Battery Storage & Solar Upgrade (29kWh Fox Cube)

Full Installation Walkthrough

This project documents a substantial battery storage upgrade that took an existing solar installation to the next level with a massive 29kWh of Fox Cube battery storage. The homeowner had previously installed a solar panel system with a smaller battery and, after a year of monitoring their energy data, realised they were still exporting significant amounts of surplus solar energy to the grid during the sunnier months. They approached ALPS Electrical to explore upgrading their storage capacity to capture more of this wasted generation.

Battery storage upgrades are becoming increasingly common as electricity prices remain high and homeowners with existing solar installations recognise the value of storing more of their own generation rather than exporting it at the much lower Smart Export Guarantee rate. The economics are compelling: electricity imported from the grid costs approximately thirty pence per kilowatt-hour, while the export rate is typically only fifteen pence. Every kilowatt-hour you store and use yourself rather than exporting and then reimporting later saves you approximately fifteen pence.

The existing system included a hybrid inverter that was already compatible with the Fox Cube battery platform, which meant we could add additional battery modules without replacing any of the existing equipment. The Fox Cube system is designed with modularity in mind: each battery module provides 5.76kWh of storage and multiple modules can be stacked together to create larger storage capacities. For this project, we installed enough modules to bring the total storage capacity to 29kWh, which is an exceptionally large amount of residential battery storage.

The physical installation involved mounting the additional Fox Cube battery modules on the garage wall alongside the existing equipment. Each module was securely bracket-mounted and connected to the existing battery communication bus, allowing the inverter to manage all the modules as a single unified storage system. The wiring between modules was carried out using the manufacturer-specified cables and connectors, ensuring reliable communication and safe power transfer between units.

With 29kWh of total storage, this system can capture an enormous amount of surplus solar energy. During peak summer months, a typical residential solar system can generate ten to fifteen kilowatt-hours more than the house consumes during daylight hours. Without adequate storage, this surplus is exported to the grid and lost from the homeowners perspective. With 29kWh of storage, even on the sunniest days of the year, the battery can absorb all of the surplus with capacity to spare.

The system was also configured to take advantage of time-of-use electricity tariffs. The homeowner is on a tariff that offers cheap overnight electricity between midnight and five in the morning. The Fox inverter was programmed to charge the battery from the grid during this cheap window, filling any remaining capacity that was not utilised by solar generation during the previous day. This dual charging strategy ensures the battery starts every day at full capacity, maximising the savings during the expensive peak rate periods.

The commissioning process for a battery upgrade is less involved than a full new installation because the solar array and inverter are already operational. We updated the inverter settings to recognise the additional battery capacity, verified that all modules were communicating correctly, and ran several charge and discharge cycles to confirm the system was operating within its normal parameters. The Fox Cloud monitoring platform was updated to show the new total storage capacity, and all the charge and discharge schedules were adjusted to reflect the larger battery bank.

Testing included verification of the battery management system behaviour under various scenarios: full charge, full discharge, simultaneous charge from solar and grid, discharge to household load while solar is generating, and the emergency backup functionality if the homeowner had opted for that feature. All tests confirmed correct operation across every scenario.

The financial impact of this upgrade is substantial. The homeowners own monitoring data from the previous twelve months showed that they were exporting an average of eight kilowatt-hours per day during summer and four kilowatt-hours per day during winter. The additional storage capacity will capture virtually all of this previously exported energy, saving the homeowner the difference between the import and export rates on every kilowatt-hour retained. Over a full year, this translates to savings of several hundred pounds annually from the battery upgrade alone, providing a payback period of approximately four to five years on the additional investment.

This project is an excellent example of how solar and battery systems can evolve over time. You do not need to install the largest possible system on day one. Starting with a solar array and modest battery, monitoring your actual energy patterns for a year, and then upgrading the storage capacity based on real data is a perfectly sensible approach. The modular nature of the Fox Cube platform makes this kind of incremental expansion straightforward and cost-effective. If you have an existing solar installation and feel you could benefit from additional battery storage, contact ALPS Electrical for a free assessment and upgrade quote.