How Much Can Plug-in Solar Actually Save on Your Energy Bills?

Concrete numbers for how much you'll save based on your system size, location, and how you use electricity.

The most common question about plug-in solar isn't "Is it worth it?" It's "How much will I actually save?"

And it deserves a concrete answer, not a vague one.

The honest baseline, from Carbon Brief's analysis of real UK data, is £110 per year. But that's an average. Your specific savings depend on five variables: system size, location, orientation, self-consumption, and energy prices. Change any of those, and your savings change significantly.

This guide gives you the maths so you can estimate your own savings.

The Variables

Before we look at numbers, here are the five factors that determine your specific savings.

1. System Size

You can install up to 800W (the UK regulatory cap). Most people install either:

400W: One panel, cheaper upfront, reasonable output
800W: Two panels, higher cost, roughly double the output

A 400W south-facing system in southern England generates about 350–400 kWh per year. An 800W system generates about 700–800 kWh per year.

These are gross generation figures before accounting for self-consumption.

2. Location (Climate)

Southern England gets the most solar irradiance. Northern Scotland gets the least.

As a rough rule:

Southern England (London, Bristol, Cornwall): ~900–1,000 kWh/kW annually
Midlands and Wales: ~850–900 kWh/kW annually
Northern England (Manchester, Leeds): ~800–850 kWh/kW annually
Scotland: ~700–750 kWh/kW annually

For an 800W (0.8kW) system:

Southern England: 720–800 kWh/year
Midlands and Wales: 680–720 kWh/year
Northern England: 640–680 kWh/year
Scotland: 560–600 kWh/year

Your postcode matters. A system 100 miles north generates about 15% less. Use the savings calculator to get a precise figure for your postcode.

3. Orientation (Angle and Direction)

South-facing is 100%. Everything else is less:

Southwest or southeast: 90–95% of south output
East or west: 70–80%
North: 40–50%

For an 800W south-facing system generating 700 kWh in southern England:

South: 700 kWh
Southwest: 630–665 kWh
East/West: 490–560 kWh
North: 280–350 kWh

North-facing is economically weaker. But it still generates. Don't assume north-facing means zero savings—it just means lower savings.

4. Self-Consumption Rate

Here's where behaviour matters.

Your panels generate peak electricity from 10am to 4pm on sunny days. If you're consuming electricity during those hours, you use the solar directly (self-consumption). If you're out, that electricity feeds back to the grid.

Self-consumption savings: if you generate 1 kWh and consume it, you save the full 27p (the grid price).

Grid export earnings: if you generate 1 kWh and export it, you earn typically 5–10p (the export payment rate, which is much lower than the grid purchase price).

Most households have a self-consumption rate of 60–75%. It depends on:

Work from home? Your self-consumption is 75–85%. You're present for peak generation.
Office job, 9–5? Your self-consumption is 40–50%. You're out when the sun is highest.
Shift worker with flexible hours? Your self-consumption varies based on your pattern.

Let's model some scenarios.

Real Numbers: Different System Sizes and Locations

Scenario 1: 400W system, Southern England, south-facing, 70% self-consumption

Annual generation: 350 kWh
Self-consumed: 245 kWh
Exported: 105 kWh
Savings from self-consumption: 245 kWh × 27p = £66
Earnings from export: 105 kWh × 8p = £8
Total annual benefit: £74
Annual cost (amortised over 4.5-year payback): ~£100
Annual net cost: −£26 (but you've still reduced your grid consumption)

Actually, plug-in solar at 400W in southern England is borderline. It saves money if you've got high self-consumption and energy prices stay at 27p+. At lower self-consumption, it's less compelling financially.

Scenario 2: 800W system, Southern England, south-facing, 70% self-consumption

Annual generation: 700 kWh
Self-consumed: 490 kWh
Exported: 210 kWh
Savings from self-consumption: 490 kWh × 27p = £132
Earnings from export: 210 kWh × 8p = £17
Total annual benefit: £149
Annual cost (amortised over 4.5-year payback from ~£650 kit): ~£145
Annual net benefit: ~£4 (or break-even)

Plus: the export payments and import savings continue for years 5+ without cost, netting real savings.

Scenario 3: 800W system, Southern England, south-facing, 85% self-consumption (work from home)

Annual generation: 700 kWh
Self-consumed: 595 kWh
Exported: 105 kWh
Savings from self-consumption: 595 kWh × 27p = £161
Earnings from export: 105 kWh × 8p = £8
Total annual benefit: £169
Annual cost (amortised): ~£145
Annual net benefit: ~£24

This is better. Work-from-home households see stronger returns because of higher self-consumption.

