Quick Summary (TL;DR)
A battery in your garage does not automatically mean your sockets will work in a blackout. Backup requires an inverter capable of forming a local AC supply, an approved means of disconnecting your installation from the public grid, suitable protection and earthing arrangements, and circuits actually connected to that backup supply. A normal grid-tied solar inverter shuts down when the grid fails unless it is part of a manufacturer’s supported backup architecture. An inverter advertised with an EPS, backup, emergency power or off-grid output may protect only a dedicated group of loads, not the entire property.
Our buying recommendation: first list the appliances you cannot afford to lose, their simultaneous and starting loads, and how many hours you want them to run. Then ask an installer for a written single-line diagram, backup circuit schedule, usable battery capacity, inverter continuous and surge power, grid-isolation method and commissioning test. Prioritise fridges, broadband, lighting, essential heating controls, security equipment and any medically necessary devices; large water heaters, ovens and EV chargers usually deserve a separate decision. If a device is medically critical, seek a purpose-designed independently assessed UPS or backup solution rather than relying on a domestic solar battery alone.
The first distinction: battery storage, EPS and whole-home backup
A home battery may be installed purely to reduce electricity bills by shifting consumption from sunny or cheap periods to expensive ones. In normal operation, it exchanges power with the house and public network. That says nothing about whether it is allowed—or able—to energise the home when the utility supply disappears. Anti-islanding protection normally ensures a grid-connected generator does not feed a dead public grid. A properly designed backup installation separates designated local circuits from the grid and establishes a safe independent power source.
Some hybrid solar inverters include a dedicated backup or Emergency Power SupplyAliExpress price (EPS) terminal. Other systems use a separate inverter/charger and automatic changeover equipment. An integrated package such as Tesla Powerwall may use a Backup Gateway, Gateway 3 or an approved Backup Switch, with partial-home and whole-home layouts available depending on jurisdiction and design. Tesla also offers a non-backup Powerwall 3 configuration in certain markets, proving that buying the same battery model does not necessarily mean buying the same outage capability. See the Tesla system design guide and UK non-backup configuration explanation.
| System arrangement | What happens when the grid fails? | What can be powered? | What to check before buying |
|---|---|---|---|
| Solar PV with conventional grid-tie inverter, no backup equipment | Solar production generally stops for anti-islanding safety | Nothing from the PV system | Whether backup retrofit is supported at all |
| Battery used only for grid-connected self-consumption | Battery normally cannot provide household AC during the outage | None of the house circuits unless a supported backup path is installed | Product variant, changeover equipment and quote exclusions |
| Hybrid inverter with dedicated EPS/backup terminals | Supported inverter can form an isolated supply subject to battery, PV and control conditions | Loads specifically wired to its protected output | Continuous rating, phase, surge, switch-over and supported circuits |
| Battery inverter/charger plus protected distribution board | Grid is isolated and inverter powers the designated backed-up board | Essential circuits in that board | Transfer scheme, earth/neutral provisions and circuit selection |
| Whole-home backup system | Supported changeover isolates the house and supports its installation within power limits | Whole-home circuits, unless heavy loads are shed or restricted | Inverter headroom, service size, EV/heating loads and island-mode restrictions |
| Separate outlet or manual emergency supply | May provide limited manually accessed AC on certain products | Only equipment expressly supported by that outlet | No improvised connection to house wiring |
Important: these are architectures, not a guarantee about a particular product. Manufacturer variants, firmware, single- versus three-phase configurations, market rules and installer design can change the outcome.
What actually happens during a power cut?
In an approved automatic-backup installation, the gateway, transfer system or hybrid inverter detects grid loss. It disconnects the backed-up electrical installation from the utility before the system supplies a local reference voltage and frequency. The battery inverter then holds the islanded AC supply within its operating limits; the PV subsystem may continue contributing only if it is compatible with the islanded system’s control and frequency/voltage behaviour. When utility power returns, the equipment checks conditions, synchronises and restores the normal grid configuration in accordance with its design.
