Battery Storage

Why storage is the decision that matters

Solar generates hardest at the point in the day when the average house is at its quietest. Without somewhere to put it, a typical household uses roughly a third of what it generates and sends the rest to the grid for a fraction of what it costs to buy back that evening.

A battery moves your midday surplus into the evening, which is when the house is actually busy — cooking, laundry, television, hot water, everybody home. That single shift is usually worth more than adding panels, because every unit you use yourself is worth the full retail price rather than the export rate.

Sizing: your evenings, not your roof

Battery sizing is a question about consumption, not generation. We want your annual kWh figure and, ideally, half-hourly data from your smart meter, because what we are really trying to find out is how much electricity you use between four in the afternoon and midnight, and how consistent that is.

Oversize the battery and you pay for capacity that sits empty most of the year. Undersize it and you are back on the grid by eight o’clock in December. We model both against your own data and show you the working rather than quoting a round number because it is the one in the brochure.

Time-of-use tariffs: the second job

On a time-of-use tariff a battery does something solar cannot. It charges from the grid overnight at a low rate and carries the house through the following evening peak regardless of what the weather did. In a British winter that is not a minor detail — it is most of the value.

This is why we look at your tariff options as part of the design rather than as an afterthought, and why a smaller array with a well-sized battery on the right tariff can beat a bigger array on a flat rate.

Adding a battery to solar you already have

If you already have panels, you do not need to disturb them. An AC-coupled retrofit battery sits alongside the existing installation with its own inverter, works with whatever array is already up there and whoever fitted it, and leaves your existing generation arrangements intact.

It is one of the most sensible upgrades available at the moment, particularly for older systems on legacy export arrangements where using more of your own generation is plainly the better move. We are happy to add storage to somebody else’s solar installation, and we will tell you honestly if your existing inverter or consumer unit needs attention first.

Hybrid inverters for new systems

Where solar and battery go in together, a hybrid inverter runs both as one system: DC-coupled, one set of electronics, one app, slightly better round-trip efficiency and a tidier installation. It is the right answer for a new system and the wrong answer for a retrofit, which is the distinction most quotes gloss over.

Round-trip losses and honest modelling

No battery gives back everything you put into it. Real round-trip efficiency sits somewhere below the nameplate figure once inverter losses and standby draw are counted, and usable capacity is below rated capacity because the cells are not run flat. We model with realistic figures. If a quote you are comparing shows savings built on nameplate capacity at one hundred per cent efficiency, that is where the difference is coming from.

Backup during a power cut

Not by default. For the safety of anyone working on the network, grid-tied systems disconnect when the supply fails — battery or no battery. Some systems can be configured with a backup circuit that keeps selected loads running through an outage, but it has to be designed in from the start and it changes the consumer unit work. If it matters to you, say so at survey rather than afterwards.

Where it goes, and what that involves

Batteries need somewhere ventilated, dry, within a sensible temperature range and reachable for service — commonly a garage, utility room, loft or an external wall. Weight matters on an upper floor, and cable runs matter for losses. We work out siting at survey alongside the inverter position and the consumer unit work, so the price you are quoted is the price that gets installed.

Notifying the network operator

Smaller domestic systems are notified to the Distribution Network Operator after commissioning under G98. Larger systems, and those with substantial battery capacity, need G99 approval before installation. We make the application either way and build the operator’s response time into the programme, so the date we give you is a date we can keep.

VAT

Qualifying battery storage installed in residential property is currently zero-rated for VAT until 31 March 2027, after which the reduced 5% rate is due to apply. Batteries retrofitted to an existing solar system qualify too — the battery does not have to be fitted at the same time as the panels.

Send us your annual kWh figure and a photo of the roof and we will tell you what is realistic before anyone visits.

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