Solar Panel Output: Rated Power vs Real-World Generation
A "400W panel" produces 400 watts under perfect lab conditions — bright sun hitting the panel at the ideal angle, 25°C cell temperature, no shading. In reality, panels almost never operate at their rated peak.
Real-world output depends on:
- Sun hours — the number of "peak sun hours" your location receives per day.
- System losses — inverter conversion, wiring, dust, temperature, and degradation reduce output by 14–20%.
- Orientation and tilt — south-facing panels (in the northern hemisphere) at a 30–35° tilt produce the most.
- Shading — even partial shading on one panel can reduce output for the entire string.
A practical rule of thumb: multiply your system size (kW) by your local "solar yield factor" (kWh/kW/year) to get annual output.
Annual Solar Generation by Country
The solar yield factor tells you how many kWh each installed kW produces per year in your region:
| Country | Typical Yield (kWh/kW/year) | 6 kW System Annual Output |
|---|---|---|
| US Southwest (AZ, NV) | 1,600–1,750 | 9,600–10,500 kWh |
| US Northeast | 1,100–1,300 | 6,600–7,800 kWh |
| UK (Southern England) | 900–1,000 | 5,400–6,000 kWh |
| UK (Scotland) | 750–850 | 4,500–5,100 kWh |
| Australia (Queensland) | 1,600–1,700 | 9,600–10,200 kWh |
| Canada (Ontario) | 1,100–1,300 | 6,600–7,800 kWh |
| New Zealand (Auckland) | 1,350–1,450 | 8,100–8,700 kWh |
| Ireland | 800–950 | 4,800–5,700 kWh |
Want to see what a specific location yields? Our solar map estimator lets you pick a point on the map and get a location-specific generation estimate.
Monthly Output: Why Summer and Winter Differ
Solar generation is not evenly distributed through the year. In the northern hemisphere, a typical system produces:
- June–July: 12–15% of annual total (peak months).
- December–January: 3–5% of annual total (lowest months).
This means a 6 kW UK system producing 5,000 kWh annually might generate 600+ kWh in June but only 150–200 kWh in December. If you are comparing your system's output to your electricity bill, remember this seasonal pattern — you will likely export surplus in summer and draw from the grid in winter.
In the southern hemisphere (Australia, New Zealand), the pattern is reversed — peak production is December–January.
Daily Output: What to Expect
Your daily output depends on your system size and local conditions:
- 4 kW system in the UK: 8–14 kWh/day in summer, 2–5 kWh/day in winter.
- 6 kW system in the US (average): 20–30 kWh/day in summer, 10–15 kWh/day in winter.
- 6 kW system in Australia: 25–35 kWh/day in summer, 15–20 kWh/day in winter.
The average UK household uses about 9–10 kWh per day. The average US household uses 28–30 kWh per day. So a well-sized system can cover most or all of your daytime consumption in the summer months.
How to Maximise Your Solar Output
You cannot control the weather, but you can optimise what you have:
- Orientation — face panels south (northern hemisphere) or north (southern hemisphere) for maximum annual yield. East/west splits work well if you want to spread generation across morning and evening.
- Tilt — match your latitude for a good year-round angle. Typical sweet spot: 25–35° in the US and UK.
- Keep panels clean — rain handles most cleaning, but dusty or bird-heavy areas benefit from an annual wash.
- Minimise shading — even small shadows (satellite dishes, chimneys, new tree growth) can disproportionately reduce output.
- Add a battery — doesn't increase generation, but lets you use more of what you produce instead of exporting at low rates.