System & energy
Shared by both models
kW DCFrom Panel Arrays
kWhTotal of your panel arrays (PVWatts)
%
Size and year-1 generation come from your Panel Arrays.
Electricity & incentives
What you pay for each kWh, or are credited for each kWh you send to the grid under net metering. Include energy (supply) and distribution (delivery) charges, not fixed monthly fees. Your bill's supply + delivery charges divided by the kWh used gives a good estimate. Example: $0.14.
$Energy + distribution (net-metering rate)
How fast you expect your electricity rate to rise each year. Each year's price is the previous year's price × (1 + this rate), so a higher rate makes later years' savings larger. Example: 1%.
%
The return your money could earn elsewhere, or your cost of borrowing. Each year's savings are divided by (1 + rate)^years to give their value today, which is summed into the net present value (NPV). A higher rate makes future savings worth less today. Example: 6.75%.
%
Solar Renewable Energy Certificates. Your system earns one SREC per MWh (1,000 kWh) it generates, which you can sell in states with an SREC market such as Pennsylvania, New Jersey, Maryland and DC. Enter the price you expect per MWh, or 0 if your state has no market. Example: $34 (Pennsylvania, August 2023).
$/ MWh
A one-time rebate some utilities pay, based on the system's first-year production. It is credited in year 1 only. PECO, for example, paid $0.10 per kWh. Enter 0 if your utility has no such program.
$/ kWhPaid once on year-1 kWh (e.g. PECO $0.10)
Yearly cost of owning the system: maintenance, monitoring, added insurance, or money set aside for a future inverter replacement. It is subtracted from the savings every year. Enter 0 if the warranty covers everything.
$
Purchase
Cash / purchase option
$
Federal clean-energy tax credit, as a share of the system cost. Homeowners: the residential credit (Section 25D) ended for systems installed after December 31, 2025, so use 0%. Businesses, and systems a leasing company owns (leases and PPAs), may still get the 30% business credit (Section 48E) if construction starts by July 4, 2026 or the system is in service by December 31, 2027. With a lease, the leasing company claims the credit and usually passes it on through a lower price. Confirm eligibility with a tax professional.
%= $0 credited in year 1
Net cost after ITC$160,974
Cost per watt$2.50
Net cost per lifetime kWh$0.099
Net present value
$3,241
Sum of discounted net savings, 25 years
ROI
2.0%
NPV ÷ system cost ($160,974)
ROI (annualized)
0.08%
(1 + ROI)1/25 − 1
Payback
Year 13
Cumulative savings turn positive
Cumulative net savings
$156,642
Nominal dollars over the model period
Federal tax credit
$0
Credited in year 1 with the utility incentive
25-year cash ROI model
Mirrors the spreadsheet columns| Year | Name | Generation (kWh) | Price / kWh | Electric value | Rebates & credits | SREC trades | Costs | Total revenue | Net savings | PV of savings | Cumulative | PV cumulative |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2024 | 69,869 | $0.1400 | $9,782 | $6,987 | $2,376 | $160,974 | $19,144 | ($141,830) | ($141,830) | ($141,830) | ($141,830) |
| 2 | 2025 | 69,450 | $0.1414 | $9,820 | — | $2,361 | — | $12,181 | $12,181 | $11,411 | ($129,649) | ($130,419) |
| 3 | 2026 | 69,030 | $0.1428 | $9,859 | — | $2,347 | — | $12,206 | $12,206 | $10,711 | ($117,443) | ($119,708) |
| 4 | 2027 | 68,611 | $0.1442 | $9,897 | — | $2,333 | — | $12,229 | $12,229 | $10,053 | ($105,214) | ($109,655) |
