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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 |
Check your numbers
Enter your kit, your daytime use and your evening consumption in the battery size calculator to see how much surplus you would store and what it is worth, before spending money on storage.
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.
Sources
- Anker SOLIX Solarbank 2 E1600 Pro, Anker SOLIX (EU).
- EcoFlow Stream Ultra X review, TechRadar.
- Energy storage system testing and certification (UL 9540), UL Solutions.
- PVWatts Calculator, National Laboratory of the Rockies (formerly NREL).
Sources checked in September 2026. Laws, prices and product details change; if you spot something out of date, tell us.