A battery retrofit for an existing solar home
A 13.5 kWh battery added to a five-year-old 5.4 kWp roof, so the household uses its own power after dark.
- Battery size
- 13.5 kWh
- Yearly output
- 5,600 kWh
- Payback
- 7.5 years
- Location
- Willow Lane
A couple had a 5.4 kWp roof array fitted five years ago, before batteries were affordable. They were exporting most of their daytime power for very little and buying it back every evening.
The challenge
The existing inverter was not designed to work with a battery, and the panels were still under warranty with another installer. The owners did not want to replace equipment that was working well.
The system we designed
We checked the existing system, kept the panels and inverter as they were, and added an AC-coupled battery that works alongside them. The battery charges from surplus solar and covers the evening and early-morning load.
- A 13.5 kWh AC-coupled battery with its own inverter
- Backup circuit for the fridge, lights, and router
- Time-of-use settings that also charge cheaply overnight in winter
- One app for both the panels and the battery
The result
The household now uses 78% of its own solar power, up from 35%, and buys far less electricity in the evening. The retrofit took one day, and at current tariffs it pays back in about seven and a half years.
“We had panels for years but still paid for power every evening. Since the battery went in, the house runs on its own sunshine well into the night.”
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