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Connecting a PV system: here's what you need to know

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If you want to use free solar power in your home, you have to connect a photovoltaic system. A few things must be borne in mind, however, as there are some risks associated with this and PV systems typically have an impact on the public grid. In addition to working through each step in the right order, for example, it's important to ensure that the PV modules are wired correctly. We provide an overview here and answer the most important questions about connecting photovoltaics to a home network.

Overview of the connection steps

More and more households want to connect a PV system to cover their electricity needs with free energy from their own roof. The right approach is essential to ensuring a safe and reliable setup:

  • Step 1:  Call in the professionals: before connecting a photovoltaic  system to your home network, make sure everything has been properly planned. Contractors and engineers can design the best system to suit your home and preferences.  
  • Step 2:  Submit a connection request to the grid operator: a connection request must be submitted to the respective grid operator with the required information. The grid operator examines the plans and issues a connection offer containing all information on the individual requirements, costs and next steps.
  • Step 3:  Have the solar PV system professionally installed: once the grid operator authorises the connection of the photovoltaic system, a contractor fits the technology. This involves installing the mounting system, attaching the solar modules and wiring them together. The experts then install inverters and storage units.  
  • Step 4:  Establish a connection to your home network: once the technology has been installed, a contractor can connect the PV system. Grid operators (and installers registered with them) are authorised to carry out this step. The experts will replace your meters if necessary and commission the solar PV system.

Please note: Connection and commissioning usually take place a few days or weeks after installation. Then your PV system is recorded in the core energy market data register and registered with the tax authority.

Installation requirements  

Generally speaking, connecting a PV system also has an impact on the public grid. For this reason, and because electrical installations harbour a number of risks, legal requirements must be observed.

Connecting a photovoltaic system to the grid

Section 8 of the Renewable Energy Sources Act (EEG) forms the basis. This obliges grid operators to purchase electricity generated from renewable sources and regulates the connection process. The following (and more) applies to homeowners:  

  • Up to 30  kWp, the connection is usually to the existing grid connection point

  • Up to 10.8  kWp, the grid operator has four weeks after the connection request has been submitted to provide information on the next steps and the details required  

  • If homeowners do not receive a response within four weeks, they may have the PV system connected (up to 10.8  kWp) "in compliance with the relevant regulations for the implementation of a grid connection"

  • Once all the information has been submitted, the grid operator has eight weeks to review the application and provide the following information: a schedule for establishing the grid connection, information for testing the connection point and on the grid operator's obligation to be present when the PV is connected, and a cost estimate

  • If homeowners do not receive a timely response, they may have the PV system connected (up to 30  kWp) "in compliance with the relevant regulations for the implementation of a grid connection"

Please note: The timelines above will change from 1  January 2025, when grid operators will have to provide the most important information on connecting photovoltaics on their website. They will also have to set up a web portal for grid connection requests and process applications via this within four weeks instead of eight.

Connecting a photovoltaic system to a home network

When it comes to the practical implementation of the connection, the requirements of the Low Voltage Connection Ordinance (NAV) apply. This states that any electrical installation work downstream of the domestic distribution box may only be carried out by registered installers. Specialised companies with the appropriate qualifications can register with the grid operators (Section  13 NAV).  Furthermore, only grid operators and registered installers are authorised to connect a solar PV system to a home network. The connection point is usually located between the main/distribution fuse box or another isolator (Section  14 NAV).

Connecting to a home network

If all the technical requirements are met and the grid operator has approved the connection request, assembly can begin. Fitters first install the mounting system on the roof. They attach the modules and wire them together. Installers then lay cables from the roof to the mechanical room for connecting the PV system to the home network. They integrate the inverter(s), install a storage unit (optional) and equip the meter box with the necessary technology. It's important to note that meter boxes have to be replaced during this stage if they are found to be too small or outdated.

As solar PV systems generally affect the public grid, only grid operators and installers authorised by them may connect a PV system. Once the solar PV system has been successfully installed, the experts replace the meters if necessary and commission the system. This usually takes place a few weeks after the system has been installed.

