Existing solar park or new build: what changes when the plant is already running?

The offer often reads like this: ground-mounted plant, connected since 2019, measured yields available, lease and direct marketing in place, the current operator wants to sell. Next to it sits a new build that will connect next year and until then consists of drawings, a yield report and a payment schedule. Which of the two direct investments is the better one? The answer depends on fewer things than you might think, and on different ones than most offer documents put up front.

So we have taken apart, one by one, the properties that change hands with the plant: the applicable value (anzulegender Wert), the commissioning date and the negative-price rule attached to it, the remaining term, the condition of the equipment and the contracts. The result is an own calculation for three plant generations and a checklist that looks different for a running plant than for a new build.

What distinguishes a running plant from a new build from the investor's point of view?

The plant has a past, and that past determines its future. With a new build, the award of the Federal Network Agency (Bundesnetzagentur) sets the tariff, commissioning starts the 20 years, and every contract is concluded for the investor. With a running plant, all of that happened long ago: the rate is fixed, the clock has been running for years, the contracts were negotiated with another operator, and the equipment has an age. The investor acquires not only modules and inverters but a legal position with a fixed expiry date.

Which EEG rules stay with the plant when the operator changes?

All of them. The EEG ties its rights to the plant, not to the person: the plant operator is whoever uses the plant, "irrespective of ownership" (§ 3 no. 2 EEG), and the applicable value is the value the Federal Network Agency determined in the award or the value the law sets for the commissioning year (§ 3 no. 3). Commissioning is the first putting into operation of the plant; replacing modules or inverters does not change it (§ 3 no. 30). Whoever takes over a running plant therefore steps into exactly the payment the previous operator had, with the same start date. The 20 years under § 25 (1) EEG continue, they do not restart; for plants with a statutory value until 31 December of the twentieth year, for awarded plants to the day. How commissioning and degression work in detail is explained in the article Commissioning date of a solar park.

The plant also carries its version of the law with it. For plants commissioned before 2023 or awarded before 2023, the EEG as of 31 December 2022 continues to apply (§ 100 (1) EEG); for plants commissioned or awarded between 1 January 2023 and 24 February 2025, the version as of 24 February 2025 (§ 100 (46)). Only plants commissioned since 25 February 2025 fall under today's § 51: every quarter-hour with a negative spot price reduces the applicable value to zero, and in return § 51a extends the payment period, for solar plants by half of the affected quarter-hours as a full-load quota. Older plants have neither the strict rule nor the extension. The transitional rule in § 100 (47) even allows plants without a negative-price rule to switch voluntarily into the new system; a case that is rarely favourable in practice.

This ladder is the real difference between plant generations. The EEG 2014 introduced the rule: payment lapses only when the price is negative for six consecutive hours, and expressly not for plants commissioned before 1 January 2016 (§ 24 (1) and (3) EEG 2014). The EEG 2021 shortened it to four hours for plants of 2021 and 2022, the EEG 2023 set a staircase: four hours in 2023, three hours in 2024 and 2025, two hours in 2026, one hour from 2027. Since 25 February 2025, every quarter-hour counts for new plants. We counted what that would have meant for a sample plant in Lower Saxony in the 2025 price year.

The jump from "six hours" to "every quarter-hour" costs around nine percentage points of annual yield in the 2025 price year; from four hours downwards the difference is small, because negative prices in summer 2025 mostly came in long blocks. Two things belong with this table. First: whoever curtails in the affected hours loses the payment, but no more than that; whoever feeds in pays the negative price. Second: for new plants, § 51a appends half of the lost quarter-hours at the end, shifted by 20 years. How negative prices arise and what a battery next door changes is explained in the article Negative electricity prices: what they mean for solar and storage investors. Then comes the next cut: the draft EEG 2027 changes the market premium for plants from 2027, existing plants keep their system; the details are in the article EEG 2027: what the refinancing contribution means for a solar park direct investment.