The exact sequence and interruption vary. Some products aim for very short transfers and can keep many appliances running; others have a noticeable interruption while the EPS output starts. A standard domestic backup system should not be assumed equivalent to an online no-break UPS. Computers, networking hardware, medical electronics and controls that cannot tolerate any interruption may still need a separate correctly sized UPS.
Victron’s MultiPlus-II description explains that its AC-out-1 can maintain a UPS-style supply, while AC-out-2 disconnects during battery operation—a useful way to omit a large water heater or air conditioner. The actual installation must still follow the correct model’s design instructions. Tesla’s backup operating guidance describes its own grid disconnection, backup operation and load-saving measures; do not generalise one manufacturer’s transfer time to another.
Five prerequisites for real backup
- Grid isolation: a manufacturer-approved transfer device, gateway or compliant internal switch must prevent energising utility lines and provide appropriate reconnection logic.
- Grid-forming ability: the inverter must create and regulate AC when the utility reference is absent. Many normal PV inverters are grid-following instead.
- Backup-capable wiring: the intended loads must physically sit on the protected side of the arrangement. A dashboard label does not move a circuit onto an EPS board.
- Adequate instantaneous power and battery energy: the inverter must accommodate running demand and starting current, while the battery must last the required period.
- Correct protection and controls: suitable isolation, fault protection, neutral-earth behaviour, RCD arrangements and battery safety must be engineered for island mode and local rules.
Grid-isolation, distribution-board changes and earthing design are not DIY wiring projects. Never connect an EPS output through a plug, extension lead, improvised changeover, or a back-fed circuit. A qualified electrician familiar with the inverter and applicable standards must design, install and test these connections.
EPS output versus essential-load board versus whole-home backup
EPS output describes a facility on some hybrid inverters, not a universal power rating or wiring standard. On one product it may be an automatically energised output behind a switching device; on another it may require a particular mode, battery state or additional switching accessories. Some installations have a manual-only emergency outlet. Never assume the acronym implies automatic, uninterrupted, three-phase or whole-house supply.
An essential-load board separates priority circuits so the inverter can protect them without supporting every major appliance. This often gives the best balance for an ordinary home: fewer peak-load conflicts, less chance of battery depletion and a smaller inverter requirement. A refrigerator circuit, a few lights, the internet connection, door security and boiler controls might belong there, subject to the site assessment. Loads deliberately left on the normal board simply go off in a blackout.
Whole-home backup is convenient but not an unlimited power socket. A house with 100 A supply could theoretically draw much more instantaneous power from the utility than a single domestic battery inverter can deliver. During a blackout the system may require automatic load shedding, limits on EV charging or restrictions on simultaneous cooking and heating. Tesla’s partial- versus whole-home documentation explicitly ties coverage to installed system size, backup configuration and appliances.
| Requirement | Essential-load EPS board | Whole-home backup |
|---|---|---|
| Initial circuit selection | Installer moves approved priority circuits to backup board | Installer evaluates the entire existing distribution arrangement |
| Backup inverter sizing | Based on critical coincident loads and surge | Based on household peaks or controlled load shedding |
| Large electrical appliances | Usually excluded unless deliberately selected | Physically present but may need blocking/shedding |
| Outage runtime | Often longer for same usable kWh | Shorter if occupants continue normal high demand |
| Retrofitting complexity | Additional circuit separation and protection | Service coordination and changeover can be more involved |
| Best for | Reliable essentials and predictable budget | Homes that want convenience and accept greater system cost |
| Main purchasing trap | Assuming a socket is protected when it is not | Assuming whole-home means unlimited power |
What about a three-phase house?
Three-phase architecture is a frequent source of unpleasant surprises. A single-phase EPS output does not magically reproduce a three-phase grid. It can serve only properly allocated compatible loads within its circuit and current limits. Three-phase motors, three-phase EV charging, certain heat pumps and phase-dependent controls may not operate on it. Some three-phase backup systems have unequal per-phase constraints or require a coordinated multiple-inverter architecture; other products cannot energise all three phases in island mode. Confirm the exact inverter model, phase allocation, neutral design, maximum unbalanced load and region-specific approval in writing. Do not bridge phases together to imitate a three-phase source.
