Multiple PV systems at one site – remuneration, meters, and billing rules at a glance

More and more commercial businesses operate PV systems from different construction years on the same roof. A system from 2010 with a high EEG remuneration rate, an expansion from 2017 with a significantly lower rate, perhaps even another addition from 2025. What appears confusing at first glance follows clear rules—provided you know the key differences.

This article explains:

• which constellations occur with multiple PV systems at one site,

• how remuneration is calculated in each case,

• when separate meters are required,

• and how the rules on negative electricity prices affect mixed systems.

Why this topic is becoming relevant now

Since 2021, additional PV systems have been exiting the 20-year EEG support scheme every year. At the same time, existing systems are being supplemented with new installations—whether for higher self-consumption, for combination with battery storage, or for participation in direct marketing.

The result: at one site, there are increasingly systems with very different remuneration rates, commissioning dates, and marketing models. For project developers and energy consultants, it is no longer sufficient to calculate with a single remuneration rate.

The three typical constellations

Depending on which systems are combined at one site, different rules apply for meters, remuneration, and billing. The three most common cases are considered individually below.

Case 1: Same marketing form, different vintages

Example: Two PV systems, both in the market premium model—one from 2010 with 39 ct/kWh, one from 2017 with 10 ct/kWh.

Meters

With the same marketing form (e.g., both market premium or both fixed feed-in tariff), the systems can be billed via a shared metering device (§24 para. 3 EEG 2023). A separate feed-in meter per system is not required.

Remuneration: blended remuneration by kWp

The measured total feed-in is allocated to the individual systems proportionally by installed capacity (kWp). Each system then receives its individual remuneration rate. The result is a capacity-weighted blended remuneration.

Calculation example:

• System A: 100 kWp, commissioned in 2010, applicable value 39 ct/kWh

• System B: 300 kWp, commissioned in 2017, applicable value 10 ct/kWh

Blended remuneration = (100 × 39 + 300 × 10) / 400 = 17.25 ct/kWh

Important: the system aggregation under §24 para. 1 EEG—which combines systems within 12 consecutive calendar months into one system—does not apply here, since the commissioning dates are years apart. Each system retains its individual remuneration rate.

Negative electricity prices (§51 EEG)

The following also applies to remuneration reductions due to negative electricity prices: Each system retains the §51 version applicable at its commissioning date (§100 para. 46 EEG). The shared metering device does not change this.

This means: during a negative price period, systems can drop out of remuneration at different times—depending on their individual threshold.

Example:

With 5 consecutive hours of negative exchange prices, the following happens:

• System A (6h threshold not reached): its 40% share of feed-in continues to be remunerated at 10 ct/kWh.

• System B (3h threshold exceeded from hour 3): its 60% share of feed-in is set to 0 ct/kWh from the 3rd hour onward.

The effective remuneration of the overall system therefore decreases during the negative price period—but not to zero as long as the older system is still within its threshold.

Case 2: Different marketing forms

Example: A system from 2012 with a fixed feed-in tariff, and a new system from 2025 in direct marketing (market premium model).

Meters

As soon as systems use different marketing forms, separate meters are mandatory. The EEG Clearing House (Frequently Asked Legal Question 123) explicitly excludes shared metering devices in this case.

The reasons:

• Different metering requirements: Direct marketing requires quarter-hourly metering (§21b EEG), fixed feed-in tariff does not.

• Sanction in case of violation: If billing is nevertheless done via a shared meter, remuneration for all electricity is reduced to the market value MWSolar(a)—a drastic loss.

Remuneration

Due to separate meters, each system is billed completely separately. Blended remuneration is neither necessary nor permitted. In practice, these are two independent systems that merely share the same grid connection point.

Negative electricity prices (§51 EEG)

Here too, each §51 rule applies individually per system. Since the systems are measured separately anyway, the allocation is clear.

Case 3: Post-EEG system and new system

Example: A system from 2004 whose 20-year EEG support expired in 2024, plus a new expansion from 2025.

Meters

Whether a shared meter is possible depends on the marketing form in which each system is operated:

• Both in direct marketing: Shared meter possible → Case 1 (blended remuneration)

• Different marketing forms: Separate meters → Case 2

Remuneration of the post-EEG system

Systems whose EEG support has expired have several options:

1. Other direct marketing: Electricity is marketed on the spot market. The system receives the exchange price—no market premium, no guaranteed minimum price.

2. Follow-up regulation (§21 para. 1 no. 4 EEG): For smaller systems up to 100 kWp, there is an entitlement to the market value minus a marketing flat-rate.

Remuneration of the new system

The new system receives the regular EEG remuneration applicable at its commissioning date—regardless of the fact that an older system exists at the same site.

Since commissioning dates are far more than 12 months apart, no system aggregation under §24 para. 1 EEG takes place. The new system is treated as if the old system did not exist.

Negative electricity prices (§51 EEG)

The post-EEG system in other direct marketing receives only the exchange price anyway—so at negative prices, remuneration is automatically negative (or zero if no feed-in occurs). For the new system, the current §51 rules of its commissioning date apply.

Summary

Conclusion

Multiple PV systems on one roof are no longer a special case, but increasingly the norm. The regulatory foundations are clear: systems with the same marketing form can be billed via a shared metering device, remuneration is allocated proportionally by capacity, and each system retains its individual §51 rules.

The challenge lies in the correct representation in profitability calculations. Anyone planning storage and a new expansion for an existing building with an older PV system must clearly separate the different remuneration mechanisms and negative price thresholds. A single flat remuneration rate leads to incorrect return expectations—depending on the constellation, either too optimistic or too conservative.

For project developers, this means: before planning, check which case applies, clarify the meter structure, and calculate remuneration precisely per system.

Sources:

• §24 para. 3 EEG 2023 – Shared metering device

• §51 EEG 2023 – Remuneration reduction for negative electricity prices

• §100 para. 46 EEG 2023 – Transitional provisions

• EEG|KWKG Clearing House, Frequently Asked Legal Question 123 – Shared metering device

• EEG|KWKG Clearing House, Frequently Asked Legal Question 264 – Remuneration reduction for negative prices