What Will My Balcony Solar Kit Actually Produce?
The number on the box is a laboratory figure. A south-facing 800W kit on a real railing delivers around 490W — here is what yours will do.
Realistic output
490W
61% of the 800W on the box
Per year
751
kWh generated
Off your bill
$113
at 15.1¢/kWh
What each direction costs you
An 800W kit, no shade, flat against the railing.
| Balcony faces | Realistic output | kWh / year |
|---|---|---|
| South | 490W | 751 |
| Southeast | 442W | 678 |
| Southwest | 442W | 678 |
| East | 340W | 521 |
| West | 340W | 521 |
| North | 190W | 292 |
What shade costs you
Same 800W kit, facing south.
| Shading | Realistic output | kWh / year |
|---|---|---|
| Open sky all day | 490W | 751 |
| Clipped morning or late afternoon | 416W | 638 |
| A building or tree blocks part of the day | 343W | 525 |
| Shaded more often than not | 245W | 375 |
Common questions
Why doesn't my 800W solar kit produce 800 watts?
800W is the panels' rating under laboratory conditions: perfect perpendicular light, 25°C, brand new and clean. A real balcony panel hangs vertically rather than tilted to the sun, loses some output to inverter conversion and heat, and only sees full sun for part of the day. Around half the rated figure is normal for a south-facing railing mount.
Does a north-facing balcony make solar pointless?
Not pointless, but marginal. A north-facing vertical panel produces roughly a quarter of what the same panel does facing south, which usually pushes payback past the life of the equipment. A smaller, cheaper kit is the sensible move if you want one anyway.
Is it worth tilting the panels?
Yes, where the railing allows it. A tilted bracket typically recovers 15 to 20 percent over a flat vertical mount, because the panel sees the sun closer to head-on for more of the day.
How much does shade actually cost me?
More than most people expect, because panels within a string drag each other down. A balcony that loses part of the day to a neighbouring building can give up 30 percent; heavy shade halves the output.
How this is worked out
Output is the panel rating multiplied by an orientation factor for a vertical railing mount, a shading factor, and a 0.85 system derate covering inverter conversion, wiring, heat and dust — the standard PVWatts assumption. Annual kWh uses 4.2 peak sun hours a day, a US average.
That national average is the biggest simplification here. Real peak sun hours run from roughly 3.5 in the Pacific Northwest to 5.7 in the desert Southwest, so treat the annual figure as a range rather than a promise. The orientation and shading comparisons hold either way.