Episode 2‑2: How We Decided to Install a Home Battery
Once I finalized the specifications for my solar panels, I began thinking about how far I could push my self‑consumption rate.
The next item on the list was a home battery.
After researching various options, it quickly became clear that Tesla’s Powerwall was the strongest candidate. The reasons were straightforward:
- Low cost per kWh of capacity
- A highly intuitive and user‑friendly app
- A strong global track record
Unfortunately, Japanese‑made batteries felt less competitive in terms of cost and usability.
I requested estimates from two installers who could handle the Powerwall, and the prices were nearly identical.
So I compared them based on:
- Reliability of installation
- Warranty coverage
- Responsiveness when issues occur
In other words, I focused on whether they would support a long‑lifespan product until the very end.
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Solar + Battery: A Significant Boost in Self‑Consumption
I also learned that adding a battery would dramatically increase my self‑consumption rate.
While the primary purpose of a home battery is emergency backup during outages, rising electricity prices have made higher self‑consumption increasingly valuable.
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Final Specifications
- Battery capacity: 13.5 kWh
- Self‑consumption rate with solar + battery: 87%
- Cost: 2.3 million yen (installation included)
- Solar panels: 2.1 million yen → Total: 4.5 million yen
- Annual benefit: approx. 210,000 yen
- Payback period: approx. 21.6 years
Looking at the numbers alone, the payback period for a solar + battery system is still challenging.
Even so, I decided to move forward for two key reasons:
- Electricity prices are unlikely to decline in the current economic environment
- The need to prepare for outage risks is increasing
From here, my mindset shifted from “earning through feed‑in tariffs” to “energy independence through self‑consumption.”
Since posting the previous article, tensions in the Middle East—particularly involving Iran—have worsened, and crude oil prices continue to rise.
Considering that electricity prices typically increase with a delay of several months, this reaffirmed how important the concept of energy independence truly is.
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Episode 2‑3: How Much Did My Self‑Consumption Improve with Solar + Battery?
What factors do you prioritize when evaluating a home battery system?
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