{"id":16565,"date":"2026-11-05T15:45:13","date_gmt":"2026-11-05T14:45:13","guid":{"rendered":"https:\/\/pvprosolar.de\/?p=16565"},"modified":"2026-11-05T15:45:13","modified_gmt":"2026-11-05T14:45:13","slug":"extending-a-pv-system","status":"publish","type":"post","link":"https:\/\/pvprosolar.de\/en\/extending-a-pv-system\/","title":{"rendered":"Extending a PV System: Technology, EEG Rules and Costs"},"content":{"rendered":"

Extending a PV system usually has a concrete reason: a heat pump, an electric car or higher consumption has made your existing system too small. Technically, an extension is almost always possible if roof space, inverter and meter cabinet allow it. Legally, however, the new part is usually a separate system: it gets its own commissioning date, the feed-in tariff valid at that time and the rules of the German Solar Peak Act, while your existing system keeps its previous tariff. Here you will learn what is checked beforehand, which EEG rules apply, how registration works and what costs to expect.<\/p>\n

Request your free, no-obligation quote now<\/a>: we check your existing system, even if another installer built it.<\/p>\n

Extending a PV system: the key facts<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n
Topic<\/th>\nWhat applies<\/th>\n<\/tr>\n<\/thead>\n
Legal status<\/td>\nThe new part has its own commissioning date and its own tariff; the existing system keeps its old rate<\/td>\n<\/tr>\n
Tariff for the new part (up to 10 kWp)<\/td>\n7.70 ct\/kWh for partial feed-in, 12.22 ct\/kWh for full feed-in (commissioning since 1 August 2026)<\/td>\n<\/tr>\n
12-month rule<\/td>\nSystems on the same building commissioned within twelve consecutive calendar months are added together to determine their size (\u00a7 24 EEG)<\/td>\n<\/tr>\n
Technical check<\/td>\nInverter headroom, meter and meter cabinet, free roof space and structural load<\/td>\n<\/tr>\n
Solar Peak Act<\/td>\nThe new part may feed in at most 60 % of its capacity until a smart metering system with a control device is installed<\/td>\n<\/tr>\n
Registration<\/td>\nWith the grid operator before connection, in the Market Master Data Register within one month of commissioning<\/td>\n<\/tr>\n
Taxes<\/td>\n0 % VAT; income tax exemption up to 30 kWp per residential or commercial unit<\/td>\n<\/tr>\n
Costs<\/td>\nGuide value \u20ac1,450\u20131,750 per kWp for the new modules; meter cabinet if needed \u20ac1,200\u20132,500 (up to \u20ac3,500)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

When is extending your PV system worth it?<\/h2>\n

An extension pays off above all when you use more electricity than your system currently delivers. Solar power fed into the grid earns only a few cents, while solar power you use yourself replaces expensive grid electricity.<\/p>\n

Higher consumption from a heat pump and an EV<\/h3>\n

A heat pump and an electric car raise annual consumption considerably. In the Hannover region you can cautiously expect around 893 kWh per kWp per year, so five additional kWp deliver roughly 4,465 kWh a year. The extra yield helps most when you charge the car with daytime surplus and control the heat pump through energy management. How the three components work together is explained in our guide to photovoltaics with heat pumps and wallboxes<\/a>.<\/p>\n

Extending an old PV system after the 20-year EEG tariff<\/h3>\n

After 20 years plus the year of commissioning, the fixed EEG tariff ends. The system may keep running. A small system whose support has ended can still pass its surplus to the grid operator, but only receives the market value minus a marketing deduction (\u00a7 21(1) No. 4 and \u00a7 53(4) EEG). For these systems, self-consumption is what counts. Many older systems feed in all their power and need a different meter for self-consumption, and their inverter is often near the end of its life. If you want to extend an old PV system, the meter conversion, a new inverter, storage and extra modules can be planned in one step.<\/p>\n

Storage first or modules first?<\/h3>\n

If you export a lot at midday and buy power in the evening, a battery is often enough. It raises self-consumption from around 25\u201335 % to about 55\u201370 %; see retrofitting a solar battery<\/a>. If your annual consumption exceeds your annual yield, for example because of a heat pump in winter, you need more module area. Often both together make sense: one installation date, one registration and one metering concept.<\/p>\n

Technical check before extending a PV system<\/h2>\n

Inverter: headroom, second unit or replacement<\/h3>\n

First we check whether the existing inverter can take the additional modules. What matters are free MPP trackers and the voltage, current and power limits in the datasheet. Often there is too little headroom. Then there are two options: the new part gets its own inverter, or an old inverter is replaced with a larger hybrid unit that also manages a battery. We diagnose and repair inverters on systems we did not build as well, and replace the unit if a repair no longer pays off. More on the technology: solar inverters<\/a>; on faults: inverter fault<\/a>.<\/p>\n

