Performance and output

Monthly kWh output estimator

Enter your annual output, latitude, and hemisphere. Get a full 12 month breakdown instead of a flat annual average.

Your system and location

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Your system and location
Use your system's rated annual output, or run the annual output estimator first.
Higher latitude means a bigger swing between your peak and lowest months.
Sets whether your system peaks in summer (June, Northern) or (December, Southern).

How it works

Two steps to a month by month view

Step 1

Enter your yearly total

Pull your system's annual kWh from a utility statement or spec sheet, or use the annual output estimator to get one before you continue. Working backward from that figure, the system size by monthly kWh usage gives the system size behind it.

Step 2

Enter your latitude and hemisphere

These two inputs set the shape and timing of your seasonal curve. Check the seasonal output calculator too for a four-season summary version of this same breakdown.

Understanding your monthly output curve

Why the swing between months can be significant

At 38 degrees latitude, a system's peak month typically produces around 74% more output than its lowest month. A 10,500 kWh/year system would produce roughly 1,111 kWh in June and 639 kWh in December under those conditions. This swing is bigger than most people expect from looking at an annual number alone. A DOE study of 75 federal PV systems compared measured monthly production against modeled estimates to establish realistic month-to-month benchmarks.

Why a flat monthly average misses the real picture

The sun's angle and day length change substantially across the year, so summer months always produce more than a simple average would suggest, and winter months always produce less. This monthly curve matters for budgeting and for sizing a battery meant to cover winter shortfalls, since a flat average would understate your summer surplus and overstate your winter output. National Solar Radiation Database show this same month-by-month swing visually across the country, with the gap between a location's sunniest and dimmest months varying by both latitude and regional weather patterns.

How hemisphere flips the calendar

Yes. Northern Hemisphere systems peak around June and trough around December, while Southern Hemisphere systems peak around December and trough around June, since the seasons are reversed. If you're comparing notes with someone in the opposite hemisphere, keep this flip in mind before assuming your calendars line up.

Using this for budgeting, not just curiosity

Compare your monthly output estimate against your monthly usage pattern rather than your annual totals, since a month with high usage and low production, like a cold winter month, can still mean a real utility bill even if your system nets out positive over the full year. The output vs usage gap analyzer is built specifically for this comparison. If your goal is battery backup through a rough winter stretch rather than just tracking the bill, the winter storm backup planning calculator works from that same seasonal low point.

What to do with this number next

Break any individual month down further with the daily output estimator if you want an even finer-grained view.

Questions

Frequently asked

At 38 degrees latitude, a system's peak month typically produces around 74% more output than its lowest month. A 10,500 kWh/year system would produce roughly 1,111 kWh in June and 639 kWh in December under those conditions.

The sun's angle and day length change substantially across the year, so summer months always produce more than a simple average would suggest, and winter months always produce less. This monthly curve matters for budgeting and for sizing a battery meant to cover winter shortfalls.

Yes. Northern Hemisphere systems peak around June and trough around December, while Southern Hemisphere systems peak around December and trough around June, since the seasons are reversed.

Compare your monthly output estimate against your monthly usage pattern rather than your annual totals, since a month with high usage and low production, like a cold winter month, can still mean a real utility bill even if your system nets out positive over the full year.

Related tools

Keep exploring your output

Annual kWh output estimator Daily kWh output estimator Seasonal output by latitude Output vs usage gap analyzer Snow loss estimator, Northeast Peak sun hours by latitude Capacity factor calculator All performance and output tools