How Much Electricity Does 800W Solar Generate? UK Annual Output Explained
Real annual output figures for 800W plug-in solar systems across the UK. Exact kWh and savings by region and property type.
How Much Electricity Does 800W Solar Generate? UK Annual Output Explained
"800W solar system" is the headline. But what does 800W actually generate in the UK? How many kWh per year? What does that mean in pounds saved? And does output vary if you're in London vs Scotland?
This article gives you the exact answer: real annual generation figures for 800W systems across the UK, showing how location, aspect, and placement affect output.
The Baseline Answer: 800W South-Facing Roof, Tilted
An 800W south-facing plug-in solar system, installed on a tilted roof (25° angle, optimal for the UK), in a sunny region generates approximately:
850 kWh per year in London (South-East England) 750 kWh per year in Manchester (North-West England) 680 kWh per year in Edinburgh (Scotland)
These are typical values based on 30 years of PVGIS solar irradiance data. Real-world performance will vary ±5% depending on weather, shading, and cleanliness.
In money terms (assuming 30p/kWh):
- London: 850 kWh × 30p = £256/year
- Manchester: 750 kWh × 30p = £225/year
- Edinburgh: 680 kWh × 30p = £204/year
How 800W Output Varies by UK Region
Here's the full regional breakdown:
| Region | Annual Generation | Daily Average | Annual Saving (30p/kWh) | Payback Period |
|---|---|---|---|---|
| South-East (London, Brighton) | 850 kWh | 2.3 kWh | £256 | 3.1 years |
| East Anglia (Norwich, Peterborough) | 820 kWh | 2.2 kWh | £246 | 3.2 years |
| South-West (Bristol, Exeter) | 800 kWh | 2.2 kWh | £240 | 3.3 years |
| Midlands (Birmingham, Coventry) | 770 kWh | 2.1 kWh | £231 | 3.4 years |
| North-West (Manchester, Liverpool) | 750 kWh | 2.1 kWh | £225 | 3.5 years |
| Yorkshire (Leeds, Newcastle) | 730 kWh | 2.0 kWh | £219 | 3.6 years |
| Wales (Cardiff, Swansea) | 740 kWh | 2.0 kWh | £222 | 3.6 years |
| Scotland (Edinburgh, Glasgow) | 680 kWh | 1.9 kWh | £204 | 3.9 years |
| Northern Ireland (Belfast) | 700 kWh | 1.9 kWh | £210 | 3.8 years |
Spread: London generates 25% more than Edinburgh. That's significant, but not dramatic. Every 200 km north costs ~3–5% generation.
 kit](/images/products/stream-hero.png)
- 800W dual-panel balcony or garden kit
- 600Wh plug-in battery included
- App with live monitoring & smart scheduling
- Balcony, garden & flat-roof mount options
How Aspect (Direction) Affects 800W Output
The above figures assume south-facing systems. Here's how other aspects compare:
| Aspect | Annual Generation | vs South | Annual Saving (30p/kWh) |
|---|---|---|---|
| South (0°) | 850 kWh | 100% | £256 |
| South-East (135°) | 810 kWh | 95% | £243 |
| South-West (225°) | 810 kWh | 95% | £243 |
| East (90°) | 640 kWh | 75% | £192 |
| West (270°) | 640 kWh | 75% | £192 |
| North-East (45°) | 500 kWh | 59% | £150 |
| North-West (315°) | 500 kWh | 59% | £150 |
| North (180°) | 150 kWh | 18% | £45 |
South-east and south-west lose only 5%. East and west lose 25% (but still viable). North is unusable.
See South-Facing vs East/West for deeper analysis.
How Placement (Roof, Balcony, Garden) Affects 800W Output
Same 800W system, different mounting:
| Placement | Angle | London Output | vs Tilted Roof |
|---|---|---|---|
| Roof (south-facing, tilted 25°) | 25° | 850 kWh | 100% |
| Garden (south-facing, tilted 25°) | 25° | 850 kWh | 100% |
| Flat-roof (south-facing, tilted 25°) | 25° | 850 kWh | 100% |
| Balcony (south-facing, vertical) | 90° | 663 kWh | 78% |
| Wall-mount (south-facing, vertical) | 90° | 663 kWh | 78% |
| Ground-mount (east/west facing, tilted) | 25° | 640 kWh | 75% |
Key insight: Tilt angle (25°) matters far more than placement type (roof vs garden vs flat-roof frame). The difference between roof and balcony (22% loss) is driven by tilt angle, not placement.
Vertical balcony systems are the trade-off: simpler to install (clamp-on), less output (22% loss).
See Balcony Solar Output for details.
How Shading Affects 800W Output
Shading is ruthless:
| Shade Source | Shade Pattern | Output Loss | Annual Generation (London) |
|---|---|---|---|
| None | Unshaded all day | 0% | 850 kWh |
| Tree shadow | Morning shade (8–11am) | 5–10% | 765–808 kWh |
| Building shadow | Afternoon shade (3–5pm) | 10–15% | 722–765 kWh |
| Chimney shadow | Winter midday (10am–12pm) | 5–8% | 782–808 kWh |
| Neighbouring building | All-day partial (30% blocked) | 25–35% | 553–638 kWh |
| Heavy shade | All-day significant (50%+ blocked) | 40–60% | 340–510 kWh |
A single tree casting morning shade: -5–10% output. A building to the west casting afternoon shade: -10–15% output. A heavy neighbouring building shadowing half the day: -40–50% output.
Use the Solar Report to assess shading on your property.
See Is My House Suitable for Solar? for shade assessment checklist.
