Choosing the right components for your solar energy system is key to maximising efficiency, reliability, and long-term performance. With so many products and brands now available in the UK, two names that stand out in the domestic solar market are Sigenergy and Fox ESS.
Although Sigenergy is a relative newcomer, its impact has been immediate, quickly positioning itself as a serious contender thanks to their innovative technology and forward-thinking design. Fox ESS, while only a few years older in the UK market, has already become a trusted favourite among both installers and homeowners thanks to its balance of performance and affordability.
Each brand has its own unique strengths and approach to the solar industry, raising the big question: which one is better suited to your needs?
In this guide, we break down the Sigenergy vs Fox ESS debate, exploring the pros and cons of each so you can make an informed choice and find the solar PV system that best fits your home.
Sigenergy Vs Fox ESS: Brand History & Presence
About Sigenergy
Sigenergy was founded in 2022 by Tony Xu, formerly the head of Huawei’s Fusion Solar division, as a technology company specialising in smart energy solutions. The company has focused on providing an integrated approach to solar inverters, energy storage and EV charging. As a company they have invested heavily in research and development with a view to producing cutting edge technology for their customers. By doing so Sigenergy has rapidly become a respected player within the domestic renewable energy sector. This is very impressive for such a young company especially when we consider that Sigenergy only introduced its solar systems to the UK at the Solar & Storage Live 2023 event in Birmingham on 17 October 2023, less than 2 short years ago!
As a newcomer, we can’t expect Sigenergy to have collected too many awards just yet, but they have already received international recognition by winning the “2024 Responsible Brand Award” at the 14th Philanthropy Festival in Beijing. Their products have also been consistently praised by both customers and installers as a genuine competitor to established market leaders like the Tesla Powerwall 3.
To see how they stack up directly, check out our blog on Sigenergy Sigenstor vs Tesla Powerwall 3.
About Fox ESS
Co-founded in 2019 by current CEO is Michael Zhu, Fox ESS has quickly established itself as a major player in the global solar market. Zhu, formerly Sales Director at SolaX, another well established solar company, was named one of Energy Box’s “Top Ten Photovoltaic Influencers” in 2022, and a year later Fox ESS earned a spot on the Forbes Global 2023 Unicorn List.
Fox ESS is currently a subsidiary of the Tsingshan Group which is a Fortune 500 company and in 2021 was the world’s largest nickel producer. This relationship provides Fox ESS with a significant advantage as Tsingshan’s various mining and refining operations provide an integrated supply chain for materials needed to produce lithium-ion batteries. This is a great advantage in times of global disruption and shortages. Fox ESS launched its product range in the UK in 2020 and has since become a major player in the UK domestic solar marketplace.
Fox ESS has built a strong global presence with sales networks across Europe, Australia, South America, and Africa, alongside subsidiaries in the UK and a European headquarters in Germany, with further expansion into North America and Asia underway. The company has earned multiple awards, including EUPD Research’s “Top Brand PV” seals in 2023 and 2024, BloombergNEF Tier 1 Energy Storage Leader status, 2025 A-Class Certification from HTW Berlin, and EUPD’s “Top Innovation Award” for its G-MAX commercial system in 2025.
Sigenergy or Fox Ess Inverters
Both Sigenergy and Fox ESS offer a range of different types of inverters for both residential and commercial scenarios with options available for both single phase and three phase supplies. For the purpose of this review we will concentrate of the single phase / residential offerings from both companies.
