PV on someone else's roof: what investors should check on commercial rooftops

Not every photovoltaic system in a direct investment stands on open land. Some offers are systems on warehouses, logistics centres and production buildings whose roof belongs to someone else. For the investor this is a different construction from a solar park: they own the system but not the surface it stands on, and that surface is a building with its own financing, its own age and often a user who also buys the electricity.

The questions that follow rarely appear in the prospectus. Does the system stay mine when it is bolted to the roof? What happens if the building is sold, the roof starts leaking or the tenant who bought the electricity moves out? We go through them one by one, each with its legal reference.

Who owns a PV system on someone else's roof?

The investor, as long as it has not become an essential component of the building. Under the German Civil Code (BGB), a thing passes into the property of the landowner when it becomes an essential component of the land or the building; under Sec. 94 (2) BGB the building includes things inserted to construct it. Sec. 95 BGB sets the counterweight: what is connected to the land or inserted into the building only for a temporary purpose does not become a component. German lawyers call this a Scheinbestandteil, an apparent component. Only as such does the system stay with the investor, can be transferred separately from the building and serve as collateral.

For ground-mounted systems the Federal Court of Justice answered the question in 2021. If a tenant or lessee connects a thing to the land, there is a factual presumption that this happens only temporarily, even if the system is meant to stay there for its whole useful life; a contractually agreed removal at the end supports the presumption (BGH, judgment of 22.10.2021, V ZR 69/20, paras. 8 f.). For rooftop systems no such ruling exists. In two cases where the court had a system on a roof before it, it left the question open because the outcome did not depend on it (judgment of 02.06.2016, VII ZR 348/13, para. 22; judgment of 20.03.2019, VIII ZR 88/18, para. 27). Applying the ground-mounted principles to roofs is plausible, but it has not been decided.

Two practical differences follow. The first is the design: a system mounted on rails above the existing roof covering can be taken off without destroying the roof. A roof-integrated system whose modules replace the covering is part of the building envelope, and for it the objection that it was inserted to construct the building is closer at hand. The second is the contract: it should expressly describe the system as a Scheinbestandteil, require its removal at the end of the term and give the investor the right to dismantle it at any time. For tax purposes the allocation is clearer. The Federal Fiscal Court assumes that a rooftop system is an operating installation and thus an independent asset separate from the building (BFH, judgment of 16.09.2014, X R 32/12); depreciation and the investment deduction therefore attach to the system, not to the roof.

What secures the roof right if the building is financed?

An easement registered in the land register, at a rank that survives a forced auction. The roof-use contract binds the parties and, through tenancy law, also a buyer of the building; the next section shows where that binding ends. The easement, by contrast, burdens the property itself and applies against every owner. Commercial buildings add a particular point: if the building is financed, the bank's land charge is already in the register before anyone talks about the solar system.

An easement registered later then ranks behind that land charge. If the bank enforces a forced auction, rights ranking behind its own generally lapse, and the system would lose its roof right at exactly the moment the owner is in difficulty. The remedy is a subordination by the bank behind the easement, which it is not obliged to grant and which should therefore be declared before installation. How rank and subordination work in detail is described in Grid connection, easement, building rights: how to tell whether a direct investment has truly secured its site.

When an existing rooftop system is acquired, transfer becomes an issue. A limited personal easement is in principle not transferable. Sec. 1092 (3) BGB makes an exception for installations using solar radiation, but only if the easement is held by a legal entity or a partnership with legal capacity. If it is registered for a natural person, it does not pass on; the building owner then has to grant it again. How the contract passes to the investor on acquisition of the system is shown in The land lease of a solar park from the investor's side: why it is a Mietvertrag, what the rent costs per kilowatt and how you step into the contract.

What happens if the building is sold or the owner becomes insolvent?

In an ordinary sale, the buyer steps into the roof-use contract; in insolvency and forced auction, the acquirer receives a special right of termination. A contract that grants the use of a roof area against payment is usually a lease (so held by the Federal Court of Justice for a use contract over roof and open areas, judgment of 07.03.2018, XII ZR 129/16), and through Sec. 578 BGB the principle of Sec. 566 BGB applies to it: sale does not break a lease. The buyer takes over the contract with all rights and obligations. The condition is form: a contract for more than one year that is not concluded in text form is deemed concluded for an indefinite period (Sec. 578 (1) sentence 2 BGB) and can be terminated with ordinary notice, whatever term it states.

