STORAGE · BESS
Battery storage (BESS) business plan: the financial model
Practical guide · ~9 min read
A battery storage (BESS) project does not "produce" energy: it buys, stores and resells, and provides services to the grid. Its business plan therefore rests on a different revenue logic from a solar plant.
1. Revenue stacking
- Arbitrage: charge when the price is low, discharge when it is high (market spread).
- Ancillary / reserve services: payment for the flexibility provided to the grid.
- Capacity mechanisms: depending on the schemes in force.
The value of a BESS = the sum of these sources, which vary with the market and regulatory change — hence the importance of testing scenarios.
2. The technical parameters that drive value
- Power (MW) and energy (MWh) → the battery's "duration" (e.g. 2h, 4h).
- Round-trip efficiency (cycle losses) and number of cycles.
- Degradation of capacity over time (and the replacement / augmentation strategy).
3. CAPEX, OPEX and life
The CAPEX is often expressed in €/MWh installed; the OPEX covers operation, possible capacity augmentation and warranties. The useful life is shorter than PV and depends heavily on usage (cycles).
4. PV + BESS hybridisation
Pairing storage with a solar plant (see self-consumption) allows you to shift injection, smooth generation and share the grid connection — often a better risk/return pair than a standalone asset.
5. Financing and returns
As market revenue is more volatile, financing is more prudent (lower gearing, contracted revenue where possible). The project is evaluated with the same metrics: IRR, NPV, DSCR.
6. Why a BESS is harder to finance
Unlike a plant under a PPA, a "merchant" BESS lives on volatile, uncertain market revenue over 10-15 years. Lenders are therefore more cautious: lower gearing, higher DSCR requirement, and a preference for contracted revenue. Tolling (a third party leases the battery's capacity for a fixed fee) or a floor guaranteed by an aggregator turn part of the merchant revenue into predictable revenue — which unlocks more debt, at the cost of a cap on the upside.
7. Modelling a revenue, not a generation
The modelling difficulty of a BESS is that there is no stable "yield": revenue depends on a dispatch strategy (when to charge/discharge) against uncertain future prices. A credible business plan relies on prudent revenue curves (often from specialised simulations), models degradation and cycles, and tests several market-spread scenarios. This is typically a case where a spreadsheet quickly reaches its limits against a dedicated financial model.
FAQ
Where does a storage battery's revenue come from?
From a stack of sources (revenue stacking): arbitrage (buy electricity when cheap, sell when expensive), ancillary / reserve services to the grid, and sometimes capacity mechanisms. The mix depends on the market and the configuration.
Why is degradation key for a BESS?
A battery loses capacity with cycles and time. The business plan must model this degradation (and any replacements / capacity augmentation) because it reduces revenue and value over time.
What does PV + BESS hybridisation add?
Pairing a solar plant with a battery smooths generation, raises self-consumption, shifts injection to high-price hours and shares the grid connection — often more value than a standalone asset.
What is tolling for a battery?
Tolling is a contract by which a third party (often a market player) leases the battery's capacity and controls its charge/discharge, paying the owner a fixed fee. It turns volatile merchant revenue into contracted, predictable revenue, which improves bankability at the cost of capped upside.
How is the cost of a BESS expressed?
Often in €/MWh of installed energy (capacity), sometimes in €/MW of power. The battery's "duration" (power / energy, e.g. 2h or 4h) is decisive: it conditions the possible uses and therefore the accessible revenue.
PUT IT INTO PRACTICE
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P50/P90 generation, offtake contracts (feed-in, PPA, merchant), debt, taxes, NAV valuation — from a single asset to the consolidated portfolio, with bankable figures.
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