- Chinese manufacturer founded in 2019, headquartered in Wenzhou with a main R&D centre in Wuxi
- Makes hybrid solar inverters (single-phase H1 and three-phase H3 series) alongside its own EP, ECS and Mira lithium battery ranges
- EP batteries use LiFePO4 chemistry and can be stacked, with the EP11 reaching around 41.6 kWh and the EP12 a confirmed 46.08 kWh across four parallel modules
- Monitored through the FoxESS Cloud app (rebranded Fox Cloud 2.0), with real-time and historical performance data
- Popular with UK solar installers for competitively priced, modular hardware; Octopus Agile automation is available but has to be requested from Fox ESS support rather than working out of the box
Independent coverage
This page reflects our own independent assessment of Fox ESS, not a sponsored placement. If we later add affiliate links to Fox ESS's site, any commission we might earn does not change what we say about the brand here.
Who is Fox ESS
Fox ESS is a Chinese energy technology company that was founded in September 2019. It is headquartered in Wenzhou, with its main research and development centre in Wuxi. The company describes itself as a global leader in inverter and energy storage solutions. Its product line-up has grown accordingly, expanding from solar inverters into batteries, EV chargers and, more recently, heat pumps.
In 2023, Fox ESS completed a pre-IPO funding round, raising more than CNY 1 billion. This valued the business at more than CNY 10 billion, around $1.4 billion or roughly £1.1 billion at the time. That yuan figure comes from reporting by DealStreetAsia and AVCJ. Fox ESS’s own announcement did not give the figure in those terms. Forbes also named Fox ESS to its Global Unicorn List that year.
In the UK, Fox ESS sells through a network of solar installers rather than direct to homeowners. As a result, its hybrid inverters and EP battery range have become a common sight on UK installer price lists. They appear there alongside brands such as GivEnergy and Sunsynk.
The Fox ESS product range
Fox ESS’s core UK offering pairs its own hybrid inverters with its own battery modules. The single-phase H1 series covers smaller homes. It runs from 3 kW to 6 kW, according to Fox ESS’s own UK product range page. The three-phase H3 series, by contrast, covers larger homes and small commercial sites. It runs from 5 kW up to 30 kW, across its residential and small-commercial Smart and Pro lines. A separate H3 Plus commercial line then extends that range further, from 50 kW to 125 kW. Both the H1 and H3 ranges integrate Fox ESS’s own batteries directly. AC-coupled options are also available, for retrofitting a battery onto an existing solar inverter rather than replacing it.
On the battery side, the EP series is the flagship high-voltage line. A single EP11 module holds a nominal 10.36 kWh. About 90% of that is usable according to Fox ESS’s own datasheet, so around 9.3 kWh in practice. Up to four modules can then be stacked in parallel, for a maximum of around 41.6 kWh. The newer EP12 follows the same pattern, at a nominal 11.52 kWh per module. However, it scales to a confirmed maximum of 46.08 kWh across four units. That figure comes from Fox ESS’s own EP12 datasheet, rather than a reseller estimate. Alongside this, Fox ESS also sells a lower-voltage ECS/EQ range as a more modest stacking option. A Mira series completes the line-up, for installers who want a smaller entry point.
10.36 kWh
nominal capacity of a single EP11 module, about 90% usable per its datasheet
46.08 kWh
maximum stacked capacity across four parallel EP12 modules, per Fox ESS's own datasheet
10-12 yrs
performance warranty on registered EP, ECS and EQ batteries
Key technology behind Fox ESS batteries
Across its EP, ECS/EQ and Mira ranges, Fox ESS uses lithium iron phosphate (LiFePO4) cells. This is the same broad chemistry family most established home battery brands now use. They favour it for its stability and safety record compared with older lithium-ion chemistries. The EP series runs at a higher nominal voltage window than most. On the EP11, that window is around 384V nominal, with an operating range of roughly 348 to 438V. Fox ESS says this higher voltage improves efficiency when the batteries are paired with its own hybrid inverters.
Monitoring runs through the FoxESS Cloud platform, rebranded Fox Cloud 2.0 and available as an app for installers and homeowners. It tracks solar generation and battery status in real time. The app also logs historical performance data and sends alerts for low charge, faults or maintenance.
Fox ESS also ties its full performance warranty on registered EP and ECS/EQ batteries to this connectivity. To unlock the extended terms, the system must be registered within a set window of manufacture. It must also stay connected to Fox Cloud through a Fox datalogger. In other words, those extended terms are not granted automatically on every system.
Strengths and limitations
As with any brand, Fox ESS’s own marketing understandably leads with its strengths. Here is a more balanced picture.