It is different for a sale out of insolvency or at a forced auction. If the insolvency administrator sells the building, the acquirer may terminate the contract with the statutory notice period, but only for the first permissible date (Sec. 111 InsO); the buyer at a forced auction has the same right (Sec. 57a ZVG). Measured against twenty years of system life, that notice is short. Only the well-ranked easement from the previous section closes this gap, because it continues independently of the contract. The details on form and special termination are in The land lease of a solar park from the investor's side: why it is a Mietvertrag, what the rent costs per kilowatt and how you step into the contract; what applies if not the building owner but the provider or operations manager fails is covered in Provider or operator insolvency: what happens to your direct investment.

Who pays if the roof has to be renovated during the term?

Only the roof-use contract settles that, and if it is silent, both sides will argue about it. A PV system runs for twenty years and more. Whether the roof membrane lasts that long is therefore the first question before installation, and it can only be answered with the year of construction and a condition survey. If the roof has to be opened during the term, the system must be dismantled wholly or partly, stored and reinstalled, and in the meantime it generates nothing. The contract should settle four points: who pays for dismantling and reinstallation, how long an interruption may last at most, whether and how the loss of yield is compensated, and what applies if the building is demolished early or not rebuilt after a fire.

How much the timing matters is shown by our own calculation for a 500 kWp example system with a flat east-west orientation: three months of standstill from June to August cost 44 percent of the annual yield, three months from November to January 4.5 percent. With the assumptions from the section on the electricity customer, that is around 14,500 euros against around 1,500 euros. A contract clause that places roof works in the low-yield months or compensates the loss by monthly shares is therefore worth more than a flat maximum duration.

Before installation, a structural check also belongs on the table, calculating the weight of the system, the mounting structure and any ballast against the reserve of the load-bearing structure, including snow and wind loads. It stays relevant over the term: if the building is converted or the roof is renovated with heavier material, the reserve must not be used up. Finally, in the event of damage the question arises whose insurance pays: the owner's building insurance, the investor's system insurance, or the investor's liability cover if the system caused the damage. Which policies belong to an operation is shown in Insuring a solar park or battery storage asset: which policies belong to a direct investment, and who holds them; what happens to the system at the end of its term in Decommissioning a solar park: who pays, how large the bond is and what it costs.

What changes if the roof user also buys the electricity?

The investor then depends twice on the same site: on the roof and on the customer. Rooftop systems are often planned this way because electricity consumed in the building fetches a higher price than electricity fed into the grid. A supply contract with the user of the hall makes the system more profitable while it runs. It also makes it dependent on that customer: if the tenant moves out, becomes insolvent or relocates production, the higher revenue disappears while the roof contract with the owner continues. The term and termination rights of the supply contract are therefore at least as important as its price; how such contracts are structured is described in Understanding PPAs: how power purchase agreements make solar park revenues predictable.

Some aspects of supply within the building are settled. Electricity tax does not apply to electricity from a renewable installation of up to two megawatts if it is supplied to final consumers in spatial proximity to the installation (Sec. 9 (1) no. 3 (b) StromStG); the ordinance sets the radius at 4.5 kilometres (Sec. 12b (3) StromStV), and for solar installations of up to one megawatt the required permit is deemed generally granted (Sec. 10 (2) no. 1 StromStV). Anyone supplying on site in this way is, subject to further conditions, not a supplier within the meaning of electricity tax law (Sec. 1a (5a) StromStV). The notification as an energy supplier under Sec. 5 EnWG applies only to supplying household customers, not a commercial business.

What remains open is the classification of the line. Until now, supply within a building usually ran through a Kundenanlage, a customer installation that does not count as a regulated energy supply network (Sec. 3 no. 65 EnWG). Following a judgment of the Court of Justice of the European Union of 28.11.2024 (C-293/23), the Federal Court of Justice ruled that only an energy installation that is not a distribution network can be a Kundenanlage, and that what matters for a distribution network is sale to final customers, not size (BGH, order of 13.05.2025, EnVR 83/20). The case concerned line systems supplying hundreds of flats. Whether the reasoning also covers a single commercial customer in the same building was not decided. For customer installations connected by 23 December 2025, the rules of network regulation apply only from 1 January 2029 (Sec. 118 (7) EnWG); there is no transition period for those connected later.

