Upgrade Your Balcony Power Plant with a Battery: How to Make Your Existing System Ready for the Night?

Retrofitting a Balcony Power Plant Battery: How to make your existing system fit for the night?

Anyone who bought a balcony power plant without a battery a year or two ago often regrets it today: During the day, when the sun is blazing and no one is at home, valuable solar power is given away to the grid operator. In the evenings and at night, when the TV, refrigerator, and standby devices are running, you pay for expensive grid electricity again.

The good news: You don't have to completely replace your existing system. Whether you use a Hoymiles microinverter or a Deye inverter – retrofitting a storage unit is simpler than ever before. But how exactly does it work, which systems are compatible, and what does AC coupling vs. DC coupling actually mean for your setup? This guide will shed some light on the matter.

Why is retrofitting a storage unit worthwhile in 2026?

Balcony power plants without storage usually only cover the so-called base load during sunny hours. As soon as the module output exceeds the magical limit of 600 or 800 watts, the surplus flows into the public grid unremunerated.

With a retrofitted battery storage (usually based on durable and safe LiFePO4 technology), you increase your self-consumption from a meager 30% to up to 85%. This not only saves money but also makes you a little more independent of the price fluctuations of energy companies. Thanks to the Solar Package I, registration in the market master data register is now also a breeze.

AC Coupling vs. DC Coupling: Which system suits your balcony power plant?

If you want to expand your existing Deye microinverter or your Hoymiles device, you face a fundamental architectural decision: AC-coupled (alternating current coupled) or DC-passed / DC-coupled (direct current coupled)? Both approaches have specific advantages and disadvantages in terms of efficiency and wiring.

1. DC Coupling (DC-passed / Interposed Systems)

This is the most common method for classic Plug & Play retrofitting. The storage unit is simply connected between the solar modules and your existing inverter.

• How it works: The MC4 cables of your solar modules go directly into the input of the storage unit (e.g., Zendure SolarFlow, Anker Solix, or Marstek). The storage unit taps the power, charges the battery, and, via a controllable output, feeds exactly the amount of DC current to your Hoymiles or Deye inverter that you are currently consuming in your home.

• Advantage: Extremely high efficiency, as the power is only converted to AC in the inverter when it is actually needed. In addition, your old inverter remains integrated into the system.

2. AC Coupling (AC-coupled / Grid-connected Systems)

With AC coupling, the storage unit operates completely independently of the solar modules and the inverter on the 230V AC side.

• How it works: Your existing system remains physically absolutely unchanged. The AC storage unit is plugged into a normal socket (or a fixed connection). A smart electricity meter (e.g., a Shelly 3EM in the fuse box) measures whether power is being fed into the grid. If so, it signals to the AC storage unit: "Now charge the battery with the surplus from the socket."

• Advantage: Maximum flexibility. It doesn't matter which inverter you use – compatibility is always 100% guaranteed. In addition, the storage unit can be installed spatially separated from the modules (e.g., in a cool cellar instead of on a hot balcony).

Retrofitting Hoymiles: Step-by-step to a smart battery

Hoymiles inverters (such as the HM-600, HM-800, or the newer HMS series) are among the absolute bestsellers in Germany. Retrofitting Hoymiles with a DC-coupled storage unit is basically child's play thanks to standardized MC4 connectors.

Wiring in the Plug & Play process:

1. De-energize the system: Unplug the Schuko or Wieland plug of your inverter from the socket.

2. Disconnect modules: Loosen the MC4 connections between your solar modules and the Hoymiles inverter.

3. Connect storage unit in between: Connect the MC4 cables of the solar modules to the PV inputs of the storage unit.

4. Connect inverter: Use the MC4 output cables included with the storage unit and connect them to the inputs of your Hoymiles inverter.

5. Switch on: Plug the inverter back into the socket and switch on the storage unit.

Important expert tip for control: So that the storage unit doesn't feed full power (e.g. 800W) into your Hoymiles at night and the battery is empty after two hours, you need smart control. Modern storage apps allow you to set a fixed output power (e.g. 150W base load for the night). It becomes even smarter with zero export via a Shelly sensor, which dynamically adjusts the output to your actual household consumption.

