Tools
Commercial ROI and payback calculator
Enter a bill and a target offset. The model sizes an array in kW DC, prices it, applies the credit and depreciation, then runs twenty-five years of degradation against utility escalation. Every figure is a sample.
- Yield assumption
- 1,620 kWh per kW DC
- Model horizon
- 25 years
- Degradation
- 2.0% then 0.45% a year
- Status
- Planning model, not a quote
The model
Size it, price it, then run the years
Modelled result
Simple payback
4.1 years
25-year net position
$4.9M
Cost per kWh produced
$0.033
Cumulative position, selected years
| Year | Production kWh | Energy value | O&M | Net that year | Cumulative |
|---|---|---|---|---|---|
| 1 | 792,212 | $148,144 | $6,986 | $141,158 | -$418,334 |
| 2 | 788,647 | $151,901 | $7,126 | $144,776 | -$273,558 |
| 3 | 785,099 | $155,754 | $7,268 | $148,486 | -$125,072 |
| 5 | 778,049 | $163,756 | $7,562 | $156,194 | $183,414 |
| 10 | 760,699 | $185,605 | $8,349 | $177,256 | $1,026,507 |
| 15 | 743,737 | $210,369 | $9,218 | $201,151 | $1,983,267 |
| 20 | 727,153 | $238,437 | $10,177 | $228,260 | $3,068,983 |
| 25 | 710,938 | $270,251 | $11,237 | $259,014 | $4,300,995 |
What sits under the numbers
Every assumption, written down
A model you cannot audit is a sales tool. These are the inputs behind the arithmetic above, all of them sample figures for this demonstration site.
| Assumption | Value used | Basis |
|---|---|---|
| Specific yield | 1,620 kWh per kW DC per year | Fixed tilt, south facing, Bakersfield latitude |
| Installed cost | $2.15 per watt DC | Rooftop, ballasted, before incentives |
| Federal tax credit | 30 percent of eligible basis | Sample rate; confirm current terms |
| Depreciation benefit | 21 percent of net cost in present value | Sample, assumes a taxpaying entity |
| Blended energy value | $0.187 per kWh | Weighted across time-of-use periods |
| Utility escalation | 3.0 percent per year | Sample assumption |
| Year one degradation | 2.0 percent | Light-induced degradation |
| Annual degradation | 0.45 percent per year thereafter | Typical warranted rate |
| O&M cost | $14 per kW DC per year | Monitoring, washing and inspection |
Answers
About this model
Not covered here? Our engineers answer directly, not through a call centre.
Ask a question(661) 555-0183It is a planning model built on sample assumptions, not a quotation. It is useful for deciding whether a project is worth investigating and useless for deciding what to sign. The real model runs on your interval data, your tariff and a priced design.
Because demand savings depend on the shape of your peak and on whether storage is in the system, which this model cannot know. Our demand charge page models that part separately, and the combined model in your assessment brings the two together.
Commercial solar has historically been depreciable on an accelerated schedule, and for a taxpaying entity the present value of that deduction can be a substantial share of system cost. The figure here is a sample. Your entity, your tax position and current law all change it, so confirm it with a tax professional.
Modules degrade. There is a larger drop in the first year from light-induced degradation, then a slow annual decline. Manufacturers warrant both figures, and any twenty-five year model that holds production flat is overstating the return.
It is the single most influential assumption in any long-range solar model and nobody can guarantee it. We show it explicitly and adjustable so you can see how much of the answer depends on it. If a proposal does not disclose its escalation rate, ask.
The real model runs on your data, not a slider
Twelve months of interval data, your actual tariff and a priced design. That version comes with the basis of design, and it is free.
CSLB #1071482 (sample). Prevailing wage on public works. Engineers answer, not a call centre.