Formally the change is unspectacular: the new operator registers the change of operator in the Market Master Data Register (Marktstammdatenregister) within one month (§ 7 (1) MaStRV), the grid operator switches the settlement, the direct marketer is taken over contractually or newly appointed. What does not work: "converting" an old plant to today's law to obtain the higher ceiling price or the extension under § 51a. The generation stays.

What is a running plant worth per kilowatt compared with a new build?

That depends above all on the product of tariff and remaining years, less on the age of the modules. We ran three plants of the same design at the same site and determined the present value of the remaining EEG years per kilowatt, each from the perspective of an acquisition in 2027. The new build receives the weighted award value of the round of 1 July 2026 and the full term, but the quarter-hour rule. Plant A comes from the tender round of 1 October 2018 at 4.69 cents, was commissioned in 2019 and has twelve years left under the six-hour rule. Plant B connected in 2014 at the then statutory value of 9.23 cents, has no negative-price rule and eight years left until the end of 2034.

Three observations. First: plant A earns more per kilowatt today than a new build, because the six-hour rule saves it nine percentage points of yield. Nevertheless it is worth only about three quarters as much per kilowatt, because eight of its twenty years are gone. Second: plant B, with eight years left, is the shortest position and at the same time the most valuable, because 9.23 cents without a negative-price rule bring in almost twice the new-build revenue. Third: a price per kilowatt that would be appropriate for a new build is too high for plant A and possibly too low for plant B. The purchase price of a running plant should therefore never be benchmarked against the new-build price per kilowatt, but against the present value of its remaining years.

What is missing from this calculation, deliberately: continued operation after the EEG. A plant from 2014 will in 2035 have modules with a performance guarantee until about 2039 and a grid connection that remains usable. Valuing this residual conservatively or not at all is the line we recommend for new builds too; what is possible afterwards is in the article A solar park after 20 years: continued operation, repowering or decommissioning?. Also not included: the discount a seller under time pressure accepts, and the premium a buyer pays for clean data. Both are negotiation variables, not model variables; the seller's side of that negotiation is described in the article Selling a direct investment early: how liquid an energy direct investment really is.

Does the operating history replace the yield report?

Partly, and that is the strongest advantage of a running plant. A yield report estimates before construction what a plant will deliver on average; the settlements of the grid operator and the direct marketer show what it actually delivered. Three to five years of measured yield say more about shading, soiling, availability and the quality of the installation than any simulation. What a report delivers and where its limits lie is explained in the article Reading a yield assessment: what P50 and P90 mean for a solar park direct investment.

Measured years are not 20 years, though. The 2025 irradiation year was 9.4 percent above the long-term average according to the German Weather Service, 2021 below it; whoever uses the history has to correct each annual figure for that year's weather, for instance with the irradiation data of the German Weather Service or a free irradiation database for the coordinates. Only the weather-adjusted specific yield in kilowatt-hours per kilowatt is comparable with the original P50 value. If it is consistently below, the plant has a problem that belongs in the purchase price; if it is above, the seller's report should not simply be extrapolated.

1. Annual yields in kilowatt-hours per kilowatt for every full operating year, from the settlements, not from the monitoring portal.
2. Weather adjustment per year; the trend across years shows the actual degradation, the spread between years the weather risk.
3. Availability and fault list: how many days did which part of the plant stand still, and why?
4. Curtailments by the grid operator and the compensation paid for them; if interventions cluster, the grid area is tight (article Curtailment of a solar park: when the grid operator pays and when it does not).
5. Maintenance records, thermography and the last inspection of the electrical installation; if they are missing, that is information in itself.
6. Direct marketer settlements with market value, market premium and lost hours, to see the plant's negative-price rule in real numbers.

How old may a plant be that you take over?

