Solar-Plus-Storage (Self-Consumption): Solar battery grants

Solar-plus-storage: the configuration most solar battery grants and reliefs are written for

If you already have rooftop solar and you are looking for the funding to add a battery, this is the configuration the tax system rewards most directly. A solar-plus-storage battery stores the daytime generation your site cannot use as it happens and releases it in the evening and early morning, lifting self-consumption from a typical 40 to 60 per cent toward 80 per cent and above. That single change converts power you would otherwise export at a low Smart Export Guarantee rate into power that displaces full-price import, and capturing the spread between the import price and the export price is where the money is. The reason this matters for funding is that the battery, like the panels before it, counts as qualifying plant and machinery, so the same Annual Investment Allowance and first-year allowances that supported your solar apply again to the storage element. The grant and relief picture is at its strongest precisely when the battery is paired with on-site generation rather than charged from the grid alone, because the self-consumption saving is large, controllable and unaffected by volatile market prices.

Most enquiries we field on this site come from businesses that have already done the solar and now want to know what funding exists for the battery half. The honest answer is that there is no single cash grant for commercial battery storage in the UK, and we would rather say so plainly than imply one exists. The value sits in capital allowances, in the Smart Export Guarantee on any surplus you still export, and, for residential-portfolio or charity-occupied buildings, in the 0 per cent VAT relief on standalone retrofit storage. Solar-only commercial sites typically self-consume only 40 to 60 per cent of what they generate and export the rest at a low rate, then re-import in the evening at full retail, which is precisely the value left on the table that a battery recovers. The job of this page is to show how those reliefs stack on a self-consumption battery, how we size the system so the funding case actually holds, and how we model the numbers from your real meter data rather than a brochure figure.

What a typical install looks like and how we size it

A solar-plus-storage battery on a commercial site usually lands between 50 kW / 100 kWh and 500 kW / 1,000 kWh, paired with your existing or new PV array rather than carrying its own panel count. The system stores rather than generates, so the headline number to watch is capacity, and the saving comes from displaced import, typically saving in the region of 10 to 120 tonnes of CO2 a year depending on how much solar surplus it captures. The single most important sizing rule is that we size the battery to your daytime export surplus, not to your headline PV kW. A large array on a site that is busy in the daytime may have very little surplus to store, while a smaller array on an evening-heavy and early-morning-heavy site may justify a large battery. The case is strongest where on-site load is daytime-light but evening or early-morning heavy, because that is where the most generation would otherwise be spilled and re-bought. We pull at least 12 months of half-hourly meter data and overlay it on your solar generation profile so the capacity matches the gap between what you make and what you use, hour by hour, half-hour by half-hour. Oversizing a battery is the fastest way to wreck the funding case, because unused capacity earns nothing while still attracting cost, and a battery that sits half full every evening is a battery half wasted. This is why we never quote a size from a rule of thumb before we have seen the data.

Costs, payback and tax relief

A solar-plus-storage project on this site typically falls between £60,000 and £600,000, with a simple payback near 7 years for a well-matched system, faster where the solar surplus and the import-export price spread are large. The biggest piece of the funding picture is the capital allowance position. Battery storage is special-rate plant, so the Annual Investment Allowance covers the first £1m of qualifying spend at 100 per cent, and a 50 per cent first-year allowance applies to anything above that cap. It is worth being precise here, because competitors routinely overstate it: the 100 per cent full-expensing regime applies to main-rate plant only, and solar and storage are special-rate, so they use the AIA up to £1m and then the 50 per cent first-year allowance on the balance. For a limited company that can still be worth up to around a quarter of the project value back as tax saved in year one, depending on how the spend sits against the £1m AIA limit, and your accountant should confirm the position for the relevant accounting period. On top of that, the Smart Export Guarantee pays for any surplus you still export, typically 4 to 15p per kWh and supplier-set, and a battery lets you shift that export into higher-priced windows on a time-of-use export tariff rather than spilling at midday for the lowest rate. Our cost guide works through how the allowance and the export income combine on a self-consumption battery.

