PV system over 20 years old: Retrofit with storage or continue feeding into the grid?

An older PV system does not need to be replaced just because of its age. If the modules and the inverter are still working reliably, a retrofitted battery storage system can open up an additional way to use the energy. Especially with a system over 20 years old (Ü20), the decision should begin with an assessment of the existing system and the previous operating model, not with the largest possible battery.

First clarify: Self-consumption or full feed-in?

Many older systems were designed for full feed-in. In that case, it is not enough to simply place a storage unit somewhere in the house: the metering concept, power routing, and the transition to self-consumption must all work together. First, have it checked how your PV system is connected to the house connection and what changes are required for the desired operation. For a system that already utilizes self-consumption, the initial situation may be different.

The consumer advice center describes the options for systems over 20 years old and points out potential additional conversion costs. You should have the current remuneration and individual connection conditions clarified directly for your specific system.

Supplementing a functioning system purposefully

An AC retrofit allows you to continue using the existing PV inverter. The storage unit is added to the alternating current side. This is particularly interesting for you if you are not already planning a complete renewal of the system anyway. If the inverter, wiring, or protective components are in need of repair, these costs must still be included in the quote. A storage unit does not replace system maintenance.

Place two separate questions side by side: What needs to be done for safe continued operation regardless? And what does the additional storage cost? This will make it clear which part of the investment is actually attributable to the storage unit.

How to check the economic benefit

By using your own solar power, you avoid a portion of your electricity purchases. For the stored energy, you simultaneously forgo the otherwise possible feed-in tariff and must take losses into account. Therefore, "no more feed-in" is not a sensible goal at any price. If there is still an attractive remuneration rate, the trade-off may differ from one made after it has ended.

A purely hypothetical calculation example: An additional usable kilowatt-hour saves 30 cents in electricity purchases. If 1.18 kWh of solar power are needed for this due to assumed storage losses, and this would have been remunerated at 8 cents per kWh, the calculated difference is around 20.6 cents before other costs. These are not current tariff figures and do not represent a yield forecast for AC Core. With your actual values and the complete installation price, a reliable decision can be prepared.

The right size comes from your daily routine

Above all, check your consumption outside of daylight hours and the regularly available excess generation. A large storage unit that is rarely charged or discharged does not become economical through its capacity alone. Even a winter with little PV yield cannot be compensated for by an arbitrary number of battery modules.

With the AC Core with 5 kWh, you can start smaller. A 10 kWh set is another option if your data shows that need. It is important to assess capacity and simultaneous power separately.

This information helps with planning

• Year of commissioning, PV output, and previous operating mode.
• Inverter model and any known maintenance or repair issues.
• Current remuneration, electricity purchase price, and annual consumption.
• Available daily profiles of consumption and feed-in.
• Planned changes such as an electric car, heat pump, or new residential usage.

Request a retrofit from WonderVolt. The technical implementation and, if necessary, the change of the metering concept will be handled by a specialist company. You can find further decision-making aids in our AC/DC comparison for existing systems and in our retrofit overview.