Introduction – Data Source and Assumptions
Data is from the NREL.gov app for average solar radiation energy per day in Milwaukee, Wisconsin. We used this reference point to compute the solar radiation energy production per day (in kWh/m²), which changes throughout the year according to the month. Each month is different due to the changing relative trajectory of the sun.
To get the monthly production, we simply multiplied by the number of days for each month. Finally to get the annual production, we added up all of the monthly values.
The average solar panel surface area is estimated to be 1.5 square meters. The efficiency of converting solar radiation into energy is estimated to be 15%.
Average Electricity Usage in Wisconsin and How Many Solar Panels You Need
The average monthly electricity usage in Wisconsin is 23 kWh per day, 694 kWh per month or 8328 kWh per year. Based on the data below, you would need 15-45 panels depending on the time of year to cover your electricity costs exactly. The variable factors are that electricity usage varies depending on how hot are summers and how cold are winters, and whether you use electricity based cooling and heating. Check with your solar system installer for exact numbers.
| Month | Solar radiation per day | Solar radiation per month | Solar energy per month 1 panel | Solar energy per month 20 panels |
| January | 2.52 kWh/m² | 78.12 kWh/m² | 17.58 kWh | 351.54 kWh |
| February | 3.74 kWh/m² | 104.72 kWh/m² | 23.56 kWh | 471.24 kWh |
| March | 4.64 kWh/m² | 143.84 kWh/m² | 32.36 kWh | 647.28 kWh |
| April | 5.38 kWh/m² | 161.40 kWh/m² | 36.32 kWh | 726.30 kWh |
| May | 5.90 kWh/m² | 182.90 kWh/m² | 41.15 kWh | 823.05 kWh |
| June | 6.60 kWh/m² | 198.00 kWh/m² | 44.55 kWh | 891.00 kWh |
| July | 6.68 kWh/m² | 207.08 kWh/m² | 46.59 kWh | 931.86 kWh |
| August | 5.98 kWh/m² | 185.38 kWh/m² | 41.71 kWh | 834.21 kWh |
| September | 5.26 kWh/m² | 157.80 kWh/m² | 35.51 kWh | 710.10 kWh |
| October | 3.77 kWh/m² | 116.87 kWh/m² | 26.30 kWh | 525.92 kWh |
| November | 2.72 kWh/m² | 81.60 kWh/m² | 18.36 kWh | 367.20 kWh |
| December | 2.22 kWh/m² | 68.82 kWh/m² | 15.48 kWh | 309.69 kWh |
Anne Lauer
Anna Lauer is a writer, gardener, and homesteader living in rural Wisconsin. She has written for Mother Earth News, Grit, and Hobby Farms magazines. Anna is writing a new book about growing your food for free and an ultimate guide to producing food at little to no cost. When she’s not writing or gardening, Anna enjoys spending time with her husband and two young daughters.