When a Balkonkraftwerk mit Speicher produces more electricity than the apartment is currently using, the surplus does not simply disappear – it is diverted into a cascade of storage, demand‑response, and grid‑export options that together shape the system’s overall efficiency and economics. In short, the excess energy is first stored in the battery (if capacity is available), then either consumed later, fed back to the low‑voltage grid under the EEG feed‑in regime, or used to drive local loads such as hot‑water heating or an EV charger, depending on the installed hardware and the home‑energy‑management settings.
Typical Energy‑Flow Diagram
- Solar generation → DC from PV panels
- Inverter → AC to household loads
- Remaining AC → Battery charge (if SOC < 100 %)
- If battery full → Grid export (feed‑in) or direct load (e.g., heat pump, EV)
- When generation < demand → Battery discharge → Grid draw (if needed)
Key Technical Parameters of a Representative System
| Component | Typical Specification | Typical Performance Data |
|---|---|---|
| PV panels (Balkonkraftwerk) | 0.6 kWp (2 × 300 W mono‑crystalline) | ≈ 540‑660 kWh / yr (≈ 1.5‑2 kWh / day) |
| Inverter | 600 W pure‑sine‑wave, Euro‑efficiency ≈ 97 % | AC output limited to panel rating |
| Battery (Li‑FePO₄) | 1.2 kWh usable capacity, 0.9 kWh usable (≈ 75 % depth‑of‑discharge) | Round‑trip efficiency ≈ 95 % |
| Smart meter | Bidirectional, 1 kWh resolution, German E‑meter | Enables accurate feed‑in and consumption logging |
| Home‑Energy‑Manager (HEM) | App‑controlled, weather‑forecast‑aware | Can shift up to 30 % of daily excess to later slots |
Four Main Destinations for Excess Energy
- Charging the Battery
If the battery’s state‑of‑charge (SOC) is below its maximum, the surplus AC is redirected to the charger. For the 1.2 kWh pack above, a 400 W excess will fully recharge an empty pack in roughly 3 hours (400 W × 3 h = 1.2 kWh). The round‑trip loss is ~5 % (≈ 0.06 kWh lost per full cycle). - Direct Load Shifting (Heat‑Pump / Water‑Heater)
Many installations tie the inverter output to a smart plug that activates a 1‑2 kW immersion heater or an air‑source heat pump when surplus ≥ 300 W. This can absorb up to 0.8 kWh of the daily excess, raising self‑consumption from ≈ 30 % (no storage) to ≈ 55 % (with storage + load‑shift). - Grid Feed‑in (Export)
When the battery is full and no deferrable load is available, the inverter’s “export‑limit” mode reduces output to a preset export cap (commonly 0 % for pure‑self‑consumption or up to 70 % of rated power for partial feed‑in). In Germany, the 2024 EEG feed‑in tariff for PV ≤ 10 kWp is ≈ 8.2 ct / kWh. A typical balcony system might export ≈ 0.3 kWh / day, earning about 2.5 ct / day (≈ 9 € / yr). - Electric‑Vehicle Charging (Opportunistic)
If an EV is plugged into a smart wallbox that supports “Solar‑Only” mode, the car’s onboard charger will draw only the surplus power. For a 7 kW charger, a 0.5 kW surplus will add ≈ 1 % range per hour – modest but useful for nightly top‑ups.