Size the power first: kW is not kWh
kW is the instantaneous load the inverter has to support. kWh is the energy the battery can deliver over time. A 10 kWh battery paired with a 3 kW backup output cannot supply a 6 kW instantaneous load simply because plenty of energy remains. Conversely, a 10 kW inverter feeding 5 kW of loads from a small battery can exhaust the available stored energy quickly.
Start with a priority load register. The following values are illustrative planning assumptions, not appliance specifications. Measure your actual equipment and consult the nameplates; compressors and pumps have transient starting currents.
| Example priority load | Typical planning running load used here | Outage considerations |
|---|---|---|
| Router, ONT and network switch | 25 W | A UPS may cover a transfer interruption; ISP equipment elsewhere may also fail |
| LED lighting across selected circuits | 70 W | Depends on occupants and circuits in use |
| Refrigerator/freezer average over a day | 65 W equivalent average | Compressor starts can be higher than the running draw |
| Security, monitoring and smart-home hub | 25 W | Keep essential gateways and switches backed up together |
| Heating circulation pump and controls | 85 W when active | Boiler or heat pump may have other power/interlock requirements |
| Laptop and one workstation | 80 W | Sensitive hardware may require an independent UPS |
| Small water pump | 500 W while operating | Motor startup surge and pressure-control system matter |
| Induction hob, electric shower or immersion heater | Several kW depending on model | Usually prioritise exclusion or load shedding |
| EV charger | Several kW; phase-dependent | Normally disable during an outage unless specifically designed for backup |
For a simple calculation, suppose the essential loads average 320 W over the outage, while occasional equipment causes short peaks. If the battery has 8 kWh usable at the beginning of the outage, and the simplified inverter/distribution efficiency from battery output to delivered AC is 90%, usable AC energy is 7.2 kWh. Estimated runtime is 7.2 / 0.32 = 22.5 hours. This is a modelling example, not a guaranteed autonomy. Cold weather, standby overhead, operating limits, battery reserve, temperature and degradation can change it.
At 800 W sustained, the same model returns 9 hours. At 2.4 kW, it returns just 3 hours. That is why a carefully chosen critical-load board is often more useful than a nominally larger inverter running every appliance in the home.
| Illustrative continuous load | Available AC energy | Simple estimated runtime |
|---|---|---|
| 0.20 kW | 7.2 kWh | 36 hours |
| 0.32 kW | 7.2 kWh | 22.5 hours |
| 0.50 kW | 7.2 kWh | 14.4 hours |
| 0.80 kW | 7.2 kWh | 9 hours |
| 1.20 kW | 7.2 kWh | 6 hours |
| 2.40 kW | 7.2 kWh | 3 hours |
An accurate site-specific runtime calculation should subtract both the backup reserve you choose to preserve and any energy the battery cannot deliver at its current state of charge. A battery displayed as 70% full at the start cannot be modelled as if it were 100% full.
Check continuous power, surge power and inverter starting restrictions
A motor may briefly demand substantially more power when it starts than while running. Pumps, fridges and compressors deserve explicit surge checks; the nameplate and manufacturer’s start method matter. A system can have sufficient nominal kWh yet trip when two compressors start together. Continuous ratings, surge ratings, operating temperature and battery-imposed discharge-current limits may also differ. Ask the installer to document the combined worst credible load rather than merely adding annual kWh figures from a utility bill.
For sensitive medical devices, a home battery is not a substitute for the product’s approved independent power arrangement and emergency plan. For critical refrigeration or medical needs, consider redundant supplies, monitoring and locally appropriate emergency contingencies.
What happens to solar panels while the grid is down?
Solar PV is not an automatic outage generator. A standard grid-following inverter normally disconnects when its grid reference disappears. In a suitable backup system a grid-forming inverter can provide a stable local AC reference, allowing supported PV equipment to operate inside the island. Whether that works, and whether solar can restart from an empty or deeply depleted battery, depends on the specific topology and product configuration.
