The best solar battery setup for running air conditioning

Search "best solar battery for air conditioning" and you'll get a parade of brand names, each one crowned the winner by whoever's selling it. That's the wrong question. Solar already runs your air conditioning for free in the middle of a sunny day — that part sorts itself out. What you're actually shopping for is the thing that lets you run cooling in the evening and overnight, when the panels have stopped and you're trying to sleep. That thing is a battery, and "best" comes down to sizing and setup, not a logo.

So this guide skips the beauty contest. Instead, here's how to work out roughly how much battery a night of cooling needs, what specs actually matter when you compare units, and how a time-of-use tariff quietly makes the whole thing cheaper.

Why a battery is the piece that matters for cooling

During the day, the case for solar and air conditioning is almost too easy: cooling works hardest when the sun is strongest, so your roof is generating exactly when the AC wants power. We've covered that alignment in full in our guide to solar panels and air conditioning.

The problem is that the main reason most people want air conditioning is to sleep — and at 2am your panels are producing nothing. Night-time cooling has to come from somewhere: either a battery you filled during the day, or the grid at whatever rate you're on. A battery is what carries the daytime benefit into the night, which is the exact window you care about most. That's why, for cooling specifically, the battery isn't an accessory. It's the point.

How much battery does a night of cooling actually need?

Let's build the number up from parts, using ranges rather than false precision.

A home air conditioning unit draws roughly 0.5–1.5 kW while it's actively cooling, depending on the size of the unit and how hard it's working. Run something like 0.7 kW for around six overnight hours and you're looking at roughly 4–5 kWh for the cooling alone.

Now add the rest of the house overnight — fridge, standby loads, a bit of evening use before bed. That's commonly another 2–4 kWh. Put them together and a typical night of cooling plus normal household draw lands somewhere around 6–9 kWh of stored energy.

That points to a usable battery in the 5–10 kWh range for a single-unit setup — enough to cover a typical night of cooling and the usual evening load, with the exact figure depending on your unit size, how long you run it, and how well your home holds its temperature once it's cool. A well-insulated home that the AC only needs to top up occasionally will draw far less than a leaky one fighting the heat all night.

These are planning numbers, not a spec. The honest version is that an MCS-certified installer measures your actual cooling and evening load and sizes the battery to it — which is worth far more than any rule of thumb.

What to look for in a battery (the criteria that matter)

When you compare batteries, ignore the marketing and look at five things:

1. Usable capacity, not nominal. A battery advertised as "10 kWh" might only give you 9 kWh in practice, because you don't fully drain it — that's the depth of discharge. Usable capacity is what actually powers your AC overnight, so compare on that number, not the headline one.
2. Round-trip efficiency. Some energy is lost storing and retrieving electricity. Around 90% or better is a good sign; it means most of what you put in comes back out.
3. Continuous power output. This is easy to overlook and important. The battery's continuous power rating (in kW) must comfortably exceed your AC's draw plus whatever else is running. A unit pulling 1.2 kW alongside household load needs headroom above that, or it can't supply everything at once.
4. Warranty — cycles and years. Batteries are rated for a number of charge cycles and a number of years. A longer, higher-cycle warranty tells you the manufacturer expects it to last through daily cooling-season use.
5. Time-of-use charging support. Can the battery be told to charge from cheap overnight grid electricity, not just from solar? This one unlocks the money-saving move below, so it's worth confirming before you buy.

Any of the well-known home batteries — a Tesla Powerwall, a GivEnergy unit, a Sungrow, and plenty of others — can do this job. The right one for you is whichever hits your usable capacity and power needs within budget, not whichever brand shouts loudest.

The time-of-use trick: cheap electricity in, cool night out

Here's where the setup gets genuinely clever. A battery doesn't only fill from solar surplus. On a time-of-use tariff, you can also charge it from cheap overnight import when grid electricity is at its lowest unit price, then lean on that stored energy to run cooling through the expensive evening peak.

