Solar payback calculator
Computes the payback from your location instead of two guessed figures: annual yield and self-consumption share come from the same hourly chain as the annual yield and self-consumption calculators. For 10 kWp near Berlin with 4,000 kWh household consumption that is 9.7 years simple and 11.6 discounted — the usual rules of thumb (9,500 kWh, 30 %) would give 7.9 years and land two to three years too optimistic.
The formulas behind the calculator
Every number above can be recomputed: the full calculation path, all assumptions and the data source with retrieval date — plus cross-validation against independent references. Disclosed, not claimed.
An estimate based on the stated assumptions. The final design must be checked by a qualified professional against the rules that apply where you are.
Data as of: 2026-08-06
| Step | Formula | Value | Provenance |
|---|---|---|---|
| First-year cash flow | E_self*p + E_feed*v - OM | 1,023.5 Waehrung/a | exact |
| Simple payback | min T: Σ CF_t >= I_0 | 9.723 a | exact |
| Discounted payback | min T: Σ CF_t/(1+r)^t >= I_0 | 11.628 a | exact |
- Formula
CF_t = E_self,t · p_t + E_export,t · v − OM_t − replacement_t · simple: min T with Σ CF_t ≥ I₀ · discounted: min T with Σ CF_t/(1+r)^t ≥ I₀- Valid for
- Grid-tied rooftop system, annual resolution, constant self-consumption share (calculator 43 supplies it hour-accurately via handoff). Feed-in remuneration per the official German EEG rates for 08/2026–01/2027 (partial feed-in ≤10 kWp: 7.70 ct/kWh, BNetzA). Reference case: 10 kWp, €10,150, 30% self-consumption → 7.5 years simple at the existing-customer price, 8.6 discounted — and 5.9 to 8.9 years depending on the price segment (computed with 2% price escalation and 0.5% degradation).
- Not covered
- Tax effects, financing costs, subsidised loans, direct marketing, dynamic tariffs, full-feed-in remuneration, the Solarpaket I bonus (+1.5 ct — not yet legally effective). Battery economics is calculator 44.
- Data sources
- Bundesnetzagentur SMARD electricity price analysis, StromAuskunft price index (as of 2026-08-06) and EEG remuneration rates per § 48 EEG 2023 · Q3/2026 (EEG-Sätze H2/2026) · retrieved 2026-08-06
Frequently asked questions
How fast does a solar system pay off in 2026?
The reference case (10 kWp, €10,150 investment, 30% self-consumption, German feed-in tariff of 7.70 ct/kWh as of 08/2026) pays off in about 7.5 years at the existing-customer power price of 31.1 ct — or, more honestly discounted at 3% cost of capital, in 8.6 years. Across the price segments the band runs from 5.9 to 8.9 years. The calculator always shows both figures and the full band.
Why does the calculator output a band instead of one number?
Because the payback of the identical system swings by about half depending on what you pay for electricity today: German new-customer tariffs (~24 ct), the existing-customer average (31 ct) and basic supply (43 ct) sit almost a factor of 1.8 apart. That one contract number moves more than any technical optimisation — a calculator quoting a single favourable figure is selling you something.
What is the difference between simple and discounted payback?
Simple payback counts cash flows until the investment is recovered. Discounted payback converts every future euro to today's value using the cost of capital (default 3%) — €1,000 in ten years is worth less than €1,000 now. In the reference case this pushes payback back by a good year. The discounted figure is the honest one; most sites publish only the simple one.
Why does the inverter replacement appear in the calculation?
Because it happens: inverters typically last 10–15 years, and the replacement costs €1,500 in year 13 in the reference case — a visible setback in the cumulative curve. Most calculators omit this item; it shifts payback by typically one to one-and-a-half years. If no replacement year is set, the calculator warns.
Which input moves the result the most?
The tornado chart ranks it for your configuration; in the reference case: electricity price (±3.0 years across the segment band), then self-consumption share (±2.8), investment cost (±2.4) — only then annual yield (±1.3). The order is the message: money inputs dominate while the technical yield everyone debates sits in fourth place.
Where do the tariff and power prices come from, and how current are they?
The feed-in remuneration follows the official German BNetzA EEG rates (partial feed-in ≤10 kWp: 7.70 ct/kWh for commissioning 01.08.2026–31.01.2027; the semi-annual 1% degression is applied, the not-yet-approved Solarpaket I bonus deliberately is not). The three retail price segments come from the BNetzA/SMARD price analysis. Any data change breaks a frozen reference test on our side and forces a changelog entry.
When does a solar system actually pay for itself?
For 10 kWp at 10,150 euros in the Berlin region, with a household using 4,000 kWh a year and a 31.1 ct electricity price: 9.7 years simple, 11.6 years discounted. For a working household using 3,000 kWh it is 11.1 and 15.4 years, because less power is consumed on site. The widespread rules of thumb (9,500 kWh yield, 30 % self-consumption) give 7.9 years — two to three years too optimistic.
Why does this calculator give different numbers from other payback tools?
Because it does not take yield and self-consumption share as inputs but computes them. Most calculators default to 1,000 kWh per kWp and 30 % self-consumption — round numbers that almost never hold for a specific site and a specific household. This one takes the hourly data of your location plus a household load profile and derives both. If you have your own measured values, you can enter them under “Advanced assumptions”.
What affects the payback time most?
Your electricity price, by a wide margin. Between a cheap new-customer tariff (23.9 ct) and the default supply (42.8 ct) there is over 50 percent difference in payback time — for an identical system. Self-consumption share and total investment follow. The tornado chart ranks every input by leverage, and the system technology itself sits further down than most expect.
Should I compute with or without discounting?
With both — the calculator reports both, and the difference is the point. Simple payback only counts when the money is back. Discounted payback accounts for what the same money would have earned elsewhere. In the example that is 9.7 versus 11.6 years at a 3 % discount rate. If you finance the system with a loan, use the loan rate; if you use your own capital, use a realistic alternative return.
Does a bigger system pay back faster?
Not necessarily, and the calculator shows why: a bigger array yields more, but the extra power arrives at midday when the household does not need it. The self-consumption share falls, and the surplus only earns the 7.7 ct feed-in tariff instead of the 31.1 ct saved. Because system cost per kWp falls with size there is still a sensible range — the calculation decides, not the rule of thumb.
What is the self-consumption share really?
Considerably lower than the 30 percent quoted everywhere. For 10 kWp and a family household using 4,000 kWh a year in the Berlin region the calculator finds 16 percent — for a working household with 3,000 kWh only 11 percent. The reason is the mismatch: the array delivers at midday while the household consumes morning and evening. That difference explains why the payback takes longer than rule-of-thumb calculations suggest, even though the yield comes out higher than assumed. A battery raises the share substantially — the self-consumption calculator computes that.