Model electricity price growth and present value
Calculates the present value of your future electricity savings in three named scenarios (0/2/4 % per year) — and explicitly makes NO forecast: in 2026 new-customer prices fell after years of rises. The self-consumed energy multiplying every result comes from your location and a household profile rather than a guess (Berlin, 10 kWp: 1,650 instead of an assumed 2,000 kWh). Plus the reverse question: what growth rate would your system need to pay back in the target time? Implausible values are named as such.
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 |
|---|---|---|---|
| Present value of the savings | Σ_t (E_self * p_0 * (1+g)^(t-1)) / (1+r)^t | 7,632.5 EUR | exact |
| Required annual increase | g: Σ_t E * p_0 * (1+g)^(t-1) = I | 0.17887 | exact |
- Formula
E_self = Σ_h min(PV_h, household_h) · p_t = p₀ · (1+g)^(t−1) · Present value = Σ (E_self · p_t)/(1+r)^t · Reverse question: solve Σ (E·p₀(1+g)^(t−1))/(1+r)^t = I for g- Valid for
- Three fixed scenarios as named assumptions, discounting with a visible rate, starting price from the BNetzA/SMARD price analysis (existing-customer average 31.1 ct). Self-consumption comes from the site hourly year (PVGIS-SARAH3 TMY) and the household load profile — the same chain as calculators 41 and 43. Reference case: 10 kWp in Berlin, 4,000 kWh consumption → 1,650 kWh self-consumed (16 % of the yield), present value €7,633 flat to €10,936 at 4 %, required growth for ten years 17.89 %. The reverse question is solved numerically; implausible results (doubling within a few years) are named as such.
- Not covered
- Historical price curve as a chart (needs a committed time series — a sourcing task), feed-in revenue (calculator 48; this page is only about the avoided bill), dynamic tariffs, standing charges, regional grid fees, system degradation, forecasts of any kind — deliberately.
- 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
What annual electricity price increase would my system need to pay back within my target period?
That reverse question is exactly what the calculator solves: it finds the growth rate at which nominal savings reach the investment within your target years, using bisection because the equation has no closed-form solution. If the required rate exceeds the plausibility threshold, the calculator says so and translates it into the price doubling time as a tangible yardstick.
Are the price scenarios a forecast of electricity prices?
Explicitly not — they are scenarios and are labelled as such. In 2026 new-customer prices actually fell year on year after years of increases; anyone extrapolating the 2022 trend would be far off today. Historical development is deliberately not projected forward.
Why does the price formula use the exponent t−1 rather than t?
Because the first year's price is today's price p0 — hence (1+g)^(t−1). Using t instead shifts the whole series by one year and systematically overstates the savings. Also outside the model: system degradation, changes to levies and charges, tariff model switches and time-of-use pricing.
What does price escalation change in the reference case, concretely?
In the reference case (10 kWp in Berlin, 4,000 kWh household consumption → 1,650 kWh self-consumed, 31.1 ct today's energy price, 20 years, 3 % discount rate) the discounted saving is €7,633 with no price rise, €9,094 at 2 % per year and €10,936 at 4 % per year. About €3,300 separates the lowest from the highest scenario — that is what the assumption is worth, and it is why the calculator shows a range rather than a single number.
Why are future savings discounted at all?
Because a euro in twenty years is worth less than a euro today: it could have been invested elsewhere in the meantime, and it carries risk. The discount rate makes future savings comparable to today's investment. Without escalation this reduces to the familiar annuity formula: €622 per year × factor 14.88 (20 years, 3%) = €9,254. Skipping the discounting compares today's apples with pears from 2046 — and systematically overstates the system.
What does it mean when the required growth is flagged as implausible?
In the reference case electricity would have to rise 17.89 % per year for a €12,000 investment to pay back within ten years from savings alone — a doubling of the price roughly every four years. Germany has never sustained such a phase. The calculator does not serve that expectation; it says: use a longer horizon, a smaller investment or a higher self-consumption share — and include the feed-in revenue, which this calculator deliberately leaves out.
Where does the self-consumed energy come from?
From your location. It used to be an input field defaulting to 2,000 kWh — and at the same time the factor sitting in front of every result on this page. Now the same hourly calculation runs as in the payback and self-consumption calculators: 10 kWp in Berlin with 4,000 kWh household consumption gives 1,650 kWh self-consumed, or 16 % of the yield. If you know your measured figure, the switch takes it.
Why is a guessed figure especially damaging here?
Because it enters every amount linearly. The 2,000 kWh default was about 21 % above what the reference case actually gives — and every present value was too high by exactly that share: €9,254 instead of €7,633 in the flat scenario. The reverse question amplifies it further, because it solves for the growth rate: 17.89 % instead of 13.95 %.
Why is my self-consumption only 16 % of the yield?
Because a 10 kWp roof in Berlin delivers a good 10,000 kWh while a four-person household needs only 4,000 kWh — much of it in the evening, when the system delivers nothing. Without a battery, heat pump or car it therefore stays near one sixth. To raise that share, the battery, heat-pump and EV-charging calculators hold the relevant levers.
Does this calculator include the feed-in tariff?
No, deliberately not. It answers only what the avoided electricity bill is worth. Feed-in revenue depends on entirely different quantities — tier structure, the 60 % cap, the negative-price rule — and therefore lives in its own calculator. The payback calculator combines both.
Why is there no historical price chart?
Because that would require a freely usable time series committed to the project, and it has not been sourced yet. Until then, a curve drawn from memory would be exactly what this calculator exists to avoid. The gap is stated openly under “Not covered” — hiding it would be worse than showing it.