- “Specific yield” is how many kWh one kW of panels produces in a year at a given place.
- It ranges from about 800 in Scotland to 1,800 in Arizona for well-tilted panels.
- Multiply by your kit size and a mounting factor to estimate yearly output.
- Vertical balcony mounting delivers 55-72% of the ideal tilted figure in US cities: close to 70% in the North, about 60% in the South.
Two identical balcony kits can produce very different amounts of electricity. The biggest factor you cannot change is where you live. Here is how to estimate it.
In this article
The formula
Yearly kWh ≈ kit size (kW) × specific yield × mounting factor × shade factor
For example: an 800 W kit (0.8 kW) in Denver (yield ~1,620) mounted vertically on a south railing (factor ~0.68) with light shade (~0.85): 0.8 × 1,620 × 0.68 × 0.85 ≈ 750 kWh a year.
Typical specific yields
For south-facing panels (north-facing in Australia) at a good tilt, after normal system losses:
| Region | kWh per kW per year |
|---|---|
| Arizona, Nevada, New Mexico, Southern California | ~1,700-1,800 (San Diego’s coastal clouds: ~1,550) |
| Colorado, Utah | ~1,500-1,650 |
| Northern/Central California | ~1,600-1,700 |
| Texas, Oklahoma | ~1,450-1,550 |
| Florida, Georgia, the Carolinas | ~1,450-1,550 |
| Mid-Atlantic, Midwest | ~1,300-1,400 (Pittsburgh: ~1,150) |
| New York, New England | ~1,200-1,350 |
| Pacific Northwest | ~1,100-1,200 |
| Hawaii (Honolulu) | ~1,650 |
| Southern England | ~950-1,050 |
| Northern England, Wales | ~850-950 |
| Scotland | ~780-860 |
| Germany | ~950-1,050 |
| Spain, Portugal, Southern Italy | ~1,450-1,700 |
| Sydney / Melbourne / Brisbane / Perth | ~1,450 / 1,300 / 1,550 / 1,600 |
| Southern Ontario, Quebec | ~1,150-1,250 |
US rows: rounded from our PVGIS runs with NSRDB satellite data for 30 cities (our 30-city data). Other rows: rounded typical values from long-term solar resource data (PVGIS and similar tools). For your exact address, run PVWatts from the National Laboratory of the Rockies (formerly NREL) or the EU’s PVGIS.
Mounting factors
| Mounting | Factor vs ideal |
|---|---|
| Tilted ~30°, facing the equator | 1.00 |
| Nearly flat | ~0.83-0.93 |
| Tilted, facing east or west | ~0.80-0.85 |
| Vertical, facing the equator | ~0.55-0.72 (Hawaii: ~0.47) |
| Vertical, facing east or west | ~0.42-0.53 |
The flat and vertical factors come from our PVGIS runs for 30 US cities. At higher latitudes the vertical penalty is smaller, because the sun is lower: about 0.70 in Boston or Minneapolis, 0.61 in Phoenix. See best angle for balcony panels.
Do it for your address
- Use our calculator for a quick regional estimate.
- For precision, use PVWatts or PVGIS (for US addresses in PVGIS, choose the NSRDB database), entering your panel tilt (90° for vertical) and azimuth.
- Adjust for shade by watching your balcony for a day.
Why yields differ so much
- Latitude: closer to the equator, the sun is higher and days are more even across the year.
- Cloud cover: the desert Southwest has far more clear days than the Pacific Northwest or the UK.
- Altitude and air clarity: high, dry places like Denver get more intense sunlight.
- Temperature: very hot places lose some efficiency; mild sunny climates are ideal.
Three quick examples
| Setup | Calculation | Estimated kWh/year |
|---|---|---|
| 400 W, vertical south, Seattle | 0.4 × 1,160 × 0.69 | ~320 |
| 800 W, tilted south, Phoenix | 0.8 × 1,800 × 1.0 | ~1,440 |
| 800 W, vertical west, London, light shade | 0.8 × 1,000 × 0.55 × 0.85 | ~374 |
Frequently asked questions
What’s the difference between kWh and kWp?
kWp (kilowatt-peak) is a panel’s rated power under test conditions. kWh is energy produced over time. Specific yield connects them: kWh per kWp per year.
How accurate are these figures?
They are long-term averages. Any single year can be about 10% higher or lower depending on weather.
Why does PVWatts give me a different number?
It uses your exact location and lets you set tilt, azimuth and losses. Use it for precision; our table is for quick comparison.
Does altitude of the balcony matter?
Not directly. Higher floors often have less shade from trees and neighboring buildings, which does matter.
Sources
- PVWatts Calculator, National Laboratory of the Rockies (formerly NREL).
- Photovoltaic Geographical Information System (PVGIS), European Commission, Joint Research Centre.
- Energy Department renames NREL ‘National Lab of the Rockies’, U.S. Department of Energy.
- Solar photovoltaic performance and efficiency basics, U.S. Department of Energy.
Sources checked in September 2026. Laws, prices and product details change; if you spot something out of date, tell us.