Financing a battery energy storage system for your company: investment, control and grants

A battery storage system can reduce certain power draws, increase solar self-consumption, secure a critical power supply or make it possible to monetise the site's flexibility. However, it is not a universal solution: profitability depends on the hourly consumption profile, contract tariffs, connection costs, round-trip efficiency, lifespan and the uses that can actually be controlled. Before seeking a grant, the company must therefore turn the idea of a battery into a measurable energy project, with several comparable technical and financial scenarios.

1. Define the service the battery must provide

Start by distinguishing the objectives. Self-consumption involves shifting part of the solar electricity produced during the day to later use. Peak shaving aims to reduce the power drawn during certain periods, when the contract or the grid makes those peaks costly. Backup power seeks to maintain critical functions during an outage, but requires a suitable architecture and should not be confused with storage connected to the ordinary grid. Finally, flexibility can allow an operator to aggregate the site's charging or discharging capacity. These services can be combined, but not always at the same time: a battery charged for backup is not necessarily available to arbitrage prices. The specification must prioritise uses, availability windows and business-continuity constraints.

2. Build a reliable energy baseline

Gather at least twelve months of invoices, load curves at as fine a time step as possible, the subscribed power, any overshoots, operating hours and solar production data. Identify atypical days, shutdowns, seasonality and planned changes in pace. An annual average can mask a brief power peak or, conversely, give the impression that a battery will be used when activity stops at night. The engineering firm must simulate charging and discharging over representative sequences, including losses, unavailability and ageing. Require the assumptions, source data and hourly results so the model can be recalculated if the electricity tariff changes.

3. Sizing power, capacity and duration of use

Power, expressed in kW, determines the amount of electricity the system can inject or absorb at a given moment. Usable capacity, expressed in kWh, determines the amount of energy that can be mobilised. A high-capacity but low-power battery will not necessarily solve a short peak; a powerful but low-capacity battery will only shift a limited amount of energy. Sizing must take into account the permitted depth of discharge, efficiency, temperature, degradation and the reserve required by the manufacturer. Request a guarantee of residual capacity and a clear definition of guaranteed performance, measured at the connection point and not only at the cell output.

4. Identify the expenses that make up the project

The budget goes beyond the price of the cells. It includes the feasibility study, the connection analysis, electrical cabinets, converters, the battery management system, the energy control system, protections, measurement equipment, slab and access works, any adaptation of the electrical substation, fire-risk detection and control, tests and training. Add the operating costs: maintenance, monitoring, insurance, energy losses, any replacement of components and end-of-life treatment. Separate the expenses essential to storage from those relating to a general electrical renovation, a separate solar plant or a building extension. This breakdown helps check the eligibility of each item without presenting the whole project as automatically eligible for a grant.

5. Identify the families of funding to test

Public grants for energy investment are often conditional on the nature of the beneficiary, the company's size, environmental performance, location and the existence of a call for projects. Standalone storage mainly intended to arbitrage prices is not equivalent to an energy-efficiency project or storage associated with renewable production. Review current national and regional programmes, territorial schemes and any calls for projects on flexibility, self-consumption or decarbonisation. Also ask the grid operator and market players about accessible flexibility mechanisms. The scheme must be checked in the version applicable at the time of submission: neither the presence of a battery nor its association with solar panels guarantees a grant.

6. Assess revenue and savings without double counting

Build a baseline scenario without a battery, then scenarios with different control profiles. Separately measure savings on purchased energy, any power-related savings, flexibility revenue and additional costs. The same unit of energy cannot simultaneously be counted as self-consumed, sold and mobilised for a grid service. Use the prices actually applicable to the company's contract and test several assumptions: a smaller price spread, faster degradation, fewer cycles, higher connection cost or system unavailability. The decision must remain acceptable under a cautious scenario, not only in an optimistic simulation from the supplier.

