Battery Storage Installation

Without storage, a typical Wiltshire solar array exports roughly half of everything it generates. The sun is strongest around midday, which is exactly when most households use the least, so that surplus flows back to the grid for a modest Smart Export Guarantee payment while you buy expensive power back at teatime. A home battery closes that gap by capturing daytime surplus and releasing it when you actually need it. In practice it earns its keep three ways at once.

1. Self-consumption. Instead of exporting midday surplus at roughly 4-16p per kWh (a good rate in 2026 sits around 10.8p), the battery stores it and you draw on it that evening in place of grid electricity costing about 27p per kWh. Every stored kWh you use yourself is worth the difference, so lifting self-consumption from around 40% to 80%+ is where most of the savings come from. Our solar and battery systems are sized specifically to hit that band.

2. Peak-shifting (tariff arbitrage). On a time-of-use tariff such as Octopus Intelligent Go, off-peak overnight units can fall to roughly 7p per kWh. The battery charges cheaply overnight and discharges through the expensive peak, so it pays even in a dark Wiltshire December when solar contributes little. This is why a battery can be worth fitting on the right tariff regardless of the season.

3. Smart Export Guarantee. Genuine surplus, after your home and battery are satisfied, is still exported for a per-kWh SEG payment. A well-sized system keeps most generation on-site and exports only what you truly cannot use. We explain the mechanics fully on our Smart Export Guarantee explained page.

Round-trip efficiency (energy in versus energy out) is typically 90-95% on modern lithium iron phosphate (LFP) batteries, so a small amount is lost in the cycle, and that is factored into every payback figure we quote. Whether the battery is best coupled to your solar on the AC or DC side depends on your existing kit, which we cover further down. If you are still weighing the decision, our honest guide to whether battery storage is worth it walks through the numbers for a typical household.

The most common mistake is sizing a battery to the solar array rather than to how the home actually uses power. What matters is your evening and overnight demand, because that is the load the battery has to cover. A typical Wiltshire household uses around 2,700-3,500 kWh a year, and lead engineer Matt Butler sizes every system from your real consumption pattern, half-hourly data where available, and your tariff, not a rule of thumb.

Capacity (kWh) is only half the picture. You also need enough peak power (kW) to run several appliances at once. A battery rated at 13.5 kWh but only 3 kW output will trip or fall back to grid the moment the kettle, oven and immersion run together; one rated at 7-11.5 kW comfortably carries whole-home evening load. We match both figures to your property.

• 1-2 bed / low usage (under 2,500 kWh): around 5 kWh usable is usually the sweet spot. A modular Sigenergy SigenStor lets you start small and stack later.
• 3-4 bed family (3,000-4,500 kWh): 9.5-13.5 kWh usable typically captures a full day's surplus without oversizing.
• EV owner or heat pump (5,000 kWh+): 13.5 kWh as a baseline, often stacked or paralleled, so the battery can both cover the home and pre-charge cheaply overnight for the car.

Oversizing wastes money: a battery so large it rarely reaches full charge in winter simply never earns back its extra cells. We model your likely daily cycles across summer and winter before recommending a size. Usable capacity also matters more than the nameplate figure, LFP batteries with 100% depth of discharge give you the whole stated capacity, while some chemistries hold back a reserve.

If you already have panels, you almost certainly do not need to touch them, a retrofit battery for existing solar is straightforward and covered below. For a fresh install we design the array and storage together as one solar panel installation. Homeowners in Chippenham and Devizes can see indicative figures on our Wiltshire solar panel costs page.

Two questions decide the hardware: how the battery connects to your solar, and whether you want it to keep working in a power cut. Both change which product is right for you.

DC-coupled (single hybrid inverter). The panels and battery share one hybrid inverter, so solar charges the battery on the DC side without an extra conversion. That is the most efficient route, the Tesla Powerwall 3, for example, reaches around 97.5% when DC-coupled with panels, and it is the neatest option for a brand-new solar-and-battery install. The Sigenergy SigenStor is likewise a hybrid, integrating inverter, battery and even EV charging in one unit.

AC-coupled (separate battery inverter). Here the battery has its own inverter and simply sits alongside whatever solar you already own. This is the standard, low-disruption way to add storage to an existing array without replacing a working solar inverter. A GivEnergy All-in-One is commonly deployed this way. There is a small efficiency trade-off versus DC coupling, but for a retrofit it is almost always the sensible choice.

Backup and EPS. A standard grid-tied battery does not power your home in an outage, for safety it disconnects (anti-islanding, per G99). To keep running you need an EPS (Emergency Power Supply) or backup gateway that isolates your home from the grid and switches the battery to supply your circuits. There are two levels:

• Essential-loads backup: a backup circuit carries key loads, boiler, fridge, lighting, broadband, a cost-effective way to ride out a cut.
• Whole-home backup: a gateway (such as the Tesla Backup Gateway or GivEnergy Gateway) backs up the whole consumer unit and changes over in a fraction of a second, so you may barely notice the grid has gone.

Backup capability adds hardware and cost, so we only specify it where a household genuinely wants resilience. If you run an EV, the same hybrid inverters that manage the battery can also coordinate EV charging from solar, which we cover next.

Thanks to the 0% VAT on domestic battery storage, in place until 31 March 2027, 2026 is an unusually good window to install. As a rough guide, a battery-only retrofit runs from around £4,500 for a compact modular system up to £9,000-12,000 for a 13.5 kWh unit with whole-home backup, before any solar. Fitted alongside a new array, a combined solar-and-battery system typically pays back in 7-9 years and then runs for the remainder of a 20-25 year lifespan largely for free.

Three levers drive your payback: the price you avoid paying to import (about 27p per kWh in 2026), how much of your generation you keep on-site, and your tariff. On a smart tariff, peak-shifting overnight units at roughly 7p and using them through the peak can roughly halve the cost of the power the battery covers, which is why storage now stacks up even for homes that use most of their electricity after dark. A 4 kWp array generating around 3,900 kWh a year already saves roughly £950-1,100 annually; a correctly sized battery meaningfully increases the share of that generation you actually consume.

Spreading the cost. Many homeowners fund the system over time rather than up front, our solar finance options can make the monthly saving cover much of the repayment. See the current deals on our 0% solar finance for 2026 guide.

Adding an EV charger. If you drive electric, pairing the battery with the right charger multiplies the benefit. A Zappi (from around £1,000-1,365 installed) has Eco+ solar-divert modes that push genuine surplus straight into the car, potentially adding a couple of thousand free miles a year. An Ohme (from around £500-950 installed) integrates directly with smart tariffs to charge automatically in the cheapest overnight windows. Note the OZEV chargepoint grant, raised to £500 per socket from April 2026, now applies only to renters and flat owners with off-street parking, not to houses. We handle the full EV charger installation alongside the battery. Homeowners in Melksham and across the wider region can book a survey to get exact figures for their property.