In short
The remaining value of a PV system is the present value of its future surpluses until decommissioning, minus replacement investments and removal. While the feed-in tariff runs, it carries almost the entire value. After that, self-consumption decides.
Remaining value, net book value and purchase price
Three figures are often confused. The net book value is the purchase price minus depreciation; in Germany PV systems are depreciated over 20 years, after which the balance sheet shows zero. The purchase price is history. The remaining value in the economic sense only looks forward. A fully depreciated system with high self-consumption can therefore still be worth a five-figure sum.
How the remaining value is calculated
We calculate every year separately: yield from meter readings, degradation, tariff rate until the end of the 20th year after commissioning, then revenue from direct marketing or the follow-up payment. Costs rise by 2 % per year. The decommissioning year is chosen so that the value is highest: as soon as operation costs money, it ends in the model.
Worked example 1: commercial roof, 250 kWp, built 2011
Assumptions: 960 kWh/kWp last year (240,000 kWh), degradation 0.5 % per year, full feed-in at an assumed 26.6 ct/kWh until the end of 2031, then 4.5 ct/kWh. Operating costs €8,000 in the first year (€32/kWp). Original inverters, replaced in 2027 at €130/kWp. Useful life 27 years, removal €25/kWp, discount rate 5.5 %. Valuation date 1 January 2027.
| Year | Yield kWh | Revenue € | Costs € | Capex € | Net cash flow € | Present value € |
|---|---|---|---|---|---|---|
| 2027 | 240,000 | 63,840 | 8,000 | 32,500 | 23,340 | 22,123 |
| 2028 | 238,800 | 63,521 | 8,160 | 0 | 55,361 | 49,739 |
| 2029 | 237,606 | 63,203 | 8,323 | 0 | 54,880 | 46,737 |
| 2030 | 236,418 | 62,887 | 8,490 | 0 | 54,398 | 43,911 |
| 2031 | 235,236 | 62,573 | 8,659 | 0 | 53,913 | 41,251 |
| 2032 | 234,060 | 10,533 | 8,833 | 0 | 1,700 | 1,233 |
| 2033 | 232,889 | 10,480 | 9,009 | 0 | 1,471 | 1,011 |
| 2034 | 231,725 | 10,428 | 9,189 | 0 | 1,238 | 807 |
| 2035 | 230,566 | 10,375 | 9,373 | 0 | 1,002 | 619 |
| 2036 | 229,413 | 10,324 | 9,561 | 0 | 763 | 447 |
| 2037 | 228,266 | 10,272 | 9,752 | 0 | 520 | 289 |
| 2038 | 227,125 | 10,221 | 9,947 | 6,250 | −5,976 | −3,143 |
| Sum of present values (indicative income value) | 205,022 | |||||
Result: around €205,000, roughly €820/kWp. Almost 98 % of the value comes from the years up to 2031. The seven years after that bring in less in total than removal costs. Anyone buying this system is essentially paying for five years of secured tariff and needs to know whether the inverters will hold out that long.
Worked example 2: single-family home, 10 kWp, built 2012
Assumptions: 950 kWh/kWp, degradation 0.5 %, 30 % self-consumption at an electricity price of 35 ct/kWh, feed-in at 19.5 ct/kWh until the end of 2032, then 4.5 ct/kWh. Operating costs €150 per year, inverter already replaced in 2024. Useful life 30 years, removal €600, discount rate 3.5 %.
| Year | Yield kWh | Revenue € | Costs € | Capex € | Net cash flow € | Present value € |
|---|---|---|---|---|---|---|
| 2027 | 9,500 | 2,294 | 150 | 0 | 2,144 | 2,072 |
| 2028 | 9,452 | 2,283 | 153 | 0 | 2,130 | 1,988 |
| 2029 | 9,405 | 2,271 | 156 | 0 | 2,115 | 1,908 |
| 2030 | 9,358 | 2,260 | 159 | 0 | 2,101 | 1,831 |
| 2031 | 9,311 | 2,249 | 162 | 0 | 2,086 | 1,757 |
| 2032 | 9,265 | 2,237 | 166 | 0 | 2,072 | 1,685 |
| 2033 | 9,219 | 1,258 | 169 | 0 | 1,089 | 856 |
| 2034 | 9,172 | 1,252 | 172 | 0 | 1,080 | 820 |
| 2035 | 9,127 | 1,246 | 176 | 0 | 1,070 | 785 |
| 2036 | 9,081 | 1,240 | 179 | 0 | 1,060 | 752 |
| 2037 | 9,036 | 1,233 | 183 | 0 | 1,051 | 720 |
| 2038 | 8,990 | 1,227 | 187 | 0 | 1,041 | 689 |
| 2039 | 8,945 | 1,221 | 190 | 0 | 1,031 | 659 |
| 2040 | 8,901 | 1,215 | 194 | 0 | 1,021 | 631 |
| 2041 | 8,856 | 1,209 | 198 | 0 | 1,011 | 603 |
| 2042 | 8,812 | 1,203 | 202 | 600 | 401 | 231 |
| Sum of present values (indicative income value) | 17,986 | |||||
Result: around €18,000. Without self-consumption the value would be €10,100. After the tariff ends in 2032 the system remains economic because every self-consumed kilowatt-hour saves 35 ct. When the house is sold, this value belongs in the price negotiation.
Both examples are anonymised model calculations with typical assumptions from our practice, not specific mandates. Tariff rates do not replace a look at your own statement.
Remaining value after 10, 15, 20 and 25 years
| Age | Typical situation | What carries the value | What we check |
|---|---|---|---|
| 10 years | 10 tariff years left | secured tariff | yield versus forecast, first inverter replacement |
| 15 years | 5 tariff years left | final tariff years | inverters, mounting structure, roof |
| 20 years | tariff ends | self-consumption, market value | costs versus revenue, metering, direct marketing |
| 25 years | after the tariff | self-consumption | remaining life of modules and roof, removal costs |
Advice portals quote rules of thumb such as "30 to 40 % of the purchase price after 10 years". For a negotiation they are worthless: they depend on the historical price (€1,000 to €5,000/kWp depending on the year) instead of future revenue.
Frequently asked questions
How do you calculate the remaining value of a PV system?
Add up the discounted annual surpluses until decommissioning and deduct replacement investments and removal. The basis is actual yields, the tariff rate, costs and remaining useful life.
Is net book value the same as remaining value?
No. Book value follows depreciation over 20 years and says nothing about future revenue. A fully depreciated system can still be worth a lot, a young system with defects less than its book value.
What is the difference between remaining value and residual value?
In everyday use both terms mean the same. Strictly, residual value is the value at the end of a defined period, such as a financing or lease term. More on the page residual value of a PV system.
How does the feed-in tariff affect remaining value?
While it runs, it carries almost the entire value. For systems from 2009 to 2011 with 25 to 43 ct/kWh, the value lies almost entirely in the remaining tariff years.