| Sigenergy | Fox ESS | |
|---|---|---|
| Single Phase Hybrid Inverters Sizes | Energy Controller 3.6kW 4kW 5kW 6kW 8kW 10kW 12kW Hybrid Range 2kW 3kW 3.6kW 4kW 4.6kW 5kW 6kW | H Series 3kW 3.7kW 4.6kW 5kW 6kW K Series 7kW 8kW 9kW 10kW |
| Start Up Voltage | Energy Controller = 100V Hybrid Range = 180V | 75V |
| Max PV Efficiency (European) | Energy Controller = Up to 97.4% Hybrid Range = 98.6% | H Series = 96.33% K Series = 97.4% |
| Number of MPPT Trackers | Energy Controller 3.6kW – 6kW = 2 MPPTs 8kW = 3MPPTs 10kW - 12kW = 4 MPPTS Hybrid Range = 2 MPPTs | H Series = 2MPPTs K Series = 7kW – 8kW = 3 MPPTs 9kW – 10kW = 4 MPPTs |
| IP Rating | IP66 | IP65 |
| Max DC Power | x2 The Size of The Inverter | H Series 3kW – 4.5kW 3.7kW – 5.5kW 4.6kW – 6.9kW 5kW – 7.5kW 6kW – 9kW K Series 7kW – 10.5kW 8kW – 12kW 9kW – 13.5kW 10kW – 15kW |
| Warranty | 10 Years | 10 Years (5 on Installation +5 Once Registered) |
| Battery Compatibility | SigenStor Batteries (5.0, 6.0, 8.0, 10.0) | Fox ESS EP & EQ Batteries |
| Monitoring | mySigen | FoxCloud |
| Protection | - DC Ground Fault Protection - Arc Fault Circuit Interrupter - DC Reverse Polarity Protection - Insulation Monitoring - Residual Current Monitoring - Type II DC/AC Surge Protection - Anti-islanding Protection - AC Overcurrent / Overvoltage / Short-Circuit Protection. | H Series - Insulation Monitoring - Residual Current Monitoring - DC Reverse Polarity Protection - Anti-islanding Protection - AC Overcurrent / Overvoltage / Short-Circuit Protection - DC Switch - Type II DC / Type III AC Surge Protection. K Series all above plus - Leakage Current Protection - Over Temperature Protection. |
Sigenergy Inverters
Ranging from 2 kW to 12 kW and supporting single-panel systems and up to 24 kW of DC input, the Sigenergy inverter range is impressive in terms of scalability and input capacity. While the Sigenergy Energy Controller remains their most popular and renowned model, the company also offers a range of hybrid inverters and microinverters that are separate yet compatible with the SigenStor. These provide a more affordable option for smaller systems, ideal for social housing projects, solar balconies, and new builds.
Compared to Fox ESS, the Sigenergy range is slightly more efficient and has a higher IP rating, offering better protection from the elements, including high-pressure water jets. Although, both Sigenergy or Fox ESS inverters are well suited for outdoor installation.
Sigenergy inverters come with a 10-year warranty out of the box, while Fox ESS inverters and batteries include a standard five-year warranty, extendable to 10 years when registered and monitored via Fox’s platform.
Fox ESS Inverters
Fox ESS offers a wide range of PV inverter options, covering both string-only and hybrid models. Their single-phase string inverters include the S, F, T, V, R, and G Series, while the hybrid range features the H and K Series. With flexible string inverter and AC Controller options, this also means that unlike Sigenergy the Fox ESS can can integrate well with other brands of systems.
Fox ESS inverters are available in multiple forms, from traditional standalone wall-mounted units, to stackable solutions such as the Power Q inverter, through to all-in-one systems in the EVO range. Making this competitive with both modular systems such as Sigenergy’s SigenStor and inclusive all-in-one systems like the Tesla Powerwall 3.
Efficiency across their inverters is strong, ranging between 97.2% and 97.8%, which is highly competitive. Fox ESS inverters also have a lower start-up voltage than Sigenergy, combined with a wide voltage range, enabling them to begin generating power earlier in the day and handle a variety of array configurations.
While Sigenergy’s inverters can support a larger PV input without paralleling the units, both Fox ESS and Sigenergy support a maximum of 10 inverters in parallel making them incredibly scalable systems. More than enough to power 99% of UK homes.
All Fox ESS inverters come with optional EPS (Emergency Power Supply) as standard, providing backup for essential loads during power cuts with a seamless <20ms changeover time.
Key reasons why you should choose A Fox ESS Inverter
- You are looking to install a standalone string, AC Controller or hybrid inverter, that is compact, cost-effective and flexible.
