A home battery earns its keep two ways: storing your solar so you use it instead of exporting it, or charging cheaply at night and running the house through the expensive peak. Tell us your usage and your rates — this sizes a sensible battery and shows the payback honestly, including when the answer is “buy it for backup, not for the maths.”
This decides which sum matters. A battery only earns the gap between two prices — either your import rate minus your export rate (storing solar), or your peak rate minus your night rate (arbitrage).
Your main reason for a batteryA battery can only save you money on energy you'd have used anyway in the evening and overnight — it can't discharge into a house that's empty and asleep with everything off. Bigger households shift more, so they can justify more capacity.
Use the figures on your own bill — they're what make or break the case. Enter usable capacity (what the battery actually delivers), which is a touch below the nominal size printed on the box.
Retrofit batteries in Ireland run roughly €600–1,000 per usable kWh fitted, so a 10 kWh unit is about €6,000–9,000. There's no standalone SEAI grant for a battery on its own — the solar PV grant covers panels, not storage bought separately. Default assumes ~€700/kWh.
Since the Clean Export Guarantee started paying for exports (~20c in mid-2026, down from ~24c peaks), storing solar only saves you the gap between what you'd pay to import it back and what you gave up by not exporting it.
Arbitrage needs a smart meter and a night/EV tariff — a cheap window (often 2am–5am, sometimes ~8–14c) and a dearer peak (often ~5–7pm). That's the free half of the win: the meter and tariff cost you nothing and unlock most of the saving before you spend a cent on a battery.
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The 90% is round-trip efficiency (you lose ~10% charging and discharging). The cycle-day count is deliberately below 365: no battery fills and empties perfectly every single day, and solar storage in particular does little from November to February.
Get a smart meter and move to a night/EV tariff before you buy a battery. Both are free, and most of the arbitrage saving a battery unlocks is actually the tariff doing the work — shifting your dishwasher, immersion, washing machine and EV charging into the cheap window costs nothing and captures a big share of the win. Only once you've done that, and you can see there's still a peak-time chunk a battery would shift, does the battery maths become worth committing thousands to. If your verdict below is “backup, not savings,” that's the honest signal to treat the battery as resilience spending — and our backup-power runtime tool is the better place to size that.
Installed price per kWh swings widely between installers and brands, and that price is what decides your payback. Get a couple of quotes for the size above before you commit.
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The euro figures here are planning anchors, not a quote. Value per kWh comes straight from the rates you enter — the tool invents no prices. The fixed assumptions are: 90% round-trip efficiency; a shiftable daily load scaled by household size; ~220 useful cycle-days a year for solar storage (winter solar is too weak to fill a battery most days), ~330 for night arbitrage (the cheap window is there year-round), ~320 blended; and installed cost you set yourself, anchored at ~€700 per usable kWh. Battery warranties are typically ~10 years or several thousand cycles, so at these cycle counts the warranty is rarely the limiter — the payback-versus-warranty-life comparison is the honest test. Nothing here counts the value of backup power in a cut, which is real but not a cash saving. Figures last reviewed July 2026 — check current CEG export rates, night-tariff prices and battery install costs before you rely on them.
Honestly, for most homes it doesn't pay back on solar storage alone any more. Before the Clean Export Guarantee, solar you didn't use spilled to the grid for free, so a battery that let you use it in the evening saved the full import price — a strong case. Now exports are paid (~20c/kWh), so storing solar only saves the gap between your import rate and that export rate — often just 15c or so. Over a battery's life that rarely clears a €6,000–9,000 install. The case that does stack up is night-rate arbitrage: charge the battery at ~8–14c overnight and run the house on it through the dear peak. Many people still buy a battery for backup and independence rather than pure payback — which is a legitimate reason, just not the one this saving figure measures.
Match it to the energy you can realistically shift into the evening and overnight, not to your roof or your ambition. For most Irish homes that's somewhere around 5–10 kWh usable; going bigger just means capacity that sits half-full because you don't use enough after dark to empty it. A battery you can fill and empty most days earns its keep; one sized for a day you rarely have does not. The size figure above is our sensible-fit suggestion for your household — treat a much larger quote with suspicion.
Nominal (or gross) is the number printed on the box; usable (or net) is what you actually get out, because batteries hold a little back to protect their lifespan. Modern lithium-iron-phosphate (LFP) batteries are usable to about 90–100% of nominal, so the gap is small — but always compare quotes on usable kWh, since that's what does the work and what this tool asks for.
No standalone grant. The SEAI solar PV grant is for the panels; battery storage isn't separately grant-aided, so you pay for a retrofit battery in full. That's exactly why the payback sum matters — there's no grant softening the cost the way there is with panels or a heat pump.
No. A battery with no panels can still profit from a smart-meter night tariff: charge it during the cheap overnight window and discharge it through the expensive peak, pocketing the difference on every kWh. In fact, at current export rates, this arbitrage case is usually stronger than the solar-storage one. You do need a smart meter and a time-of-use tariff for it to work — both of which are free to get.
If you have solar surplus, a diverter (which pushes it into your immersion) is far cheaper than a battery — a few hundred euro versus several thousand — and for using up daytime surplus it often makes more financial sense. A battery is more flexible (it powers anything, and enables night arbitrage and backup), but that flexibility costs a lot more per kWh moved. They're not mutually exclusive, but if the only goal is “use my solar surplus,” price a diverter first. Our solar-diverter payback calculator does that sum.
Typically a warranty of around 10 years or a set number of cycles (often several thousand), whichever comes first. LFP chemistry — now standard for home storage — is rated for a lot of cycles and degrades slowly, usually guaranteeing ~70% capacity at end of warranty. At the roughly 220–330 useful cycles a year an Irish home puts through one, you'll generally reach the year limit before the cycle limit. The practical question isn't “will it wear out” but “will it pay for itself before the warranty runs out” — which is the number this tool puts front and centre.
Only if it's specified to. A standard grid-tied battery shuts down in an outage for safety unless it's fitted with a backup/islanding function and (usually) a changeover switch — an option worth asking for after Storm Éowyn made outages a live concern for a lot of households. If resilience is your real reason, size it around the essentials you'd want to keep running (fridge, freezer, broadband, a few lights, maybe the heating pump) rather than around bill savings — our backup-power runtime calculator is built for exactly that.