Funding routes in detail

There is no headline cash grant for a commercial battery, so the funding routes are reliefs and income streams, and the order they matter in is this. First, the Plant and Machinery Capital Allowances: 100 per cent AIA on the first £1m, then 50 per cent first-year allowance on the balance, applied to the battery and its associated infrastructure as special-rate assets, and worth up to roughly a 25 per cent effective tax saving in year one for a limited company. Second, the Smart Export Guarantee, where the battery adds value not by exporting more but by timing exports into higher-priced periods rather than passively spilling at the lowest midday rate. Third, for the narrow but real case of a building used solely for a relevant charitable purpose or residential accommodation, the 0 per cent VAT on Energy Saving Materials, which since 1 February 2024 covers standalone retrofit battery storage connected to the grid, runs to 31 March 2027, and is then set to move to 5 per cent rather than back to 20 per cent. General commercial premises do not qualify for that VAT relief, a point routinely mis-stated across the market, and we will tell you plainly if your building falls outside it; it is relevant mainly for mixed-use, residential-portfolio and charity-occupied sites. We model capital, asset finance, lease and shared-savings routes side by side so the funding fits your balance sheet rather than forcing a capital outlay, because for many businesses the answer to "we would rather invest in the core business" is asset finance or a shared-savings arrangement, not a cheque.

Compliance and sector considerations

A solar-plus-storage battery needs a G99 application where the combined generation and storage export exceeds your DNO limits, and a G100 export limitation scheme is often used to keep the site within its agreed export capacity so the project can proceed without waiting for a network upgrade. The storage element should be installed to MCS or an equivalent standard, with the battery and inverter built to BS EN 62619 for cell safety and BS EN 62933 for system safety. Across the site level, that sits within the wider standards framework: PAS 63100:2024 principles for fire protection, NICEIC or NAPIT electrical registration, BS 7671 for the electrical installation itself, and CDM 2015 where the work exceeds 30 person-days. The fire and insurance scrutiny on lithium-ion storage has tightened, which is why we specify lithium-iron-phosphate cells, which are far more thermally stable than older nickel-manganese-cobalt chemistry, and engage your insurer up front. Insurers are comfortable with correctly specified, standards-compliant systems; the risk and the higher premiums lie in cheap, non-compliant kit, which we do not install. None of this affects your existing solar certification, but it does shape where the battery enclosure can sit and how it is separated, which we resolve at survey rather than on the day.

How we approach this kind of project

We start from your half-hourly meter data and your solar generation profile, not a generic kWh-per-pound rule of thumb, because the funding case on a self-consumption battery lives or dies on how much surplus there actually is to capture. We size for self-consumption first and treat any export income as secondary. Where the roof or plant room needs checking, including asbestos checks on older buildings before any enclosure or cabling work, we do that before we quote a fixed price, not on the day of the install. We submit the G99 application and open the DNO conversation early, because the connection timeline is usually the longest item and starting it on day one protects your programme. You receive a fixed-price proposal with the warranted cycle count, throughput and degradation curve stated, so there are no surprises late in life, and the work carries a 10-year insurance-backed workmanship warranty. The model is shared in full so your finance team can stress-test every assumption and feed it into your own capital appraisal, and if your profile does not justify a battery, for instance if your surplus is small, we will tell you so rather than sell you one.

An illustrative example

As an illustrative composite based on typical UK solar-plus-storage projects, and not a real named client or real project: a Midlands precision-engineering plant on a single-shift-plus profile had a sharp weekday late-afternoon demand peak and an existing 300 kW rooftop array exporting surplus at midday. Its annual electricity bill ran around £420,000, with non-commodity charges a growing share, and the finance director was sceptical after a previous inflated battery quote. A 250 kW / 500 kWh lithium-iron-phosphate battery integrated with the existing PV lifted solar self-consumption from 52 per cent to 84 per cent and cut red-band import sharply, for an indicative annual saving near £71,000 and a payback close to 6.4 years. The model was built from 12 months of half-hourly data and handed to the finance director to stress-test, with any frequency-response income treated as unmodelled upside rather than part of the case. The figures are illustrative and depend on your generation profile, tariff and demand shape.

If your interest is more about cutting demand charges than lifting self-consumption, see our pages on peak shaving and load shifting and backup power and resilience. When you are ready, read the cost and payback guide, review the grants and funding routes, request a feasibility from your meter data, or work through the battery storage FAQs first.