Balcony Solar Payback Calculator

Use the balcony solar calculator to estimate how long it could take for your system to pay for itself through electricity savings. Enter the purchase cost, estimated annual generation, self-consumption share and electricity price. You can also include a grant and annual running costs.

This calculator and its legal and technical context are for Germany. All defaults are example assumptions. You enter the year-one generation, the self-consumption share and the electricity price yourself — the calculator does not simulate solar yield.

Cost and grant

Purchase cost (€, purchase + installation)

Purchase price including installation and accessories.

One-time grant (€, optional)

Optional grant; cannot exceed the purchase cost.

Generation and consumption

Estimated year-one generation (kWh)

Expected electricity generation in the first year.

Self-consumption share (%)

The share of generated electricity you use directly yourself.

Electricity price (€/kWh, incl. VAT)

Your electricity unit rate per kWh, including VAT.

Annual running cost (€/year, optional)

Optional running costs, such as insurance.

Planning horizon (whole years)

The period covered by the model, in whole years.

Advanced assumptions (optional)Electricity price change and generation decline

Optional assumptions — 0 by default. These are your assumptions, not forecasts.

Annual generation decline (%/year)

Assumed annual decline in generation, as a percentage.

Annual electricity-price change (%/year, may be negative)

Assumed annual electricity price change, as a percentage (can be negative).

Your result

–

–Investment after grant
–Year-one generation
–Of which self-used (year 1)
–Exported (year 1, valued at €0)
–Gross saving (year 1)
–Net saving (year 1)
–Simple payback
–Payback within the horizon
–Total net savings (before deducting the investment)
–Net result at the end of the horizon

Year-by-year breakdown
Year	Generation	Self-used	Price	Net saving	Cumulative

Legal and technical context in Germany (as of 3 October 2026)

EEG limits (simplified rules)

In Germany, plug-in solar devices assigned to unpaid feed-in (unentgeltliche Abnahme), with total installed module power of up to 2,000 W and total inverter power of up to 800 VA, fall under the simplified connection rule (§ 8 Abs. 5a EEG 2023). Registration in the Marktstammdatenregister is still required; since 16 May 2024, separate notification to the grid operator is no longer required within these limits (Bundesnetzagentur).

Technical product and connection requirements (separate from the EEG limits)

The product pre-standard DIN VDE V 0126-95 (published December 2025) allows connection via a household (Schuko) plug only with additional protective measures and up to 960 Wp of module power; with a special energy plug connector (e.g. per DIN VDE V 0628-1), up to 2,000 Wp is permitted. The inverter feed-in power is at most 800 VA.

None of this means “2,000 Wp + 800 W = always Schuko-legal”: the EEG limits and the product standard are separate rule sets. This calculator gives no compliance verdict — check your device documentation and the requirements currently in force. A storage battery changes self-consumption and the economics and needs a separate model; it is not part of this calculator.

If you do not know your annual generation yet, you can estimate it with tools such as HTW Berlin’s Stecker-Solar-Simulator.

This calculator needs JavaScript because the calculation runs entirely in your browser – so your inputs never leave your device. Two fully worked examples are shown further down this page.

How this calculator works

The investment is I = purchase cost − grant (at least 0). In year one the self-used electricity = year-one generation × self-consumption share; only that part avoids buying from the grid. The gross saving is self-used electricity × price per kWh, and the net saving subtracts the annual running cost. Exported surplus is valued at €0 in this version.

Over the horizon two assumptions are carried forward geometrically: generation declines each year by the decline rate ((1 − d)^(y − 1)), and the price changes each year by the price-change rate ((1 + g)^(y − 1)). Both default to 0 and are your assumptions, not forecasts.

The simple (static) payback is I divided by the year-one net saving and is not capped by the horizon. The payback within the horizon follows the cumulative path (cumulative in year y = −I + the sum of net savings up to year y) and is linearly interpolated in the crossing year; if the cumulative total does not reach zero within the chosen horizon, it is left open and never extrapolated beyond it.

The calculator does not simulate solar yield, uses no location or irradiation data and no storage model. Internal arithmetic is unrounded; rounding happens only for display.

Formula and variables

Investment I = max(purchase cost − grant, 0)Self-used (kWh) = year-one generation × self-consumption shareExported (kWh) = year-one generation − self-used (valued at €0)Gross saving = self-used × price per kWhNet saving = gross saving − annual running costGeneration in year y = year-one generation × (1 − decline)^(y − 1)Price in year y = price per kWh × (1 + price change)^(y − 1)Simple payback = I / net saving (year 1)Cumulative in year y = −I + sum of net savings up to year y

Payback within the horizon = (y − 1) + amount still open at the start of year y / net saving in year y (first year with cumulative ≥ 0; otherwise not reached)

I: investment after grant: purchase cost minus the one-time grant, at least 0
year-one generation: estimated generation in the first year in kWh (your input; no simulation)
self-consumption share: share of generation you use at the moment it is produced
price per kWh: your unit rate incl. VAT (year 1)
annual running cost: optional yearly cost, e.g. insurance (your assumption)
decline: assumed annual generation decline in % (advanced assumption, default 0)
price change: assumed annual price change in % (advanced assumption, may be negative)
horizon: number of whole years covered by the year-by-year breakdown