Meter and meter cabinet<\/h3>\n

When you extend, the grid operator looks at the meter position. Older meter cabinets often no longer meet the technical connection conditions (TAB) and VDE-AR-N 4100. Your grid operator decides whether an upgrade is mandatory. If the meter cabinet has to be upgraded or replaced, this usually costs \u20ac1,200\u20132,500, up to \u20ac3,500 for extensive work. How total system costs are made up is shown in our guide to solar panel costs<\/a>.<\/p>\n

Roof space, structure and orientation<\/h3>\n

The new modules need free space: the second roof face, a garage or a carport. An east-west layout delivers around 80 % of the yield of a south-facing roof in Hannover and matches morning and evening consumption well. Before installation we check whether the roof can carry the extra load. If roof space is lacking, we also build solar carports including the structure.<\/p>\n

EEG rules for extending a PV system<\/h2>\n

New part, its own tariff<\/h3>\n

Under the EEG, each solar module essentially counts as a system of its own. That is why the new part gets the commissioning date of its modules and the tariff valid at that time. Since 1 August 2026 this is 7.70 ct\/kWh for partial feed-in and 12.22 ct\/kWh for full feed-in up to 10 kWp, with proportionally less for capacity above 10 kWp. Your existing system keeps its old rate until the end of its own 20 years. If you commission by 31 December 2026, you secure the fixed tariff for 20 years. For later systems, the federal cabinet draft of the EEG 2027 plans a different model that has not yet been passed. More: EEG amendment<\/a> and EEG law for photovoltaics<\/a>.<\/p>\n

The 12-month rule under \u00a7 24 EEG<\/h3>\n

Solar systems on the same plot or building that are commissioned within twelve consecutive calendar months count as one system for determining size. For building-mounted systems this only applies if they sit behind the same grid connection point. Example: 8 kWp in March and 6 kWp in December of the same year count as 14 kWp together, so part of the new capacity receives the lower rate of the band above 10 kWp. If the old system is more than twelve months old, the new part is assessed on its own.<\/p>\n

Partial or full feed-in for the new part<\/h3>\n

Under \u00a7 48(2a) EEG you can choose for each system whether it feeds in everything or only the surplus. The new part could, for example, feed in fully while the existing system supplies your house. Each part then needs its own meter, and you must notify the grid operator of full feed-in in text form before commissioning. Later you can switch with effect from 1 January if you notify before 1 December. For households with a heat pump or EV, partial feed-in is usually the better choice.<\/p>\n

Solar Peak Act: what applies to the new part<\/h3>\n

Systems commissioned since 25 February 2025 are subject to new rules. Until a smart metering system with a control device is installed, the new part may feed in at most 60 % of its installed capacity (\u00a7 9(2) EEG). With self-consumption and a battery, this costs you hardly any yield. During hours with negative exchange prices, the new part receives no tariff; for systems under 100 kW this only applies after the year in which a smart metering system is installed (\u00a7 51 EEG). Nothing changes for your existing system. Details: Solar Peak Act<\/a>.<\/p>\n

Metering concept: how old and new are counted<\/h3>\n

To bill both tariffs correctly, you need a metering concept approved by the grid operator. Either a separate generation meter measures the new part, or both parts run through a shared meter, in which case the power is split in proportion to installed capacity (\u00a7 24(3) EEG). The right solution depends on feed-in type, battery and meter cabinet.<\/p>\n

Registration with the grid operator and the Market Master Data Register<\/h2>\n

Before connection, a registered electrical installer notifies the grid operator of the extension; in the Hannover region this is, depending on the area, for example enercity Netz or Avacon. The grid operator checks the connection, metering concept and meter position. After commissioning, the new part must be entered in the Federal Network Agency’s Market Master Data Register<\/a> within one month (\u00a7 5(5) MaStRV), as a separate unit with its own date. A new battery is registered too. A missing registration can reduce your tariff entitlement. We handle both registrations for you.<\/p>\n

Taxes: VAT and income tax on an extension<\/h2>\n

Since 1 January 2023, the zero VAT rate applies to the supply and installation of modules, inverters and batteries on or at residential buildings (\u00a7 12(3) UStG), and this also covers an extension. Systems up to 30 kWp meet the conditions automatically. If the meter cabinet is renewed in connection with the PV installation, the Federal Ministry of Finance says this can also fall under the zero rate; we list it separately in the quote. Wallboxes and heat pumps are not covered. More: photovoltaic system VAT<\/a>.<\/p>\n

For income tax, earnings from systems up to 30 kWp per residential or commercial unit and at most 100 kWp per person are tax-free (\u00a7 3 No. 72 EStG). The gross capacity in the Market Master Data Register is what counts, so add the existing system and the extension together. If you exceed the limit, talk to your tax adviser first. More: tax-free photovoltaic system<\/a>.<\/p>\n

