Solar & battery
Solar Panel Efficiency Calculator
Works module efficiency, which is about area rather than energy per dollar.
Result
Not all unbilled time is waste. Travel, restocking, training and warranty calls are necessary and will never be zero. The useful question is whether the share is drifting, not whether it reaches 100%.
Get a Free Business AuditHow the calculation works
Rated output divided by module area at the test irradiance, expressed as a percentage. Efficiency describes how much of the sunlight falling on the module becomes electricity, which determines how much capacity fits in a given area and says nothing directly about cost or total energy.
What moves the number
- Rated output and physical module area.
- Cell technology.
- Temperature coefficient, which is a separate specification.
- Degradation rate over life.
Where this one goes wrong
A higher efficiency module produces the same energy per watt as a lower efficiency one, so paying for efficiency buys area and not output, which is only worth it where roof area is the binding constraint. Where there is ample roof, more of a cheaper module usually costs less for the same energy. Temperature coefficient and degradation rate are separate specifications that affect real-world energy more than headline efficiency does, and they are worth comparing directly.
Before you quote
- Treat efficiency as an area question, not an energy one.
- Compare temperature coefficient and degradation rate separately.
- Pay for efficiency only where roof area binds.
Questions
About this calculator
Do higher efficiency panels produce more energy?
Not per watt. A higher efficiency module fits more capacity into a given area, which is valuable when roof space is the constraint and not otherwise. Where there is ample roof, more of a cheaper module usually costs less for the same energy.
What specifications matter more than efficiency?
Temperature coefficient and degradation rate, both of which affect real-world energy over the system's life more than headline efficiency does. They are published on the datasheet and comparing them directly is more informative than comparing efficiency.
Is efficiency improving?
Gradually, and the practical effect for most installations is that a given roof supports somewhat more capacity than it did. For a site with ample area the improvement matters less than price, which has moved more than efficiency has.
The formula
utilisation = billed hours / paid hours
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
- Paid hours per day. Enter your own figure; the page starts at 8.
- Hours that reach an invoice. Enter your own figure; the page starts at 5.2.
- Number of technicians. Enter your own figure; the page starts at 5.
- Rate charged per hour ($). Enter your own figure; the page starts at $105.
- Cost per paid hour ($). Wage plus burden.
- Working days per month. Enter your own figure; the page starts at 22.
The result updates as you type, so you can try a figure, see what it does to billable share of the day, 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 |
|---|---|
| Paid hours per day | 8 |
| Hours that reach an invoice | 5.2 |
| Number of technicians | 5 |
| Rate charged per hour | $105 |
| Cost per paid hour | $34 |
| Working days per month | 22 |
What comes out
| Result | Value |
|---|---|
| Billable share of the day main result | 65.0% |
| Unbilled hours per month | 308 |
| Revenue those hours would have carried | $32,340 |
| What the unbilled hours cost in wages | $10,472 |
65.0% of the paid day reaches an invoice. The rest is 308 hours a month, costing $10,472 in wages and carrying $32,340 of revenue that never happened.
How sensitive the answer is
Holding everything else steady and changing only rate charged per hour, this is what happens to billable share of the day. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Rate charged per hour ($) | Billable share of the day |
|---|---|
| $53 | 65.0% |
| $79 | 65.0% |
| $105 example above | 65.0% |
| $158 | 65.0% |
| $210 | 65.0% |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Paid hours per day
- A number, between 0 and 24, starting at 8.
- Hours that reach an invoice
- A number, between 0 and 24, starting at 5.2.
- Number of technicians
- A number, between 0 and 500, starting at 5.
- Rate charged per hour ($)
- A money amount, starting at $105.
- Cost per paid hour ($)
- Wage plus burden.
- Working days per month
- A number, between 0 and 31, starting at 22.
What the results tell you
| Result | What it is |
|---|---|
| Billable share of the day | The headline result. A percentage. |
| Unbilled hours per month | A number. |
| Revenue those hours would have carried | A money figure. |
| What the unbilled hours cost in wages | 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.
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.