DC-coupled hybrid solar and battery: the manufacturer’s supported inverter may manage PV input, storage charging and backup output through one control platform. Solar can potentially replenish the battery during daylight if the inverter, battery management system and operating conditions permit it. This is not a claim that every DC-coupled system will black-start after battery shutdown.
AC-coupled solar: a separate PV inverter can sometimes run on the backed-up AC bus behind a battery inverter, but only where the manufacturers permit the combination. The grid-forming inverter must control power balance as solar production and household demand change. Frequency-based or other curtailment strategies may be required, and battery power must be able to absorb fluctuations. Victron’s ESS design and installation manual sets explicit engineering limits for AC-coupled PV; it is not safe to assume any third-party PV inverter can be attached to any EPS terminal.
Low battery or no sunlight: some systems stop supplying AC below a protective threshold, then recover only when sufficient solar energy or grid power becomes available. Other systems have reserve and restart strategies. Cold batteries may refuse charging at certain temperatures. These are reasons to ask how the actual installation behaves in a multi-day winter outage, rather than assuming that the presence of panels makes backup indefinite.
| Solar/battery arrangement | Potential daytime help during blackout | Critical limitation |
|---|---|---|
| Grid-tie PV only | Normally none | Anti-islanding shutdown |
| Supported hybrid DC-coupled PV and battery | May run protected loads and recharge battery | Product-specific battery, PV and low-SOC conditions |
| Compatible AC-coupled PV with battery inverter | May supply islanded loads and recharge | Inverter coordination, curtailment, power balance and compatibility |
| Unsupported separate PV inverter attached to EPS | Do not assume operation | Unsafe or unstable arrangement; manufacturer’s approval essential |
| Cloud-based solar monitoring alone | No direct electrical backup capability | An app cannot form a safe grid |
Four product paths worth considering
There is no universal best battery. The relevant purchase is an approved backup system, not simply the highest capacity battery. Compare written quotations for all items required to deliver the outage behaviour you want, including distribution-board work and commissioning.
Tesla Powerwall: integrated backup, but check the installed configuration
Tesla’s Powerwall range can be configured for whole-home or partial-home backup using an appropriate supported gateway or switch. The installer determines how the backed-up circuits and isolation are arranged. Importantly, Tesla’s non-backup Powerwall 3 option is not equivalent to a configured backup installation until upgraded with the required components. The manufacturer’s exact rated outputs, compatible markets, grid interconnection conditions and software options must be checked against your quotation and installation documents. Read Tesla’s system design overview and Powerwall 3 installation documents.
Tesla provides integrated monitoring and reserve management, but its supported Home Assistant features can vary with the Gateway, Powerwall generation and firmware. See the official Home Assistant Powerwall integration. Don’t assume that local sensors can operate the safety-critical transfer switch.
Victron MultiPlus-II / Quattro: configurable, installer-dependent backup
Victron’s inverter/charger architectures are attractive when flexibility, compatible batteries, third-party solar and off-grid operation are central requirements. A correctly designed MultiPlus-II installation can back up designated AC-out-1 loads; many model versions provide AC-out-2 for appliances that disconnect during inverter operation. In other words, output selection itself is part of the load-shedding strategy. The 230 V MultiPlus-II technical description is a useful starting point. The design must account for battery compatibility, transfer ratings, solar coupling and applicable grid-code settings. A cheap standalone inverter price is not the installed ESS price.
Victron also has strong local monitoring options through a GX device; the official Home Assistant Victron GX integration uses local MQTT. See our Cerbo GX versus Raspberry Pi Venus OS guide for gateway trade-offs.
Hybrid solar inverter with manufacturer-supported EPS: practical essential circuits
If the homeowner is buying a new solar installation and wants a limited group of protected circuits, a hybrid inverter with an approved EPS feature can be economical. But the EPS port’s rating and external switching requirements differ by model, and certain systems cannot use it without particular batteries or accessories. Confirm the latest region-specific manual, approved battery list and installer diagram for the exact hardware code. A generic marketplace listing that says ‘EPS ready’ is insufficient proof.
