How to Connect a Battery Storage to Your Balkonkraftwerk System

The short answer is that you connect the battery storage between the PV inverter’s output and your home’s consumer unit, using either a DC‑coupled or an AC‑coupled configuration, and then let the inverter’s firmware or an external Battery Management System (BMS) handle the charge‑discharge logic. In practice this means checking inverter compatibility, selecting a battery type that meets the voltage window of your inverter, installing the proper safety gear, wiring the DC cables (or setting up an AC‑coupled inverter), and finally configuring the system settings so the storage can store excess solar power for later use.

If you’re like most balcony‑solar owners, you started with a 300‑400 W kit that feeds a small inverter, but you want to keep that electricity for evening use or for occasional power outages. A battery gives you that flexibility, while also smoothing out voltage fluctuations that can affect the inverter’s lifespan.

Why Add Battery Storage?

From a technical standpoint, a battery:

• Stores surplus generation that would otherwise be exported to the grid at a low feed‑in tariff.
• Reduces inverter “cycling” by absorbing sudden load spikes, extending component life.
• Provides a small backup reserve for critical devices (e.g., router, fridge).

Economically, you can shift consumption to peak‑rate periods, and in some German regions you can earn a small arbitrage profit. Environmentally, using stored solar instead of grid power cuts CO₂ by roughly 0.5 kg per kWh saved.

Compatibility Check – Inverter & Battery

Not every inverter can talk to every battery. Below is a quick reference table of common balcony‑inverter brands and the battery communication protocols they support:

Inverter Brand	Supported Battery Interface	Typical Voltage Window	Max. Battery Capacity (kWh)
GoodWe	CAN‑Bus (Pylontech/ BYD)	40‑60 V DC	5.0
SMA	SunSpec Modbus	48‑60 V DC	10.0
Enphase	Proprietary AC‑coupled	230 V AC	4.8
Fronius	Modbus TCP	48‑60 V DC	7.5

If your inverter isn’t listed, look for a generic “RS485” or “CAN‑Bus” port—many LiFePO4 batteries expose these pins for direct wiring.

Required Components

Here’s a checklist of everything you’ll need before you start the physical installation:

1. Battery pack (LiFePO4, NMC, or lead‑acid) – capacity between 2 kWh and 6 kWh is typical for a balcony‑scale system.
2. Battery Management System (BMS) – built‑in or external, must be able to communicate with the inverter.
3. DC disconnect switch – rated for at least 600 V DC and 20 A (German standard VDE 0100‑701).
4. Cables & conduit – use 4 mm² copper for runs up to 10 m; 6 mm² for longer distances.
5. Fuses – inline PV fuses (e.g., 10 A 1000 V) on the positive string.
6. Mounting brackets – to secure the battery to the balcony wall without penetrating load‑bearing structures.
7. Grounding rod or strap – per DIN VDE 0100‑540 for safety.
8. Smart meter or CT clamp – to monitor generation and consumption in real time.

⚡ Safety tip: Always isolate the PV array using the DC disconnect before you touch any battery terminals. Even a low‑voltage system can deliver high currents if a short occurs.

Step‑by‑Step Wiring Guide

1. Turn off the grid – open the main breaker and verify the inverter display is blank.
2. Install the DC disconnect – mount it between the PV array and the inverter, ensuring the handle is easily accessible.
3. Connect battery positive (+) to inverter DC+ – use the appropriate cable gauge (see table below).
4. Connect battery negative (−) to inverter DC− – keep the cable run as short as possible to reduce voltage drop.
5. Wire BMS communication – plug the CAN/RS485 cable into the inverter’s dedicated port and terminate the bus with 120 Ω resistors if required.
6. Ground the battery chassis – connect the grounding strap to the building’s earth terminal.
7. Re‑energize the system – close the DC disconnect and restore grid power; the inverter will start a “battery detection” routine.
8. Configure settings – enter battery capacity, max charge/discharge current, and any grid‑export limits (e.g., VDE‑AR‑N 4105).
9. Test a charge‑discharge cycle – let the PV generate, watch the battery charge, then switch on a load to verify discharge.

Cable sizing (copper, 90 °C insulation):

Run Length (m)	Current (A)	Required Cross‑Section (mm²)
≤5	10	2.5
5‑10	10	4
10‑15	10	6
≤5	20	4
5‑10	20	6

System Configuration & Monitoring

After wiring, the inverter’s firmware usually has a “Battery Settings” menu where you can set:

• Charging priority – either “Solar first, grid second” or “Battery only when excess > 10 %”.
• Discharge depth (DoD) – 80 % DoD for LiFePO4 is safe; for lead‑acid keep it ≤ 50 % to preserve cycle life.
• Export limit – most German utilities cap export at 70 % of rated inverter capacity; set this to avoid penalties.
• Smart‑meter integration – some inverters auto‑adjust charge/discharge based on real‑time consumption data.

If you want a plug‑and‑play solution that already bundles everything, the Balkonkraftwerk mit Speicher package includes a compatible LiFePO4 battery, a built‑in BMS, and pre‑configured inverter settings, so you can skip the manual configuration steps.

Economic & Environmental Impact

Typical numbers for a 4 kWh battery attached to a 300 W Balkonkraftwerk:

Metric	Value (per year)
Additional solar self‑consumption	≈ 30‑40 % of generation