Worked examples
Every figure on this page is illustrative modelling, not a quote, not a forecast and not a guarantee. Install prices are typical ranges we have chosen to make the arithmetic concrete; your price depends on your roof, your electrics and your choices. Savings depend on your tariff, your usage pattern and future energy prices, which nobody can predict. Interest rates and monthly payments depend entirely on which lender you use and what they offer you.
The scheme figures are different. The £15,000 caps, the three-year minimum term, the up-to-5-percentage-point reduction and the £300 million fund are verified scheme facts — see how the loan works. The costs and savings below are ours, clearly labelled, and we show every assumption so you can challenge them.
| Assumption | Value used | Why it matters |
|---|---|---|
| Location | South Wales | Affects solar yield |
| Solar yield | 900 kWh per kWp per year | A reasonable round number for a decent south-facing roof; east-west or shaded roofs produce less |
| Electricity import price | 26p per kWh | The value of every unit you avoid buying |
| Off-peak import price | 8p per kWh | Drives the battery case on a time-of-use tariff |
| Export price | 15p per kWh | The value of surplus you send to the grid |
| Self-consumption, solar only | 40% | How much generation you use rather than export |
| Self-consumption, solar + battery | 75% | The battery's main job |
| Loan term modelled | 10 years | Above the scheme's three-year minimum for rate support |
| Interest rate modelled | 0% | Some lenders are offering 0%; others will be higher. See the rate comparison below. |
For simplicity these examples ignore battery round-trip losses, panel degradation, inverter replacement and future price changes. Ignoring those flatters the savings — treat the payback figures as optimistic rather than conservative.
Illustrative install cost: £7,000 — within the £15,000 solar cap.
Simple payback around 10 years at 0% interest. Monthly benefit and monthly repayment are roughly in balance from day one.
Illustrative install cost: £13,500 — drawing on both caps (roughly £7,000 solar, £6,500 battery), each with £15,000 available.
Simple payback around 14 years. The battery buys you resilience and control as well as savings — judge it on both.
Illustrative install cost: £6,500 — within the £15,000 battery cap, with no solar required.
Simple payback around 14 years. This example lives or dies on your tariff: a wide peak/off-peak spread and high shiftable usage make it work, a flat tariff makes it pointless. More on battery-only.
Illustrative install cost: £14,800 — about £7,000 against the solar cap and about £7,800 against the battery cap, with the OZEV-approved charger included as an ancillary cost inside the battery figure.
Honest caveat: most of that EV saving comes from moving your car charging to an off-peak tariff, which a smart charger can achieve without a battery. The battery's contribution is running the house off cheap electricity too.
At 0% interest, simple payback and real payback are the same thing — which is precisely what makes this scheme interesting. On a conventional loan, interest can add thousands to the total and push payback years further out. That is the whole point of the rate reduction.
Illustrative comparison on a £10,000 loan. The scheme is designed to cut a lender's normal rate by up to 5 percentage points, with a floor at 0% — so the middle column shows a lender whose normal rate was 6.9% applying the full reduction.
| Term | At 0% | At 1.9% | At 6.9% | Saved vs 6.9% (at 0%) |
|---|---|---|---|---|
| 5 years | £166.67 · £10,000 | £174.84 · £10,490 | £197.54 · £11,852 | £1,852 |
| 10 years | £83.33 · £10,000 | £91.57 · £10,988 | £115.59 · £13,871 | £3,871 |
| 15 years | £55.56 · £10,000 | £63.89 · £11,500 | £89.32 · £16,078 | £6,078 |
Illustrative only. Monthly payment · total repaid. Standard amortising repayment, fixed nominal rate, no fees. Real lender products may have arrangement fees and will quote an APR; compare APRs and total cost of credit, not monthly payments alone. We are not a lender or a credit broker and this is not financial advice.
A 15-year term more than halves the monthly payment compared with 5 years. But at any rate above 0% it costs you considerably more overall, and the scheme's grant is capped — meaning on very long terms the achievable rate reduction can be smaller than the headline 5 percentage points. Ask each lender for the APR and the total amount repayable, on more than one term.
A survey, a system design, and an itemised quote with the kW system size and our MCS number — the format lenders are required to ask for. Alongside it, a realistic generation and savings estimate based on your roof, your tariff and your consumption, with the assumptions written down so you can argue with them.
Free, no-obligation
Send us your postcode, roughly what you spend on electricity and what you are considering. We will model it properly and show our working.
Prefer to talk it through? Email [email protected].