In series or parallel: connecting PV modules

Special attention should be paid to the modules of the PV system and their connection diagram. This is because solar panels on a roof can either be installed in series or side by side in parallel. While the first setup delivers a higher voltage, the current is higher for PV modules connected in parallel. Both options have their pros and cons and are therefore suitable for certain applications:

  PV modules connected in parallelPV modules connected in series
Key points
  • The total voltage is the same as the voltage of a single module, while the total current is the sum of the currents passing through each module.
  • The total current is the same as the current passing through a single module, while the total voltage is the sum of the voltage on each module.
Pros
  • High loads can be covered by a high current.
  • Less reduction in yield if individual modules are shaded.  
  • Installation is easier and cheaper.
Cons
  • Higher currents require larger cables.
  • More stringent safety requirements and increased costs.
  • If a module is shaded or some modules are aligned differently, this has an effect on the overall voltage and the yield decreases.  

Please note:  In practice, PV modules are usually connected in series. However, when it comes to supplying consumers with high currents, experts generally opt for parallel cabling when connecting the modules of a PV system.

AC or DC: connecting power storage units

How the storage unit is connected to the home network is also important for the function of the solar PV system. In simple terms, a storage unit is a battery that is installed upstream or downstream of the inverter.

  • DC: If the power storage unit is placed upstream of the inverter, experts refer to this as DC coupling. This is because the storage unit is located in the direct current (DC) network. The electricity from the roof first charges the storage unit before it reaches the consumers via the inverter. As power storage units also work with direct current, one less inverter needs to be connected to the PV system. This reduces costs and conversion losses and ensures a higher yield. Since all components must be perfectly matched to each other, a direct current connection to a photovoltaic system is particularly suitable for new installations.
  • AC: Anyone wishing to retrofit a storage unit to a PV system often opts for uncomplicated AC coupling. The power storage unit is then located downstream of the inverter in the alternating current (AC) network. As an additional battery inverter has to be connected to the photovoltaic system for this, the resulting conversion losses mean a lower yield.

Special case: zero-export photovoltaic system

Does the same connection diagram also apply to PV systems for self-consumption? Many homeowners who do not want to feed electricity into the public grid ask themselves this question. The answer is "no". That's because the technology has no effect on the public grid if there is no grid coupling. However, if there is a connection to the grid (not a standalone system), homeowners must connect a special inverter to the PV system. This communicates with an intelligent electricity meter, for example, in order to adjust the output of the solar PV system to demand at all times. Current regulations require that inverters must be able to reduce 90  % of the power in three seconds and 100  % in ten seconds.

FAQ: frequently asked questions about connecting a photovoltaic system

No. A connection request must be submitted first. This informs the grid operator that you wish to connect a solar PV system. The grid operator then checks the technical data and, if necessary, the impact on the grid before approving the application. This can currently take up to eight weeks after all the details have been submitted; in 2025, it will be reduced to four weeks.

Have the system professionally planned first and then submit the connection request to your grid operator. If the grid operator approves the installation, fitters can install the technology and wire everything up to the meter box (or have it wired). The grid operator (or an installer registered with it) then comes to connect the PV system and replace existing meters if necessary.

If you have the appropriate expertise, you can install the technology on your roof and in your home yourself. When it comes to connecting the photovoltaic system, however, you will need an installer registered with the grid operator. We recommend that you have the installation carried out by a specialised Viessmann partner.

The costs for the grid connection depend on local circumstances. For a typical domestic system, the connection costs are generally between €500 and €1000. The costs may be higher for large photovoltaic systems. You will receive a binding answer with the connection offer from your grid operator.

If you have submitted the connection request in good time and adhered to the grid operator's schedule, your PV system should be connected two to four weeks after completion. It may take longer if there is particularly high demand in your area. Grid operators will provide a binding answer in response to your specific enquiry.

Yes, that is possible. You will then need an inverter that adapts the output of the photovoltaic system to the current demand in your home. The demand can be measured using a smart electricity meter or a separate power meter.

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