Economic Impact: Feed‑in vs. Self‑Consumption
| Scenario | Self‑Consumption Share | Annual Electricity Cost Saving (≈ 0.30 € / kWh) | Annual Feed‑in Revenue (≈ 8.2 ct / kWh) | Net Financial Benefit (≈ ) |
|---|---|---|---|---|
| No battery, no load‑shift | 30 % | 0.30 € × 0.30 × 600 kWh = 54 € | 0.082 € × 420 kWh = 34 € | ≈ 88 € / yr |
| Battery only (1.2 kWh) | 55 % | 0.30 € × 0.55 × 600 kWh = 99 € | 0.082 € × 270 kWh = 22 € | ≈ 121 € / yr |
| Battery + Heat‑pump load‑shift | 70 % | 0.30 € × 0.70 × 600 kWh = 126 € | 0.082 € × 180 kWh = 15 € | ≈ 141 € / yr |
| Full‑featured (Battery + EV + Heat‑pump) | 85 % | 0.30 € × 0.85 × 600 kWh = 153 € | 0.082 € × 90 kWh = 7 € | ≈ 160 € / yr |
These figures assume an average German household electricity price of 0.30 € / kWh and an annual generation of 600 kWh from the 0.6 kWp Balkonkraftwerk. The incremental gain from adding a battery and smart loads is ≈ 30‑70 € per year, which typically offsets the battery cost within 5‑7 years.
Regulatory and Grid‑Related Constraints
- EEG Registration: All PV installations ≤ 10 kWp must be registered in the Markstammdatenregister (MaStR) and receive a feed‑in meter.
- Export Limitation: Grid operators may require a 0 % export mode for balcony systems < 600 W, but many modern inverters allow up to 70 % export with proper metering.
- Smart‑Meter Roll‑out: As of 2024, bidirectional digital meters are mandatory for new PV‑plus‑storage systems > 7 kWp; for smaller balcony kits they remain optional but recommended.
- Curtailment Risk: During extreme over‑generation events (e.g., sunny weekend with low household demand), the distribution system operator can temporarily reduce feed‑in power to avoid voltage rise on the local transformer.
Smart Energy Management – Squeezing the Most Out of Surplus
Modern home‑energy‑manager (HEM) platforms use weather forecasts and historical consumption patterns to predict when the battery will be full. The HEM can then:
- Pre‑emptively charge the battery during the early morning using cheap off‑peak grid power (if a cheap night tariff is available).
- Activate the hot‑water heater or heat‑pump precisely when the PV forecast shows a peak generation window.
- Defer EV charging until the following morning if the forecast indicates a high‑generation day tomorrow.
- Display real‑time feed‑in vs. consumption data on a smartphone app, encouraging occupants to shift high‑power tasks (e.g., washing, cooking) to sunny periods.
“A well‑configured 0.6 kWp Balkonkraftwerk mit Speicher can lift a household’s self‑consumption share from ~30 % to over 70 %, turning otherwise exported kilowatt‑hours into saved electricity costs of roughly 150 € per year.”
Real‑World Example: A Berlin Studio Apartment
Consider a 35 m² studio in Berlin (latitude 52.5°N):
- Solar yield: 950 kWh / kWp / yr → 0.6 kWp → ≈ 570 kWh / yr (≈ 1.6 kWh / day average).
- Daily consumption: Base load ≈ 2 kWh, occasional washing machine (0.8 kWh), fridge (1 kWh) – total ≈ 3.8 kWh.
- Excess on a sunny summer day: Peak generation 0.6 kW for 5 h → 3 kWh generated; household uses ~2.5 kWh → surplus ≈ 0.5 kWh.
- Battery storage (1.2 kWh): The 0.5 kWh surplus charges the battery within 1 h. In the evening, the battery releases 0.5 kWh, covering the 1‑h gap when solar drops below consumption.
- Result: Net grid import ≈ 0.1 kWh (≈ 3 ct), grid export ≈ 0.0 kWh because the battery fully absorbs the excess. Over a year, this configuration saves ~ 120 € in electricity costs and receives a modest feed‑in credit of ~ 10 €.
For a ready‑to‑use solution that bundles the right panel, inverter, and battery with intelligent management, explore the range of Balkonkraftwerk mit Speicher devices designed for German balcony installations.
Overall, the fate of excess energy in a Balkonkraftwerk mit Speicher is a dynamic interplay of storage, load shifting, grid export, and intelligent control. By leveraging a well‑sized battery and a responsive energy‑management system, homeowners can maximize self‑consumption, reduce electricity bills, and contribute to a more stable low‑voltage grid – turning what used to be