Anker Solarbank vs EcoFlow STREAM: balcony batteries in the UK and US

A balcony battery sits between your solar panels and a wall socket. During the day it charges from the panels, and in the evening it keeps feeding power into your home at a steady, capped rate, so less of what the panels make leaks out to the grid for nothing. Anker’s Solarbank and EcoFlow’s STREAM are the two best-known ranges. We haven’t tested either; this comparison is built from the makers’ spec sheets and the rules in each country, checked on 4 November 2026.

The short answer

• In the UK, neither counts as a plug-in device. The new plug-in rules exclude batteries, and both companies say a qualified electrician has to wire their unit into your consumer unit. Once it’s wired in, the Anker is the bigger, more powerful system and the EcoFlow is the cheaper way in.
• In the US, only EcoFlow sells its system. The STREAM Ultra is sold for states with plug-in solar laws, and EcoFlow says self-installation is currently allowed only in Utah. Anker’s Solarbank isn’t on its US store.

The specs side by side

Two things stand out. The Anker is a different class of product: 5 kWh and a 2.5 kW output make it closer to a small home battery than a balcony accessory, and it can take more than six times the panel power of a plug-in kit. The EcoFlow is modular. You start with one unit and add more, and its smaller sibling, the 1.92 kWh STREAM Ultra, is the entry point in both countries.

EcoFlow also sells cut-down versions with fewer solar inputs: the STREAM Pro (three, up to 1,500 W) and the STREAM Max (two, up to 1,000 W), both with 1.92 kWh batteries.

In the UK: why neither one is “plug-in”

Plug-in solar became legal in Great Britain on 27 August 2026, but only for devices that meet the government’s Interim Product Specification. Its scope is explicit: it does not cover plug-in battery systems, or plug-in solar devices combined with batteries. Approved plug-in kits even have to carry a warning that they’re not meant to be used with a battery storage system.

The makers say the same thing in their own UK FAQs:

• Anker says the Solarbank 4 Pro must be installed by a Part P-registered electrician on a dedicated, hardwired circuit, which is also what unlocks its full 2,500 W output.
• EcoFlow says UK regulations require its STREAM connection cable to be wired into the distribution board by a certified installer or electrician. Elsewhere on the same page it calls setup effortless, which applies to the parts you assemble yourself, not the connection to your wiring.

In practice that makes either one a normal battery installation. Your electrician fits a circuit, and the network operator is notified the way it would be for any small solar or battery system. Because it’s wired in rather than plugged in, it isn’t held to the 800 W plug-in limit. It also isn’t cheap to add: Anker’s own payback example notes that installation costs aren’t included.

If you want something you can genuinely plug in today, buy an approved plug-in kit without a battery (see our comparison of UK kits). If you also want backup for power cuts, a portable power station that never connects to your wiring is the legal way to get it. The government has said it is looking at standards for plug-in batteries, so this may change.

In the US: one product, a handful of states

EcoFlow launched the STREAM series in the US as a plug-and-play system for apartments and houses. On its US product page, checked on 4 November 2026, it says plug-in installation is currently permitted in Utah, Maryland, Connecticut and Colorado, while its FAQ says self-installation is only available in Utah for now. Colorado’s law takes full effect on 1 January 2027, so check the rules where you live before relying on the marketing.

The US STREAM Ultra plugs into an ordinary 120 V outlet (NEMA 5-15 or 5-20). EcoFlow rates its grid connection at 800 W, and quotes up to 1,200 W when appliances are also plugged into the unit’s own outlets. That fits under the 1,200 W limit in most state laws. When we checked, it was listed at $1,399 and out of stock until March 2027.

Certification is the other question. Several state laws refer to UL 3700, the new US safety standard for plug-in solar, and trackers in September 2026 reported EcoFlow’s certification as still in progress. Ask the seller for the certificate number before buying.

Anker’s Solarbank isn’t sold in the US. A search of Anker’s US store on 4 November 2026 found power stations and its E10 whole-home backup system, but no Solarbank.

Which one suits which home?

If you can install either, the choice mostly comes down to how much you use after dark.

• A flat with two to four panels and a modest evening load. A 1.92 kWh STREAM Ultra covers a background load of about 150 W through most of a night. It’s the cheapest way in, and you can add a unit later.
• A family home using 3 to 5 kWh in the evening. The STREAM Ultra X (3.84 kWh) or the Solarbank 4 Pro (5 kWh). The Anker’s 2,500 W output can cover bigger appliances too, and Anker says it can keep a heat pump running, rather than just the background load.
• A big array, or charging from a cheap night tariff. The Solarbank 4 Pro, with its 5,000 W of solar input, 2,500 W grid charging and expansion to 30 kWh.

Both makers sell bundles with panels and smart-meter readers. A meter reader matters more than it sounds: it lets the battery match its output to what your home is using at that moment, instead of guessing.

Does a battery pay off?

Here are two simple examples using UK prices, with electricity at 26.32p per kWh (the Ofgem price cap rate for October to December 2026).

Storing solar. An 800 W kit hung vertically on a south-facing London balcony makes about 594 kWh a year, according to the European Commission’s PVGIS model. Without a battery, a household that’s out at work might use half of that as it’s made. A battery could raise that to around 90%. The extra 238 kWh is worth about £63 a year. At £1,499 plus installation, a battery that only stores balcony solar takes more than 20 years to pay back.

Charging on a cheap night rate. Anker’s own example assumes an overnight rate of 8.5p and a daytime rate of 29.37p. On those rates, each kWh you move from night to day is worth about 20p after losses. A 3.84 kWh battery cycled once a day would save roughly £280 a year, before installation. That only works if you’re on a time-of-use tariff and actually use that much in the expensive hours.

Anker’s headline figure of up to £770 a year combines both effects, using its 5 kWh battery, its own panel bundle and a full daily cycle, and excludes installation. Treat any maker’s payback figure as a best case, and run your own numbers.

Before you buy

1. Check what’s allowed where you live: wired-in only in Great Britain, and plug-in only in certain US states.
2. In the UK, get an installation quote first. The battery price is only part of the cost.
3. Look at your evening and overnight use on your smart meter app. That sets the battery size.
4. Check the warranty terms on capacity. EcoFlow quotes 6,000 cycles to 70% capacity, and Anker 10,000 cycles.
5. If backup in power cuts is the main goal, compare against a portable power station, which needs no installation at all.