# Can Someone check my math?

Great site by the way!!!
I live in Alaska and we have a 3hour solar window here at this location. I want to make sure I'm estimating my array output correctly.

I have 20 Kyocera 210 GX LPU's grid tied for a total array wattage of 4200watts.

4200X 3(hours in solar window)= 12,600watts or 12.6Kwh generated per day on average. 12.6X30 days in the month = 378Kwh per month on average?

Is this correct?

Thanks!!!!

Mountaintrekker

Re: Can Someone check my math?

Here is the PV Watts website that you can use for calculating your solar generation...

However, it is not working right now for me. Maybe it will be up by Monday.

As a rough estimate, you also need a derating factor... For the typical Grid Tied system, that derating factor is 0.77 times the factory/marketing number for the solar panel wattage.

For an off-grid system using flooded cell batteries and a 120 VAC inverter, the derating factor goes down to ~0.52 ...

The amount of solar radiation varies by season and local weather patterns. The PV Watts program has ~20 years of data for each location and can give you a good average result (by month, by year, or even hour by hour).

I hate to give any numbers at the moment when the PV Watts program is down. There are other solar power calculators out there, but I do not know how accurate they are (and some only cover 1 state worth of data--such as those for California).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 1,571 ✭✭
Re: Can Someone check my math?

You could use the Nasa SSE dataset to find out how many full sun hours you have in a given day for a given month: http://eosweb.larc.nasa.gov/sse/
• Solar Expert Posts: 5,653 ✭✭✭✭✭
Re: Can Someone check my math?

"Station Identification"
"City:","Anchorage"
"Lat (deg N):", 61.17
"Long (deg W):", 150.02
"Elev (m): ", 35
"PV System Specifications"
"DC Rating:"," 4.2 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 3.2 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 61.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.4 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (\$)"
1, 0.83, 76, 9.42
2, 2.16, 198, 24.55
3, 3.77, 382, 47.37
4, 4.35, 411, 50.96
5, 4.88, 462, 57.29
6, 4.74, 414, 51.34
7, 4.50, 401, 49.72
8, 3.77, 338, 41.91
9, 3.28, 293, 36.33
10, 1.88, 175, 21.70
11, 1.39, 132, 16.37
12, 0.61, 53, 6.57
"Year", 3.02, 3335, 413.54
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.