The short answer
If you want one proven box that stores your solar, shifts your import into the cheap hours and backs the house up without much thought, the Tesla Powerwall 3 is the safer buy. If you want to start smaller and grow later, you are on a three-phase supply, or you want DC car charging in the same stack, the Sigenergy SigenStor fits better.
Neither is a mistake. Most of the "X destroys Y" content online is written by people who have never had either off a wall.
We fit both, which is the only reason this is worth reading. We are a Tesla Certified Installer — one of around 50 in the UK by our own count, and we are an early adopter of the Sigenergy SigenStor in the North East — we install and commission SigenStor systems and have two complete installs documented on our YouTube channel.
The specs, side by side
| Sigenergy SigenStor | Tesla Powerwall 3 | |
|---|---|---|
| Capacity | 1 to 6 modules per controller, each 5.38 kWh total / 5.2 usable up to 9.04 / 8.76. Six of the largest: 54.24 / 52.56 usable. | 13.5 kWh usable per unit, fixed. Each Expansion adds 13.5 kWh. Up to 4 units plus 3 Expansions, 94.5 kWh maximum. |
| Power | Single-phase 3.0 to 12.0 kW nominal, three-phase 5.0 to 30.0 kW. Twice nominal for 10 seconds off-grid. | Configurable 3.68 to 11.04 kW at 230 V single-phase. 185 A LRA motor start. Up to 44 kW system-wide. |
| Solar inverter | Built in. 6,000–24,000 W max PV input single-phase, 2 to 4 MPPTs, 50–550 V, 16 A per tracker. | Built in. 3 inputs on 3 MPPTs, 20 kW max solar STC input, 60–480 V, 30 A per tracker. |
| EV charging | Optional EVDC module: 12.5 kW DC, licence upgrade to 25 kW on specific models, CCS2. Needs the Energy Controller. | Not part of the unit; what is integrated is the solar inverter. The car charges from a separate point. |
| Backup | 0 ms load-side disruption, but only with a Sigen Energy Gateway, and the controller must out-rate the backup load. | Backup Gateway 2 in the UK. Whole-home or partial, set at design stage. Up to 11.04 kW. A cheaper Non-Backup option exists. |
| App | mySigen: 3D energy flow every 10 seconds, Sankey over six sources and five load categories, Shelly control, Octopus tariff data, AI layer. | Tesla app: Savings mode, Backup Reserve, Storm Watch on Met Office alerts, import and export tariffs, Octopus Flux, over-the-air updates. |
| Warranty | European terms: 10 years on modules, controller and connector, 5 on the gateway, 3 on the EVDC. 60% usable energy at 10 years or a throughput cap. | 10 years, 80% retention at 10 years on UK installs. Unlimited cycles for self-consumption, time-based control and backup. Gateway warranted 10 years. |
Two caveats: Sigenergy publishes modules in two generations, 280 Ah and 314 Ah, so ask which we are supplying; and the warranty figures above are its European terms.
Where the Powerwall 3 wins
One box, one design
Powerwall 3 holds 13.5 kWh of usable energy with the solar inverter already inside it — three inputs on three trackers, up to 20 kW of solar STC input. On a four-bedroom house with one array that is the whole electrical design in one product. It retrofits, too: Tesla says it can be added to existing solar, is compatible with all major inverter brands, and will charge from the grid with no solar at all (see adding battery storage to existing solar).
It starts heavy loads
The UK datasheet gives a load-start capability of 185 A locked rotor amps. That is the number that matters if you want a heat pump, a borehole pump or a workshop compressor to actually start once the grid has gone.
Simple warranty, mature software
Ten years, 80% retention at ten years on UK installs, unlimited cycles for self-consumption, time-based control and backup — no throughput table to work through. Storm Watch is live here: a Met Office Amber or Red warning mentioning power-cut risk charges the battery to full until it passes. And Intelligent Octopus Flux enrols the Powerwall in a virtual power plant with Octopus managing it, while Intelligent Octopus Go is not used for cost optimisation — which catches people out, as our Octopus Flux tariff guide explains.
Where the SigenStor wins
You can buy it a module at a time
One Energy Controller takes one to six modules, from 5.38 kWh up to 9.04 kWh total, so a stack is sized far more precisely than in 13.5 kWh jumps. Better, every pack carries its own DC-DC optimiser, which Sigenergy says lets packs of different capacities and states of health run in parallel — "mixed use of old & new batteries". If you expect to add capacity in three years, that is a different proposition to buying a second matched unit.
Three-phase, and bigger inverters
The UK Powerwall 3 is single-phase, 230 VAC, 50 Hz. The Sigenergy controller comes single-phase at 3.0 to 12.0 kW and three-phase at 5.0 to 30.0 kW. If you are on three-phase — as plenty of the converted barns and larger properties we survey in North Yorkshire are — that is not a preference, it is the decision.
DC car charging in the same stack
The optional EVDC module charges at up to 12.5 kW DC over CCS2, with a licence upgrade to 25 kW on specific models. The modes are the interesting part: scheduled, 100% PV surplus, battery-boost with a cut-off state of charge, straight grid, and a fast mode pulling from grid, PV and battery at once.
