Guide · Switzerland

Is retrofitting a battery worthwhile?

Your panels are already running. At midday you export electricity, then buy some back in the evening. A battery is an obvious idea to explore. The data your system already records is the best place to find out what it would actually change.

Short answer

Is retrofitting a battery worthwhile?

For a retrofit, only the new battery cost and the additional benefit over the existing PV system matter—not the PV system’s historic purchase price.

Start with the system you already own

Annual exports alone do not tell the whole story. Look for days when a solar surplus is followed by purchases from the grid. That gap is where a battery can help. Your PV system stays the same in both scenarios, so its existing savings must not be credited to the new battery.

Include the installation, not just the box

An attractive battery price is not a complete retrofit quotation. Some equipment may be reused; other parts may need work. Ask for those items separately and enter the full additional investment. That lets you compare the cost of storage with the savings it adds, rather than with the output of your entire solar installation.

The key considerations

WattBilanz adds a flat CHF 2,000 of fixed cost for a Swiss retrofit compared with a joint new installation. Also check the inverter, metering concept, switchboard and communications.

Swiss price framework 2026

WattBilanz assumptions, September 2026: new PV CHF 5,700 fixed plus CHF 1,760/kWp; new battery CHF 2,300 plus CHF 470/gross kWh; retrofit CHF 4,300 plus CHF 470/kWh. Installation and VAT included, incentives excluded.

A Bern battery retrofit example

This example uses an existing 10 kWp PV system in Bern (postcode 3011), with a south-facing 30° roof and a four-person household using about 4,050 kWh a year. Imported electricity is priced at 32 ct/kWh. Export payments are held at 7.5 ct/kWh throughout the full 20-year period: 6 ct for energy and 1.5 ct for guarantees of origin. Only the battery and its installation costs are counted; local grants are excluded.

Battery	Retrofit cost	Additional annual benefit	Result after 20 years	Self-sufficiency	Simple payback
5 kWh	CHF 6,650	CHF 367/year	+ CHF 698	76.9%	18.1 years
10 kWh	CHF 9,000	CHF 550/year	+ CHF 1,991	95.9%	16.4 years
15 kWh	CHF 11,350	CHF 576/year	+ CHF 170	98.7%	19.7 years

The step from 5 to 10 kWh is significant. At 15 kWh, self-sufficiency rises further, but annual savings increase only slightly and the 20-year economic result is lower than with 10 kWh. In this example, the largest battery therefore does not deliver the best result.

What the optimizer recommends

With these assumptions, the optimizer peaks at 9 kWh. The 8–10 kWh range achieves at least 90% of the best result. At 9 kWh, the estimated cost is CHF 8,530 and the additional 20-year contribution is about CHF 2,034. Tariffs matter: higher import prices and lower export payments generally improve the relative case for larger batteries.

The chart shows the optimizer results for this retrofit example. Die Self-sufficiency steigt weiter, doch der höchste zusätzliche Beitrag nach 20 Jahren liegt bei 9 kWh. Der grün markierte Korridor of 8 to 10 kWh erreicht mindestens 90 % dieses Maximums. Die prozentuale ROI-Kurve hat ihr Maximum bei 8 kWh.

Capacity	Self-sufficiency	Self-consumption	Annual benefit	Result after 20 years	Payback
8 kWh · 90% lower bound	90.9%	32.0%	CHF 501/year	CHF 1,963	16.1 years
9 kWh · optimum	93.7%	33.1%	CHF 528/year	CHF 2,034	16.1 years
10 kWh · 90% upper bound	95.9%	33.9%	CHF 550/year	CHF 1,991	16.4 years

Official and specialist sources

Sources and price assumptions last checked on 18 September 2026.

Continue with your own data

Use the retrofit calculator with your existing system’s data, then replace the estimated cost with the complete quotation when you have it.

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