For the investor this means: they should know on what legal basis the supply to the roof user runs, for example as a direct line connecting a single production site with a single customer (Sec. 3 no. 27 EnWG), and who bears the risk if the line is later classified as a network. Energy sharing under Sec. 42c EnWG is no way out: among other things it requires that operating the installation does not predominantly serve a commercial activity of the operator, and a direct investment run as its own business does not meet that condition.

What is left of the revenue if the electricity customer is gone?

Until the end of the year not much; from the following year considerably more, if the operator switches to full feed-in. Systems on buildings have their own anzulegende Werte (reference values) in the German Renewable Energy Sources Act (EEG), and the law distinguishes two modes of operation. In partial feed-in, part of the electricity is consumed on site and the rest is fed in; in full feed-in all electricity goes into the grid, and the reference value rises in return (Sec. 48 (2a) EEG). For commissioning between 1 August and 31 December 2026, the Federal Network Agency lists 5.84 cents per kilowatt hour for the capacity share above 40 kW in partial feed-in, and in full feed-in 8.85 cents up to 400 kW and 7.63 cents above. The values apply pro rata to the capacity in each band (Sec. 23c EEG); for a 500 kWp system this gives 5.96 and 9.00 cents. Above 100 kW there is no fixed feed-in tariff, only the market premium in direct marketing (Sec. 21 (1) EEG); how it is derived from the reference value is explained in Direct marketing and the market premium: how a solar park earns its money.

The switch is possible every year, but not immediately. Full feed-in must be notified to the grid operator in text form before 1 December of the previous year and then applies for the whole calendar year (Sec. 48 (2a) sentence 1 EEG). As long as electricity goes to the roof user, it is excluded, because it requires feeding in all electricity except the system's own consumption. If the customer leaves in February, the system runs in partial feed-in without a buyer until the end of the year; if they leave in early December, it is thirteen months. The table shows what that means in our example calculation.

Two results matter when checking an offer. First, the real risk of losing the customer lies in the transition: whoever notifies the switch to full feed-in in time loses a tenth of the revenue in our example over the long run, not four tenths. Second, the customer contributes less than the on-site price suggests. Measured against full feed-in, supplying the roof user only pays off from around 10.1 cents per kilowatt hour under our assumptions. A prospectus that calculates with an on-site price just above that has hardly any advantage over a system with no customer at all, yet carries the customer risk.

A third point is already in the figures. In periods with a negative exchange price, the reference value falls to zero (Sec. 51 (1) EEG), without exception for systems of 100 kW and more. At 2025 prices, a quarter of our example system's yield fell into such hours. Electricity the roof user consumes in those hours is not affected; in full feed-in it is all of the electricity. By our calculation Sec. 51 costs around 4,000 euros a year with the customer and around 10,100 euros in full feed-in. Sec. 51a EEG later offsets part of this by extending the support period, for solar systems by half of the affected quarter hours. More on negative prices in Negative electricity prices: what they mean for solar and storage investors.

From what size does a rooftop system need a tender award?

From an installed capacity of more than one megawatt. Rooftop systems of this size receive the market premium only with an award from the second segment of the solar tenders, which is reserved for systems on buildings and noise barriers. The statute now contains a threshold of 750 kilowatts (Sec. 22 (3) sentence 2 no. 1 (a) EEG). It may only be applied after state-aid approval, however (Sec. 101 (1) EEG), and until then the version of 15 May 2024 applies. The Federal Network Agency therefore still only accepts bids from 1,001 kilowatts. The draft EEG 2027 intends to actually introduce the 750 kilowatts.

The figures of the last five bidding dates show a segment in which supply is scarce. We compiled them from the award announcements and statistics of the Federal Network Agency.

