The right number of solar panels depends on three things: how much electricity you use, how much roof space you have, and what you want the system to do. There is no one-size-fits-all answer, but there are clear guidelines. This guide gives you a practical starting point.
Solar panels by house size
The table below shows recommended system sizes based on typical UK household electricity usage. These are guidelines — your actual needs may differ based on your specific consumption.
| Home Size | Annual Usage | System Size | Panels | Roof Space |
|---|---|---|---|---|
| 1-2 bed flat | 2,000-2,500kWh | 2-2.5kWp | 5-6 | ~10m² |
| 2-3 bed semi | 2,800-3,500kWh | 3-3.5kWp | 8-10 | ~17m² |
| 3-4 bed detached | 3,500-4,500kWh | 3.5-4kWp | 10-12 | ~20m² |
| 4-5 bed detached | 4,500-6,000kWh | 5-6.5kWp | 14-18 | ~30m² |
| Large home + EV | 6,000-8,000kWh | 6-10kWp | 15-25 | ~42m² |
Panel sizes and output
Modern residential solar panels are typically rated at 400W each. Some budget options are 350W, while premium panels reach 420-430W. Each panel measures approximately 1.7m² (roughly 1.75m tall by 1.05m wide).
A single 400W panel in Milton Keynes generates around 340-380kWh per year, depending on orientation and tilt. Ten panels (4kWp) will produce approximately 3,600kWh annually.
How to work out your electricity usage
The most accurate way is to check your electricity bills or smart meter data. Look at your annual kWh consumption. If you do not have this to hand, here are typical figures:
- Low usage (1-2 people): 2,000-2,500kWh per year
- Medium usage (2-3 people): 3,000-3,800kWh per year
- High usage (4+ people): 4,000-5,500kWh per year
- With EV charging: Add 2,000-3,000kWh per year
Your electricity bill will show your usage in kWh. If it only shows cost, divide your annual electricity spend by 28p to get an approximate figure.
Roof orientation matters
Not all roof directions are created equal. Here is how orientation affects output relative to an ideal south-facing roof:
- South-facing: 100% (best possible output)
- South-east or south-west: 95% (marginal difference)
- East or west-facing: 85-90% (still very good)
- North-east or north-west: 65-75% (workable but reduced)
- North-facing: 50-60% (generally not recommended)
Many homes across Milton Keynes have east-west facing roofs. This works well in practice. You get solar generation spread across more of the day — morning sun on the east face, afternoon sun on the west — which can actually improve self-consumption compared to a pure south-facing setup that peaks at midday.
Roof pitch
The ideal pitch angle in the UK is around 30-40 degrees. Most pitched roofs fall naturally within this range. Flat roofs need angled mounting frames, which add a small cost but allow optimal positioning. Very steep roofs (50+ degrees) lose some efficiency but still work.
Shading and obstructions
Shading is the biggest performance killer for solar panels. Even partial shade on one panel can reduce the output of the entire string if you are using a standard string inverter.
Common sources of shading:
- Tall trees (especially to the south of your property)
- Chimney stacks casting shadows across the roof
- Neighbouring buildings
- Satellite dishes and aerials
- Dormer windows
If shading is unavoidable on part of your roof, microinverters or power optimisers can isolate the affected panels so they do not drag down the rest. We assess shading during every free survey and recommend the best solution for your specific roof.
Should you oversize your system
There is a strong argument for fitting more panels than your current usage strictly requires. Here is why:
- EV ownership: If you plan to buy an electric vehicle, your electricity usage will jump by 2,000-3,000kWh per year. An EV charger paired with solar makes charging significantly cheaper.
- Battery storage: A battery stores excess solar for evening use. More panels mean more surplus to store, increasing the battery's value.
- Heat pump future-proofing: If you switch to a heat pump for heating in the future, your electricity demand will increase substantially.
- Export income: Any surplus you do not use earns 7-15p/kWh through the Smart Export Guarantee.
The cost per panel decreases as system size increases (because fixed costs like scaffolding and labour are spread across more panels). Adding two or three extra panels at installation is far cheaper than coming back to add them later.
Roof space constraints
Not every roof can fit as many panels as you might want. Common constraints include:
- Velux windows: Panels need to be arranged around them
- Hip roofs: The triangular sections near the edges cannot take full-size panels
- Vents and pipes: Soil stacks and ventilation outlets need clearance
- Structural limits: Older roofs may need assessment for additional weight
A site survey confirms exactly how many panels your roof can take. We use satellite imagery for initial assessments, then verify everything in person during the free survey.
A quick sizing rule of thumb
If you want a rough number before getting a proper survey:
- Take your annual electricity usage in kWh
- Divide by 900 (the approximate annual output per kWp in the UK)
- That gives you the system size in kWp
- Divide by 0.4 to get the number of 400W panels
Example: 3,600kWh usage / 900 = 4kWp system = 10 panels. That is a sensible starting point for a 3-bed house.
What to do next
Use our free solar calculator to get a personalised recommendation based on your home and electricity usage. It factors in your roof size, orientation, and local conditions to suggest the right system size.
For a definitive answer, book a free survey. We will assess your roof in person, check for shading, and design a system that fits your home and budget. Call us on 07516 762540 or send us a message.