Strengths
- Modular EP battery design that stacks from a single module up to around 41.6 kWh (EP11) or 46.08 kWh (EP12), covering a wide range of home sizes from one hardware family
- LiFePO4 chemistry across its EP, ECS/EQ and Mira ranges, a chemistry with a stronger safety record than older lithium-ion cells
- Both AC-coupled and hybrid inverter options, suiting retrofits onto an existing solar array as well as new-build installs
- FoxESS Cloud (Fox Cloud 2.0) app gives real-time and historical monitoring as standard, across the whole product range
Worth checking before you buy
- The full 10 to 12 year performance warranty depends on registering the system within a set window of manufacture and connecting it to Fox Cloud via a Fox datalogger; terms without that step are shorter
- Cycle life is published as an energy throughput limit rather than a simple cycle count (33.4 MWh over the EP11's 10-year performance warranty), which is harder to compare directly against brands that quote a cycle number; Fox ESS's published UK warranty documentation does not give an equivalent throughput figure for the newer EP12
- Octopus Agile automation exists in the Fox Cloud app, but UK users have to email Fox ESS support to get it switched on and may need a firmware update first, a more manual step than some UK-focused rivals' built-in tariff automation
- We have not independently tested Fox ESS's pricing, support or installation process ourselves
Where Fox ESS fits the market
Fox ESS sits in the professionally installed, whole-home battery segment, rather than the plug-in or balcony storage category. This is the same segment covered by most of the brand pages on this site. Within that segment, installers and reviewers most often compare Fox ESS with GivEnergy, Sunsynk and Alpha ESS. These are three other China-manufactured hybrid inverter brands that compete heavily on price. Each has also built a sizeable installer base in markets such as the UK. At the more premium end, reviewers also compare it with Tesla Powerwall.
We have not found independent write-ups with enough substance to rank Fox ESS against GivEnergy or Sunsynk on pricing or support responsiveness in any specific market. So we are not repeating that kind of claim here. What we can say with more confidence is drawn from Fox ESS’s own documentation rather than from a third party. Its strengths lean towards its modular hardware and detailed monitoring app. However, setting up smart tariff automation such as Octopus Agile currently needs a support request and possibly a firmware update. Some UK-focused rivals, by contrast, switch this on by default.
If you are still working out what size of system your home actually needs, our capacity guide and free calculator can help. Both work through that independently of any one manufacturer, before you start comparing specific brands.
Common questions about Fox ESS
What does Fox ESS make?
Fox ESS makes hybrid solar inverters, in the single-phase H1 and three-phase H3 series. It also makes its own lithium battery ranges, including the EP, ECS/EQ and Mira lines. These are sold in the UK through a network of solar installers. Beyond that, Fox ESS makes EV chargers and, more recently, heat pumps.
Is Fox ESS a reliable brand?
Fox ESS has grown quickly since 2019, and Forbes named it to its Global Unicorn List in 2023. Its stackable, competitively priced hardware has also made it popular with UK installers. Independent reviewers have noted there is still less long-term field data on Fox ESS than on some longer-established brands. It is worth weighing that against more established alternatives when you compare options.
How much can a Fox ESS battery system be stacked?
It depends on the model. The EP11 can be stacked up to four modules, for a nominal maximum of around 41.6 kWh. Its EP12 counterpart reaches a confirmed 46.08 kWh across four modules, according to Fox ESS's own datasheets. Always check the exact model and inverter compatibility before assuming a figure carries over to a different series.
What warranty does Fox ESS offer on its batteries?
Fox ESS's standard warranty is shorter. However, it extends to 10 years on its EP and Mira batteries and 12 years on its ECS/EQ batteries. That extension depends on registering the system within a set window of manufacture. You also need to keep it connected to Fox Cloud via a Fox datalogger. The performance warranty guarantees at least 70% capacity retention, or an energy throughput limit, whichever comes first. Fox ESS publishes that throughput figure for the EP11, at 33.4 MWh over its 10-year term. However, it had not published an equivalent figure for the EP12 in its UK warranty documentation at the time of writing.
Can Fox ESS work with solar panels I already have?
Yes. Fox ESS sells hybrid inverters, which combine solar charging and battery storage in one unit for new installs. It also sells AC-coupled battery options, designed to pair with an existing solar inverter for retrofits. Check compatibility with your specific inverter before buying.
Which markets is Fox ESS available in?
Fox ESS sells internationally through networks of solar installers, including in the UK, rather than direct to homeowners. As with any brand, it is worth getting quotes from more than one installer. Pricing and support can vary by installer, rather than by Fox ESS itself.
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