---
title: "A battery retrofit for an existing solar home"
description: "A 13.5 kWh battery added to a five-year-old 5.4 kWp roof, so the household uses its own power after dark."
url: "https://ecozen-astro.pages.dev/projects/home-battery-retrofit/"
date: "2026-03-15"
---

# 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.

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 [.h4]

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 [.h4]

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 [.h4]

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.