for tax credit), or want to run the numbers yourself, you can go to http://pvwatts.nrel.gov/ and enter your system information. PVWATTS provides an estimate of your actual monthly kwh production, which should follow historical weather data and your inverter output. It does not take into account extreme weather periods (hot or cold), or unusual rainy or cloudy periods that can occur at any time. It is mainly used as a guide, as weather predictions are difficult.
3. If you try to read your “peak” instantaneous power on your inverter and it is less than your system size, the reason is the de-rating modifiers, which must be considered. For example, a 7kw “nameplate” system will peak at maybe 5.39kw depending on environmental modifers once derated. The peak power is subject to change as modifers change.