Retrofit AC battery storage and keep the existing inverter

A battery storage system can also be added if your PV system already has an inverter. With an AC-coupled retrofit, the functional solar side remains in place. The additional storage unit operates on the home's AC power grid. This is particularly interesting if you want more self-consumption but do not want to buy a new PV inverter just for the battery.

SunEnergyXT 500 PRO AC Core main storage unit

What remains, what is added?

The solar modules deliver direct current to the existing PV inverter. This continues to supply the home grid with alternating current as before. An AC battery stores energy there and makes it available again later. Added to this are the storage unit, a suitable AC connection, and the metering for its control. The technical condition assessment remains important: an old, defective, or unsuitable inverter will not become future-proof just by adding a new battery.

The advantage lies in the separation of tasks. You can make the storage decision independently of any planned renewal of the solar side. A specialist company will check whether your specific system can be reused based on the devices and the connection concept.

AC or DC: What is crucial for a retrofit?

In a DC solution, the battery is integrated on the direct current side, often together with a matching hybrid inverter. This can be interesting for a new system or an upcoming inverter replacement anyway. In an AC solution, the existing generation in the home grid is used. Therefore, do not just compare the price of the battery, but the entire project: additional devices, installation, electrical work, metering, and commissioning.

  • Inverter is working and should be kept: Evaluate an AC retrofit specifically.
  • Inverter must be replaced anyway: Compare AC and suitable hybrid solutions as a total package.
  • You want to connect new solar modules directly to the storage unit: Consider the designated PV inputs separately; this is not the same function as an AC retrofit.

Why metering is part of the storage system

A battery does not automatically know the entire power flow in the house. The control system needs suitable measured values for demand-based charging and discharging. For AC Core, compatible devices such as the Shelly 3EM / Pro 3EM, EcoTracker, or bitShake are suitable. Which variant is appropriate also depends on the existing meter, the interface, and the installation location. A metering device for storage control is not automatically the same as a billing-capable smart metering system for an electricity tariff.

Does AC Core suit your consumption?

First, use real daily profiles: Is there a regular surplus that you would need again in the evening? The logic can be seen in an example: If 4 kWh are exported during the day and 6 kWh are drawn in the evening, a storage system can shift part of this. However, it cannot generate an additional 2 kWh; furthermore, there are losses when storing energy. The example describes the energy flow, not a guaranteed saving.

The SunEnergyXT 500 PRO AC Core is intended for this AC-side entry. More capacity can be added with the B500. If you need higher simultaneous power, however, the planning of additional main units is relevant.

Your checklist before buying

  1. Document the model and condition of the existing PV inverter.
  2. Compare surplus and subsequent consumption, if possible across different seasons.
  3. Clarify the existing meter and suitable metering device for control.
  4. Have the installation location, connection, protection, and registration planned by a specialist company.
  5. Compare the total offer including necessary additional components.

For a former full feed-in system, the metering concept should be on the list very early on. You can find more on this in the guide for post-20-year (Ü20) systems.

Keep the inverter, retrofit appropriately

Send us your device models and the desired application to support@wondervolt.de. In the overview of PV storage retrofitting, you will find the next steps and the available AC Core configurations.

Further context: Consumer advice center on battery storage. Product details and installation requirements: SunEnergyXT AC Core.


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