In three of the five rounds less was bid than tendered, and in a fourth the volume left after excluding inadmissible bids did not fill the tender. Consistent with this, the average award value rose from 9.10 to 9.72 cents while the ceiling fell from 10.40 to 10.00 cents. For due diligence this means two things. An award value close to the ceiling is no sign of particular negotiating skill in this segment; it matches the last rounds. And a rooftop system with an award earns considerably more per kilowatt hour than one just below the threshold with a statutory value, but carries the obligations and deadlines of the tender. The next round follows on 1 October 2026 with 296 megawatts and a ceiling of 10.00 cents; the draft EEG 2027 provides for 1,500 megawatts a year and a ceiling of 9.9 cents from 2027.

Why doesn't the building owner run the system themselves?

One obvious reason is tax, and the answer tells the investor something about the stability of the roof contract. If the building belongs to a company that only manages its own real estate and uses the extended deduction for trade tax for that purpose, it may sell electricity alongside only within narrow limits. Revenue from supplying electricity from renewable energy is harmless as long as it does not exceed 20 percent of the rental revenue, and it may supply final consumers only if they are its tenants (Sec. 9 no. 1 sentence 3 (b) GewStG; until 2022 the limit was 10 percent). If the limit is exceeded, the extended deduction is lost entirely. By letting the roof to a third party, the owner avoids that risk altogether, and the fee counts as rental revenue.

For the investor, a lessor with a tax motive is a good lessor: they have their own lasting interest in the contract running and in having nothing to do with the operation. Other reasons are less reassuring. An owner who lets the roof go because they know its condition, or who wants to sell the building soon, shifts risks to the investor. The question of the reason therefore belongs in every conversation about a rooftop system, together with the age of the roof membrane. How trade tax works on the investor's own side is described in Trade tax on PV and storage direct investments: how much of it actually sticks.

Does the same tax treatment apply as for a ground-mounted solar park?

Yes, as soon as the system exceeds the limits for small rooftop systems, and a system on a commercial hall normally does. The income tax exemption under Sec. 3 no. 72 EStG applies only up to 30 kWp per residential or commercial unit and a total of at most 100 kWp per taxpayer. A system of several hundred kilowatts on a hall is above that; its income is taxable, and all deductions are available. The zero VAT rate applies only to systems on residential buildings and on public and other buildings serving the common good (Sec. 12 (3) no. 1 UStG); a commercial hall is not one of them. The investor therefore acquires the system with 19 percent VAT and deducts it as input tax. Depreciation, special depreciation and the investment deduction follow the same rules as for a solar park; the details are in Deducting photovoltaics from tax: when depreciation and the §7g deduction still work and VAT on PV and storage direct investments: why 19% is charged here, and how it flows back.

Which questions should you ask the provider?

• Does the contract describe the system as a Scheinbestandteil, is removal at the end of the term agreed, and is it a system mounted above the roof or a roof-integrated one?
• Is an easement registered, for whom and at what rank, and has the building owner's bank declared the subordination?
• Is the roof-use contract concluded in text form, and does it run at least as long as the system?
• How old is the roof membrane, is there a condition survey and a structural check with a stated reserve?
• Who pays for dismantling and reinstallation during a roof renovation, how long may the interruption last, and is the loss of yield compensated?
• Who supplies electricity to whom, over which line, and on what legal basis does the supply within the building run?
• How long does the supply contract with the roof user run, and is the prospectus also calculated without them in full feed-in?
• Is the system above one megawatt, and if so: is there an award, and at what value?
• Why doesn't the building owner run the system themselves?
• Which insurance pays in the event of a fire in the building, and who is liable if the system caused it?

A provider who answers these questions with documents has thought the construction through. Further warning signs are collected in How to tell a trustworthy provider of energy direct investments, and the other checkpoints of a direct investment in photovoltaics are shown in Investing in solar parks: revenues, costs and tax leverage at a glance.

How we check rooftop systems in our project review

For a rooftop system we check the building first and the system second: land register extract with ranks, roof-use contract, age and condition of the roof membrane, statics. We calculate the revenue twice, with the electricity customer and without them in full feed-in, and disclose how large the gap is and how long the transition can last. If the system is above one megawatt, we check the award. We always ask why the owner leases the roof. We do not give return promises. If you would like a specific offer reviewed, you can bring it to a non-binding initial consultation.