Solar & battery
Solar Energy Savings Calculator
Works bill savings, where the tariff structure matters more than the production.
Result
A bill never reaches zero while the meter is connected. Fixed charges, minimum bills and demand charges survive any amount of production, and some utilities add a separate charge for solar customers. Check your own tariff rather than assuming the bill scales with usage.
Get a Free Business AuditHow the calculation works
Production valued at what it actually saves: energy offset at the retail rate it displaces, and energy exported at whatever the tariff credits exports at, less any fixed charges that continue regardless. The sum of those is the saving, which is generally less than production times the retail rate.
What moves the number
- Share of production consumed on site against exported.
- What exports are credited at under the tariff.
- Fixed charges that continue regardless of usage.
- Time of use rates, where they apply.
Where this one goes wrong
Valuing all production at the retail rate overstates savings wherever exports are credited below retail, which is increasingly common, and the error grows with the share exported. Fixed charges are the other item: connection and demand charges continue whatever the system produces, so a bill cannot go to zero even with a system producing more than the house uses. Read the tariff rather than assuming.
Before you quote
- Value exports at the tariff's export rate, not the retail rate.
- Subtract fixed charges that continue regardless.
- Model the share consumed on site, not just total production.
Questions
About this calculator
Why is my saving less than production times my rate?
Because exported energy is often credited below the retail rate, and fixed connection charges continue regardless. Valuing all production at retail overstates the saving, and the error grows with the share you export rather than use.
Can a bill go to zero?
Generally not, because fixed connection and sometimes demand charges continue whatever the system produces. A system producing more than the house uses still leaves those charges, which surprises customers who were told the bill disappears.
How do I increase the share consumed on site?
By shifting flexible loads into production hours: water heating, pool pumps, vehicle charging and laundry. Under a tariff with poor export credit, that shift is worth more than additional array capacity would be.
The formula
saving = self-used kWh x retail rate + exported kWh x export credit
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How to use this calculator
- Current monthly bill ($). Enter your own figure; the page starts at $168.
- Electricity used per month (kWh). Enter your own figure; the page starts at 950.
- Annual solar production (kWh). Enter your own figure; the page starts at 9,200.
- Fixed monthly charge ($). Connection and meter charges solar does not remove.
- Share used rather than exported (%). Enter your own figure; the page starts at 65%.
- Export credit per kWh ($). Enter your own figure; the page starts at $0.06.
The result updates as you type, so you can try a figure, see what it does to new monthly bill, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Current monthly bill | $168 |
| Electricity used per month (kWh) | 950 |
| Annual solar production (kWh) | 9,200 |
| Fixed monthly charge | $14 |
| Share used rather than exported | 65% |
| Export credit per kWh | $0.06 |
What comes out
| Result | Value |
|---|---|
| New monthly bill main result | $71.12 |
| Monthly saving | $96.88 |
| Annual saving | $1,163 |
| Share of usage covered | 80.7% |
| Your current rate per kWh | $0.16 |
The bill falls to about $71.12, saving $96.88 a month or $1,163 a year. The fixed charge of $14 stays whatever the panels produce.
How sensitive the answer is
Holding everything else steady and changing only current monthly bill, this is what happens to new monthly bill. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Current monthly bill ($) | New monthly bill |
|---|---|
| $84 | $31.18 |
| $126 | $51.15 |
| $168 example above | $71.12 |
| $252 | $111.05 |
| $336 | $150.99 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Current monthly bill ($)
- A money amount, starting at $168.
- Electricity used per month (kWh)
- A number, between 0 and 200000, starting at 950.
- Annual solar production (kWh)
- A number, between 0 and 5000000, starting at 9,200.
- Fixed monthly charge ($)
- Connection and meter charges solar does not remove.
- Share used rather than exported (%)
- A percentage, between 0 and 100, starting at 65%.
- Export credit per kWh ($)
- A money amount, starting at $0.06.
What the results tell you
| Result | What it is |
|---|---|
| New monthly bill | The headline result. A money figure. |
| Monthly saving | A money figure. |
| Annual saving | A money figure. |
| Share of usage covered | A percentage. |
| Your current rate per kWh | A money figure. |
A design still needs a site visit
Output and sizing figures use the assumptions you enter, not measured irradiance, shading or roof orientation at your address. Real production depends on all three, plus inverter behaviour and local interconnection rules.
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