Monthly Breakdown: How 800W Output Varies Throughout the Year
Here's when you actually get that 850 kWh (London example):
| Month | Generation | Daily Avg | Saving (30p) |
|---|---|---|---|
| January | 45 kWh | 1.4 kWh | £13 |
| February | 60 kWh | 2.1 kWh | £18 |
| March | 85 kWh | 2.7 kWh | £26 |
| April | 100 kWh | 3.3 kWh | £30 |
| May | 110 kWh | 3.5 kWh | £33 |
| June | 115 kWh | 3.8 kWh | £34 |
| July | 115 kWh | 3.7 kWh | £34 |
| August | 105 kWh | 3.4 kWh | £31 |
| September | 85 kWh | 2.8 kWh | £26 |
| October | 60 kWh | 1.9 kWh | £18 |
| November | 35 kWh | 1.2 kWh | £10 |
| December | 35 kWh | 1.1 kWh | £10 |
| Annual | 850 kWh | 2.3 kWh | £256 |
Summer (Jun–Aug) = 335 kWh (39% of annual). Winter (Dec–Feb) = 140 kWh (16% of annual). Seasonal ratio: 3.3:1 peak-to-trough.
See Solar Panel Output Winter vs Summer for seasonal deep dive.
How System Degradation Affects Long-Term Output
Solar panels degrade ~0.5% per year. After 10, 20, and 25 years:
800W system, London, year-1 output 850 kWh:
| Year | Degradation | Annual Output | Cumulative Output |
|---|---|---|---|
| 1 | 0% | 850 kWh | 850 kWh |
| 5 | -2.4% | 829 kWh | 4,170 kWh |
| 10 | -4.9% | 808 kWh | 8,390 kWh |
| 15 | -7.2% | 788 kWh | 12,660 kWh |
| 20 | -9.5% | 769 kWh | 16,980 kWh |
| 25 | -11.6% | 751 kWh | 21,290 kWh |
Degradation is slow. After 25 years, output is 88% of year-1. This is why payback stays short (3.1 years) even though output gradually declines.
Real-World Factors: Weather Variation Year-to-Year
PVGIS data is a 30-year average. Any single year will vary:
Typical range:
- Very sunny year: +8–12% above average (high pressure systems, fewer clouds)
- Average year: baseline (850 kWh for London)
- Very cloudy year: -10–15% below average (Atlantic depressions, more cloud cover)
Impact on savings:
- Very sunny year (920 kWh): £276 saving
- Average year (850 kWh): £256 saving
- Cloudy year (725 kWh): £218 saving
Over 20 years, average wins: 5 sunny years + 10 average + 5 cloudy = roughly on target.
Advice: Don't panic if your year-1 is cloudy and underperforms expectations. Check year-2 and year-3 averages.
How Self-Consumption Affects Real Savings
The above figures assume all generated solar is either self-consumed (saving 30p) or exported at 0p. Real savings depend on usage pattern:
If 60% self-consumed, 40% exported (0p):
- Generation: 850 kWh
- Self-consumed: 510 kWh × 30p = £153
- Exported: 340 kWh × 0p = £0
- Real saving: £153 (not £256)
If 80% self-consumed, 20% exported:
- Self-consumed: 680 kWh × 30p = £204
- Exported: 170 kWh × 0p = £0
- Real saving: £204 (not £256)
If Time-of-Use tariff (15p peak, 5p off-peak, 15p export):
- Peak self-consumption (8am–4pm): 400 kWh × 15p = £60
- Off-peak self-consumption (rest): 100 kWh × 5p = £5
- Export (at 15p): 350 kWh × 15p = £52.50
- Real saving: £117.50 (lower than standard, but depends on usage pattern—complex)
See Does Plug-in Solar Affect Energy Bill Immediately? for self-consumption analysis.
Comparing 800W to Smaller Systems: 400W and 600W
Output scales linearly:
| System Size | Annual Gen (London) | Daily Avg | Saving (30p/kWh) |
|---|---|---|---|
| 400W | 425 kWh | 1.2 kWh | £128 |
| 600W | 638 kWh | 1.7 kWh | £191 |
| 800W | 850 kWh | 2.3 kWh | £256 |
400W generates half of 800W. 600W generates 75% of 800W. Payback period is identical for all three (~3.1 years at £1/W cost), so choose based on budget and available space, not expected output.
See How Much Does Plug-in Solar Save? for size comparison.
Quick Reference: What to Expect
If you install 800W south-facing solar:
- Annual generation: 680–850 kWh depending on region (London best, Scotland lowest)
- Daily average: 1.9–2.3 kWh
- Summer peak month: 3.5–3.8 kWh/day (June)
- Winter low month: 1.1–1.4 kWh/day (December)
- Annual saving: £200–£260 at 30p/kWh (higher with ToU tariff, battery, or high self-consumption)
- Payback: 3.1–3.9 years depending on region
Key Takeaways
- 800W south-facing roof in London generates ~850 kWh/year – roughly 2.3 kWh/day average, £256/year saving
- Regional variation: 25% – Edinburgh generates 25% less (680 kWh) than London
- Aspect matters: South-west loses 5%, East/West lose 25% – but all aspects remain viable except north
- Placement impacts output via tilt angle – vertical balcony = 78% of tilted roof (22% loss)
- Shading is merciless – 30% daily shade = 30% annual output loss
- Seasonal variation: 3.3:1 – June 115 kWh/month, December 35 kWh/month
- Degradation is slow – 0.5%/year, barely noticeable over 20 years
Next Steps
- Check your region – use the table above to find typical output for your area
- Assess your aspect and shading – run Solar Report to grade sun exposure
- Calculate your real output – run the calculator with your postcode for exact figures
- Compare to your usage – if you use more electricity than 850 kWh/year, solar covers part of it; if less, you export surplus
Ready to see your exact output? Run the calculator with your postcode.
See how much plug-in solar could save you — with real data for your postcode.