Key reasons why you should choose A Sigenergy Inverter
- Sigenergy offers a wide and large range of solar inverters, capable of handling greater DC input without the need to parrallel systems, this is ideal for larger solar installations.
- Sigenergy provides a faster charge/discharge rate than Fox ESS, making it particularly well-suited for homeowners looking to maximise off-peak tariffs or power high-consumption appliances. Sigenergy provides a faster charge/discharge rate than Fox ESS, making it particularly well-suited for homeowners looking to maximise off-peak tariffs or power high-consumption appliances.
Sigenergy or Fox ESS Batteries
Sigenergy Batteries
The Sigenergy SigenStor, offers a modular, easily scalable stackable design, which incorporates both the inverter and batteries into one system. Only the SigenStor batteries can be added to the system, and currently you can have up to 6 battery modules per stack, for a maximum of 52.56kWh of usable capacity. As a maximum of 10 pieces can be installed in parallel, the Sigenergy Sigensotr is expandable up to 525.6kWh of battery capacity per phase, making it one of the most scalable battery solution on the market.
The SigenStor batteries are available in 4 sizes. The original battery packs were designated as the 5.0 and 8.0. with the the 6.0 and the 10.0 becoming available in 2025. Although a number of people have commented that the new 10.0 battery module should have been called the 9.0 as this would be a more accurate description!
| Battery Module | Total Capacity | Usable Capacity | Max Charge Rate | Max Discharge Rate |
|---|---|---|---|---|
| 5.0 | 5.38kWh | 5.2kWh | 2.5kW | Inverter Dependant |
| 8.0 | 8.06kWh | 7.8kWh | 4kW | Inverter Dependant |
| 6.0 (NEW) | 6.02kWh | 5.84kWh | 3kW | Inverter Dependant |
| 10.0 (NEW) | 9.04kWh | 8.76kWh | 4.6kW | Inverter Dependant |
Both Fox ESS and Sigenergy batteries are based on Lithium Iron Phosphate (LFP) chemistry which is currently the best and safest battery technology for home battery storage systems. LFP batteries are much less likely to undergo thermal runaway in the event of a malfunction. Sigenergy also prides itself on its 5 levels of protection for each battery module. This includes AI monitored temperature sensors, hi-tech aerogel insulation, a built-in fire suppression system, a decompression valve and finally a high temperature resistant insulation layer. With all this technology built into them, these really are some of the safest batteries available.
The battery modules come with a 10 year 10,000 life cycle warranty with a 100% depth of discharge. Each module has its own Battery Management System and an advanced optimiser which allows old and new batteries to be mixed without the need to first balance the charge in each module, allowing for full customisation. In effect a brand new module at a 50% state of charge can be added to a stack of old modules at a 100% state of charge and the modules will immediately begin to balance themselves. This isn’t possible with most battery storage systems and makes adding new battery modules a very simple task. Thanks to its modular design, the Sigenergy system can be tailored to meet a household’s current needs while remaining flexible enough to expand in the future as energy demands grow.
Like the inverter modules, the battery modules have an IP66 rating. They are also heated and have an operating window of -20 degrees to +55 degrees Celsius, making them well-suited for outdoor installations. While the SigenStor system can be either wall-mounted or floor-stacked, it only supports the weight of two battery modules when wall-mounted.
Fox ESS Batteries
From Low Voltage batteries like the LV52, LV54, and 5200, to High Voltage batteries such as the EP and EQ series, Fox ESS offers a versatile range of battery solutions to suit almost any home. With both wall-mounted and stackable modular designs, there’s a system for every space and budget. From budget-friendly models to premium options, like the Fox ESS EVO, a true Tesla Powerwall competitor, the Fox ESS battery range is known for its outstanding flexibility.
