Solar yield calculator
What does a portable solar panel really deliver at your location, month by month? Pick a city, set panel size, orientation and tilt, and see the gap between the best and the weakest month.
Monthly yield
Calculated · Engine v2.0.0 · Oct 17, 2026, 8:03 PM
How the calculation works
For every location the calculator uses the mean daily irradiation on the tilted panel plane from PVGIS, the photovoltaic information system of the EU Joint Research Centre: PVGIS-ERA5 data for 2005 to 2023, one global database so every city is comparable. PVGIS computes the irradiation on the tilted plane itself, so the seasonal effect of tilt is in the data: a steep panel gains in winter when the sun is low and loses a little in summer.
Daily yield is irradiation times panel power times a performance ratio of 0.75, which covers module temperature, charge controller and conversion losses, cabling and dirt for typical portable panels. Fixed rooftop systems reach about 0.85, a panel lying on a lawn in the shade of a wall far less.
Why the weakest month matters more than the yearly figure
Most solar calculators give you one yearly number. For emergency planning that number is useless: outages in winter storms happen when the panel delivers the least. In London a 200 W panel averages about 783 Wh per day in July and 197 Wh in December. In Phoenix the same panel still delivers about 768 Wh in December. That difference decides whether a power station recharges in a day or in a week.
What the numbers do not include
Shading by buildings or trees, snow on the panel, a panel that is not re-aimed during the day, and battery temperature. Treat the results as the upper end of what a well-placed panel achieves, and plan with the weakest month, not the average.
Frequently asked questions
How much does a 200 W solar panel produce per day?
It depends on the season far more than on the panel. A 200 W panel facing south at 30° averages about 783 Wh per day in July in London but only 197 Wh in December. In New York it is 873 Wh in July and 440 Wh in December. For winter outage planning the December figure is the one that counts.
Which tilt is best for a portable panel?
For the highest yearly yield, roughly your latitude minus 10 degrees, which is 30 to 40° for most of Europe and North America. For winter, steeper is better: a panel at 60° catches the low winter sun much better and loses only a little in summer. If you own one panel for emergencies, tilt it steeper than the "optimal" angle.
Does the calculator work in the southern hemisphere?
Yes. Sydney, Melbourne, Auckland and Johannesburg are included with their own irradiation data. Face the panel north there: in Sydney a 200 W panel facing north at 30° averages about 923 Wh per day in December and 579 Wh in June. The calculator labels the seasons by month (Jun to Aug, Dec to Feb) so the numbers read correctly on both sides of the equator.