7. Compare purchase, leasing and service contracts

Purchasing ties up capital but allows the company to retain more control over the asset and its operation. Leasing or rental can spread the expense, with a total cost and maintenance clauses to compare. A storage-as-a-service contract can limit the initial investment, but remuneration, availability commitments, profit-sharing and exit conditions must be examined. Check who bears the performance risk, who owns the operating data, who is responsible for replacing modules, and how regulatory changes are handled. The financing structure must be consistent with the duration of the electricity contract, the property lease and the project's payback period.

8. Address safety, compliance and insurance

The application must cover electrical, thermal and operational risks. Have the technology, installation conditions, distances, ventilation, detection devices, emergency procedures, emergency-service access and separation from occupied areas or combustible materials specified. Requirements vary depending on the site's configuration, power, location and applicable regulations; they must be established by competent professionals and the relevant authorities. Consult the insurer before finalising the plan, as prevention requirements may change the cost. The supervision system must report alarms, log events and allow a controlled shutdown.

9. Build a verifiable grant application

Prepare a summary of the site and the need, invoices and load curves, the energy study, the electrical diagram, the itemised quote, the financing plan, savings calculations, performance indicators, permits and the timeline. Add the annual accounts, information on company size and the aid-cumulation declarations required by the scheme. Have the date from which expenses may be incurred confirmed in writing. An order, a deposit or the start of works can jeopardise the grant where the scheme requires a prior application. The exact conditions are those of the rules and the call for projects, not those of a general article.

10. Manage delivery and measure results

The contract must specify the expected performance, acceptance tests, liability limits, availability deadlines, the warranty, penalties and data handover. At commissioning, compare the measured usable power and capacity with the contractual values. Then monitor efficiency, cycles, residual capacity, maintenance costs and net savings. If a grant is awarded, keep invoices, proof of payment, photos, acceptance reports and required indicators for the required period. Environmental communication must be based on measured results: conversion losses and the origin of the charged electricity count in the balance.

11. Common mistakes and how to avoid them

The costliest mistakes are choosing the capacity before analysing load curves, focusing only on the equipment price, assuming a battery will be eligible for a solar scheme, combining incompatible revenue streams, or forgetting connection and safety costs. Also avoid projections based on historical price spreads that are not guaranteed for the funding period. Require an adjustable model, transparent assumptions and a sensitivity scenario. Finally, do not confuse nominal capacity, usable capacity and performance guaranteed at delivery.

12. 90-day action plan

During the first two weeks, gather the energy data and appoint an internal owner. During the first month, have the objectives, grid constraints and site risks qualified. Then compare several solutions and obtain detailed quotes, including connection, safety and life-cycle cost. In parallel, map the grants actually open in the territory and ask for the rules on when expenses may start. Before the investment decision, have the cautious scenario validated by finance, operations, the safety officer and the insurer. This sequencing avoids submitting an application for poorly sized equipment or signing an irreversible commitment too early.

Expenses to budget and documents to gather

Expenses to review: Load-profile study, electrical audit, batteries, converters, management system, fire protection, civil works, connection, supervision and commissioning. Break down each item in the quotes and identify existing, new, ancillary and recurring elements. Do not assume a cost is eligible simply because it is necessary for the project.

Common documents to prepare:

• Presentation of the beneficiary, legal status, company size and project location.
• Annual or projected accounts, financing plan and monthly cash-flow plan.
• Technical study, baseline situation, performance assumptions and sensitivity scenarios.
• Detailed, comparable quotes, schedule, permits and required certifications.
• Timeline of commitments, proof of submission, cumulation rules and result-monitoring documents.

Which funding avenues to review?

The first contacts to approach are: ADEME and energy-transition schemes to check; the Région and intermunicipal bodies; the grid operator; energy suppliers and demand-response operators; banks and leasing providers. Start with the official portals and the relevant reviewing body. Check the beneficiary's eligibility, the expense base, thresholds, caps, the rate, the timeline, publicity obligations, cumulation rules and the authorised start date. A funding avenue must be recorded in the file with its official source, the verification date, the status (open, closed, to be confirmed) and the next action. Do not present a closed programme as an open opportunity.

