Keep your home powered during outages with the right solar battery backup system.

Will My Solar Battery Work During a Power Cut?

Not unless it was specifically designed to. This surprises people, and it shouldn’t be a surprise it should have been explained when the system was sold.

A standard grid-connected battery shuts down the moment the grid goes. That’s a safety requirement, not a fault: an inverter feeding a dead network could electrocute the crew working on the line. Backup requires additional equipment that isolates your house from the grid before the battery is allowed to energise anything.

batteryinstall.ie / backup runtime

How long would you actually last?

Backup isn't a feature you switch on — it's circuits you choose in advance. Tick what you'd want alive during a storm outage and we'll tell you how many hours that buys, and where the inverter runs out before the battery does.

What stays on 0 selected

Your system

Battery capacity 10 kWh usable

Inverter output 5.0 kW — this is the ceiling on what can run at once, no matter how full the battery is.

Reserve held for outages 20% — the share the battery won't spend in normal use, so there's something there when you need it.

Time of day the outage starts

Solar array With the right design, panels keep generating into the backed-up loads during a daytime outage. Not all systems support this.

Estimated runtime December

—hours

Tick the circuits you'd want alive and this fills in.

Load

—

Continuous draw.

Available

—

After reserve.

Headroom

—

Inverter spare.

Runtime by hour from the moment the lights go out

Hour 06121824

Running on stored energy Solar carrying the load Battery exhausted

Indicative. Real runtime depends on how often the fridge and freezer cycle, how cold it is, and what you switch on without thinking. Treat this as the shape of the answer rather than a promise.

The three levels of backup

1 No backup (most installations)

Grid goes, battery stops, house is dark. Everything else about the battery works normally.

2 EPS (Emergency Power Supply).

A single dedicated socket or a small dedicated circuit, energised by the battery during an outage. Cheap, simple, limited. You get a fridge, a router, phone charging, a lamp. You don’t get the house.

3 Whole-home or essential-circuit backup.

A gateway or automatic changeover device physically disconnects the property from the grid and lets the battery run selected circuits — sometimes the whole board. Switchover is typically under a second, so most things don’t notice. This is the real thing and it costs accordingly. Most households who think they want whole-home backup actually want essential circuits: heating controls, fridge and freezer, lighting, sockets in one or two rooms, broadband. It’s a fraction of the cost and covers 95% of what an outage actually disrupts.

How long will it run?

Runtime is usable capacity divided by the load you’re carrying — but the load is the part people underestimate, and the estimator above uses duty-cycle averages rather than nameplate ratings, because a fridge rated at 150W actually draws about 90W averaged over its compressor cycle.

Load	Typical average draw
Fridge-freezer	~90 W
Broadband router and modem	~15 W
Gas boiler and controls	~120 W
LED lighting, whole house	~100 W
Laptop and phone charging	~80 W
Typical “essentials” total	~400 W
Electric shower	8,500–10,500 W
Immersion heater	~3,000 W
Electric oven	2,000–3,000 W
Kettle	~3,000 W
Heat pump, running	1,000–3,000 W

At 400W of essentials, a 10 kWh usable battery runs for around 20 hours — comfortably through any outage Ireland realistically produces outside a named storm.

Put the kettle on and you’re drawing 3 kW, which the battery can supply but which costs you an hour of essential-load runtime for three minutes of tea. And an electric shower will exceed the continuous output of most residential battery inverters entirely, so it simply won’t run. This is the constraint people meet on day one of an outage: not capacity, but power.

Does solar recharge the battery during an outage?

Sometimes and it’s a significant advantage when it works.

In a properly designed backup system, the solar array can continue generating into the isolated house during daylight, recharging the battery and extending runtime indefinitely in decent weather. That turns a 20-hour outage capability into an indefinite one.

Whether it works depends on the architecture. DC-coupled hybrid systems generally manage it well, because the solar and the battery share an inverter that’s still running. AC-coupled arrangements vary — some maintain the backup grid frequency well enough for the solar inverter to stay online, others don’t. If riding out multi-day storm outages is your reason for buying, say so up front, because it narrows the product list considerably.

Is backup worth it in Ireland?

Depends entirely on where you live and what you’re protecting.

You are on a rural feeder with a history of multi-hour outages, you are on a private well (no power, no water), you have medical equipment, you work from home with no alternative, you keep livestock, or you have a freezer full of stock.

You are in an urban area with outages measured in minutes per year and your main concern is the router.

Our Position:

don’t buy backup as an insurance policy against something that doesn’t happen to you. Do buy it if outages genuinely disrupt your household, and buy essential-circuit rather than whole-home unless you have a specific reason.

Frequently Asked Questions

Will my existing battery work in a power cut?

Only if a backup gateway or EPS was installed with it. Check your handover documentation, or look for a separate changeover unit near the consumer unit. If you’re not sure, send us a photograph of the board.

Can backup be added to an existing battery?

Sometimes. It depends on whether your battery inverter supports a backup output, and whether the consumer unit can be reconfigured to split essential circuits. Worth checking before assuming either way.

Can backup be added to an existing battery?

Typically under a second on a gateway system, which most appliances ride through. Desktop computers without a UPS may still restart.

Can I run my heat pump on backup?

Startup current is the problem, not running load. Some battery inverters handle it, many don’t. It needs checking against the specific heat pump and the specific inverter, not assumed.

Do I need a generator as well?

For outages beyond two or three days with no solar contribution, possibly. Some installations interface a generator with the battery system. That’s a design conversation, not an off-the-shelf product.