Retrofitting existing solar: compatibility before brand loyalty
An existing conventional grid-tie inverter may continue operating normally while the new battery provides only self-consumption, or the retrofit may require battery-coupled backup with approved PV interaction. Whole-home protection may require substantial switchgear and distribution changes. In a retrofit, request two priced designs: one for critical-load backup, one for whole-home backup if feasible. That exposes the real cost of each rather than burying switchgear in a battery bundle.
| Buying route | Strength | Main constraint | Best candidate |
|---|---|---|---|
| Integrated Powerwall backup package | Cohesive battery/gateway ecosystem | Backup hardware variant, approved installation, model-specific controls | Homeowner seeking integrated management |
| Victron ESS / inverter-charger architecture | Configurable loads, monitoring and supported system components | Design and commissioning complexity | Technical buyer with experienced installer |
| Hybrid inverter plus EPS board | Focused critical-load backup | Exact backup output, permitted battery and phase constraints | New solar plus essential circuits |
| Battery-only self-consumption retrofit | Can reduce electricity bills | May offer no backup at all | Buyer who values tariff optimisation over outages |
| Small dedicated UPS | Designed for selected electronics | Very limited power/runtime for household appliances | Router, NASAliExpress price or computer needing uninterrupted local power |
Battery backup reserve: how much should you keep?
Many battery products allow some charge to be held aside for outages. A high reserve can improve readiness but leaves less energy for day-to-day tariff arbitrage or solar self-consumption. A low reserve may optimise bill savings while giving disappointing backup autonomy at the very moment a power cut occurs.
For illustration, a 10 kWh usable battery at a 30% reserve holds up to 3 kWh for the designated reserve segment under idealised conditions; it does not promise that all 3 kWh will reach the sockets. A winter household that requires 2 kW to run priority heating and pumps may exhaust that budget much faster than a 200 W lighting-and-network-only load. Forecast.solar predictions and local weather alarms can assist operational planning, but they should not override inverter and BMS safeguards.
Some systems have storm modes or location-dependent reserve settings. They are useful conveniences, not a replacement for the electrical design. During lengthy outages, lowering heating/cooling setpoints, pausing an EV charger and using low-power lighting can matter more than increasing nominal battery capacity.
Home Assistant’s role: visibility, not the safety controller
Home Assistant can make backup easier to understand. Depending on supported integrations, you may be able to monitor battery state of charge, inverter operating mode, grid availability, home load, solar generation and backup reserve. You can use alerts to remind occupants to stop nonessential consumption. A local monitoring server and network switch should themselves be protected if you expect them to work during outages.
However, Home Assistant is not the required anti-islanding, transfer or protective controller. The inverter, gateway, certified switching hardware and protection devices must preserve their safety functions if Home Assistant, Wi-Fi, MQTT or the internet fails. Avoid publishing recipes that command grid-isolation or change protection parameters through unsupported registers.
Useful outage monitoring design: a grid-status sensor triggers a notification; a dashboard shows battery SoC and estimated load; a low-reserve alert advises manual shedding or a manufacturer-approved low-priority appliance control; when the grid returns, a second alert confirms recovery. Manufacturer-approved load-shedding products may be supervised through local automation, but essential protections remain independent. For monitoring examples, consult the Home Assistant Powerwall and Victron GX integration documentation.
A cautious notification example
The following illustrative automation only notifies; it does not switch an electrical supply. Replace the example entity IDs with confirmed real entities from your installation. Some integrations report grid state with different values, so verify the state in Developer Tools before use.
alias: Alert when battery system reports grid outage
triggers:
- trigger: state
entity_id: binary_sensor.grid_available
to: "off"
actions:
- action: persistent_notification.create
data:
title: "Grid supply unavailable"
message: >-
The grid status sensor reports a power cut.
Review backup battery charge and essential loads.
mode: single
Do not rely on the notification as the only sign of an outage; if Home Assistant loses power or its network, the alert may never arrive. During commissioning, test how the network, hub and local logging recover after interruption.
