How many solar panels will I need to run a house?

Right, this is one of the most common questions I get asked, and the answer is always “it depends on your house.” But let me walk you through how to work it out properly, because there’s a massive difference between what you actually need and what some sales people will try to sell you.

The short answer for most North West homes

Typical 3-bedroom house: 12-16 panels (3-4kW system) Typical 4-bedroom house: 16-20 panels (4-5kW system) Typical 2-bedroom house: 8-12 panels (2-3kW system)

But honestly, those numbers are pretty useless without understanding your specific situation. Let me show you how to work out what YOU actually need.

Start with your actual electricity usage

First thing – dig out your last 12 months of electricity bills and add up the kWh usage (not the £ amounts). This tells you how much electricity your house actually uses.

Low usage (under 2,500 kWh per year):

Probably 1-2 people, quite energy-conscious
Need: 8-10 panels (2-3kW system)
Will cover: 80-100% of your electricity

Medium usage (2,500-4,000 kWh per year):

Typical family of 3-4, average consumption
Need: 12-16 panels (3-4kW system)
Will cover: 60-80% of your electricity

High usage (4,000-6,000 kWh per year):

Bigger family, home workers, higher consumption
Need: 16-24 panels (4-6kW system)
Will cover: 50-70% of your electricity

Very high usage (over 6,000 kWh per year):

Large family, electric heating, or energy-intensive lifestyle
Need: 20+ panels (5kW+ system)
Will cover: 40-60% of your electricity

What actually affects how many panels you need

Your roof space (obviously)

Each panel needs about 2 square metres of roof space. So:

20m² of roof = maximum 10 panels
30m² of roof = maximum 15 panels
40m² of roof = maximum 20 panels

But you also need space around panels for access and safety, so you typically get about 80% utilisation of available roof space.

Which way your roof faces

South-facing: Standard calculations apply Southeast/Southwest: Almost as good (90-95% performance) East/West: Decent but lower (80-85% performance) – you might need a few more panels North-facing: Don’t bother in the UK

Your consumption patterns

Home most days: You’ll use more electricity directly from panels, so fewer panels needed for good coverage

Out 9-5 weekdays: You’ll export more surplus electricity, might want slightly more panels to maximise the export income

High evening usage: Panels don’t help much with evening consumption unless you add battery storage

Whether you’re planning ahead

Getting an electric car: Add 2-4kW capacity (8-16 more panels) for vehicle charging

Planning a family: Factor in higher future electricity consumption

Adding a hot tub/pool: These use loads of electricity – factor in extra capacity

Real examples from North West homes

Example 1: Small terraced house in Manchester

2-bedroom Victorian terrace
Annual usage: 2,200 kWh
Available roof: 24m² south-facing
System installed: 10 panels (2.5kW)
Result: Covers 85% of electricity usage, bills dropped from £65/month to £15/month

Example 2: Family semi in Preston

3-bedroom 1960s semi
Annual usage: 3,400 kWh
Available roof: 35m² southeast-facing
System installed: 14 panels (3.5kW)
Result: Covers 70% of usage, bills dropped from £95/month to £35/month

Example 3: Large detached in Stockport

4-bedroom detached with home office
Annual usage: 5,200 kWh
Available roof: 55m² south-facing
System installed: 20 panels (5kW)
Result: Covers 65% of usage, bills dropped from £145/month to £55/month

The “how many panels to run my house completely” question

Here’s the thing – you probably don’t want to size your system to cover 100% of your electricity usage. Here’s why:

Winter vs summer generation

Solar panels generate about 75% of their annual electricity between April and September. So to cover your full winter consumption, you’d need a massive system that generates way too much in summer.

Better approach: Size for 60-80% annual coverage. This gives good savings without massive over-generation in summer.

Cost vs benefit sweet spot

The first few panels give you the biggest bang for your buck. Each additional panel gives slightly less financial benefit because you end up exporting more at lower rates.

Sweet spot: Usually around 60-75% of annual consumption covered by solar.

Grid connection still valuable

Even with a big solar system, you’ll want grid connection for:

Cloudy weeks in winter
Higher than normal electricity usage
Backup when something needs maintenance

Reality: Most people are happy with 60-80% solar coverage rather than aiming for 100% self-sufficiency.

How to work out what you actually need

Step 1: Check your bills

Add up last 12 months of kWh usage. This is your annual electricity consumption.

Step 2: Measure your roof

How much south/southeast/southwest-facing roof space do you have? Each panel needs about 2m².

Step 3: Calculate system size

For 60% coverage: Annual kWh ÷ 0.6 ÷ 900 = kW needed
For 80% coverage: Annual kWh ÷ 0.8 ÷ 900 = kW needed

(The 900 figure is average annual generation per kW in North West conditions)

Step 4: Convert to panel numbers

Most modern panels are 300-400W each, so:

3kW system = 8-10 panels
4kW system = 10-13 panels
5kW system = 13-17 panels

Example calculation:

Annual usage: 3,600 kWh
Target coverage: 70%
Calculation: 3,600 ÷ 0.7 ÷ 900 = 5.7kW needed
Panel count: 5.7kW ÷ 0.35kW per panel = 16 panels

What installers should tell you (but often don’t)

Start with your actual usage, not your roof capacity

Good installers size systems based on your electricity consumption, not just how many panels they can cram on your roof.

Explain the coverage percentage

They should tell you what percentage of your annual electricity the system will cover, not just how much it will generate.

Discuss your consumption patterns

Do you use more electricity during the day or evening? This affects how you’ll benefit from solar generation.

Consider future changes

Are you planning an electric car, growing family, or other changes that might affect electricity usage?

Common mistakes people make

“Maximum panels = maximum savings”

Not always true. Once you’re generating much more than you use, additional panels give diminishing returns.

“I need to eliminate my electricity bill completely”

Unrealistic and usually not cost-effective. Aiming for 60-80% reduction is more sensible.

“All south-facing roof space should be filled”

Only if you can use or profitably export all that electricity. Sometimes smaller systems give better returns.

Ignoring consumption patterns

If you use most electricity in the evening, a massive solar system won’t help as much as you’d think.

The honest recommendation

For most North West homes, 12-16 panels (3-4kW system) hits the sweet spot of good coverage without over-investment. This typically:

Covers 60-75% of annual electricity consumption
Provides payback in 6-8 years
Costs £5,500-7,000 installed
Saves £700-1,000 annually
Fits on most suitable roofs

Don’t get obsessed with covering 100% of your usage. A well-sized system that covers 70% of your electricity and pays for itself in 6-7 years is much better than an oversized system that covers 90% but takes 10+ years to pay back.

Want to know exactly how many panels your specific house needs? Get a proper survey based on your actual bills and roof situation. The calculations above are good estimates, but every house is different.

For more detailed cost information, check out our solar cost calculator or read about what solar panels actually cost for North West homes.