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Home batteries and the off-peak saving: what’s real

You may have heard that plug-in solar becomes legal in 2026, and wondered whether plug-in batteries are next. They’re not: the 27 August 2026 change is solar-only, and a home battery still needs a proper hard-wired install. But the real reason to want one was never plugging it in — it’s using a cheap off-peak tariff to charge it and running your home off it at peak. Here’s the real maths.

• First, the regulatory reality. The 27 August 2026 rule that legalises plug-in solar (SI 2026/848) excludes anything that stores energy — batteries are specifically left out. So a home battery isn’t “plug-and-play”: it still needs a proper hard-wired installation to the wiring standard (BS 7671) by a qualified installer, with your network operator notified (G98). That’s not red tape for its own sake — it’s what keeps a device that pushes power around your home safe. What the 27 August change does cover →
• The real win is rate arbitrage, not plugging in. A home battery saves money by charging when electricity is cheap — overnight, off-peak — and powering your home through the expensive early-evening peak. You’re not making energy; you’re buying it low and using it high. That only works on a time-of-use tariff with a genuine cheap window. Is a time-of-use tariff worth it? →
• What that’s worth, per unit. Each unit (kWh) you shift saves the gap between the two rates. With peak electricity around 26p a unit on the current price cap, an off-peak rate near 15p saves you about 11p a unit, and the cheapest overnight EV-style rates (around 7p) save closer to 19p a unit. Those off-peak rates are examples that vary by tariff — they’re set by your supplier, not by the price cap.
• What it really adds up to in a year. A typical 5 kWh usable battery cycled once a day shifts a bit under 1,800 units a year. After real-world round-trip losses (a battery gives back a little less than you put in), that’s roughly £131 to £277 a year off your bill. And that’s the running saving before the four-figure upfront cost of the battery and its install. The saving is real, but payback is measured in years, not months.
• Who it suits — and when it’s worth it. It stacks up best if you can get onto a cheap off-peak tariff, use a decent chunk of power at peak, and pair it with solar (store free daytime generation for the evening) or an EV. If your usage is flat and you can’t get a wide cheap window, the sums are much weaker. Like solar, the only real answer is one worked out on your usage. Economy 7, the classic off-peak tariff →

A battery only pays if the gap between your peak and off-peak rates is wide enough, and you can actually shift enough power to use it. The starting point is knowing what you pay now and how your usage falls across the day — then you can see whether the off-peak trick would genuinely pay for the kit.