Why a Battery at All?
A balcony solar system produces electricity when the sun shines -- typically between 10 AM and 4 PM with the peak around midday. Many households, however, consume most electricity in the morning and evening: cooking, washing, watching TV, lighting. This temporal mismatch means that without a battery, only 40-60% of generated electricity is self-consumed. The rest flows into the grid without compensation.
A battery storage can store this surplus electricity and make it available in the evening. This significantly increases the self-consumption rate -- from typically 50% to 70-85%, depending on battery size and consumption pattern.
What Battery Size for Which System?
The rule of thumb is: 1 kWh battery capacity per 500 Wp of module power. For an 800-watt system, a 1-2 kWh battery is sufficient; for a 1600-watt system, 2-3 kWh makes sense. Larger batteries bring little additional benefit for balcony solar systems since daily production is limited.
A concrete example: an 800-watt system in NRW generates about 4 kWh on a sunny June day. Of this, 2 kWh are consumed directly (base load). The remaining 2 kWh can be perfectly stored in a 2 kWh battery. A larger battery would rarely be fully charged.
The Economic Calculation
This is where it gets sobering. A typical 2 kWh battery for balcony solar systems costs EUR 500-1,000. The additional savings are calculated as follows: the battery increases self-consumption from 400 kWh to 550 kWh (for an 800W system). The additional 150 kWh at 35 cents/kWh correspond to savings of EUR 52.50 per year.
At acquisition costs of EUR 800 for the battery, the payback period is 15.2 years. The lifespan of most batteries is 10-15 years and 5,000-10,000 charge cycles. This means: the battery just about pays for itself within its lifespan -- an economically neutral to slightly negative result.
When Does a Battery Still Make Sense?
Despite the sobering economic calculation, there are scenarios where a battery is worthwhile. Scenario 1: you are not home during the day. Working professionals who leave home in the morning and return in the evening have a self-consumption rate of only 25-35% without a battery. A battery nearly doubles this rate.
Scenario 2: rising electricity prices. If the electricity price rises from 35 to 45 cents/kWh, battery economics improve significantly. Additional savings then rise to EUR 67.50 per year. Scenario 3: self-sufficiency matters to you. If independence from the power grid has an ideological value for you, the battery is a worthwhile investment.
Battery Technologies Compared
Most balcony solar batteries are based on lithium iron phosphate cells (LFP). These are safer than NMC batteries, have a longer lifespan (up to 10,000 cycles), and are less temperature-sensitive. Capacities range from 1 kWh to 5 kWh for the balcony solar segment.
Popular models in 2026 include the Anker SOLIX (1.6 kWh, about EUR 600), the Zendure SolarFlow (1.9 kWh, about EUR 700), and the EcoFlow PowerStream (2 kWh, about EUR 800). All three systems can be modularly expanded and work with common micro-inverters.
Retrofitting: Adding a Battery Later
A major advantage of modern balcony solar systems: the battery can be retrofitted. Start without a battery, observe your self-consumption for a year, and then decide whether the investment is worthwhile. Many battery systems are plug-and-play and can be installed without an electrician.
Conclusion: Batteries Are Optional, Not Mandatory
For most households, a balcony solar system without a battery is the economically better choice. Payback is shorter, risk is lower, and the environmental effect is nearly identical (fed-in electricity displaces fossil power elsewhere). A battery is primarily worthwhile for working professionals who want to use electricity time-shifted, or for households with high evening consumption. Use our calculator to work through the difference for your specific situation.