UK Residential Energy
Solar & Battery
ROI Calculator
Estimate your annual savings, payback period, and long-term profit from a solar or solar+battery installation. Choose the mode that matches your setup.
Step 1 — Select your setup
Solar Only
Solar panels, no battery. Excess generation is exported to the grid.
Solar + Battery
Battery stores solar surplus and may top up from grid on a standard tariff.
Battery Only
Battery storage on a time-of-use tariff, no solar panels. Charges overnight at a cheap rate.
Advanced: ToU / Arbitrage
Battery charges overnight at a cheap off-peak rate and arbitrages peak prices. Solar tops up during the day.
System Cost
The total installed cost of your solar panel system.
Total installed cost of solar system
?
Include panels, inverter, and installation labour. Typical UK 4 kWp system: £5,000–£7,000.
£
Generation & Consumption
How much electricity your panels generate and your household uses each year.
Annual solar generation
?
From your installer's estimate, or MCS certificate. Example: a 4 kWp system typically generates ~3,400 kWh/yr in the UK.
kWh/yr
Annual household consumption
?
Found on your annual energy statement or smart meter app. UK average: ~3,500 kWh/yr.
kWh/yr
Direct self-consumption (% of solar generation)
?
This is the share of your solar output used live by your home (lights, appliances running while sun is shining). It is not your total consumption — it is only the portion of solar generation consumed immediately.
• Mostly out during the day → use 25–35%
• Someone home in daytime → use 40–55%
• Retired / home all day → use 55–70%
The remaining solar is exported to the grid.
• Mostly out during the day → use 25–35%
• Someone home in daytime → use 40–55%
• Retired / home all day → use 55–70%
The remaining solar is exported to the grid.
%
Tariff Rates
Your electricity import and export rates. Find these on your bill or supplier's website. Enter rates inclusive of VAT as shown on your bill.
Import rate (day)
?
Your standard unit rate. Found on your energy bill under "unit rate". Typical UK range: 22–30p. Enter inc. VAT.
p/kWh
Export rate (SEG)
?
Paid by your supplier for excess solar sent to the grid. Check your Smart Export Guarantee (SEG) tariff. Typical range: 4–15p.
p/kWh
Daily standing charge
?
The fixed daily charge on your electricity bill — paid regardless of usage. Found on your bill next to "standing charge". UK typical range: 50–80p/day. Enter inc. VAT. Your annual standing charge = this figure × 365.
p/day
System Costs
Enter solar and battery costs separately so you can see each component's contribution.
Solar system installed cost
?
Panels + inverter + labour only. Exclude battery cost.
£
Battery installed cost
?
Battery unit + installation labour. Typical UK range: £2,500–£8,000.
£
Total system cost (auto-calculated)
£
Generation & Consumption
Your solar output and household demand figures.
Annual solar generation
?
From installer's quote or MCS certificate. Rule of thumb: system kWp × 850 kWh.
kWh/yr
Annual household consumption
?
From your annual energy bill or smart meter app. UK average: ~3,500 kWh/yr.
kWh/yr
Battery usable capacity
?
The usable kWh your battery can store. From the product datasheet. Example: Givenergy 9.5 kWh = 9.5 kWh usable.
kWh
Battery round-trip efficiency
?
From your battery's datasheet. Most modern home batteries (LFP chemistry) are 90–95%.
%
Direct self-consumption (% of solar generation)
?
The share of solar generation used by your home in real time — before the battery gets involved. With a battery, this is typically lower than without one because the battery catches what you don't use live.
• Mostly out during the day → 20–30%
• Someone home in daytime → 30–45%
The battery then stores the remainder (up to its capacity), and the rest is exported.
• Mostly out during the day → 20–30%
• Someone home in daytime → 30–45%
The battery then stores the remainder (up to its capacity), and the rest is exported.
%
Tariff Rates
Your import and export rates. If you have a time-of-use tariff with separate off-peak and peak rates, use the Advanced: ToU / Arbitrage mode instead. Enter rates inclusive of VAT as shown on your bill.
Standard import rate
?
The unit rate on your electricity bill. Typical UK range: 22–30p. Enter inc. VAT.
p/kWh
Export rate (SEG)
?
From your SEG agreement with your supplier. Typical range: 4–15p.
p/kWh
Daily standing charge
?
Fixed daily charge from your bill, inc. VAT. UK typical range: 50–80p/day.
p/day
Battery cycles per year
?
How many complete charge/discharge cycles your battery does per year. Daily solar storage use = ~250–300. Daily solar + grid arbitrage = ~350–365.
How this mode works: Your battery charges fully overnight at the cheap off-peak rate. It then powers your home through the day, avoiding the more expensive peak rate. The saving is measured against what you would have paid on a standard flat-rate tariff — your pre-install consumption multiplied by that rate. No solar generation is included.
System Cost
Battery unit and installation cost.
Battery installed cost
?
Battery unit + installation labour. Typical UK range: £2,500–£8,000.