Scenario 4: 800W system, Scotland, south-facing, 70% self-consumption

Annual generation: 580 kWh (lower due to climate)
Self-consumed: 406 kWh
Exported: 174 kWh
Savings from self-consumption: 406 kWh × 27p = £110
Earnings from export: 174 kWh × 8p = £14
Total annual benefit: £124
Annual cost (amortised): ~£145
Annual net cost (year 1): −£21

Scotland breaks even around year 5–6 due to lower generation. But still viable.

Scenario 5: 800W system, Southern England, southeast-facing, 65% self-consumption

Annual generation: 630 kWh (90% of south-facing due to orientation)
Self-consumed: 410 kWh
Exported: 220 kWh
Savings from self-consumption: 410 kWh × 27p = £111
Earnings from export: 220 kWh × 8p = £18
Total annual benefit: £129
Annual cost (amortised): ~£145
Annual net cost (year 1): −£16

This also breaks even around year 5, driven mainly by orientation loss.

The Pattern

Looking at these scenarios, a few patterns emerge:

800W performs better than 400W because the cost per watt is lower and generation is double
South-facing outperforms other orientations by 20–30%
High self-consumption (75%+) drives faster payback than low self-consumption (50%)
Southern location significantly outperforms Scotland (about 20% difference)
£110–£170 annual savings is the realistic range for a typical 800W system in southern UK with moderate self-consumption

Why the Carbon Brief £110/Year Becomes Relevant

When you see "£110 per year" quoted repeatedly, that's not a random number. It's the Carbon Brief baseline: 800W system, southern England (weighted average), 70% self-consumption, south-facing.

It's not a maximum. It's not a minimum. It's a representative middle case.

You could beat it (work from home, southern location, optimal orientation, high energy prices). You could fall short of it (north-facing, low self-consumption, Scotland, lower energy prices).

But £110 is a reasonable target to plan for.

What Happens Years 2 Onwards

Here's where the payback case gets stronger.

Year 1 cost: You've paid for the system.

Years 2–5: You're saving £110–£170 annually with no additional cost. You're in profit.

Year 5 onwards: The system is paid for. Every £110–£170 saved is pure profit.

Over 15 years (typical panel life), at £130 annual average savings, you're looking at £1,950 in gross savings. Subtract the initial £600–£700 cost, and you're netting £1,200–£1,350.

That's the power of payback. It's not exciting in year 1. It's very exciting by year 10.

Maximising Your Savings

You can improve your actual savings beyond these baseline numbers by changing behaviour:

1. Shift high-demand appliances to peak sun hours: Run your dishwasher, washing machine, and dryer at midday when solar is generating. That moves demand from grid hours to solar hours. You effectively increase self-consumption.

2. Charge devices at midday: Charge your laptop, phone, electric toothbrush, and any rechargeable devices during peak generation (11am–3pm on sunny days).

3. Adjust heating/cooling to midday: If you use electric heating or air conditioning, running it at midday means some of it comes from solar instead of grid.

4. Monitor and plan: Most plug-in solar systems come with a monitoring app showing real-time generation. Watch it. On sunny days, get a sense of when you're generating peak and plan appliance use around that.

These aren't massive optimisations. But they can move you from 65% to 75–80% self-consumption, which adds £15–£25 per year. Over 15 years, that's £250–£375 extra benefit.

Energy Price Inflation

One final variable worth thinking about: energy prices.

The Carbon Brief baseline assumes 27p/kWh (current price cap). But energy prices fluctuate. If prices rise to 30p/kWh, your annual savings rise proportionally to £120–£190.

The UK government's central scenario is that energy prices will remain elevated or rise gradually. If that happens, plug-in solar's payback improves over time.

If prices fall to 24p/kWh, savings drop to £85–£130. That would extend payback slightly.

For long-term planning, assume moderate price inflation. That trend is more likely than deflation.

Using the Calculator

All of this is guidance. The real answer for your specific property is in the savings calculator.

It takes your postcode, orientation, and consumption, and outputs your specific savings.

Run it. See what the numbers say for your situation. That's the number you should plan around, not these generic scenarios.

But now you understand what drives the maths. You know why a south-facing system in southern England with high self-consumption beats a north-facing system in Scotland with low self-consumption.

And you know why £110 per year isn't a guarantee—it's a reasonable baseline that many households will beat or fall slightly short of, depending on their specific circumstances.