Retrofitting a Balcony Power Plant with Storage: The Ultimate Guide for Existing Systems

Anyone who invested in a balcony power plant in recent years benefits from clean, free electricity during the day. But as soon as the sun goes down or no one is home during the day, the valuable solar power flows uncompensated into the public grid. The solution is obvious: Retrofit a balcony power plant with a storage system.

However, many owners of existing systems with microinverters from established manufacturers like Hoymiles (e.g., HM or HMS series) or Deye face crucial questions: Will a modern battery work with my existing solar modules and my old inverter? What about the wiring, and will the system remain truly plug & play?

In this comprehensive guide, you will learn everything about system compatibility, technical connection principles (DC bypass vs. AC coupling), and how to safely upgrade your setup without an electrician.

Storage for balcony power plant with inverter: Which system fits Hoymiles, Deye & Co.?

When retrofitting a battery storage system to an existing mini PV system, there are two fundamental technical approaches:

1. DC-coupled systems with DC bypass (standard for modern retrofit storage systems)

With DC coupling, the storage unit is connected between the solar modules and the existing microinverter.

• Functionality: The direct current (DC) from the solar modules flows directly into the storage unit. The battery charges via an integrated charge controller (MPPT). The storage unit then supplies controlled DC power to your existing Hoymiles or Deye inverter, which in turn converts it into grid-compliant alternating current (AC) for your socket.

• Advantage: High efficiency, as the solar power is charged directly into the battery without unnecessary conversion losses. Your old inverter remains fully integrated into the system.

2. AC-coupled systems (storage connected to the socket)

With AC coupling, the storage unit is connected on the AC side. The inverter first converts the solar power into AC power, the storage unit takes this in via the Schuko or Wieland socket and converts it back into DC for the battery.

• Functionality: Extremely universal, but prone to double conversion losses (DC $\rightarrow$ AC $\rightarrow$ DC $\rightarrow$ AC).

• When does it make sense? If your inverter is installed in an extremely inaccessible location or if you are looking for an absolutely manufacturer-independent solution.

Compatibility check for existing components:

Important for solar modules: Pay attention to the maximum input voltage ($V_{oc}$) and current ($I_{sc}$) of the storage unit. Modern storage units usually support module voltages of up to $60\text{ V}$ and currents up to $15\text{ A}$ to $20\text{ A}$ per input.

Important for the inverter: The DC output of the storage unit simulates a solar module for your Hoymiles or Deye. Check in the storage unit's app whether your inverter model can be selected as the target device to avoid overvoltages or error messages from the MPPT tracker.

Wiring diagram for retrofitting balcony power plant storage: Detailed wiring instructions

Much of the concern about incompatibilities arises when looking at the tangle of cables. However, the functional principle of a DC-coupled retrofit can be presented very simply.

[ PV-Modul 1 ] --(MC4 DC)--\
                            +--> [ Smart Storage ] --(MC4 DC)--> [ Existing Microinverter ] --(AC Schuko)--> [ Home Grid ]
[ PV-Modul 2 ] --(MC4 DC)--/     (e.g. 500 PRO / Zendure)        (e.g. Hoymiles HM-800 / Deye)

Step-by-step wiring instructions (Plug & Play):

1. Safety first: Unplug the Schuko plug of your existing inverter from the socket to de-energize the system.

2. Disconnect solar modules: Disconnect the MC4 plug connections between your PV modules and the inverter.

3. Connect PV modules to the storage unit: Plug the MC4 cables of the solar modules into the DC inputs (PV input) of the new storage unit.

4. Connect storage unit to the inverter: Connect the DC outputs (Out) of the storage unit to the DC inputs of your old inverter using the supplied MC4 connection cables.

5. Establish grid connection: Plug the AC cable of the inverter back into the household socket.

6. Setup via app: Pair the storage unit via Bluetooth/WLAN and set the maximum output power to the inverter (e.g., $150\text{ W}$ base load for the night).

(Note: No special tools or electrician are required for this conversion. It involves only low-voltage DC plug connections.)

Retrofit balcony power plant storage via socket: Simple Schuko connection without an electrician

The term "Plug & Play" is paramount for balcony power plants. A modern retrofit storage unit does not interfere with your home's fixed electrical installation.

• No structural changes: The storage unit uses the existing plug system.

• Feed-in via Schuko or Wieland: Since the storage unit supplies DC power to the inverter, and only the inverter handles the feed-in into the 230V household grid, the safety chain of your Schuko or Wieland connection remains fully intact.

• Smart control via smart plugs or smart meters: So that the storage unit knows how much electricity you are currently consuming in the household, it can be wirelessly coupled with WLAN sockets or a smart meter in the meter box. This way, the storage unit outputs exactly the amount of electricity currently needed – a so-called zero feed-in.

