On May 15th, I installed a home battery to store solar power and reduce my reliance on the grid. In my previous post /“Green Energy/”, I outlined the reasons for going solar. But now the numbers are in, and the story is more complex than I initially expected.

How the System Works Here’s a quick summary of the energy flows:

energy streams

  • Solar generation: 776.99 kWh
    • 480.00 kWh fed directly to the grid
    • 149.10 kWh used immediately in the home
    • 237.70 kWh stored in the battery
      • After 10.49% storage loss, 183.71 kWh went to the home and 29.04 kWh back to the grid
  • Grid import: 1217.60 kWh
    • 168.00 kWh direct to the home
    • 1049.60 kWh stored in the battery
      • Resulting in 929.30 kWh sent back to the grid during demand peaks
      • Only 10.15 kWh used by the home

📉 Battery Round-Trip Efficiency (RTE): 89.51% ⚠️ Total loss due to storage inefficiency: 135.10 kWh

Unexpected Insight: I’m Paying for Zonneplan’s Strategy

Soon after installation, I was informed by Zonneplan that they expected me to consume about 1200 kWh more per year. Why? Because my battery is used for grid balancing:

  • Zonneplan charges the battery when there’s excess renewable energy on the grid (cheap times),
  • Then discharges it during peak demand (when energy is expensive).

It’s a smart system for the grid, but here’s the catch: 🔌 I’m the one absorbing the storage losses (~135 kWh so far) 💸 And I still pay taxes over that energy, even though I never actually “used” it myself.

That’s about 100 kWh/month of loss—energy lost purely through this trading mechanism.

My Solution: Solar Scaling

To compensate for these systemic losses, I decided to accelerate the installation of 4 additional solar panels on my shed.

  • These new panels are expected to generate an extra 1706 kWh/year
  • This boosts my total solar output by about 65%
  • It helps offset:
    • Battery losses
    • Additional grid use for balancing
    • Future increased consumption

I also created a forecast model to project my net energy balance over the year. Here’s what it shows:

forecast

As of now, the forecast suggests I’ll end the year with a net surplus of around +260 kWh, staying above the breakeven line—even with battery inefficiency and grid trading.

What I’ve Learned

  1. Home batteries are powerful tools, but they are also used by third parties (like Zonneplan) to serve grid needs—often without a full breakdown of how the losses and costs affect the user.
  2. More solar panels = more control: By expanding my generation capacity, I can protect myself against energy losses and future cost increases.
  3. Modeling helps: Creating my own predictive chart made it clear how my system behaves over time and reassured me that my choices are sustainable.

Financial Outcome So Far As of today, the battery system has already generated €170 in compensation through grid balancing (selling back during peak demand). This income appears to offset the energy losses (135 kWh so far), which would otherwise lead to extra taxation or costs.

🔍 Projection: If this trend continues, the battery would generate approximately:

€170 / 1.5 months × 12 months = €1,360 per year (estimated)

That amount not only covers the storage loss (~100 kWh/month) but also suggests the extra grid usage will not result in additional taxes at year-end. Instead, the battery is financially self-sustaining — and possibly even profitable.

Final Thoughts

While I’m still adjusting to the fine print of battery-powered energy balancing, I’m confident that the steps I’ve taken—both in awareness and infrastructure—are leading me in the right direction. The energy future is not just about tech, but understanding where your power goes, and who benefits.