Plug-in solar payback explained: how long until it pays for itself?
30 August 2026 · Savings
The headline question for any solar purchase is: how long until it pays for itself? For plug-in solar, the honest answer is usually 4-8 years - and panels last 25+ years, so the remaining years are effectively free electricity.
The simple formula
Example: a £599 kit saving £110 a year pays back in 5.4 years. A £900 kit saving £150 a year pays back in 6 years.
Where the savings come from
Your annual savings are made of two parts:
- Self-consumption - every kWh you generate and use yourself is a kWh you don't buy at your full electricity rate (~22-25p). This is the valuable part.
- Export - surplus power sold to the grid. Smart export tariffs (like Octopus Outgoing) pay around 12p/kWh; basic SEG rates pay 4-5p.
The mix matters. If you use 40% of your solar and export 60%, at 24.5p electricity and 5p export, roughly 75% of your savings come from self-consumption. That's why daytime usage is the single biggest factor in payback.
Realistic numbers for an 800W kit
An 800W system in southern England generates roughly 650-850 kWh per year (about 0.95 kWh per watt). Here's how payback varies:
Working from home, no battery: 50% self-consumption → saves ~£130-£150/year. £799 kit pays back in ~6 years.
Out all day, no battery: 25% self-consumption → saves ~£80-£95/year. £599 kit pays back in ~7 years.
With 1.92 kWh battery: 75% self-consumption → saves ~£160-£180/year, but kit + battery costs £1,300+ → payback ~8 years.
What speeds up payback
- Use more power during the day - run the dishwasher, washing machine and charger when the sun is out. Every kWh you shift into daylight is worth 4-5x an exported kWh.
- A good south-facing position - adds 10-20% generation vs east/west.
- Switch to a smart export tariff - Octopus Outgoing pays ~12p/kWh vs 4-5p basic SEG. If your export rate is low, a battery (or daytime usage) matters more.
- Buy when prices are competitive - the government expects kit prices to fall to £510-£770 as the market opens; buying at launch is fine, but shopping around saves real money.
What slows it down
- Shading - even partial shading can cut generation by 20-50%
- Being out all day with no battery - most of your solar exports at a low rate
- Importing an overpriced kit - compare at least two retailers before buying
- Low electricity prices - the lower your tariff, the longer payback (though UK prices are currently around 22-25p and expected to stay similar)
Degradation and long-term maths
Panels degrade about 0.4% per year, so a 25-year-old panel generates roughly 10% less than a new one. Over 25 years, that trims your total savings by about 5-7% - worth knowing, but not a dealbreaker. Most panels carry 25-year performance warranties guaranteeing at least 80-85% of rated output at year 25.
Payback vs total savings
Payback is one way to look at it, but total savings matter more. A £700 kit saving £120/year:
- Pays back in ~6 years
- Saves £2,150 over 20 years after the kit cost
- Saves £2,850 over 25 years after the kit cost
Even at a modest £90/year saving, a £600 kit saves about £1,500 over 20 years. Not a get-rich scheme - but for a weekend DIY project, it's a solid return that also cuts your carbon footprint.
Try it with your own numbers
Every home is different. Use our savings calculator to enter your region, kit size, battery choice and tariff - it shows your estimated annual savings, payback period and 25-year net savings in seconds.