Solar system yields too little output
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Your rights in case of reduced yield and incorrect profitability calculations
What owners can do if electricity yield and savings consistently fall short of the forecast.
Is your solar system generating significantly less electricity than promised, or are the savings falling far short of your calculations? Then you may have warranty rights or claims for damages due to incorrect advice. Rogert & Ulbrich compares forecasts, contracts, and actual yields and enforces your claims against the seller, installer, or broker.
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3When a lower yield becomes legally relevant
Every photovoltaic system delivers different yields from year to year. Sunshine hours, temperature, and snow cover cause natural fluctuations that you have to accept. A shortfall in yield becomes legally relevant if the system consistently and significantly falls short of what was contractually agreed upon or what a professionally planned system at that location typically produces.
For an initial assessment, compare your actual annual yield with the forecast from the offer. The specific yield, i.e., the kilowatt-hours generated per kilowatt peak of installed capacity, is particularly meaningful. Freely accessible tools such as the EU's Photovoltaic Information System (PVGIS) provide site-specific reference values. If your yield is significantly lower than projected over several months, a more detailed examination is warranted.
Has your yield been below forecast for months? Secure your monitoring data now before it's lost.
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Earnings forecast and profitability calculation: What the seller owes
Many systems are sold based on a profitability calculation. This calculation includes assumptions about electricity yield, self-consumption rate, electricity price trends, feed-in tariff, and amortization period. Whether this information is legally binding depends on its wording. If a specific yield was agreed upon as a characteristic of the system, a significant shortfall constitutes a defect (§ 434 para. 2 BGB, § 633 para. 2 BGB).
Even if the forecast is not formulated as a firm commitment, the provider is not without consequences. Anyone who bases a sale on a calculation must prepare it with due diligence. If it is based on unrealistic or incorrect assumptions, claims for damages due to breach of pre-contractual obligations may be considered (Sections 280 Paragraph 1, 311 Paragraph 2, and 241 Paragraph 2 of the German Civil Code). If you were deliberately deceived, you may also be able to contest the contract (Section 123 of the German Civil Code).
For installations commissioned since February 25, 2025, the regulations of the Solar Peak Act apply. Without a smart meter and control box, in many cases only 60 percent of the installed capacity may be fed into the grid. Feed-in tariffs cease when electricity prices on the exchange are negative, as soon as a smart metering system is installed. A profitability calculation that ignores these limitations may be flawed.
Do not sign any settlement agreement until the calculation has been reviewed.
The math doesn't add up? Have your supplier's calculations checked to see if they were incorrect from the start.
Typical causes for insufficient electricity yield
A lower yield almost always has a specific cause. Often it is due to planning or execution errors attributable to the supplier:
- Shading: Trees, dormers, chimneys or neighboring buildings were not taken into account or were incorrectly considered during the planning.
- Orientation and tilt: The modules are poorly aligned, even though the forecast assumed optimal conditions.
- Low-performing modules: Individual modules may underperform due to microcracks, hotspots, or manufacturing defects.
- Incorrect sizing: Inverter or string planning is not suitable for the module power output, the system is unnecessarily throttled.
- Storage without power: The battery storage system does not reach the agreed capacity, and self-consumption remains low.
- Faulty configuration: Feed-in limitation, energy management or monitoring are incorrectly configured.
- Other components: Instead of the offered brand-name products, components with inferior performance values were installed.
A lower yield often indicates a defect that can be remedied. Have the cause investigated before the warranty expires.
Your claims in case of reduced yield
Your rights depend on the cause and the type of contract. If the reduced yield is due to a defect, you must first give the supplier the opportunity to remedy the situation, for example by replacing defective modules, revising the design, or replacing the inverter.
If the subsequent performance is unsuccessful, you can reduce the price in proportion to the diminished value or claim damages. Compensable expenses include, in particular, lost electricity revenue, higher grid electricity costs, lost feed-in tariffs, and expert fees. In the case of a significant breach of contract, rescission of the contract is an option: you receive a refund and return the system. If the problem stems from a carelessly prepared profitability calculation, you can also claim the difference between the promised and actual profitability as damages.
A minor defect does not entitle the buyer to rescind the contract (§ 323 para. 5 sentence 2 of the German Civil Code). Whether the threshold is exceeded depends on the extent of the defect and the cost of its rectification. A careful assessment is warranted to determine which legal option offers the greatest economic advantage.
Every month with lower yields costs you money. Have your situation reviewed to determine which claim would be most beneficial in your case.
This is how you prove the lower yield
In court, you must prove the discrepancy and its cause. Complete yield data is essential. Export the values from your monitoring system regularly and also record the meter readings. Many portals only store data for a limited time or are shut down if the provider becomes insolvent.
The cause can usually only be determined by an expert. Common methods include characteristic curve measurement, which determines the actual module performance, thermography to detect hotspots, and electroluminescence testing for microcracks. Independent proceedings for the preservation of evidence (§§ 485 et seq. of the German Code of Civil Procedure) are suitable for securing evidence admissible in court. This also suspends the statute of limitations for your claims (§ 204 para. 1 no. 7 of the German Civil Code).
Evidence can be lost quickly. Secure data and the condition of the system before third parties intervene.
What you should do now if your yield is too low
First, compare the offer, yield forecast, and profitability calculation with the actual figures. Export the monitoring data for the entire operating period and note the meter readings with the dates. Also, save brochures, emails, chat messages, and notes from the sales meeting, as these document what was promised to you.
Next, notify the supplier in writing of the reduced yield and set a reasonable deadline. At the same time, clarify whether the two-year or five-year statute of limitations applies to your system and when it began.
The warranty period runs regardless of whether the supplier responds. Act promptly.
FAQs – Frequently Asked Questions about the Reduced Yield of the Solar System
Rogert & Ulbrich – Your lawyers in solar law
Rogert & Ulbrich is a nationwide law firm specializing in the enforcement of consumer economic claims. The lawyers Dr. Marco Rogert and Tobias Ulbrich With their team, they have handled over 40,000 cases and filed more than 25,000 lawsuits. In solar law, they combine experience in sales and works contracts with an understanding of technical contexts and the sales practices of the solar industry.
We review your contract, offer, profit forecast, invoices, financing documents, and all previous correspondence. We pursue your claims against the seller, installer, manufacturer, financier, or insolvency administrator out of court. If necessary, we conduct independent evidence proceedings and file lawsuits. The entire process, from initial engagement to all correspondence, is fully digital; your online file is accessible at any time.
Is your solar system consistently producing less electricity than promised, or is the profitability calculation incorrect? Get in touch and protect your rights.
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