Should you add a battery to balcony solar?
A battery only earns back what would otherwise flow to the grid for free, and for an 800 W railing kit that’s not much. In California our model puts it at about 183 kWh a year, worth roughly $55. A battery makes sense with a bigger kit, a small always-on load, or if you want backup power.
Updated October 2026
What a battery could add
Most of the time your home uses what the panel makes. The battery only matters for the rest: the midday surplus. We take that surplus, assume about 10% is lost charging and discharging, and price what’s left at your power price. 800 W kit, south-facing railing:
| State | Surplus per year | Most a battery could add |
|---|---|---|
| California | 183 kWh | $55 |
| New York | 168 kWh | $43 |
| Connecticut | 180 kWh | $49 |
| Maryland | 169 kWh | $34 |
| Virginia | 169 kWh | $26 |
| Utah | 218 kWh | $26 |
If a battery adds several hundred dollars to the price, those numbers show why it rarely pays back on its own with a small kit.
When a battery does make sense
- A bigger kit. A 1,200 W kit sends much more to the grid, so there’s more to store.
- Nobody home during the day. A low daytime load means more surplus.
- Time-of-use rates. Storing midday power for the 4–9 p.m. peak is worth more than its average price.
- Backup. If you want power in an outage, value that separately from the savings.
Try this first
Move what you can into the day: dishwasher, laundry, charging. That uses the surplus for free. See your surplus in the calculator.
Common questions
How big a battery do I need?
Size it to your daily surplus. For an 800 W railing kit in California that's about half a kWh a day on average, so a small battery around 1 kWh covers most days. Bigger only helps with a bigger kit.
Do batteries wear out?
Yes. They slowly lose capacity as they charge and discharge. Check the warranty: how many years and how many cycles it covers.
Will a balcony solar battery power my home in a blackout?
Only if it's built to. Some plug-in battery systems stop feeding your outlets when the grid goes down, just like the panels. If backup matters to you, check that the product has its own outlets that work off-grid.
Are plug-in batteries allowed under state laws?
The rules for batteries are less settled than for panels. Check your state's law and the product's certification before you buy.
Sources
- Production and savings: our calculation method.
- Electricity prices: U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A (March 2026 data).