The caveat: it is marketed as bi-directional, but Sigenergy's own page says V2X is limited by the vehicle and can be upgraded over the air once standards are published. Treat it as V2X-ready and vehicle-dependent. If you only want an AC charge point, our EV charger installation page is cheaper reading.
Whole-home backup, and a deeper app
Sigenergy quotes 0 ms disruption at switchover, footnoted as needing a Sigen Energy Gateway alongside the controller and battery, with the controller out-rating the backup load. HomePro comes as SP (12 kW / 54.6 A), SP-F (22 kW / 100 A) and TP (30 kW / 45.6 A), and Sigenergy says the SP-F "fully supports 100 amp single-phase backup power for the entire home". mySigen also adds an AI layer; Sigenergy claims its AI Mode gives up to 50% higher average returns than self-consumption mode, a manufacturer claim we have not verified.
Who each one is actually for
Choose the Powerwall 3 if
- Solar and battery are going in together and you want the fewest boxes.
- You want backup that is simple to specify: Gateway 2, whole-home or chosen circuits.
- Heavy motor loads matter to you.
- You are on, or heading for, Intelligent Octopus Flux.
Choose the SigenStor if
- You want 5 or 6 kWh now and the option to grow later without matching modules.
- You have a three-phase supply.
- You want DC car charging integrated rather than a separate charge point.
- You want whole-home backup on a 100 A single-phase service.
Where each one loses
Powerwall 3 loses when the budget is phased: 13.5 kWh is the smallest step there is. It cannot be added to an existing Powerwall 2 either — Tesla is explicit that it combines only with other Powerwall 3 units — and in the UK it is single-phase, full stop.
SigenStor loses on simplicity: a controller, a stack, a connector and optionally a gateway and an EV DC module is more parts to explain to whoever owns the house next. Both lose if the system sits offline. Sigenergy drops a SigenStor into Safe Operation Mode after 90 days without internet and cuts ten-year cover to five if it is offline for over a year in total; Tesla says its warranty may be limited to four years where the connection is not maintained.
Our take from installing both
We have two complete SigenStor installs filmed end to end — a solar and battery install on a slate roof and a SigenStor with full home backup — plus a three-part film of a 19.1 kW array with a Tesla Powerwall.
Sigenergy claims a 15-minute stackable installation and five-minute commissioning, and the stacking genuinely is quick: modules connect through guided quick connectors that plug themselves once stacked, not hand-wired. But the battery does not decide the day. The consumer unit, the cable route and the network operator's paperwork do, and that is the same on both.
Tesla says a typical install is a full day with the power off for four to six hours, or eight and more where extra electrical work is needed, which matches how we plan it. On handling, a Powerwall 3 is 1,105 x 609 x 193 mm and 130 kg; a Sigenergy 6.02 kWh module is 62 kg and a 9.04 kWh module 78 kg. Neither is better for it, but it changes how a unit gets into a tight utility room.
Both sit outside happily: Powerwall 3 is IP55 with IP67 battery and power electronics and under 50 dB(A) typical at a metre; Sigenergy's modules, controller and EV DC module are IP66, though we have not found a published SigenStor noise figure, so there is no like-for-like number.
Cost, VAT and what to ask for
Neither manufacturer publishes a UK price. Tesla's order page connects you to a Tesla Certified Installer who then contacts you about pricing. Our own quote guidance is from £8,500 installed for a Powerwall 3 — our figure, not Tesla's, and it moves with the backup configuration and the electrical work. Sigenergy publishes no UK price either, and a SigenStor has more variables: modules, controller, gateway or not, EV DC module or not. Ask us for a fixed price rather than a comparison site's range.
On tax, HMRC's VAT Notice 708/6 zero-rates the installation of specified energy-saving materials until 31 March 2027, reverting to the 5% reduced rate from 1 April 2027, and electrical storage batteries in residential accommodation have qualified since 1 February 2024, retrofitted or standalone. If you were going to do this "at some point", that end date is the reason to pick a point.
Three questions for whoever quotes you
- Which backup configuration, whole-home or selected circuits? Powerwall 3's Non-Backup option uses a Tesla Remote Meter instead of the gateway — cheaper, but no backup power, Storm Watch, Backup Reserve or Go Off-Grid.
- Is the network operator application included? The UK Powerwall 3 is certified to G98 Issue 1 Amendment 7, G99 Issue 1 Amendment 9 and G100 Issue 2 Amendment 2, but somebody still has to apply.
- What does the warranty cover, and does the internet reach where the unit is going?
Getting either one fitted
We install across Teesside, County Durham and North Yorkshire from our base in Yarm. How far we travel depends on the job — just ask.
If you know which way you are leaning, start on the product page: Tesla Powerwall installer or Sigenergy installer. For local detail there are regional pages for Tesla Powerwall across Teesside and County Durham, Tesla Powerwall across North Yorkshire, Sigenergy across Teesside and County Durham and Sigenergy across North Yorkshire. Weighing a third option? Fox ESS is the value-led system we also fit.
Not sure yet is the normal position. Send your postcode through our contact page and Andy Pemberton, who surveys and specifies every system we quote, will tell you which he would fit and why — including "neither yet, get the solar right first". More on battery storage, or read our reviews.