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In Montana, 6.5 kW of panels costs about $18,200 and pays for itself in 12 years and 5 months, saving roughly $28,420 over 25 years.
The average Montana home uses 852 kWh of electricity a month and pays $125 for it. Covering 90% of that takes roughly 6.5 kW of panels, which at the Montana average of $2.80 per watt is about $18,200 installed. Against a bill that drops to around $25 a month, the system breaks even in 12 years and 5 months and leaves about $28,420 in your pocket over a 25-year life.
Two things drive that number more than the panels themselves. Montana power costs 14.67¢ per kWh, so every kilowatt-hour you generate is worth exactly that much and rises with the utility every year — the model assumes 4% a year. And since the 2026 tax year there is no federal residential tax credit: the 30% credit under Section 25D ended on 31 December 2025, so a cash or loan purchase now carries the full price. The calculator below opens on the Montana numbers; replace them with your own quote, your own bill, and any rebate your utility still offers.
Estimate upfront costs, monthly utility savings, and the break-even payback period of your solar panel system
Payback Period
25-Year Utility Savings: $79,247 · Net Upfront Cost: $24,000
Net Lifetime Savings
$55,247
Return on Investment (ROI): 230.2%
Internal Rate of Return (IRR)
10.23%
Annual Savings: $2,040
Monthly Bill Savings
$170
Net Upfront Cost: $24,000
Cumulative Savings vs. Net Upfront Cost
| Year | Panel Output | Annual Savings | Net Cash Flow |
|---|---|---|---|
| 1 | 100.0% | $2,040 | -$21,960 |
| 2 | 99.5% | $2,111 | -$19,849 |
| 3 | 99.0% | $2,184 | -$17,665 |
| 4 | 98.5% | $2,260 | -$15,404 |
| 5 | 98.0% | $2,339 | -$13,065 |
| 6 | 97.5% | $2,421 | -$10,644 |
| 7 | 97.0% | $2,505 | -$8,140 |
| 8 | 96.6% | $2,592 | -$5,548 |
| 9 | 96.1% | $2,682 | -$2,866 |
| 10 | 95.6% | $2,775 | -$90 |
| 11 | 95.1% | $2,872 | +$2,782 |
| 12 | 94.6% | $2,972 | +$5,754 |
| 13 | 94.2% | $3,075 | +$8,829 |
| 14 | 93.7% | $3,182 | +$12,012 |
| 15 | 93.2% | $3,293 | +$15,305 |
| 16 | 92.8% | $3,408 | +$18,713 |
| 17 | 92.3% | $3,526 | +$22,239 |
| 18 | 91.8% | $3,649 | +$25,888 |
| 19 | 91.4% | $3,776 | +$29,665 |
| 20 | 90.9% | $3,908 | +$33,572 |
| 21 | 90.5% | $4,044 | +$37,616 |
| 22 | 90.0% | $4,184 | +$41,800 |
| 23 | 89.6% | $4,330 | +$46,130 |
| 24 | 89.1% | $4,481 | +$50,610 |
| 25 | 88.7% | $4,636 | +$55,247 |
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Same 6.5 kW system and the same $125 bill — only the installer quote changes. No federal credit, no state rebate, 4% annual utility inflation.
| Quoted price per watt | System cost | Payback | Net 25-year saving |
|---|---|---|---|
| $2.40 | $15,600 | 10 years and 11 months | $31,020 |
| $2.60 | $16,900 | 11 years and 8 months | $29,720 |
| $2.80 | $18,200 | 12 years and 5 months | $28,420 |
| $3.00 | $19,500 | 13 years and 1 month | $27,120 |
| $3.20 | $20,800 | 13 years and 10 months | $25,820 |
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