Expanding Deye Microinverters: What do you need to consider?

Owners of systems with a Deye microinverter (e.g., Deye SUN600G3 or SUN800G3) can also easily retrofit a storage unit. Since Deye devices have integrated relay protection and historically have an integrated WLAN module, a few software-side details need to be considered here.

Since the DC characteristics of Deye inverters harmonize very well with common smart PV hubs, the DC-passed principle works smoothly.

• Observe starting voltage: Make sure that the voltage output by the storage unit is above the minimum starting voltage of the Deye inverter (usually approx. 20-22V). However, most modern storage systems perfectly simulate the characteristics of a solar module, so the Deye inverter "thinks" it's bright sunshine – even in the middle of the night.

Compatibility Check: Avoid these typical mistakes when buying

Before you hastily order a storage unit, you should check the following points to avoid expensive mispurchases:

Criterion	DC Coupling (e.g., Zendure, Anker)	AC Coupling (e.g., Sax Power, EcoFlow)
Inverter brand	Must fit DC side (Hoymiles, Deye etc. mostly fully compatible)	Completely irrelevant (works with any inverter)
Connector type	Standardized MC4 connectors	Schuko / Wieland plugs
Efficiency (Conversion Rate)	Higher (approx. 85-90%), due to fewer conversion steps	Slightly lower (approx. 75-80%) due to DC-AC-DC conversion
Installation location	Mostly near the modules / Outdoor (observe IP65)	Flexible indoors possible

Conclusion: Is the upgrade worth it for you?

Retrofitting a balcony power plant storage unit is the logical evolution for all pioneering users of recent years in 2026. Anyone looking for a simple Plug & Play solution and who can easily access their solar modules should opt for a DC-passed system to continue operating their proven Hoymiles or Deye microinverter. Those who desire maximum flexibility and do not want to touch the wiring on the roof or balcony will find an elegant, albeit usually slightly more expensive, alternative in AC coupling.

Frequently asked questions

Can I use any storage unit with my old Hoymiles or Deye inverter?

Using the DC-passed method (direct current), you can use almost all common balcony power plant storage units (such as Zendure SolarFlow or Anker Solix), as these use universal MC4 connectors and imitate the electrical specifications of solar modules. With AC coupling, the storage unit is always compatible regardless of the manufacturer, as the systems operate electrically separately from each other.

Do I need an electrician for the installation of the storage unit?

For classic Plug & Play DC-based systems, which are connected between the module and inverter using MC4 connectors, you do not need an electrician. You can do this completely independently and safely. Only if you want to have a three-phase smart meter (like the Shelly 3EM) installed in the fuse box for smart zero export, an electrician must be called.

How is it controlled that the storage unit only releases power at night?

This is done via the control unit of the storage (the so-called PV hub). In the associated smartphone app, you can define time windows and power limits. For example, you set: "From 10:00 PM to 06:00 AM, constantly deliver 150 watts to the inverter." Dynamic controls that communicate with smart sockets or an electricity meter in the fuse box and precisely adjust the output to live consumption are even more efficient.

What happens if the battery gets freezing cold in winter?

Most balcony power plant storage units use LiFePO4 (lithium iron phosphate) cells. These are extremely durable, but they don't like charging at temperatures below 0 °C. If you have the storage unit outside on the balcony in winter, you should make sure to buy a model with an integrated heater, or operate the storage unit in a frost-free room (e.g., basement or garage) during the cold months.

Do I have to register the retrofitted storage unit with the grid operator?

Yes, any change to your PV system must be reported. However, retrofitting a battery storage system for a balcony power plant can now be registered online extremely easily and free of charge via the Market Master Data Register (MaStR) of the Federal Network Agency. A separate approval from the grid operator is generally not required for plug-and-play storage solutions.