Cash-flow positive from month one: the loan costs 77 €/month but the panels save about 106 €/month. Over 25 years the loan nets 31,868 € versus 34,463 € paying cash; in present-value terms (3% return on savings) paying cash is better by 1,244 €.
Monthly loan payment
€77
10 years at 7% on 6,600 €
Monthly savings (year 1)
€106
value 0.174 €/kWh
Net monthly cash flow (year 1)
€24
savings − payment − maintenance
Total interest & fees
€2,596
Net benefit with loan (25 years)
€31,868
Net benefit paying cash (25 years)
€34,463
NPV loan vs cash
−€1,244
at 3% opportunity cost; positive favours the loan
Cash payback
5 yr 2 mo
Loan break-even
0 yrs
cumulative net ≥ 0
Return if paying cash
20.4%
IRR of the investment
Year by year
| Year | Savings | Loan payments | Maintenance | Net (loan) | Cumulative loan | Cumulative cash |
|---|---|---|---|---|---|---|
| 1 | 1,270 | 920 | 60 | 291 | 291 | -5,390 |
| 2 | 1,303 | 920 | 61 | 322 | 613 | -4,148 |
| 3 | 1,337 | 920 | 62 | 355 | 968 | -2,874 |
| 4 | 1,371 | 920 | 64 | 388 | 1,356 | -1,566 |
| 5 | 1,407 | 920 | 65 | 422 | 1,778 | -224 |
| 6 | 1,443 | 920 | 66 | 457 | 2,236 | 1,153 |
| 7 | 1,481 | 920 | 68 | 493 | 2,729 | 2,566 |
| 8 | 1,519 | 920 | 69 | 530 | 3,260 | 4,016 |
| 9 | 1,558 | 920 | 70 | 568 | 3,828 | 5,504 |
| 10 | 1,599 | 920 | 72 | 607 | 4,435 | 7,031 |
| 11 | 1,640 | 0 | 73 | 1,567 | 6,002 | 8,598 |
| 12 | 1,682 | 0 | 75 | 1,608 | 7,610 | 10,206 |
| 13 | 1,726 | 0 | 976 | 750 | 8,360 | 10,956 |
| 14 | 1,771 | 0 | 78 | 1,693 | 10,053 | 12,649 |
| 15 | 1,816 | 0 | 79 | 1,737 | 11,790 | 14,386 |
| 16 | 1,863 | 0 | 81 | 1,783 | 13,573 | 16,169 |
| 17 | 1,912 | 0 | 82 | 1,829 | 15,402 | 17,998 |
| 18 | 1,961 | 0 | 84 | 1,877 | 17,279 | 19,875 |
| 19 | 2,012 | 0 | 86 | 1,926 | 19,206 | 21,801 |
| 20 | 2,064 | 0 | 87 | 1,977 | 21,182 | 23,778 |
| 21 | 2,117 | 0 | 89 | 2,028 | 23,210 | 25,806 |
| 22 | 2,172 | 0 | 91 | 2,081 | 25,292 | 27,887 |
| 23 | 2,228 | 0 | 93 | 2,136 | 27,427 | 30,023 |
| 24 | 2,286 | 0 | 95 | 2,191 | 29,619 | 32,215 |
| 25 | 2,345 | 0 | 97 | 2,249 | 31,868 | 34,463 |
- Savings = production × (self-consumed share × retail price + exported share × export price), with production degrading and prices escalating yearly.
- Loan: fixed-rate, monthly annuity. A dealer/origination fee is added to the amount financed, so compare the "cash price" with the financed price before signing.
- Tax credits or grants should be deducted from the system price; if a credit arrives later and is used to prepay the loan, model it as a down payment.