Worked examples

Example 1: a €500 device with no grant

Example inputs
Purchase cost	€500.00
Grant	€0.00
Year-one generation	600 kWh
Self-consumption share	70%
Price per kWh	€0.30
Horizon	20 years

Example results
Investment after grant	€500.00
Self-used (year 1)	420 kWh
Exported (year 1)	180 kWh
Gross saving (year 1)	€126.00
Net saving (year 1)	€126.00
Simple payback	about 4.0 years (3.97)
Payback within the horizon	about 4.0 years
Net result after 20 years	€2,020.00

The investment is €500.00 (no grant). Of 600 kWh, 70% is self-used (420 kWh); 180 kWh is exported and valued at €0.00. The saving is 420 × €0.30 = €126.00 per year (with no running cost, gross equals net). The simple payback is €500.00 / €126.00 ≈ 4.0 years, and after 20 years the net result is €2,020.00. All figures are example assumptions.

Example 2: with a grant and running cost

Example inputs
Purchase cost	€500.00
Grant	€100.00
Year-one generation	500 kWh
Self-consumption share	50%
Price per kWh	€0.40
Annual running cost	€20.00
Horizon	20 years

Example results
Investment after grant	€400.00
Self-used (year 1)	250 kWh
Gross saving (year 1)	€100.00
Net saving (year 1)	€80.00
Simple payback	5.0 years
Payback within the horizon	5.0 years
Net result after 20 years	€1,200.00

The €100.00 grant lowers the investment to €400.00. Of 500 kWh, 50% is self-used (250 kWh), which is 250 × €0.40 = €100.00 gross saving; after €20.00 of running cost, €80.00 net saving per year remains. The simple payback is €400.00 / €80.00 = 5.0 years, and the net result after 20 years is €1,200.00. All figures are example assumptions; your values may differ.

Assumptions

Exported surplus is valued at €0 (the ordinary unpaid feed-in case in Germany); a feed-in tariff is not part of the model.
Year-one generation, self-consumption share, price and all other values are your inputs or example assumptions — real values vary.
Generation decline and price change act geometrically over the years and default to 0.

Limitations of this calculator

The calculator does not simulate solar yield and uses no location or irradiation data; you enter the year-one generation yourself.
No storage/battery model, no live electricity or product prices and no subsidy database.
No compliance or legal verdict and no buying or installer recommendation; the stated limits are not an approval.
A static view without interest or present value; taxes and financing are out of scope.

Frequently asked questions

Does this calculator work out the solar yield?

No. You enter the estimated year-one generation yourself. It can come from an independent yield tool such as the HTW Berlin Stecker-Solar-Simulator, from your own measured values or from a quote. Orientation, tilt, shading, location and the number of modules change generation materially.

Why is exported electricity valued at €0?

In the ordinary unpaid feed-in case in Germany there is no payment for the exported surplus, so the calculator values it at €0; the economics come from the self-used electricity. This does not mean a feed-in tariff is impossible in general.

What does the self-consumption share mean?

It is the share of generated electricity you use at the moment it is produced. Only that part lowers your grid purchases. It depends on your daytime consumption and the system size; there is no universal value.

Does the calculator include a battery?

No. A storage battery changes self-consumption and the economics and needs a separate model. This version works without storage.

Do 2,000 Wp and 800 VA mean a Schuko plug is approved?

No. The EEG limits (up to 2,000 W of module power, up to 800 VA of inverter power) and the technical product standard are separate rule sets. The calculator gives no compliance verdict — check your device documentation and the requirements currently in force in Germany.

Sources and further reading

Official and independent sources on this topic. The links open each website in a new tab; no content is loaded from them into this page.

§ 8 Abs. 5a EEG 2023 – connection of plug-in solar devicesFederal Ministry of Justice (gesetze-im-internet.de)Legal basis of the simplified rule in Germany: up to 2,000 W module power and 800 VA inverter, assigned to unpaid feed-in.
Balcony solar systems – questions and answersBundesnetzagentur (German regulator)Registration in the Marktstammdatenregister; since 16 May 2024 no separate notification to the grid operator within the limits.
World's first product standard for plug-in solar devices (DIN VDE V 0126-95)VDE/DKETechnical product pre-standard (December 2025): Schuko up to 960 Wp only with protective measures, up to 2,000 Wp a special energy plug connector, inverter max 800 VA.
Plug-in solar devices (balcony power plants)Umweltbundesamt (German Environment Agency)Context on self-consumption and on treating storage separately.
Stecker-Solar-Simulator (plug-in solar simulator)HTW Berlin, Solar Storage Systems research groupIndependent tool to estimate year-one generation and self-consumption for your own location.

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Last reviewed: 04/10/2026 · All calculations run in your browser – inputs are not stored. ·How we check our calculators