What does extending a PV system cost?<\/h2>\n

There is no flat price for extensions because every existing system is different. These values help you get oriented:<\/p>\n\n\n\n\n\n\n\n\n\n
Component<\/th>\nGuide value<\/th>\n<\/tr>\n<\/thead>\n
New modules including installation<\/td>\n\u20ac1,450\u20131,750 per kWp as a guide value<\/td>\n<\/tr>\n
Inverter<\/td>\nKeep, second unit or replacement: price after diagnosis in the quote<\/td>\n<\/tr>\n
Meter cabinet (if needed)<\/td>\n\u20ac1,200\u20132,500, up to \u20ac3,500 for extensive work<\/td>\n<\/tr>\n
BYD HVS 10.2 battery (optional)<\/td>\nan additional \u20ac7,700\u20139,200<\/td>\n<\/tr>\n
Registration with grid operator and Market Master Data Register<\/td>\nhandled by us<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The per-kWp value is a guide value we use for complete systems. For small extensions the price per kWp can be higher because scaffolding, electrical work and registration are spread over fewer modules; if the existing inverter can keep running, costs go down.<\/p>\n

Request your free, no-obligation quote now<\/a>: you receive a written fixed price for your extension.<\/p>\n

How we extend your PV system, even if we did not build it<\/h2>\n

Survey of your existing system<\/h3>\n

We extend not only our own systems but also existing systems built by other installers. For this we need the datasheets of modules and inverter, the commissioning report and the Market Master Data Register number. During the free on-site visit we check inverter, meter cabinet and roof and prepare a yield forecast for the new area.<\/p>\n

Brand components and our own installers<\/h3>\n

We plan with modules from AIKO, JA Solar or Longi, Fronius inverters, BYD batteries and K2 Systems mounting systems. Installation and connection are carried out by our own certified installers in line with VDE and TAB, without changing subcontractors.<\/p>\n

Fixed price and 30\/70 payment model<\/h3>\n

You receive a written fixed price and pay 30 % on order and 70 % after installation. After commissioning we set up the app so you can monitor the old and new parts.<\/p>\n

    \n
  1. Enquiry and documents for the existing system<\/li>\n
  2. On-site check and planning with yield forecast<\/li>\n
  3. Fixed-price quote and order<\/li>\n
  4. Registration with the grid operator<\/li>\n
  5. Installation, meter and meter cabinet work<\/li>\n
  6. Commissioning and entry in the Market Master Data Register<\/li>\n<\/ol>\n

    Extending a commercial PV system<\/h3>\n

    For commercial roofs in the city of Hannover there is the \u00abGro\u00dfe D\u00e4cher\u00bb funding programme, which also funds extensions of 35 kWp or more. The conditions are explained under solar funding for businesses in Hannover<\/a>.<\/p>\n

    FAQ: extending a PV system<\/h2>\n
    \n
    \n\t\t\t\t

    Can an existing PV system be extended?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tYes, in most cases. You need free roof space, a suitable inverter or room for a second unit, and a meter cabinet that meets the grid operator's connection conditions. Legally, the new part is usually a separate system with its own tariff. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Do the new modules get the old feed-in tariff?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tNo. The new part receives the tariff valid at its commissioning; since 1 August 2026 this is 7.70 ct\/kWh for partial feed-in and 12.22 ct\/kWh for full feed-in up to 10 kWp. Your existing modules keep their old rate until the end of their 20 years. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Do I need a second inverter?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tNot always. If the existing inverter has free inputs and enough headroom according to its datasheet, the new modules can be connected to it. Often that headroom is missing; then the new part gets its own unit, or an old inverter is replaced with a hybrid unit. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Do I have to register the extension?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tYes. Before connection, a registered electrical installer notifies the grid operator. After commissioning, the new part must be entered in the Market Master Data Register within one month. We handle both for you. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Does the Solar Peak Act apply to my old system?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tNo. The 60 % limit and the loss of the tariff during negative prices apply to systems commissioned since 25 February 2025, so only to the new part. Your existing system keeps its previous rules. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Is VAT charged on the extension?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tNo, the zero rate applies to modules, inverters, batteries and installation on or at residential buildings. Systems up to 30 kWp meet the conditions automatically. Wallboxes and heat pumps are not covered. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Is extending a system after the 20-year EEG tariff worth it?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tOften yes, if you use the power yourself. After the EEG period, the old part only receives roughly the market value for surplus power. An extension with a new inverter, battery and conversion to self-consumption makes the system economical again, and the new part receives the current tariff. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t

    \n
    \n\t\t\t\t

    Does PVPro Solar also extend systems built by other installers?<\/h3>
    \n\t\t\t\t\t

    \n\t\t\t\t\t\tYes. We also extend existing systems we did not build, and repair or replace the inverter there if needed. After an on-site check you receive a written fixed-price quote. <\/p>\n <\/div>\n <\/div>\n <\/section>\n\t\t\n