Understanding how much electricity your solar panels actually generate — month by month, across different UK regions — is essential for checking your system is performing correctly and for planning how to use your solar power most effectively.
Average Monthly Solar Output by System Size
The following data is based on PVGIS calculations for a south-facing, 35° tilted system in the UK Midlands (representative of central England — South East will be ~5% higher, Scotland ~10% lower).
| Month | 3kW System (kWh) | 4kW System (kWh) | 6kW System (kWh) |
|---|---|---|---|
| January | 85 | 113 | 170 |
| February | 130 | 173 | 260 |
| March | 235 | 313 | 470 |
| April | 310 | 413 | 620 |
| May | 380 | 507 | 760 |
| June | 390 | 520 | 780 |
| July | 385 | 513 | 770 |
| August | 340 | 453 | 680 |
| September | 255 | 340 | 510 |
| October | 165 | 220 | 330 |
| November | 90 | 120 | 180 |
| December | 70 | 93 | 140 |
| Annual Total | 2,835 kWh | 3,778 kWh | 5,670 kWh |
Note: Real-world annual outputs typically range from 800–900 kWh per kWp (kilowatt-peak) installed in the UK. This table uses 850 kWh/kWp as a conservative central estimate.
Regional Variation Across the UK
| Region | Annual kWh/kWp | 4kW System Annual kWh |
|---|---|---|
| South West England | 950–1,000 | 3,800–4,000 |
| South East England | 920–970 | 3,680–3,880 |
| East Anglia | 900–950 | 3,600–3,800 |
| Midlands | 850–900 | 3,400–3,600 |
| North West England | 800–850 | 3,200–3,400 |
| Yorkshire/North East | 790–840 | 3,160–3,360 |
| Scotland (Central) | 750–800 | 3,000–3,200 |
| Northern Scotland | 700–760 | 2,800–3,040 |
| Wales | 830–880 | 3,320–3,520 |
| Northern Ireland | 780–830 | 3,120–3,320 |
Cornwall and parts of the South West get more peak sun hours than northern Germany — a country that has installed over 100GW of solar. The UK’s climate is more solar-viable than many people assume.
How to Check Your System Is Performing Correctly
Use your inverter’s monitoring app (GivEnergy, SolarEdge, Fronius Solar.web, Enphase Enlighten) to compare your actual monthly generation against these benchmarks. Allow ±15% for normal weather variation.
Red flags that warrant investigation:
- Monthly output more than 20% below expected (correcting for weather)
- Sudden unexplained drops between months
- Zero output on a sunny day
- Consistently lower output in the afternoon vs morning without shading explanation
A quick sanity check: on a clear summer day, a 4kW system should generate 20–28 kWh. On an overcast winter day, 1–4 kWh.
Factors That Affect Your Real-World Output
| Factor | Impact on Output |
|---|---|
| Shading (even partial) | -10 to -50% on affected strings |
| Soiling/dirty panels | -3 to -15% |
| Inverter efficiency loss | -2 to -5% |
| Temperature in heatwaves | -3 to -8% (panels work better cool) |
| Panel degradation (year 10) | -3 to -5% below rated |
| Orientation (SW vs S) | -5 to -8% |
Peak Summer vs Winter Output
The contrast between summer and winter solar generation in the UK is dramatic:
- June (peak month): 520 kWh from a 4kW system — equivalent to 17 kWh/day average
- December (lowest month): 93 kWh from a 4kW system — equivalent to 3 kWh/day average
This seasonal swing is the primary reason batteries and flexible tariffs are so valuable — you generate far more than you need in summer and far less in winter.
Frequently Asked Questions
Q: Why does my solar output vary so much day to day?
A: Cloud cover is the main cause. A completely overcast day generates 10–25% of clear-sky output; light cloud cover generates 50–70%. The UK’s variable weather means day-to-day variation of 50% or more is entirely normal.
Q: My monitoring app shows less output than expected — what should I check first?
A: First rule out shading — new obstructions (tree growth, new buildings) are a common cause. Then check for inverter fault codes (a flashing light or error notification). Check that panels appear visually clean. If none of these explain the shortfall, contact your installer.
Q: Does rain clean my solar panels?
A: Light rain helps rinse dust, but heavy soiling (bird droppings, lichen) is not adequately removed by rain alone. A professional clean once or twice a year keeps panels at peak output.
Q: Can solar panels generate electricity at night?
A: No — solar panels require daylight. Any electricity at night comes from your battery (if you have one) or the grid. Some inverter apps can show grid import data alongside solar generation.
Q: What’s the best time of year to install solar?
A: Any time of year. Installation itself takes 1–2 days regardless of season, and your system starts generating immediately. Installing in autumn or winter means you’re ready to capture the full summer generation season ahead.