Older than many think, as long as two things are in the price: the inverter replacement and the missing warranty. Modules lose between 0.15 and 0.5 percent of output per year according to the measurement series of recent years; a plant from 2019 therefore still delivers around 96 to 99 percent of its initial output in 2027, and that is already included in our present-value calculation. The inverter, on the other hand, is replaced between the tenth and fifteenth operating year according to experience. Whoever takes over a plant in its eighth year buys this item with it; whoever takes over one from 2014 should know whether the replacement has already happened. Figures, guarantee lines and the tax treatment of the replacement are in the article Module degradation and inverter replacement: what ages in a solar park and what it means for returns.

The second point is legal. With a new build, the builder is liable for defects, and the manufacturer guarantees start on the day of delivery. When buying a used plant, sales law applies: claims for defects become time-barred two years after handover (§ 438 (1) no. 3 BGB), and in practice purchase contracts for used plants largely exclude liability. § 444 BGB draws the line: the seller cannot rely on an exclusion if he fraudulently concealed a defect or gave a guarantee of quality. It therefore pays to write assurances about condition, yield and freedom from faults into the contract as agreed quality, rather than leaving them in the offer document. Manufacturer guarantees for modules and inverters are often tied to the first buyer or require notification of the change of ownership; whether they transfer is in the guarantee terms, not in the purchase contract.

Insurance, by contrast, transfers by law: if the insured object is sold, the buyer steps into the contract (§ 95 VVG). Both sides may then terminate, the insurer with one month's notice, the buyer immediately (§ 96 VVG). For the buyer this means: check the policy, sums insured and deductibles, but above all request the claims history of recent years, because storm and hail damage with partial repairs is otherwise invisible in the yield history. What a policy for ground-mounted plants should cover is in the article Insuring a solar park or battery storage asset: which policies belong to a direct investment, and who holds them.

Which contracts transfer with the plant, and which do not transfer by themselves?

Only the building permit and the insurance change holder automatically; everything else needs an agreement. Building permits apply for and against the legal successor (for instance Art. 54 (2) sentence 3 of the Bavarian Building Code; the other state building codes contain the same sentence), with all conditions, including the decommissioning obligation. The decommissioning security the previous operator deposited with the municipality, however, is transferred to the new operator or newly provided; whoever overlooks this provides it twice or not at all (Decommissioning a solar park: who pays, how large the bond is and what it costs).

The land lease does not transfer automatically. The buyer either steps into the existing contract with the landowner's consent or becomes a subtenant of the previous operator, a markedly weaker position. The limited personal easement (beschränkte persönliche Dienstbarkeit) in the land register is transferable only if it belongs to a legal entity or partnership for operating an energy plant (§ 1092 (3) BGB); otherwise it has to be newly registered. Both, the entry clause and the easement, are explained in the article 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.

Grid connection and feed-in contracts are contracts with the grid operator; taking them over is a contract assumption that needs its consent (§ 415 (1) BGB for the debt side). In practice grid operators consent, but demand complete documents and registration of the change of operator. The direct marketing contract has a term and usually a clause on the change of operator; whether the buyer has to continue it or can put it out to tender again decides marketing fees and flexibility. The operation and maintenance contract, finally, is freely negotiable; with older plants in particular it is an opportunity to reset availability commitments and response times.

What stands in this place for a new build is the construction-phase risk: payments before completion, transfer of ownership only after acceptance, insolvency of the builder. The running plant has this risk behind it; it is the one point where it is clearly superior to the new build. Which safeguards take its place for a new build is shown in the article Provider or operator insolvency: what happens to your direct investment.

What changes for tax when the plant is used?

Less than often assumed, and in one respect in the buyer's favour. The investment deduction under § 7g (1) EStG requires a depreciable movable fixed asset, not a new one; the Federal Ministry of Finance letter of 15 June 2022 says so expressly in paragraph 6: "for new or used" assets. The same applies to the special depreciation of up to 40 percent under § 7g (5) and to the declining-balance depreciation under § 7 (2) EStG for acquisitions between 1 July 2025 and 31 December 2027. All requirements, the profit limit of 200,000 euros, use in a domestic permanent establishment, the retention period, apply unchanged; they are in the article Investitionsabzugsbetrag: all §7g EStG requirements, and who can use it.