For this Sigenergy vs Fox ESS comparison, we’ll focus on the EP and EQ series batteries (commonly paired with Fox H and K series hybrid inverters) as well as the EVO, which are among the most popular systems installed by Deege Solar.
| Battery | Total Capacity (kWh) | Usable Capacity (kWh) | Cycle Life | Scalability |
|---|---|---|---|---|
| EP5 | 5.13 | 4.62 | 4000 | Up to 4 (parallel) |
| EP6 | 5.76 | 5.18 | - | Up to 4 (parallel) |
| EP11 | 10.36 | 9.32 | 4000 | Up to 4 (parallel) |
| EP12 | 11.52 | 10.37 | - | Up to 4 (parallel) |
| EQ2900 | 2.88 | 2.59 | 6000 | Up to 7 (series) |
| EQ4300 | 4.14 | 3.72 | 6000 | Up to 7 (series) |
| ECS4100 | 4.03 | 3.63 | 6000 | Up to 7 (series) |
| EQ4800 | 4.66 | 4.19 | 6000 | Up to 9 (series) |
| EVO | 10.24 | 9.73 | 6000 | Up to 3 (parallel) |
The Fox ESS EP Series
The EP series batteries from Fox ESS offers a high performance, high voltage scalable battery storage system with a 90% depth of discharge. These can be floor or wall mounted and now feature an upgraded heating element, making them suitable for unheated areas. With an IP65 ingress protection rating, they are also ideal for outdoor installations.
The Fox ESS EP batteries represent the more budget-friendly option. There are currently four different capacity options: the EP5, EP6, EP11, and EP12. The older modules, EP5 and EP11, feature an anthracite grey finish, while the newer EP6 and EP12 models match the style of the inverter range with a white finish.
Up to four of the EP batteries can be mounted in parallel so if we have four EP12 batteries at a 90% depth of discharge this gives us 41.5kWh of usable capacity. However, due to the wall space required, the stackable EQ series is often the preferred choice for larger storage needs.
The Fox ESS EQ Series
The EQ series of batteries from Fox ESS is a more premium home battery storage option, effectively serving as a refined version of their popular Energy Cube or ECS series, the main upgrade being scalability. While the ECS series supported a maximum of seven battery modules, the EQ series allows stacks of up to nine modules. Despite the improvement, the ECS and EQ modules remain so similar that they can be combined in a single stack as long as the capacity of each module is the same. The ECS series is available in capacities of ECS4800, ECS4300, ECS4100, and ECS2900, while the EQ battery range offers the EQ3300, EQ4800, EQ5000, and EQ6000 Plus models.
Each EQ battery stack is made up of a master module, which contains a battery and a Battery Management System (BMS) that controls and manages the entire stack. Additional “slave batteries” can be then added onto this system. For the EQ6000 Plus this would be the master plus 8 slave modules giving a total capacity of 41.94kWh (37.73kWh usable).
These batteries have an operational window of 0 to +55 degrees Celsius for charging and -10 to +55 degrees Celsius for discharging and come with a 12 year warranty as standard. Internal heating systems are available where EQ master and slave units are used.
As a final addition to the EQ battery series Fox ESS has released a stackable inverter, the PowerQ that can be paired with last EQ batteries, including the EQ2900, EQ4300 and EQ4800. This creates a sleek all-in-one design offering up to 30 kWh of storage, with inverter sizes ranging from 3.7 kW to 11 kW. Alongside the EVO system, the PowerQ highlights Fox ESS’s commitment to expanding its product line and meeting the needs of a diverse global customer base.
The Fox ESS EVO Series
Brand new to the Fox ESS Battery range, the Fox EVO is an all-in-one inverter and battery solution. The Fox ESS EVO all-in-one is offered in 3 inverter sizes of 5kW, 8kW and 10kW, with 3 MPPTs, capable of 200% PV oversizing.
The EVO includes a 10.24kWh LFP battery offering a 95% depth of discharge and an impressive 6,000-cycle lifespan. This equates to more than 16 years of use if fully cycled daily. Once registered online, the EVO series includes a 12-year warranty, and if 10.24kWh of battery storage isn’t enough, up to three units can be mounted in parallel to provide 27.65 kWh of usable capacity.
