Two months of overnight to daytime electricity arbitrage on a Scottish time of use tariff cut a household bill roughly in half; here is the rate spread, the friction, and the two conditions that decide if it works in your home.
A home battery is one of the more expensive appliances a household can buy, so the obvious question is whether the math actually works without rooftop solar. A WIRED reviewer's two-month test of the EcoFlow PowerOcean suggests it can, in the right conditions: the reviewer cut their electricity bill roughly in half by charging the unit overnight at a cheap EV rate and discharging it during expensive daytime peak hours.
The setup matters. The reviewer runs a Scottish household with an EV and an air-source heat pump, no rooftop solar, and a time-of-use tariff that prices overnight power at roughly 5 pence per kilowatt-hour and daytime power near 25 pence. That 4x price gap is the engine of the savings, and it is the single most important number for any reader trying to decide if a home battery makes sense in their own home. Without a meaningful spread between cheap and expensive hours, the arbitrage simply does not exist.
The hardware is a modular system, scalable from 5 kWh to 45 kWh, rated IP65 for outdoor use, and backed by an advertised 15-year warranty, with a starting price around $10,000 per the WIRED review of the EcoFlow PowerOcean. The actual installed cost will depend on the home, the local labor market, and the electrical work required. Adding more capacity to the system is not a do-it-yourself job: the same review notes that adding batteries requires professional installation, and the reviewer separately had to coordinate a cut-out fuse upgrade with the local distribution network operator, a process that was free in this case but came with slow response times. That last friction is the kind of thing that does not show up in product marketing but can quietly shape the experience.
The software side is a mixed bag. The companion app is described as slick and supports useful automations for energy management, but the PowerInsight companion tablet is slow enough that the reviewer flagged it as a real annoyance. A home battery is the kind of device a household interacts with for years, so a sluggish interface is not a minor footnote.
The real question is what this means for someone reading this from a different country, on a different tariff, with a different load profile. The arbitrage logic generalizes in two directions. First, the rate spread has to be large enough that the round-trip cost of charging and discharging leaves real savings after battery degradation. The reviewer's 4x overnight-to-daytime gap is generous. Many US time-of-use plans offer a 2x to 3x spread, which extends the payback horizon. Second, the household needs a nightly load that can be shifted: an EV that charges overnight, a heat pump that runs in colder hours, or a pool pump that can be rescheduled. A household with low overnight demand and no flexibility on when appliances run will not see the same result.
The headline number, "cuts bill in half," is the reviewer's outcome on a specific tariff, not a universal promise. The WIRED review gives the product an 8/10, but the more useful takeaway for a reader considering a similar purchase is the framework: check the overnight-to-daytime rate spread, estimate the kilowatt-hours of flexible load, and ask the local installer about distribution network operator work and permitting before signing anything. The product can deliver, but only when the grid tariff and the household load line up.