Charge overnight on a lower tariff and use stored energy during expensive peak periods.
Charging a Solar Battery on a Night Rate — What It’s Worth in Ireland
A solar battery doesn’t only store sunshine. On a time-of-use tariff, it fills overnight at the cheap rate and discharges through the evening peak, when electricity costs three to five times more.
That works in January as well as June. It’s the reason battery economics in Ireland have improved even as export rates have fallen — and for many households it’s now worth more than solar self-consumption on its own.
batteryinstall.ie / tariff arbitrage
What's the spread worth to you?
Your battery has two ways to earn. Storing your own solar is the obvious one — and in an Irish December it does very little. Buying cheap overnight and spending it through the expensive evening works identically in every month of the year. This is that second number.
Your battery
Your rates c per kWh
How hard it works
Annual arbitrage saving Solar + night rate
This is the weather-independent half of a battery's return. It doesn't care whether the sun shone.
Effective spread
—
After round-trip losses.
Cycles a year
—
Grid-charged cycles only.
Per cycle
—
What one night is worth.
Already have one? We can reconfigure it — no hardware, no disruption.
Where it comes from per stored kWh
What this doesn't include: the saving from storing your own solar, which is counted separately. On a system with both, the two add together — and this half is the one that still works in December.
Getting this wrong is common
01Charge window overrunning
A window that runs fifteen minutes past the cheap period buys the tail of every charge at the expensive rate. Silent, daily, and it eats a meaningful slice of the figure above.
02Schedule set for a tariff you left
Switch supplier and the battery carries on charging at the old times. We see this constantly.
03Discharge starting too early
Battery empty by four o'clock, nothing left for the peak. The energy was used — just not where it was worth most.
04No seasonal profile
Summer wants the battery arriving at morning with room for solar. Winter wants it full. One setting cannot do both.
The spread is the whole story
Irish time-of-use tariffs currently look roughly like this below taken from August 2026 data
| Band | Typical window | Typical rate |
|---|---|---|
| Evening peak | 17:00–19:00 | up to ~48c/kWh |
| Day | 08:00–23:00 | ~30–35c/kWh |
| Night | 23:00–08:00 | ~10–18c/kWh |
| EV / night boost | ~02:00–06:00 | ~6–12c/kWh |
Suppliers structure these differently and it matters. Electric Ireland’s Home Electric+ splits the day into three bands with a Night Boost window at 2am–4am. Energia’s EV Smart Drive runs a super-off-peak band from 2am to 6am. SSE Airtricity’s Smart EV Max uses a wider 11pm–5am window at a slightly higher rate.
The trade-off is straightforward:
Narrow windows are cheaper per unit, wide windows deliver more cheap kWh.
For a battery, the wide window is often the better fit, because a 10 kWh battery charging at 3.6 kW needs about three hours to fill and a two-hour boost window won’t do it.
That’s a detail almost no comparison site mentions, because they’re all modelling EV charging rather than battery charging.
How much a battery can actually earn from Grid arbitrage
The arithmetic is simple; the constraints are where people get it wrong.
The theoretical maximum:** usable capacity × (peak rate − night rate) × cycles per year × round-trip efficiency.
For a 10 kWh usable battery, charging at 10c and displacing electricity at 35c, cycling 330 nights a year at 92% efficiency, that’s roughly **€760 a year before you count any solar at all.
The constraints that reduce it:
Realistically, most Irish households with a correctly sized battery on a good night tariff see €400–€900 a year from grid arbitrage, on top of solar self-consumption savings.
The calculator above works it out on your figures rather than ours.
Frequently Asked Questions
Can any solar battery charge from the grid?
Most modern hybrid and AC-coupled systems can, but it’s configurable rather than automatic, and a few older units can’t. Check before buying if arbitrage is part of your reasoning.
What’s the cheapest night rate in Ireland?
The EV boost windows are cheapest per unit — currently around 6–12c/kWh depending on supplier and window, against roughly 30–35c on a flat rate. The cheapest headline rate isn’t always the best total bill, because a low night rate is usually paired with a high evening peak. Compare total annual cost on your own usage.
Does grid charging damage the battery?
No. A cycle is a cycle regardless of where the energy came from. It does consume warranty throughput, so check whether your warranty is expressed in years, cycles or MWh — a battery cycling 330 times a year gets through a cycle-limited warranty faster than one cycling 150 times.
Do I need a smart meter?
Yes, for any time-of-use tariff. ESB Networks installs them free on request, and over two million Irish homes already have one.
What about dynamic tariffs?
The CRU required the five major suppliers to offer dynamic, half-hourly-priced plans from June 2026. A battery is the ideal device for a dynamic tariff — it can buy in the cheapest half hours and avoid the most expensive. Whether it beats a fixed night rate in practice depends on the plan and how well your system automates against it; we’d want a year of real data before making claims about it.