Home batteries are getting all the attention. But there's a cheaper, quieter piece of kit already sitting in your home that does a similar job - the electric water heater. 

Why Hot Water Is Really Energy Storage

Heating water and storing electricity solve the same problem: using power when it's cheap and abundant, then using it later when it's not. A battery does this with lithium cells. An unvented cylinder or immersion heater does it with hot water and it's already installed in millions of homes and offices. 

Hot water accounts for roughly a quarter of a typical home's energy use, and most of that use is flexible. Heat the water overnight on a cheap tariff and it stays hot enough to use all day. No new hardware, no lithium, no five-figure installation. The same applies to offices, schools, and gyms. A well sized cylinder can heat overnight and coast through a full working day. 

Why This Matters More Now 

Time-of-use tarriffs like Octopus Go offer a fixed cheap window overnight, with peak rates running two or three times higher during the evening. That gap is exactly what a battery is built to exploit, and exactly what a timed water heater exploits toom, just without the install cost or the maintenance schedule. 

Our Take 

A home battery still wins on flexibility as it can power anything in the house, not just hot water. But pound for pound, a water heater on a timer or smart control is the cheapest "battery" most households and small commercial sites will ever own. On Octopus Go, overnight rates can run at a third of poeak price, and an unvented cylinder holds that cheap energy as usable hot water for hours. 

The Smarter Choice 

If your water heater runs on a terrible thermostat with no timer, that's the gap. A basic timer retrofit, or a cylinder with smart controls built in, gets you most of the benefit of a battery without the battery price tag. Size matters too, a cylinder that's too small will run out of stored hot water before the next cheap window comes round. 

Bottom line: You don't need to buy a battery to start storing cheap energy, you just need your water heater working harder for you.