Revenue Assessment
Revenue Assessment for Battery Storage
A battery storage system does not generate electricity. Its revenue comes from shifting energy in time and from providing ancillary services. An assessment based on generated volume, which is what a yield assessment provides for PV plants, cannot be applied to a storage system.
Revenue depends on how the system is operated and how its capacity is marketed. Technically identical systems at the same grid connection point can therefore achieve different results. We assess the expected revenue with time resolution, in a scope agreed for the question at hand.
Frequently Asked Questions on Revenue Assessments
A revenue assessment sets out the revenue an asset can be expected to earn over its service life. For battery storage this covers trading on the power markets, the sale of balancing capacity and the interaction with a connected generation asset. The result is stated in euros.
A yield assessment determines a generated volume. A storage system does not generate energy; it absorbs and releases it. What matters are price differences and ancillary services, and these are not the subject of a yield assessment.
Typically trading on the day-ahead and intraday markets and the sale of balancing capacity. For storage at a generation asset, the absorption of energy that would otherwise be curtailed or exported without payment is added. Which streams are covered depends on the project.
Because they compete for the same capacity. Power held in reserve for balancing services is not available for trading in the same period. Adding the individual figures overstates the result.
Where the manufacturer’s data allows, yes. Capacity loss depends on cycle count and operating regime, and supply contracts usually include warranties on this. An operating regime with high short-term revenue can be disadvantageous over the full service life.
We obtain price forward curves from a provider specialising in power market forecasts. Alternatively we work with scenarios supplied by you or your lender. The curve used and its vintage are stated in the report.
Yes. Often a revenue model prepared by the developer or a trading partner already exists. We check the assumptions it makes against the technical side and state which of them hold and which do not.
Location and grid connection point, power rating and capacity of the system, and the data sheet stating round-trip efficiency and cycle warranties. For a connected generation asset, its layout as well; for existing installations, operating data from previous years. Missing information can be replaced by assumptions, which are disclosed in the report.
Both depend on the scope. Send us a short description of the project and we will provide a quotation.
Typical Situations
Revenue assessments for storage are usually needed for financing, for sizing decisions or for transactions.
Project financing
Storage projects have no fixed feed-in tariff to fall back on. Lending banks therefore require a traceable revenue projection as the basis for their credit decision.
Sizing
Power rating and storage duration determine achievable revenue. Sizing options can be compared against each other under identical assumptions.
Storage at a PV plant
Where generation and storage share a grid connection, they affect one another. The assessment then covers the combined installation.
Acquisition and sale
The revenue assumed largely determines the purchase price. An independent assessment gives both sides a common basis for negotiation.
Possible Components
There is no standard definition of a revenue assessment, and the scope offered differs between providers. What makes sense in a given case depends on the purpose and on the data available, and is agreed beforehand. Depending on the question, this may include:
- Revenue streams reported separately: trading on the day-ahead and intraday markets, and the sale of balancing capacity.
- Interaction between the revenue streams, which compete for the same capacity and whose individual figures therefore cannot simply be added up.
- Backtesting on historical price data: this shows what revenue would have been achievable in past years and needs no forecast.
- Forward calculation on price forward curves, which we obtain from a provider specialising in power market forecasts. Alternatively we use scenarios supplied by you or your lender. The curve used and its vintage are stated in the report.
- Cycling and degradation: capacity loss as a function of cycle count and operating regime, as far as the manufacturer’s data allows.
- Round-trip efficiency and auxiliary consumption of the system over its service life.
- Storage at generation assets: shared grid connection, export limits, and whether charging from the grid is permitted.
- Hours of negative prices and the effect of Section 51 EEG on a connected generation asset.
- Ranges and sensitivities on the key assumptions.
- Financial metrics, if required and if the necessary cost and financing data are available.
- Review of existing revenue models prepared by third parties: we check their assumptions against the technical side and state where they hold and where they do not.
Simulation-Based Storage Sizing
Before the revenue question comes another one: how large should the system be? Power rating and storage duration determine achievable revenue, capital expenditure and the requirements placed on the grid connection. Once ordered, none of this can be changed.
We compare sizing options under identical assumptions: different combinations of power and capacity, with and without coupling to a generation asset, and where useful across different marketing routes. The result shows the point beyond which additional revenue no longer covers the additional cost.
We prepare this work for community energy cooperatives and utilities, among others. It can stand on its own or serve as a first step towards a revenue assessment; the calculations are the same.
Price Spreads as the Basis for Revenue
A storage system earns its trading revenue from price differences within a single day. These differences have widened as photovoltaic capacity has grown. In 2025 the annual capture price for solar in Germany was 4.508 ct/kWh, while the average spot price was 8.932 ct/kWh.
How spreads develop from here depends on the build-out of generation and storage capacity and on fuel prices, and carries considerable uncertainty. Extrapolating today’s figures across the entire service life is not defensible.
We therefore work with several price scenarios and state their source and vintage, rather than presenting a single curve as settled. For storage projects the range of outcomes is part of the result, not a weakness of the calculation.
Negative Prices and Section 51 EEG
By the end of October 2025 Germany had seen 576 hours of negative exchange prices. In those hours a storage system can absorb energy and be paid for doing so.
Under the Solarspitzengesetz of February 2025, new installations lose their remuneration under Section 51 EEG from the first quarter-hour of negative prices; the previous grace period of three consecutive hours has been removed. Section 51a EEG provides for the forgone remuneration to be made up month by month at the end of the twenty-year support period.
A storage system at the same grid connection point can absorb energy that would otherwise be exported without payment or curtailed. How much that amounts to depends on the sizing.
Revenue Assessment or Yield Assessment?
A yield assessment determines the energy a photovoltaic plant will produce in kilowatt-hours, including losses and the confidence level of the forecast. A revenue assessment evaluates what revenue that generation, and the operation of a storage system, can be expected to earn.
For photovoltaic plants on a feed-in tariff, a yield assessment is usually sufficient. For storage it does not apply, because there is no generated volume. The two can build on each other: an existing yield assessment can serve as the basis, including one prepared by another author.
Your Contact
Dr.-Ing. Stefan Bofinger
Stefan Bofinger has worked as an expert for photovoltaics since 2002 and advises investors and banks on project development as an independent consultant. He holds a doctorate on power grids with a high share of photovoltaic generation, focusing on site assessment, solar power forecasting and grid integration.
Phone +49 (0) 4103 121 4221
Email kontakt@sonnwinn.de