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- A plug-in kit works fine without a battery; you use solar power as it is produced.
- A battery helps when you export a lot at midday and use most power in the evening.
- Batteries roughly double the system price, so payback is usually longer.
- Time-of-use pricing, high electricity prices and backup needs make storage more attractive.
Battery makers market storage as the natural next step after a balcony kit. Sometimes it is. Often it is not. Here is how to tell.
In this article
What a battery does
At midday your kit may produce 600 W while your home uses 200 W. Without storage, the extra 400 W flows to the grid, usually for no payment. A battery stores that surplus and releases it in the evening, when you would otherwise buy power. The result is higher self-consumption: typically from 60-75% up to 85-95%. Self-consumption explained.
Signs you don’t need one
- Your kit is 400-600 W and you have steady daytime use (someone home, fridge-freezer, home office).
- Your app or meter shows little export on sunny days.
- Your electricity price is modest (below about $0.20/kWh).
- Budget is limited: a second east- or west-facing panel may add more value per dollar.
Signs you might
- You are out all day and use most electricity in the evening.
- You regularly export more than 1 kWh on sunny days.
- You pay high prices, especially with an expensive evening peak.
- You want backup power during outages (with a battery that supports it).
- Your local rules allow more panels behind a battery than a direct kit (common in Europe).
A quick calculation
Suppose you export 1.5 kWh on a typical sunny day, and there are 200 such days a year. A battery could capture about 1.5 × 200 × 90% efficiency = 270 kWh a year. At $0.25/kWh, that is $68 a year. A $900 battery would take over 13 years to pay back, likely beyond its warranty. At $0.40/kWh peak pricing, $108 a year and about 8 years. That is why storage makes more sense in high-price markets. Full payback analysis.
Alternatives to a battery
- Shift loads to midday: free and immediate.
- Use smart plugs to run flexible loads on surplus. Automations.
- Add a panel facing a different direction to spread production.
- A portable power station if backup is the main goal.
Measure before you buy
Run your kit without a battery for a few weeks in spring or summer and check how much it exports on sunny days. If exports are under 0.5 kWh a day, a battery will struggle to pay back. If they are 1.5 kWh or more, storage deserves a closer look.
Decision table
| Your situation | Battery? |
|---|---|
| 400-600 W kit, someone home during the day | No |
| 800 W kit, home empty on weekdays, flat rate | Probably not; shift loads first |
| 800 W kit, high evening TOU peak | Worth calculating |
| Frequent outages, need backup | Yes, with an off-grid outlet |
| More panels than your inverter limit allows (Europe) | Often yes |
Frequently asked questions
Can I add a battery later?
Yes. AC-coupled batteries work with any existing kit; DC-coupled ones need to be placed between panels and inverter. AC vs DC.
How long does a balcony battery last?
LFP batteries are typically warrantied for about 10 years and rated for several thousand cycles. LFP guide.
Does a battery use power itself?
Yes, typically 5-20 W in standby. Over a year that can be 40-175 kWh, a real cost for small systems. Spec sheets.
Is a battery safe on a balcony?
Many are rated for outdoor use; placement still matters. Battery safety.