Looking ahead, a battery-only expansion module is expected in 2026, enabling owners to increase storage capacity without additional inverter hardware, mirroring Tesla’s approach with the Powerwall 3 expansion packs.
The EVO is also IP66 rated, and comes with a host of safety features including a fire suppression system. With integrated battery warm-up technology, and an operating temperature range of -20 to +55 degrees Celsius, the EVO is suitable for both indoor and outdoor installation. A whole home backup gateway is also available with the EVO system.
Designed to compete with some of the best solar batteries on the market, the Fox ESS EVO combines style and substance. Its slim 19.7 cm depth, magnetic panels to conceal inputs, and sleek glossy front finish creates a clean, modern aesthetic.
Key reasons why you should choose A Fox ESS Battery
- You are looking for a budget friendly yet powerful solution with great product diversity.
Key reasons why you should choose A Sigenergy Battery
- Sigenergy battery storage is built with scalability and flexibility at its core, offering greater expandability and ease of growth compared to Fox ESS.
- Thanks to its modular, parallel-connected design, expanding your system is quick and efficient, with no need for cell balancing. This means you can easily add capacity later, even if there’s a disparity in the State of Health between battery cells, allowing your storage to grow alongside your energy habits.
- Warrantied for 10,000 cycles the SigenStor battery offers superior long-term reliability.
Price: Is Sigenergy or Fox ESS Cheaper?
From a pricing perspective, both Sigenergy and Fox ESS offer excellent value for money, with the final cost largely depending on the options selected by the consumer. The examples below illustrate two comparable systems that are commonly chosen by buyers of each brand.
| Sigenergy | Fox ESS | |
|---|---|---|
| Panels | 16 x 475W Aiko All Black Panels | 16 x 475W Aiko All Black Panels |
| Inverter | 8kW Sigenstor Energy Controller | 8kW K Series Hybrid Inverter |
| Battery Storage | SigenStor 10.0 Battery Module | EP11 |
| Extras | Energy Gateway | |
| Fitted Price* | £14,600 | £12,400 |
*This price includes installation, IWA registration, MCS certification, 1 side of access equipment, DNO registration and 5 years workmanship warranty.
In the example above, the Sigenergy Gateway has been included, as it is almost always selected in the systems we install. It is widely regarded as an essential component by most buyers, even in areas where power network disruptions are uncommon. The Sigenergy system is generally positioned as a slightly more premium option, and additions such as a DC EV charger can further increase the overall cost.
Sigenergy or Fox Ess: Home EcoSystem
The Fox ESS ecosystem offers a comprehensive and versatile suite of energy solutions designed to work seamlessly together. From high and low-voltage battery storage to a wide range of hybrid and string inverters, all components are designed for compatibility and scalability. The ecosystem also includes the all-in-one EVO series, a smart monitoring platform, and even integration with Fox ESS home energy devices such as EV chargers and, more recently, heat pumps. This interconnected approach allows homeowners to optimise energy generation, storage, and consumption while maintaining flexibility for future expansion, making the Fox ESS ecosystem a truly complete solution for modern solar-powered homes.
Whilst the Sigenergy ecosystem doesn’t include a Heat pump as of yet, Sigenergy have focused on a different aspect of future proofing, and intelligent energy management. The system can be expanded easily thanks to its parallel-connected, stackable battery design, allowing homeowners to grow their storage capacity alongside their energy needs. With the MySigen app providing granular monitoring, AI-driven tariff optimisation, and smart home integration, the Sigenergy ecosystem gives users full control over solar generation, battery storage, and energy consumption, creating a future-proof, high-performance solution for modern homes.