Commissioning checklist: make the installer demonstrate backup
Do not accept ‘backup compatible’ as proof of the finished installation. Before final payment, request a safe, controlled outage simulation conducted by the qualified commissioning electrician using the manufacturer’s procedure and any necessary utility authorisations. You are not being asked to pull fuses or switch utility conductors yourself.
| Test / document | What satisfactory evidence looks like |
|---|---|
| Signed single-line diagram | Identifies utility supply, isolation device, inverter, battery, EPS output and protected distribution |
| Circuit schedule | Names every backed-up circuit, every excluded circuit and any automatic load-shed relay |
| Installed model and firmware | Exact inverter/gateway/battery part numbers and approved configuration |
| Continuous and transient ratings | Documented loads within output and starting-current limits |
| Simulated outage | Specified backed-up circuits remain supplied or recover within declared transfer time |
| Phase and protection tests | Qualified electrician confirms local requirements, earthing, RCD and fault protection in island mode |
| Solar in island mode | Demonstrated only if contract promises this, including curtailment and battery charging behaviour |
| Battery low-SOC behaviour | Clear documented reserve, shutdown, recovery and restart sequence |
| Internet/router loss | Backup safely continues without Home Assistant or cloud access |
| Grid restoration | Correct automatic or documented manual reconnection and normal supply restoration |
| Handover | User instructions, circuit labels, emergency stop/isolation details and warranties |
Ask for a second check during a real or simulated high-load event if the contract promises heavy appliances. A test with only an LED light running reveals little about motor starting or concurrent demand.
Common outage surprises and how to recognise them
‘I have a battery but everything went dark.’ Look for a battery installed for self-consumption only, omitted backup gateway, non-backup Powerwall configuration, unsupported EPS mode or circuits outside the protected distribution. Do not alter wiring yourself; ask for the as-built diagram and site commissioning report.
‘The lights work but the kitchen sockets do not.’ This can be entirely normal in a partial-home setup: only nominated circuits are energised. Check the electrician’s backup-circuit label schedule rather than assuming a product failure.
‘The inverter trips when the pump starts.’ The instantaneous starting current may exceed inverter, battery or phase limits, even where steady-state energy seems modest. The installer needs to verify actual startup characteristics and manufacturer limits.
‘Solar panels stopped despite sunshine.’ A conventional PV inverter may not be supported in an island, the battery may be full, the AC coupling may need curtailment or the system may have reached a protective limit. Manufacturer diagnostics matter more than a Wi-Fi graph.
‘The system worked for hours then died and did not restart at sunrise.’ Investigate reserve threshold, battery BMS shutdown, black-start requirements, temperature limits and the product’s permitted recovery process. Avoid manually bypassing a BMS or protective relay.
‘My monitoring disappeared, so I thought the battery stopped.’ Router, internet, mobile-phone reception and monitoring gateway can all fail independently of the protected AC supply. Design the network on backed-up circuits if monitoring is a requirement, but always confirm actual electrical operation safely.
Installation cost: compare complete packages, not headline battery prices
Headline batteries, inverters and switch prices are rarely a fair comparison of installed backup. An honest written quotation includes all necessary changeover equipment, electrician labour, essential-load board, new protective devices, cable routes, permitted meter arrangement, battery communication cabling, commissioning and applicable approvals. The price varies substantially with a site’s existing distribution, service capacity, location and local rules, so we do not claim a universal installed price.
| Cost item | Why it matters | Ask the supplier |
|---|---|---|
| Battery modules | Runtime, power, warranty and expansion | Usable kWh at rated conditions and supported life/warranty |
| Grid-forming inverter / hybrid hardware | Peak load capability and phase behaviour | Continuous, surge and EPS ratings in local grid-code mode |
| Backup gateway / changeover | Safe grid isolation and reconnection | Included, approved and wired for proposed backup scope? |
| Essential-load board and circuits | Determines what actually stays on | Exact labelled circuit list and exclusions |
| Protection, earthing and tests | Safe operation in both grid and island conditions | Certificates, test results and installer responsibility |
| Solar compatibility work | Determines daytime recharge during grid loss | Tested AC/DC coupling and low-battery recovery support |
| Monitoring and networking | Helps plan usage; not safety-critical control | Local access without internet and backed-up network supply |
| Warranty and maintenance | Determines long-run value | Scope of labour, parts and battery capacity coverage |
An expensive backup upgrade may not be the financially optimal way to reduce annual electricity bills. Backup value is primarily the avoided disruption and convenience that you place on continuity. Our companion guide, Home Battery ROI: Degradation, Electricity Tariffs and Backup Value, explores the distinction between financial savings and resilience. It is available as another draft in this article series.