| 5 | 2028 | 68,192 | $0.1457 | $9,935 | — | $2,319 | — | $12,253 | $12,253 | $9,436 | ($92,961) | ($100,219) |
| 6 | 2029 | 67,773 | $0.1471 | $9,972 | — | $2,304 | — | $12,276 | $12,276 | $8,856 | ($80,684) | ($91,363) |
| 7 | 2030 | 67,353 | $0.1486 | $10,010 | — | $2,290 | — | $12,300 | $12,300 | $8,312 | ($68,384) | ($83,052) |
| 8 | 2031 | 66,934 | $0.1501 | $10,047 | — | $2,276 | — | $12,323 | $12,323 | $7,801 | ($56,062) | ($75,251) |
| 9 | 2032 | 66,515 | $0.1516 | $10,084 | — | $2,262 | — | $12,345 | $12,345 | $7,321 | ($43,717) | ($67,930) |
| 10 | 2033 | 66,096 | $0.1531 | $10,120 | — | $2,247 | — | $12,368 | $12,368 | $6,870 | ($31,349) | ($61,060) |
| 11 | 2034 | 65,677 | $0.1546 | $10,157 | — | $2,233 | — | $12,390 | $12,390 | $6,447 | ($18,959) | ($54,613) |
| 12 | 2035 | 65,257 | $0.1562 | $10,193 | — | $2,219 | — | $12,412 | $12,412 | $6,050 | ($6,548) | ($48,562) |
| 13 | 2036 | 64,838 | $0.1578 | $10,229 | — | $2,204 | — | $12,433 | $12,433 | $5,678 | $5,885 | ($42,885) |
| 14 | 2037 | 64,419 | $0.1593 | $10,264 | — | $2,190 | — | $12,454 | $12,454 | $5,328 | $18,339 | ($37,557) |
| 15 | 2038 | 64,000 | $0.1609 | $10,299 | — | $2,176 | — | $12,475 | $12,475 | $4,999 | $30,815 | ($32,558) |
| 16 | 2039 | 63,581 | $0.1625 | $10,334 | — | $2,162 | — | $12,496 | $12,496 | $4,691 | $43,311 | ($27,867) |
| 17 | 2040 | 63,161 | $0.1642 | $10,369 | — | $2,147 | — | $12,516 | $12,516 | $4,401 | $55,827 | ($23,466) |
| 18 | 2041 | 62,742 | $0.1658 | $10,403 | — | $2,133 | — | $12,536 | $12,536 | $4,130 | $68,363 | ($19,336) |
| 19 | 2042 | 62,323 | $0.1675 | $10,437 | — | $2,119 | — | $12,556 | $12,556 | $3,875 | $80,918 | ($15,462) |
| 20 | 2043 | 61,904 | $0.1691 | $10,470 | — | $2,105 | — | $12,575 | $12,575 | $3,635 | $93,493 | ($11,827) |
| 21 | 2044 | 61,485 | $0.1708 | $10,503 | — | $2,090 | — | $12,594 | $12,594 | $3,410 | $106,087 | ($8,416) |
| 22 | 2045 | 61,065 | $0.1725 | $10,536 | — | $2,076 | — | $12,612 | $12,612 | $3,199 | $118,699 | ($5,217) |
| 23 | 2046 | 60,646 | $0.1743 | $10,568 | — | $2,062 | — | $12,630 | $12,630 | $3,001 | $131,329 | ($2,216) |
| 24 | 2047 | 60,227 | $0.1760 | $10,600 | — | $2,048 | — | $12,648 | $12,648 | $2,815 | $143,977 | $600 |
| 25 | 2048 | 59,808 | $0.1778 | $10,632 | — | $2,033 | — | $12,665 | $12,665 | $2,641 | $156,642 | $3,241 |
| Totals | 1,620,956 | $255,517 | $6,987 | $55,112 | $160,974 | $317,616 | $156,642 | $3,241 | ||||
Highlighted row: payback year (13).
Assumptions & method
- All power generated is either consumed on site or credited at the same rate it is charged (net metering).
- Annual electrical demand stays similar over the model period.
- Panel output declines linearly: year-n kWh = year-1 kWh × (1 − degradation × (n − 1)).
- SREC trade income continues at the entered price for the whole period (program assumed not to expire).
- All material and labor is covered by warranty over the period unless you enter an annual reserve.
- Federal tax credit: 0% by default, because the residential credit (Sec. 25D) ended for systems installed after December 31, 2025. Commercial and leased (third-party-owned) systems may still qualify for 30% (Sec. 48E) if construction starts by July 4, 2026 or the system is in service by December 31, 2027.
- Cash model: year-1 includes the system cost, the federal investment tax credit and the utility incentive. Savings are discounted from year 1 (PV = net ÷ (1 + r)n−1). ROI = NPV ÷ system cost.
Estimates for planning only — not financial, tax or legal advice. Confirm incentive eligibility with your installer and tax professional.