Solar & battery
Solar Carbon Savings Calculator
Works avoided emissions, where the regional grid factor decides the answer.
Result
Grid carbon intensity varies enormously by region and by hour, and displacing a coal-heavy grid avoids roughly nine times more carbon than displacing a hydro-heavy one. Embodied carbon estimates differ substantially between studies depending on where the panels were made and on what energy. Treat the figures as an order of magnitude rather than an audited number.
Get a Free Business AuditHow the calculation works
Energy produced multiplied by the emissions intensity of the electricity it displaces. That intensity varies enormously by region depending on the generation mix, so the same array avoids very different quantities of emissions in a coal-heavy region and a hydro-heavy one.
What moves the number
- Regional grid emissions intensity.
- Energy produced annually.
- Whether a marginal or average emissions factor is used.
- Time of day, since the marginal generator varies.
Where this one goes wrong
Average and marginal emissions factors answer different questions: the average describes the grid's overall intensity while the marginal describes what generation is actually displaced at the time, and they can differ substantially. Published regional data gives the average and is the appropriate figure for most purposes. A national figure is the least useful choice, since regional variation is the dominant term and using a national average can be wrong by a large factor either way.
Before you quote
- Use the regional emissions factor, not a national average.
- State whether the factor is average or marginal.
- Use published data rather than an assumed figure.
Where the rules come from
Questions
About this calculator
Does location affect carbon savings?
Substantially, because the emissions intensity of the electricity displaced varies enormously by region. The same array avoids very different quantities in a coal-heavy region and a hydro-heavy one, so a national average can be badly wrong.
What is the difference between average and marginal factors?
The average describes the grid's overall intensity; the marginal describes what generation is actually displaced at a given time. They can differ considerably, and which is appropriate depends on the question being asked.
Where does the emissions data come from?
The EPA publishes regional electricity emissions data, which is the appropriate source rather than an assumed figure. Using published regional data is what makes an avoided emissions claim defensible rather than decorative.
The formula
avoided CO2 = kWh x grid carbon intensity; carbon payback = embodied carbon / annual avoided
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
How to use this calculator
- Annual production (kWh). Enter your own figure; the page starts at 9,200.
- Grid carbon intensity. Enter your own figure; the page starts at US average (0.37 kg per kWh).
- Years. Enter your own figure; the page starts at 25.
- Manufacturing carbon per kW (tonnes). Enter your own figure; the page starts at 1.4.
- System size (kW). Enter your own figure; the page starts at 7.2.
The result updates as you type, so you can try a figure, see what it does to avoided per year, 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 |
|---|---|
| Annual production (kWh) | 9,200 |
| Grid carbon intensity | US average (0.37 kg per kWh) |
| Years | 25 |
| Manufacturing carbon per kW (tonnes) | 1.4 |
| System size (kW) | 7.2 |
What comes out
| Result | Value |
|---|---|
| Avoided per year main result | 3.4 |
| Avoided over the period | 85.1 |
| Manufacturing carbon | 10.1 |
| Net avoided | 75.0 |
| Carbon payback | 3.0 |
About 3.4 tonnes of CO2 a year, 85.1 over 25 years. Manufacturing the system cost 10.1 tonnes, repaid in 3.0 years, leaving 75.0 tonnes net.
How sensitive the answer is
Holding everything else steady and changing only annual production (kwh), this is what happens to avoided per year. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Annual production (kWh) | Avoided per year |
|---|---|
| 4,600 | 1.7 |
| 6,900 | 2.6 |
| 9,200 example above | 3.4 |
| 13,800 | 5.1 |
| 18,400 | 6.8 |
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
- Annual production (kWh)
- A number, between 0 and 5000000, starting at 9,200.
- Grid carbon intensity
- Choose from Coal heavy (0.90 kg per kWh), US average (0.37 kg per kWh), Mostly gas (0.45 kg per kWh), Hydro or nuclear heavy (0.10 kg per kWh).
- Years
- A number, between 0 and 40, starting at 25.
- Manufacturing carbon per kW (tonnes)
- A number, between 0 and 10, starting at 1.4.
- System size (kW)
- A number, between 0 and 5000, starting at 7.2.
What the results tell you
| Result | What it is |
|---|---|
| Avoided per year | The headline result. A decimal figure. |
| Avoided over the period | A decimal figure. |
| Manufacturing carbon | A decimal figure. |
| Net avoided | A decimal figure. |
| Carbon payback | A decimal 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.
Keep going
Related calculators
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.