Mieterstrom

Supplying is not the same as distributing

Offering Mieterstrom makes you an electricity supplier in the regulatory sense. That is a role with duties attached, not a label: full supply of every participant including the residual power drawn at night, individual metering and billing per occupant, a metering concept approved by the grid operator, terms of supply, and the tax treatment that follows. The burden is permanent and it starts before the first kilowatt hour is delivered.

Shared building supply under § 42b EnWG, introduced with the Solarpaket I reform, is the smaller path: only the solar power is distributed. Each participant keeps buying residual power from their own retailer. The supplier role falls away, and with it most of the operating burden, but so does the surcharge.

The numbers

The Mieterstrom surcharge is banded by system size and follows the same half-yearly degression as the feed-in tariff. For systems commissioned between 1 August 2026 and 31 January 2027 it is 2.51 ct/kWh up to 10 kW, 2.33 ct/kWh up to 40 kW and 1.57 ct/kWh up to 1,000 kW. In the preceding window, commissioned 1 February to 31 July 2026, the bands were 2.54 / 2.36 / 1.59 ct/kWh, and systems from that window keep those rates. The surcharge is paid for 20 years on every kilowatt hour delivered. The price charged to participants is capped at 90% of the local default supplier tariff. Since Solarpaket I, commercial buildings qualify too, not only residential ones, and the former 100 kW capacity limit is gone. From June 2026 energy sharing under § 42c EnWG adds a third route that reaches beyond a single building.

What it actually turns on

Not the surcharge, but the metering concept. Whether additional generation and bidirectional meters are needed is the grid operator's call, based on the specific meter layout in the building, and that answer often arrives after the system has been designed. In mixed-use buildings there is a second complication: commercial and residential participants need different contracts and are treated differently for tax.

When a building is being assessed, Mieterstrom is rarely the first question. The first questions are whether the roof carries the load and whether the connection absorbs the capacity. Mieterstrom then decides how much of the generated volume stays in the building, and therefore the revenue per kilowatt hour, not whether the project is feasible at all.

The comparison that matters economically is against export: a kilowatt hour consumed in the building displaces a retail purchase price, while an exported one earns the EEG rate. The gap between those two is the real lever. The surcharge shifts that gap, it does not reverse it.

In a lender's pack only one thing counts here: is the metering concept approved, or is it an assumption. A model that books Mieterstrom revenue before the grid operator has confirmed the concept gets re-run on the export case during underwriting.