Useful next calculations
Rates and sources
Quote-led present-value comparison. The calculator does not supply installation costs, grants, tariffs or saving claims; all financial assumptions are entered by the user.
| Band or figure | Rate |
|---|---|
| Installation cost | confirmed net quote entered |
| Bill saving | quote or survey assumption entered |
| Energy-price change | entered by you |
| Grant eligibility | not assessed |
Source: GOV.UK — find energy grants. Check the linked guidance and any live quote before acting.
When to use this calculator
- Before switching supplier, upgrading equipment or comparing energy-saving changes.
- When you want to test different usage or price scenarios quickly.
- When you need a simple estimate before requesting installer or supplier quotes.
- When a tariff is about to change and you want to model the bill impact.
A worked example
These are the example figures the calculator opens with.
| Input | Value |
|---|---|
| Upgrade A | Solar panels |
| Upgrade A net upfront cost after confirmed grant (£) | £6,500 |
| Upgrade A first-year bill saving from quote (£) | £750 |
| Upgrade A annual maintenance/running-cost increase (£) | £100 |
For those figures the calculator returns:
- Higher present-value option: Upgrade A — Solar panels
- Upgrade A: Solar panels
- Upgrade A NPV: £2,304.52
- Upgrade A nominal lifetime net: £5,808.43
- Upgrade A simple payback: 11 years
- Upgrade B: Solar panels
- Upgrade B NPV: £-994.83
- Upgrade B nominal lifetime net: £1,344.75
- Upgrade B simple payback: 13 years
- NPV difference A minus B: £3,299.34
How to read your results
Upgrade A Simple Payback
How long it takes to recover the upfront cost through the ongoing saving or income you entered.
Upgrade B Simple Payback
How long it takes to recover the upfront cost through the ongoing saving or income you entered.
Method & assumptions
This comparator is deliberately quote-led. For each upgrade, enter the price you would actually pay after any confirmed grant, the first-year bill saving from the survey or quote, annual running or maintenance cost, comparison life and saving degradation.
The nominal lifetime net adds the modelled annual net savings and subtracts the upfront cost. NPV discounts those future savings using the rate entered. Simple payback is the first whole year when cumulative nominal savings recover the net upfront cost.
Energy prices, weather, occupancy, export tariffs, equipment performance and maintenance are uncertain. Financing interest, tax, replacement components, residual value, carbon savings and interactions between two upgrades are not modelled. Compare like-for-like scopes and verify certification, warranties and grant conditions independently.
Common mistakes
- Using the current tariff without testing a higher unit rate.
- Forgetting the standing charge when comparing annual bills.
- Treating the result as a supplier quote.
- Using optimistic savings figures for an upgrade without a written estimate.
What to do next
- Run the same scenario with a 10% higher unit rate.
- Compare this result with a related energy calculator before requesting installer quotes.
- If you are evaluating an upgrade, rerun with actual quote figures.
- Set a reminder to rerun the calculation when your tariff renews.