Plug-In Solar (Balkonkraftwerk) in Frankfurt: Register Only in the Marktstammdatenregister, NRM Meter Rules and the Tenant's Right
A plug-in solar device of up to 2,000 W of modules and 800 VA of inverter output only has to be registered in the federal Marktstammdatenregister (MaStR), and you do not have to notify the grid operator unless you want a feed-in payment. In Frankfurt, NRM Netzdienste Rhein-Main confirms this and says the meter operator replaces an old meter without a reverse-flow block by a two-way meter after your registration, so give your correct meter number. Tenants have a legal claim against the landlord under § 554 BGB. The city's Klimabonus grant for mini PV systems has no funds left.
What Counts as a Plug-In Solar Device
A Steckersolargerät, usually called a Balkonkraftwerk, consists of one or more solar modules, an inverter, a cable and a plug for the final circuit of a household. The Umweltbundesamt explains that if the total module power does not exceed 2,000 W (direct current) and the inverter does not exceed 800 W (alternating current), the device only has to be registered in the Marktstammdatenregister. NRM Netzdienste Rhein-Main, the operator in the Frankfurt grid area, gives the same limits: at most 2 kW installed and 800 VA from the inverter. A bigger system counts as a normal PV system that has to be registered with NRM through its Netzportal and approved by an installer.
Registration: One Place, Not Two
| Case | Marktstammdatenregister | NRM (grid operator) |
|---|---|---|
| Up to 2,000 W modules and 800 VA inverter, no feed-in payment | Register | No notice needed |
| The same device, but you want a feed-in payment | Register | Register in the NRM-Netzportal, installer approval needed |
| Larger than the limits | Register | Register under VDE 4105 in the NRM-Netzportal, installer approval needed |
The Marktstammdatenregister help states that every Balkonkraftwerk must be registered like any other power generation system. Since 16 May 2024, the duty to notify the grid operator drops for devices within the limits that waive a feed-in payment, because the register passes the data on automatically. Register the first commissioning, which for plug-in solar is the moment the device first feeds into the house network, usually when the plug first goes into a socket. Have ready the address, the date, the technical data of the device, the connection details and your meter number.
The Meter: Why the Number Matters
Many Frankfurt flats still have an old meter. NRM explains the rule: a normal one-way meter without a reverse-flow block has to be exchanged for a two-way meter, and even a one-way meter with a reverse-flow block is not enough, because the energy fed into the public grid must be measured. If an exchange is necessary, the metering point operator does it automatically after your registration, so the correct meter number in the MaStR entry is the important detail. The Umweltbundesamt adds that the device may run in the meantime and that the exchange causes no extra costs compared to the old meter. Our guide to submitting your meter reading explains who reads your meter in Frankfurt.
Renting: Your Legal Claim
If you rent, the first step is the landlord, not the register. § 554 BGB lets a tenant demand permission for structural changes that serve electricity generation with plug-in solar devices. The landlord must allow it unless it cannot be expected of him, even after weighing the tenant’s interests, and an agreement that disadvantages the tenant is void. In practice, write to the landlord or the owners’ association with a short description: where the modules are attached, how, and the size of the device. The LEA Hessen checklist puts “inform the landlord” as an early step, before you check grants and compare offers.
Money: What the City Offers and What It Does Not
The City of Frankfurt runs a Klimabonus programme with grants for green roofs, rainwater storage, solar systems and more. Mini PV systems are on the list, but the city portal states that no further funds are available for them, so plan without a grant. Other items continue, for example solar systems with 20 percent of eligible costs. The programme requires that you do not start the measure before the approval, and an investment must not lead to a rent increase, which matters if you are a tenant. The LEA Hessen says there is no special grant from the federal government or from Hesse for plug-in solar.
Step by Step
- Check the limits: modules up to 2,000 W, inverter up to 800 VA.
- Ask your landlord or owners’ association in writing, citing § 554 BGB if needed.
- Mount the device and check shading and the socket, using the LEA checklist.
- Register in the MaStR with the correct meter number and keep the confirmation.
- Wait for the meter exchange if your meter is an old one-way meter.
- Skip NRM’s portal unless you want a feed-in payment or your system is larger than the limits.
Compliance Note
This guide summarises the pages of NRM Netzdienste Rhein-Main, the Marktstammdatenregister, the Umweltbundesamt, the LEA Hessen, the City of Frankfurt and § 554 BGB as read in October 2026. Technical rules, grants and procedures change, and electrical work beyond plugging in a compliant device should be left to a qualified electrician. This is not legal advice. Confirm the current rules with NRM and the MaStR before you register.
FAQ & Common Pitfalls
Do I have to tell Mainova or NRM before I plug it in?
Not if you do not apply for feed-in compensation. NRM Netzdienste Rhein-Main, the operator in the Frankfurt grid area, writes that since the Solarpaket I took effect on 16 May 2024 the obligation to notify the grid operator is dropped when no feed-in payment is requested, and registration in the Marktstammdatenregister is enough. The MaStR help says the registration passes the data on to the grid operator automatically.
What are the size limits?
According to NRM, a device may have at most 2 kW of installed capacity and 800 VA of inverter output. The Marktstammdatenregister and the Umweltbundesamt give the same figures, 2,000 W of module power and 800 W of inverter power. A larger system counts as an ordinary PV system. It then has to be registered with NRM through the NRM-Netzportal under VDE 4105 and approved by an installer.
When do I have to register in the MaStR?
The MaStR help says the first commissioning has to be registered, and for a plug-in solar device that is the moment it first feeds alternating current into the house network, usually when it is mounted and the plug is first put into a socket. It does not give a fixed number of days on that page, so register as soon as you start, and keep the confirmation: a grant application or an installer may ask for it.
Do I need a new meter?
It depends on your existing meter. NRM says a standard one-way meter without a reverse-flow block has to be replaced by a two-way meter, and a one-way meter with a reverse-flow block is also not enough because the energy fed into the grid must be recorded. The metering point operator exchanges it automatically after you register in the MaStR, which is why you must enter the correct meter number. The Umweltbundesamt adds that a reverse-running old meter is tolerated meanwhile and that the exchange causes no extra costs for the operator of the device compared to the old meter.
Can my landlord say no in Frankfurt?
Under § 554 BGB, a tenant can demand permission for structural changes that serve electricity generation with plug-in solar devices. The landlord must allow it unless it cannot be expected of him even when the tenant's interests are weighed, and a contract term that puts the tenant at a disadvantage is void. The LEA Hessen still advises telling the landlord or the owners' association before you mount anything. Ask in writing, say how and where it is attached, and keep the answer.
Is there a grant for plug-in solar in Frankfurt?
Not at the moment. The city's Klimabonus programme lists mini PV systems, so-called Balkonkraftwerke, but the city portal states that no further funds are available for them. Other parts of the programme, such as solar systems on roofs with 20 percent of eligible costs, continue to run. The LEA Hessen says that there is no special grant from the federal government or the state of Hesse. The Klimabonus rules say that a measure must not be started before approval, so do not count on a refund for a device you have already bought.
Can I use an ordinary household socket?
According to the LEA Hessen, the Solarpaket I allows plug-in solar systems to be run through an ordinary Schuko plug, as long as the conditions of the VDE standard are met. The same page lists the practical checks before you buy: sun and shading, where the nearest socket is, whether any structural work is needed, and any restriction such as heritage protection in an old town centre.