EV Charging
While both Fox ESS and Sigenergy offer AC EV chargers, Sigenergy goes a step further by also providing a bi-directional DC EV charger. The optional DC EV charger occupies one module in the SigenStor stack and provides the homeowner with DC fast charging at 12.5kW or 25kW, this is significantly faster than the 7kW AC chargers installed at most homes. The DC charger also has a bidirectional capability which supports Vehicle to Home (V2H) and Vehicle to Grid (V2G) functions. This allows the car’s battery to power the home during a blackout or sell electricity held in the car to the grid during peak times. Whilst the DC charger is an innovative piece of equipment, it does have one drawback in particular – the price. The DC charger module costs around £4000, on top of the SigenStor system, which is significantly more expensive than a regular EV charger but may be an important option for an all electric home that has more than one electric vehicle.
Back Up Power
Another key ecosystem option for Sigenergy buyers is the Solar Gateway. While Fox ESS has only recently introduced full home backup with the new EVO battery, Sigenergy’s Gateway is a more established and mature solution. It offers full home backup with UPS (Uninterrupted Power Supply), automatically detecting outages and seamlessly switching the home to backup power without user intervention. During an outage, the system enables full use of the inverter and batteries, and can even trigger a generator for extended blackouts. Priced at around £900, the Gateway is considered by most buyers an essential feature. As Fox ESS’s gateway is still new to the UK market, its price and performance remain to be seen.
Sigenergy or Fox Ess: App Monitoring
mySigen App
Sigenergy has invested heavily in designing their app, resulting in one of the best monitoring platforms available. It is a key component of their home energy storage system, giving homeowners comprehensive control and oversight of their solar panels, battery storage, and EV charging. The app keeps even the most enthusiastic users fully informed, providing some of the most detailed system performance data available from any manufacturer.
Users can monitor real-time energy flows, track individual battery cell voltages and temperatures, and view detailed breakdowns of solar production, consumption, and grid usage. All of this is delivered through a user-friendly interface, reflecting the significant development effort invested in the platform.
Leveraging GPT-4, the built-in AI Assistant provides intelligent recommendations and optimises the system based on each household’s usage patterns and energy tariff. The AI interface can even respond directly to customer queries. This combination of detailed insights and technical sophistication sets Sigenergy apart from many of its competitors.
As a relatively new system with advanced technology, some users have reported occasional software bugs. This contrasts with more established apps, such as Tesla’s, which have a long track record of delivering a polished user experience. The average rating of around 3.5/5 reflects these “growing pains” as the app continues to mature. Despite this, many reviews highlight the unique features that attract users to Sigenergy systems.
For homeowners who prioritise home automation, the Sigenergy system can communicate with Home Assistant via the Modbus TCP protocol. Additionally, the system is compatible with Smart tariffs, including advanced options like Intelligent Octopus Flux and Agile Octopus. While direct API integration with Octopus Energy is still in progress, the AI-driven tariff optimisations in the MySigen app already allow the SigenStor system to operate effectively with even the most sophisticated tariffs. Full integration and an official API partnership are expected in the near future.
FoxCloud 2.0 App
The FoxCloud 2.0 app is an updated and improved version of the original FoxCloud app. While it does not include the advanced AI and smart features found in the MySigen app, it provides users with all the essential data needed to monitor their Fox ESS system. Some users with older Fox ESS systems have reported challenges transitioning to the latest version, which may be partly due to the wide range of hardware solutions that the app needs to support.
The FoxCloud 2.0 app has an average rating of 2.6 out of 5, lower than the MySigen app. Some users have noticed discrepancies in reported data and differences from the previous version, suggesting occasional inaccuracies or a lag in reporting data. However, there are still many users who are satisfied with the new app, with it providing the essential day-to-day information required.
While Fox ESS systems can integrate with Home Assistant and Smart tariffs like Octopus Energy, support is currently limited. Many Fox ESS products work with Flux, but compatibility with Octopus’ “Intelligent” tariffs is restricted to select models. Like Sigenergy, Fox ESS is actively working to achieve official support for Intelligent Octopus Flux and Agile Octopus, particularly for newer systems such as the Fox ESS EVO all-in-one.
While Sigenergy views its app as a vital part of their ecosystem, Fox ESS does not appear to offer the same level of detail. For homeowners who value comprehensive data and monitoring, a Sigenergy system could be a compelling choice.