£
Baseline — Without the System
What you would have paid without a battery on a standard flat-rate tariff. Used only to calculate your saving.
Pre-install annual consumption
?
Your annual electricity import before installing the battery — from a bill or smart meter from the 12 months prior to install.
kWh/yr
Baseline unit rate (standard tariff)
?
The unit rate on a standard flat-rate tariff without the battery. Use your actual previous rate, or ~24p as a typical UK figure (Ofgem price cap, inc. VAT).
p/kWh
Baseline standing charge
?
Daily standing charge you would pay on a standard tariff, inc. VAT. If unsure, your current standing charge is a reasonable estimate.
p/day
Consumption & Battery
Your household demand and battery specification.
Annual household electricity consumption
?
Your total annual grid import with the battery installed. Higher than pre-install because overnight charging adds to your metered import. From your annual bill or smart meter app.
kWh/yr
Battery usable capacity
?
From the battery datasheet. Enter the usable figure (not total). Example: Givenergy 9.5 kWh = 9.5 kWh usable.
kWh
Battery round-trip efficiency
?
From the battery datasheet. Most modern lithium iron phosphate (LFP) batteries: 90–95%.
%
Battery cycles per year
?
How many complete charge/discharge cycles per year. Nightly grid charging = ~330–365 cycles/yr.
Daytime consumption (% of annual total)
?
The proportion of your electricity used during peak hours (approx. 7am–9pm), when the battery is discharging to offset expensive grid imports.
• Mostly out during the day → 30–40%
• Someone home in daytime → 45–55%
• Retired / home all day → 55–65%
Check your smart meter's half-hourly data in your supplier app, or use 50% as a reasonable starting estimate.
• Mostly out during the day → 30–40%
• Someone home in daytime → 45–55%
• Retired / home all day → 55–65%
Check your smart meter's half-hourly data in your supplier app, or use 50% as a reasonable starting estimate.
%
Tariff Rates
Your off-peak charging rate, the peak rate you're avoiding, and your export rate. Enter all rates inclusive of VAT as shown on your bill.
Off-peak (overnight) rate
?
The cheap rate during your overnight charging window. This is the rate you pay to charge the battery each night.
p/kWh
Standard (peak) rate
?
The rate outside the off-peak window. The battery discharges to avoid paying this rate for daytime demand.
p/kWh
Export rate (SEG)
?
From your Smart Export Guarantee (SEG) agreement. Only applicable if you export battery charge to the grid. Typical range: 4–15p.
p/kWh
Off-peak window duration
?
Length of your cheap overnight window. Octopus Go: ~4–5 hrs. Economy 7: 7 hrs.
hrs
Daily standing charge
?
Fixed daily charge from your electricity bill, inc. VAT. UK typical range: 50–80p/day.
p/day
Battery Export
If you export battery charge to the grid before the overnight recharge window, enter the annual total here. Leave at 0 if you use all battery charge at home.
Annual battery export to grid (kWh)
?
How much energy you export from the battery each year. Most battery-only users export nothing and use all discharge at home — in that case leave this at 0. Only enter a figure if you actively export battery charge to the grid for SEG income.
kWh/yr
How this mode works: Your battery fully charges overnight at the cheap off-peak rate. It then powers your home through the day. Any solar generated goes first to live household demand, then tops up the battery, then exports to the grid once the battery is full. The saving is measured against what you would have paid on a standard flat-rate tariff with no system — using your pre-install consumption and a typical flat rate.
System Costs
Total investment in solar and battery.
Solar system installed cost
?
Panels + inverter + labour. Exclude battery cost.
£
Battery installed cost
?
Battery unit + installation. Large batteries (20–30 kWh) typically cost £8,000–£15,000 installed.
£
Total system cost (auto-calculated)
£
Baseline — Without the System
What you would have paid without solar, battery, or a time-of-use tariff. Used only to calculate your saving — not for the current system costs.
Pre-install annual consumption
?
Your annual electricity import before installing the system — from a bill or smart meter from the 12 months prior to install. This is the fairest baseline because it reflects actual household demand, not the inflated import you now have from overnight battery charging.
kWh/yr
Baseline unit rate (standard tariff)
?
The unit rate you would pay on a standard flat-rate tariff without the system. Without solar and battery there is no reason to be on a time-of-use tariff. Use your actual previous rate if known, or ~24p as a typical UK figure (Ofgem price cap, inc. VAT).
p/kWh
Baseline standing charge
?
Daily standing charge you would pay on a standard tariff, inc. VAT. If unsure, your current standing charge is a reasonable estimate — it appears in both baseline and actual costs so largely cancels out of the saving calculation.
p/day
Consumption & Generation
Your household demand and solar output — the two key numbers for this model.
Annual household electricity consumption
?
Your total annual electricity use, including all appliances, EV charging, and any heat pump load. Found on your annual energy statement. This is your actual import figure with the current system in place.
kWh/yr
Annual solar generation
?
From your inverter's monitoring app, installer's estimate, or MCS certificate. Rule of thumb: system kWp × 850 kWh/yr.
kWh/yr
Battery usable capacity
?
