Same panels on a Phoenix roof produce twice as much electricity as on a London roof. Enter your system size (kWp), location, panel tilt, azimuth and type to estimate annual and monthly solar energy production in kWh.
How much does a 15 kW solar system produce per year?
Same panels on a Phoenix roof produce twice as much electricity as on a London roof. Enter your system size (kWp), location, panel tilt, azimuth and type to estimate annual and monthly solar energy production in kWh.
A 15 kW solar panel system is one of the most popular residential sizes. In a sunny location like Arizona or southern Spain, it produces significantly more than the same panels in northern Germany or Washington state - the difference can reach 40-50% depending on latitude, panel tilt and shading. Enter your location and panel orientation below to see the exact annual kWh output for a 15 kW installation.
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Why location is the single biggest factor
The same 10 kWp solar array on a south-facing roof at 30 degrees tilt produces dramatically different results depending on where it sits. A homeowner in Phoenix, Arizona can expect roughly 20,000 kWh per year, while the same system in London or Berlin yields closer to 9,500 kWh. That is more than a 2:1 ratio, and the panels, inverter, and wiring are identical. The difference comes entirely from annual solar irradiance measured in kWh per kWp per year. This calculator uses region-specific irradiance data so you can compare output across the US Sun Belt, mid-latitude states, Northern US and Canada, Southern Europe, Central Europe, and Australia. Every other factor (tilt, azimuth, panel type, losses) is a multiplier applied on top of that baseline number.
Solar irradiance by region
| Region | Yield (kWh/kWp/year) | 10 kWp output (kWh) | Notes |
|---|---|---|---|
| Arizona / California | 2,000 | 20,000 | Peak US Sun Belt, 300+ sunny days |
| Australia (Sydney/Melbourne) | 1,950 | 19,500 | Reversed seasons, north-facing optimal |
| Texas / Florida | 1,850 | 18,500 | High humidity can reduce clear-sky output |
| Spain / Italy | 1,700 | 17,000 | Mediterranean climate, strong summers |
| Colorado / Utah | 1,650 | 16,500 | High altitude boosts irradiance |
| New York / Illinois | 1,550 | 15,500 | Four distinct seasons, cloud cover in winter |
| Washington / Minnesota | 1,250 | 12,500 | Short winter days, heavy cloud cover |
| Germany / UK | 1,000 | 10,000 | Lowest yield in the table, still profitable |
Real-world examples
8 kWp monocrystalline, south-facing, 30 degrees tilt, 14% losses
Result: 13,798 kWh/year (1,150 kWh/month avg)
6 kWp monocrystalline, south-east facing, 35 degrees tilt, 18% losses
Result: 7,253 kWh/year (604 kWh/month avg)
50 kWp bifacial panels, south-facing, 20 degrees tilt, 12% losses
Result: 78,472 kWh/year (6,539 kWh/month avg)
10 kWp polycrystalline, east+west, 25 degrees tilt, 16% losses
Result: 6,317 kWh/year (526 kWh/month avg)
12 kWp monocrystalline, south (equator-facing), 30 degrees, 14% losses
Result: 20,131 kWh/year (1,678 kWh/month avg)
How the calculator works
- Base yield - the calculator looks up the annual kWh/kWp value for your selected region, based on long-term average solar irradiance data.
- Tilt correction - a multiplier adjusts for the angle of your panels. Optimal tilt (30-35 degrees in mid-latitudes) gets a 1.0 factor. Flat roofs lose about 12%, and wall-mounted panels lose about 45%.
- Azimuth correction - south-facing panels get full output. South-east and south-west lose about 5%. Due east or west lose about 18%. North-facing panels in the Northern Hemisphere lose 45% or more.
- Panel type factor - monocrystalline panels are the baseline (1.0). Polycrystalline panels produce about 8% less. Bifacial monocrystalline panels capture reflected light on their rear side and produce about 8% more.
- System losses - inverter conversion, wiring resistance, temperature derating, soiling, and shading are combined into a single percentage. The default of 14% covers a clean, unshaded installation.
- Monthly distribution - the annual total is split across 12 months using seasonal profiles that vary by tilt angle and region. Summer months (May through August) typically account for 50-55% of annual output.
Tilt and azimuth correction factors
| Parameter | Value | Correction factor | Production vs. optimal |
|---|---|---|---|
| Tilt | 0 deg (flat) | 0.88 | -12% |
| Tilt | 30-35 deg | 1.00 | Optimal |
| Tilt | 45 deg | 0.95 | -5% |
| Tilt | 90 deg (wall) | 0.55 | -45% |
| Azimuth | South | 1.00 | Optimal |
| Azimuth | SE / SW | 0.95 | -5% |
| Azimuth | East / West | 0.82 | -18% |
| Azimuth | North | 0.55 | -45% |
Frequently asked questions
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Calculator verified by the LiczGrupa.pl team
Content, formulas and results have been reviewed for accuracy and relevance by our team of specialists.
Reviewed by: Natalia Skrzek