Building the financing plan

The financing plan must separate confirmed resources, pending requests and assumptions. Clearly present equity, debt, leasing, grants requested and grants awarded. Test the maximum cash-flow need: deposit, VAT, supplier balance, payment timing and any gap between commissioning and savings. Build a cautious scenario including delay, cost overrun and performance below target. If the project remains viable only with an unconfirmed grant, the timeline, scope or financing structure must be revisited.

Recommended timeline

1. Scoping: clarify the need, scope, constraints and the internal owner.
2. Diagnosis: gather baseline data, carry out studies and test assumptions.
3. Consultation: compare offers on the same functional and budgetary basis.
4. Financing: check open windows and the eligibility date of expenses before ordering.
5. Delivery: monitor works, tests, acceptance and commissioning.
6. Supporting documents: keep invoices, payments, certifications, results and inspection documents.

Common mistakes to avoid

Do not confuse the existence of a scheme with a window actually being open. Do not use a rate found in an old article without consulting the applicable rules. Do not place an order or start works before checking the rules on prior commitments. Avoid overly generic quotes, forecasts with no cautious scenario, and applications that do not link each expense to a measurable objective. Document funders' responses in writing when eligibility or cumulation is not explicit.

FAQ

Is a stationary battery always subsidised?

No. Eligibility depends on the scheme, the beneficiary, the project's objective and the eligible expenses. The applicable rules and any open call for projects must be reviewed.

Can a battery associated with solar panels be funded?

This is possible under certain frameworks, but storage may be treated differently from photovoltaic production. Separate the costs and have the eligibility of each item confirmed.

Must the grant be requested before ordering?

Often, schemes require a prior application or a precise eligibility date for expenses. Do not order before checking the official rule.

What data is essential?

Load curves, invoices, subscribed power, renewable production data and operational objectives form the basis of sizing.

How can overestimated profitability be avoided?

Test a cautious scenario, account for losses and ageing, separate the sources of gains, and do not add together services that mobilise the same capacity at the same time.

Official sources

Do not publish any rate or timeline without a link to the official version in force.

This guide is a preparation method. Criteria, amounts, dates and cumulation possibilities must be checked with the relevant official bodies at the time of the application.

Practical appendices

Weighing storage against other levers

Before buying a battery, compare it with levers that can meet the same need: shifting consumption, contractual demand response, power optimisation, improving the power factor where relevant, process control and adapting the contract. A battery can be technically effective while being less profitable than changing schedules or software-based control. The comparison must use the same time horizon, the same price assumptions and a realistic assessment of risks.

Warranties and end of life

Examine warranties covering years, cumulative energy throughput, number of cycles and residual capacity. Check exclusions related to temperature, depth of discharge and control mode. The contract must identify who is responsible for collection and the end-of-life chain, as well as the associated costs. Ask how modules will be diagnosed, replaced and transported, and whether the management system can track the indicators needed to maintain the warranty.

Questions to ask suppliers

Ask what capacity is guaranteed at the delivery point, what efficiency is guaranteed under the site's real conditions, how availability is calculated, who can change the control settings, what software fees are recurring, and how flexibility revenue is shared. Have delivery times, connection needs, parts availability, insurance requirements and data provided after commissioning specified. Compare the answers in a shared table rather than choosing solely on the initial price.

Example of a battery analysis grid

For each scenario, record usable power, usable capacity, efficiency, annual number of cycles, availability, degradation, full installed cost, maintenance cost and revenue or savings that can actually be demonstrated. Include a 'verified assumption' column and a 'source of evidence' column. The supplier can provide technical values, but tariffs, consumption profiles and connection costs must be validated by the relevant parties.

Investment decision: go/no-go criteria

The project can move to the commitment phase when the load profile is reliable, connection constraints are known, safety is validated, the cautious scenario is viable and financing does not depend on a hypothetical grant. Otherwise, keep the project at the study stage or reduce its scope.

Checking operating assumptions

The model must also specify operating limits: minimum charging power, reserve thresholds, ambient temperature, planned unavailability, the control system's response time and constraints imposed by the energy supplier. If a battery contributes to several services, document the order of priority and the arbitration rules. A transparent simulation must show when one service is dropped in favour of another. Finally, request an export of hourly results so the calculation can be audited by a third party.