Best retrofit solutions for balcony power plant storage: A comparison

The market is dominated by various manufacturer-independent LFP storage systems (lithium iron phosphate) that have been specially developed to complement existing inverters. The new 500 PRO stands out as an absolute recommendation for future-proof retrofitting, combining universal compatibility with maximum performance.

Recommendation: The 500 PRO All-in-One Storage System

The new 500 PRO was specially developed for seamless integration into existing balcony power plants. It is characterized by maximum compatibility and can be combined completely problem-free with over 99% of the microinverters available on the market (such as Hoymiles, Deye, NEP, and others).

The highlights of the 500 PRO at a glance:

• Highly efficient MPPT charge controllers: Equipped with $4 \times 625\text{ W}$ independent MPPT solar charge controllers, the 500 PRO allows direct connection of up to four high-performance PV modules with optimal yield – even with partial shading.

• Powerful bi-directional inverter: An integrated $2400\text{ W}$ bi-directional inverter ensures maximum flexibility for fast charging and discharging as well as grid connection.

• Massive & Secure Storage Capacity: With a long-lasting $5\text{ kWh}$ lithium iron phosphate battery (LiFePO4), the 500 PRO offers sufficient capacity to reliably cover the electricity needs of even busy households throughout the night.

Test insight: If you are looking for a compact, highly compatible, and at the same time extremely powerful solution, the 500 PRO sets the new standard for retrofitting existing systems with its combination of $5\text{ kWh}$ LFP capacity, $2400\text{ W}$ bi-directionality, and 4 powerful MPPTs.

Retrofitting balcony power plant storage 5 kW: Does XXL storage capacity make sense?

When searching for retrofit options, users often encounter storage sizes of $5\text{ kWh}$ or more. However, it is important to weigh the economic and technical aspects carefully:

How much storage does a balcony power plant really need?

A typical balcony power plant with 2 to 4 modules ($800\text{ W}$ to $2000\text{ Wp}$ module power) generates considerable amounts of electricity on a sunny summer day.

• The advantage of modern $5\text{ kWh}$ systems (like the 500 PRO): Thanks to modern $4 \times 625\text{ W}$ MPPT inputs, you can directly connect up to 4 large PV modules to systems like the 500 PRO. This ensures that the $5\text{ kWh}$ storage unit is optimally charged even on high-yield days. This guarantees maximum self-sufficiency and allows you to cover even larger household consumption in the evening.

• When is $5\text{ kWh}$ ideal? A storage capacity of $5\text{ kWh}$ is particularly worthwhile if you upgrade your balcony power plant to 3 to 4 modules, have a high base load in the household (e.g., home office, aquarium, heat pump), or want to absorb peak loads in the evening without expensive grid electricity.

Conclusion: Worry-free retrofitting and doubling self-consumption

Concerns about incompatibilities with older balcony power plants are largely unfounded with modern LFP storage systems. Thanks to standardized MC4 standard connectors and universally compatible all-in-one solutions like the 500 PRO, storage units can be easily combined with your old Hoymiles, Deye, or NEP inverter. You increase your self-consumption from an average of $30\%$ to up to $80\%$ and make your mini PV system future-proof.

Frequently Asked Questions (FAQ)

1. Can I keep my old Hoymiles or Deye inverter when retrofitting a storage unit?

Yes, absolutely. When using a universal retrofit storage unit like the 500 PRO or Zendure SolarFlow, the storage unit is simply connected between the modules and your existing microinverter. The inverter continues to operate as usual, converting the DC power supplied by the storage unit into AC power for your home grid.

2. Is the 500 PRO also compatible with older solar modules and microinverters?

Yes. The 500 PRO is characterized by over $99\,\%$ compatibility with commonly available microinverters (including Hoymiles, Deye, NEP). Thanks to the standardized MC4 connectors and flexible MPPT inputs, older PV modules can also be connected without problems.

3. Do I need an electrician for the installation of a retrofit storage unit?

No. The retrofit is carried out entirely via touch-safe plug connections (Plug & Play). The solar modules are connected to the storage unit via MC4 connectors, and the storage unit is connected to the inverter. No intervention in the fuse box is required.

4. What happens to the storage unit if the battery is completely empty in winter?

Modern balcony power plant storage units have an intelligent battery management system (BMS) with deep discharge protection. At very low temperatures or if there is no sunlight for several days, the storage unit switches to a protective mode. In bypass mode, the system passes the low PV power directly to the inverter or protects the battery cells.

5. Do I have to register the retrofit of the storage unit in the market master data register (MaStR)?

Yes. Even if the effort is minimal: If you expand your existing balcony power plant with a stationary electricity storage unit, it must be added or registered in the market master data register of the Federal Network Agency. This can be done online in a few minutes free of charge.