What differs is the depreciation period. For new photovoltaic plants, the official depreciation table names 20 years; it is expressly a reference point for the ordinary useful life (§ 7 (1) sentence 2 EStG). Whoever acquires a plant in its eighth operating year does not depreciate the purchase price over 20 years, but over the expected remaining useful life, which has to be estimated and justified, for instance with the term of the performance guarantee and the condition of the plant. Twelve or 15 years instead of 20 means a higher annual depreciation on the same purchase price. This includes allocating the purchase price to modules, inverters, mounting structure, grid connection and, where applicable, prepaid lease; each item has its own useful life, and the inverter becomes maintenance expense after replacement anyway.

For VAT, acquiring a running plant with its contracts is usually a transfer of a going concern (Geschäftsveräußerung im Ganzen): not taxable, no VAT on the purchase price and no input tax deduction, the buyer steps into the seller's position (§ 1 (1a) UStG). He thereby also takes over the running correction period under § 15a UStG, and the seller is obliged to give him the information needed for it (§ 15a (10) UStG). The details are in the article VAT on PV and storage direct investments: why 19% is charged here, and how it flows back. For trade tax, the business is deemed discontinued by the seller and newly founded by the buyer when it is transferred as a whole (§ 2 (5) GewStG); trade losses of the previous operator are therefore of no use to the buyer, and the new business is registered with its own municipality.

Which documents belong on the table before signing for a running plant?

More than for a new build, because they already exist. Whoever does not receive them has their answer. The list is deliberately about documents, not assurances.

1. Extract from the Market Master Data Register with commissioning date, registered operator and capacity; plus commissioning protocol and the award notice of the Federal Network Agency or the grid operator's tariff confirmation.
2. Settlements from grid operator and direct marketer for at least three full years, with market value, market premium and lost hours.
3. Monitoring export per inverter and fault list with downtimes.
4. Maintenance records, thermography, last inspection of the electrical installation, proof of cleaning and mowing.
5. Age, type and guarantee status of the inverters; module guarantees including the transferability clause.
6. Land lease with term, entry or transfer clause, landowner's consent; land register extract with easement and its beneficiary.
7. Grid connection and feed-in contract, grid operator's consent to the takeover, proof of grid connection capacity.
8. Direct marketing contract with term, fee and provision for the change of operator.
9. Insurance policy with cover and deductible plus the claims history of the last five years.
10. Building permit with all conditions, decommissioning obligation and proof of the deposited decommissioning security.
11. Information under § 15a UStG on the running correction period and the VAT classification of the sale.
12. Open items: outstanding compensation for curtailment, ongoing warranty cases, disputes with grid operator, landowner or neighbours.
13. Draft purchase contract with quality assurances on yield, condition and freedom from encumbrances, and a provision on who receives the revenue up to the handover date.

Plus three questions for the provider that the previous operator must be able to answer: why is it being sold? Which years were below the yield report, and what was the reason? And which investments are due in the next three years that are not yet visible in the history? Whoever answers the first question with "portfolio streamlining" and the third with "none" has not answered the two difficult questions.

How we check a running plant and a new build

With the same calculation but different inputs. For the running plant we replace the yield report with the weather-adjusted yield history, apply the negative-price rule of its generation to real settlements and value the present value of the remaining years without residual value after the EEG; then we put the purchase price next to it, not the price per kilowatt of a new build. For the new build we check the yield report, the payment schedule and the safeguards for the construction phase. In both cases we go through the contracts for transfer and entry and coordinate the tax points with your tax adviser before you sign. That is exactly what we do in a non-binding initial consultation; we give no return guarantees in the process, neither for old nor for new plants.