Final buying checklist: ten questions before signing
- Does the exact installed product configuration provide backup, or only normal-time battery savings?
- Is backup automatic or manual, and what is the manufacturer’s specified switchover behaviour?
- Which named circuits and phases will actually be powered, and which remain unprotected?
- What are the inverter’s continuous kW, surge/starting limits and per-phase restrictions?
- What is the minimum usable battery energy during an outage after reserve and conversion losses?
- Can the solar panels continue and recharge the battery in island mode? Under which limits?
- What happens if the battery runs flat overnight, the next morning is cloudy or the internet fails?
- How are neutral, earth, RCDs, fault protection and utility isolation handled under local regulations?
- What complete equipment, electrical work, commissioning, service and warranty costs are included?
- Will the installer demonstrate a controlled, documented power-cut test and give a labelled circuit schedule?
If these questions cannot be answered before purchase, the system’s promised outage performance is not adequately specified. In most ordinary homes, a properly engineered and tested essential-load backup board is a better first target than chasing an impressive whole-home marketing claim. If you need several large appliances, three-phase loads or near-zero-transfer-time continuity, design specifically for those requirements rather than assuming that more battery kWh alone will solve them.
Frequently asked questions
Will my solar panels work without grid power?
Usually not if they are connected only to a conventional grid-tie inverter. They may continue in a manufacturer-supported battery backup island with the correct grid-forming inverter and wiring. Ask for an explicit test, not just a solar-capacity number.
Is an EPS output the same as a UPS?
No. EPS describes an emergency AC output on certain equipment. Transfer time, behaviour and sensitive-electronics suitability vary. Where uninterrupted operation is vital, use an appropriate independently specified UPS and plan for its recharge during an extended outage.
Does a 10 kWh battery mean ten hours of backup?
Only for an idealised 1 kW load with no losses or reserve. Real delivery depends on starting state of charge, permitted discharge, conversion efficiency, ambient conditions and household demand. Use the formula available AC kWh ÷ average backed-up kW and then check peak loads separately.
Can I run the induction hob, EV charger and heat pump?
Possibly in some larger, deliberately designed systems, but not automatically. They can have high power, startup or three-phase requirements. Many essential-load installations exclude EV charging and immersion heaters during outages. Obtain written installer confirmation and suitable load-shedding arrangements.
Can I add a backup socket or feed the house through an extension lead?
Never back-feed house wiring with an improvised plug or extension lead. A manufacturer’s supported emergency outlet may power only appliances connected in the exact permitted way. House distribution backup requires compliant isolation, protection and professional installation.
Will Home Assistant keep the battery safe during a blackout?
Home Assistant can display information and send alerts, but it must not be the sole anti-islanding, transfer or protection system. Certified hardware and its safety controllers need to work even when Home Assistant and the internet are unavailable.
Official sources and further reading
- Tesla: Powerwall system design, whole-home and partial-home configurations
- Tesla: What can Powerwall back up?
- Tesla UK: Powerwall 3 non-backup configuration
- Tesla: Powerwall blackout best practices
- Victron: MultiPlus-II 230 V — description and AC output operation
- Victron: ESS design and installation manual
- Home Assistant: Tesla Powerwall integration
- Home Assistant: Victron GX integration
Editorial note (October 2026): Features and local approval requirements depend on exact models, firmware, installer configuration and country. Example power figures are illustrative, not equipment ratings. This guide is a buying and planning resource, not instructions for live mains wiring or altering grid-isolation hardware.
