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Amperecalc

Cost & footprint

When has your investment paid for itself?

Payback is more than investment divided by savings. Rising electricity prices shorten it; degradation and operating costs lengthen it. This calculator models both across the full horizon.

How we calculate

Calculation model

  1. 01

    For each year the benefit is escalated by the price increase and reduced by degradation, net of operating cost.

  2. 02

    Break-even is the year in which cumulative cash flow first exceeds the investment — interpolated within the year.

  3. 03

    Net present value discounts all future payments to today, using your discount rate as the alternative return.

  4. 04

    The internal rate of return is found numerically as the rate at which net present value becomes zero.

Good to know

  • The discount rate should reflect the return you forgo — a savings rate for equity, the loan rate for debt.
  • A positive net present value means the investment beats your alternative.
  • Payback period alone is a weak criterion, because it ignores everything after break-even.

Law & subsidies

What applies in Germany

Regulation determines the limits and tariffs this calculator works with.

Zero VAT and income tax exemption up to 30 kWp

Supply and installation of PV systems up to 30 kWp on residential buildings carry no VAT, and the income is exempt from income tax.

VAT
0 % up to 30 kWp
Income tax
exempt up to 30 kWp
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The zero rate covers modules, inverter, storage and installation. You pay the net price without needing to reclaim input tax — the old optimisation via standard taxation is obsolete.

The income tax exemption applies per taxpayer for up to 100 kWp in total and usually removes the need for a trade registration.

The feed-in tariff is guaranteed by statute

Surplus from systems up to 10 kWp earns a statutory rate, guaranteed for 20 years plus the year of commissioning.

Surplus up to 10 kWp
around 7.9 ct/kWh
Guarantee
20 years + commissioning year
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The rate falls every six months for new systems; once set, it stays fixed for the whole term. Full feed-in earns higher rates but rarely pays where self-consumption is high.

During extended periods of negative exchange prices, newer systems lose the tariff for those hours. So far this affects a low single-digit percentage of annual output.

This compilation is orientation, not legal advice. Rules in this field change several times a year — check the linked primary source before you invest, or ask a certified specialist.
See all regulatory topics

Frequent questions

Answered briefly.

What price escalation is realistic?

German household electricity prices have risen by about three percent a year on average over the past two decades, with considerable swings. Three percent is a cautious assumption; run zero percent as a sanity check.

Net present value or internal rate of return — which should I look at?

Net present value if you want to know how much money the investment brings you in absolute terms. Internal rate of return if you want to compare it against other investments.

Do I have to account for degradation?

For solar modules yes, though at 0.4 to 0.5 percent a year it is small — over 20 years roughly equal to two years of price escalation. For batteries, capacity fade matters considerably more.

Balcony solar calculator

Yield, self-consumption and savings for your postcode and orientation.

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Yield, self-sufficiency and return of a rooftop array over 25 years.

Heat pump calculator

Running cost, investment, subsidy and payback in a direct comparison.

All results are model calculations based on your inputs and statistical reference data. They do not replace individual professional planning.

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