Aggregation of installations (§ 9 EEG)

Why the rule exists

Almost everything in the EEG scales with size: the anzulegender Wert steps down by capacity band, direct marketing becomes mandatory above a certain output, further thresholds route a project into an auction, and individual support categories stop at a fixed kilowatt-peak figure. Without a counter-rule every one of those thresholds could be avoided by division: one 900 kWp roof would become three 300 kWp installations.

§ 9 EEG closes that. Installations that belong together spatially and were commissioned within a twelve-month period count as one installation when remuneration is determined. Technically they stay separate, keeping their own inverters and their own registration; only the calculation sees a single installation.

Two axes: place and time

The first axis is place. What matters is whether the installations sit on the same building or plot, or otherwise in immediate spatial proximity. The precise criteria are in the statute and are applied by the grid operator, not interpreted by the operator of the installation.

The second axis is time, and it is regularly misread. The twelve-month period means twelve consecutive calendar months, not a calendar year. A commissioning in November and the next one in the following February fall inside the same period, even though two year numbers sit between them.

Ownership does not break it

Aggregation does not ask who owns what. Two companies, two operators and two purchase agreements change nothing once place and period are met. Setting up a separate project company per phase changes liability and financeability, but not the treatment under § 9 EEG.

In practice the rule is rarely noticed during planning. It is noticed on the grid operator's first settlement, by which point the model carries a rate the aggregated installation does not receive. Around the thresholds below one megawatt that difference is often a low single-digit figure in cents per kilowatt hour. Across twenty years it is not a rounding difference.

For a portfolio the time axis is therefore a decision rather than a footnote. Deliberately spacing two phases more than twelve months apart costs construction time and interest, and can still pay. That calculation belongs before the grid connection application, not after it.

For underwriting, the evidence is the commissioning date of each installation as registered in the Marktstammdatenregister, together with a site plan showing how they sit. Where a seller values installations as separate, this is the first item a buyer recomputes, because a wrong rate moves every cash flow in the model.