Why that matters for AC: even after a dull, cloudy day when your panels barely generated, you can still run the evening's cooling on cheap stored electricity rather than pricey peak-rate grid power. Buy low, use later — it's the closest thing UK solar-and-storage has to a repeatable winning move, and it takes cooling from "only works on sunny days" to "works most nights." The full mechanics are in our guide to Octopus Go and time-of-use tariffs.

Bigger is not automatically better

It's tempting to read "5–10 kWh" and just buy the biggest battery you can. Resist that. A battery only earns its keep if you regularly fill it and regularly draw it down. Oversize it — buy 15 kWh when your cooling and evening load only ever use 7 — and you've spent money on capacity that mostly sits idle. That's slower payback, not more comfort.

The sensible move is to size to your actual cooling plus evening load, leave a little headroom for the odd hotter night, and stop there. If your ambitions grow later, most modern battery systems can be expanded. Under-buying slightly and topping up is usually cheaper than over-buying up front.

How solar, cooling and the battery work together

Put the pieces in order and a good day looks like this:

1. Through the day, panels generate and the AC runs on that free electricity directly, with any surplus charging the battery.
2. Into the evening, as generation fades, cooling shifts onto the battery — the stored sunshine from earlier.
3. Overnight, if the battery runs low or the day was dull, cheap time-of-use import tops it back up ready for the next round.

That's a system that keeps you cool through the evening and night while rarely paying peak grid rates. It only holds together if the battery is sized to the job — which loops back to the numbers above.

Modelling it before you buy

Sizing on paper is a start, but the numbers move with your roof, your tariff, your unit, and your habits. Two useful next steps: our deeper solar battery storage guide walks through storage sizing in general, and our savings calculator lets you model what a system could realistically do for your bills before you spend anything. And because a cloudless heatwave is close to a best case for generation, it's worth knowing what to expect — our guide on whether solar panels work in a heatwave covers that.

Whatever the calculator suggests, treat it as an estimate. An installer survey is what turns a rough size into a properly matched battery, cooling unit, and array.

Common questions

What size battery do I need to run air conditioning overnight?

For a single AC unit, a usable battery in the 5–10 kWh range typically covers a night of cooling plus normal evening household load. A night of cooling alone is often around 4–5 kWh, with another 2–4 kWh for the rest of the house. Your exact figure depends on unit size, run time, and how well your home holds its temperature — an installer sizes it precisely in a survey.

Which is the best solar battery for air conditioning?

There isn't a single winner — the right battery is the one whose usable capacity and continuous power output comfortably cover your cooling plus household load, within your budget. Look for round-trip efficiency around 90% or better, a strong cycle-and-year warranty, and time-of-use charging support. Well-known units from several manufacturers can all do the job; match specs to your needs rather than chasing a brand.

Can I charge my battery from cheap night electricity to run AC?

Yes, if your battery supports time-of-use charging and you're on a suitable tariff. You fill it from cheap overnight import, then run evening and overnight cooling on that stored electricity instead of expensive peak-rate power. This works even after a cloudy day when solar generation was low.

Is a bigger battery always better for cooling?

No. A battery only pays back if you regularly fill and use it, so oversizing one you can't fill wastes money and slows your payback. Size to your actual cooling and evening load with a little headroom, not to the biggest number you can afford. Most systems can be expanded later if your needs grow.

Where to start

Start with what your roof can realistically generate and what your evening and overnight cooling actually draws — those two numbers decide the battery. From there, a listed solar installer covering your area can size the panels, battery, and cooling as one joined-up system rather than three separate purchases, and confirm suitability with a proper survey.

Related

• Solar panels and air conditioning — can you run AC off solar in the UK?
• Solar battery storage UK — worth it in 2026?
• Solar with Octopus Go and time-of-use tariffs in 2026
• Do solar panels work in a heatwave?
• Estimate your savings