# Calculating solar irridiance

Registered Users Posts: 4
I have info from meteo station in my town, for daily solar irridiance.
The info is in excel table.

For summary of all year I get 40.830 W/m2.
So, daily average will be 112 W/m2.

Please someone tell me why this is so low, comparing with solar gis maps for my location with 1600 W/m2.

Zivko.

Re: Calculating solar irridiance

Assuming your are in Macedonia, I will use Romania in PV Watts to estimate the amount of sun for your area:
``````[SIZE=3]Bucharest:[/SIZE]
1      1.91
2      3.48
3      4.28
4      4.86
5      5.69
6      5.89
7      6.16
8      6.09
9      5.01
10      3.71
11      2.18
12      1.85
Year      4.26
``````

Looks like the area has a fair amount of clouds during winter... One way to look at the amount of sun is "hours of noon-time equivalent" sun per day (~1,000 Watt per meter2). So your average is ~4.26 hours of sun per day. Say you install a 3,000 Watt (3kW) solar array, the amount of electricity I would expect it to produce would be (roughly):
• 3 kWatts * 0.77 panel+inverter derating * 4.26 hours of sun per day * 365 days per year = 3,592 kWH per year

I don't have a lot of experience with this European version of PV Watts--But it may have a site closer to your location (its operation is different than PV watts--So you will have to answer the questions a bit differently than PV Watts).

PVGIS--European/African Solar Power Calculator Program

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 10,311 ✭✭✭✭
Re: Calculating solar irridiance

i don't know. i can speculate that it may be local to that point maybe due to weather. you may need to ask them questions on that as even overcast days at many locations would output more than that.