From the battery datasheet. Enter the usable figure (not total). Example: a 30 kWh unit may have 27 kWh usable.
kWh
Battery round-trip efficiency
?
From the battery datasheet. Most modern lithium iron phosphate (LFP) batteries: 90–95%.
%
Daytime consumption (% of annual total)
?
Roughly what proportion of your electricity is used during daylight hours (approx. 7am–9pm). Used to estimate how much solar offsets live demand before the battery gets involved.
• Mostly out during the day → 25–35%
• Someone home in daytime → 40–55%
• Retired / home all day → 55–65%
If unsure, check your smart meter's half-hourly data in your supplier app, or use 40% as a reasonable estimate for most households.
• Mostly out during the day → 25–35%
• Someone home in daytime → 40–55%
• Retired / home all day → 55–65%
If unsure, check your smart meter's half-hourly data in your supplier app, or use 40% as a reasonable estimate for most households.
%
Tariff Rates
Your off-peak charging rate, the standard rate you're avoiding, and your export rate. Enter all rates inclusive of VAT as shown on your bill.
Off-peak (overnight) rate
?
The cheap rate during your overnight charging window. This is the rate you pay to fully charge the battery each night.
p/kWh
Standard (peak) rate
?
The rate you pay outside the off-peak window. Also used as the baseline tariff rate for calculating your saving.
p/kWh
Export rate (SEG)
?
From your Smart Export Guarantee (SEG) agreement. Applied to all grid exports — solar surplus and evening battery export. Typical range: 4–15p.
p/kWh
Off-peak window duration
?
Length of your cheap overnight window. Good Energy / Octopus Go: ~5 hrs. Economy 7: 7 hrs.
hrs
Daily standing charge
?
Fixed daily charge from your electricity bill, inc. VAT. UK typical range: 50–80p/day.
p/day
Export — Solar & Battery
How much energy you export to the grid each year, from both solar surplus and deliberate evening battery export before overnight recharging.
Annual solar export (kWh)
?
How much solar energy you export to the grid per year. Find this in your smart meter app, inverter app, or supplier account under "export". If you only have partial data, scale it up proportionally.
This figure should be solar export only if your meter separates them, or total export minus battery export if combined. If unsure, use your best estimate — the seasonal detail section below can help refine this.
This figure should be solar export only if your meter separates them, or total export minus battery export if combined. If unsure, use your best estimate — the seasonal detail section below can help refine this.
kWh/yr
Annual evening battery export (kWh)
?
How much energy you export from the battery each year before overnight recharging. If you actively force-export each evening, enter the annual total here — or use the seasonal detail section below to calculate it from your seasonal patterns. The seasonal calculation will override this field when used.
kWh/yr
▶
Seasonal detail — override annual battery export with seasonal breakdown
If your evening export behaviour varies significantly by season — as it typically does — you can enter seasonal figures here. The calculator will use these to compute a more accurate annual battery export total, which will override the annual figure above. Leave blank to use the annual figure instead.
Winter — Dec, Jan, Feb (90 days)
Export evenings per fortnight
?
Out of every 14 days in winter, how many evenings do you force-export before midnight? Battery tends to be more depleted in winter.
/ 14 days
Typical SoC at export time (%)
?
The typical battery charge level (%) when you begin exporting each winter evening. E.g. 20–40% in winter.
%
Spring & Autumn — Mar, Apr, Sep, Oct, Nov (152 days)
Export evenings per fortnight
?
Out of every 14 days in spring/autumn. Solar starts contributing more, battery less depleted by demand.
/ 14 days
Typical SoC at export time (%)
?
The typical battery charge level (%) when you begin exporting in spring/autumn. E.g. 40–50%.
%
Summer — May, Jun, Jul, Aug (123 days)
Export evenings per fortnight
?
Out of every 14 days in summer. High solar generation typically results in near-daily export.
/ 14 days
Typical SoC at export time (%)
?
The typical battery charge level (%) when you begin exporting each summer evening. E.g. 50–70%.
%
Calculated annual battery export from seasonal inputs
3,315 kWh/yr
This value overrides the annual battery export field above when the seasonal section is open.
Your Results
Estimated Total Annual Saving
£0
vs. a standard flat-rate tariff with no system
Without system
£0/yr
With system
£0/yr
Solar Savings
£0
direct use + battery
Battery Saving
£0
arbitrage / avoided imports
Export Income
£0
SEG payments
Simple Payback Period — yrs
05 yrs10 yrs15 yrs20+ yrs
20-Year Net Profit
£0
savings × 20 − system cost
System Cost
£0
total investment
Bill Reduction
0%
of baseline annual cost
Full Calculation Breakdown
Results are illustrative estimates only. Actual savings depend on weather, occupancy patterns, tariff changes, system degradation (~0.5%/yr), and future energy prices. Battery arbitrage assumes overnight grid charging at the off-peak rate. Always obtain a professional survey and MCS-certified installer quote.