We have just completed work at a vast Aylesbury estate that boasts eight distinct solar arrays, three battery systems, three heat pumps, multiple electric-vehicle charge points and a wind turbine. Originally the site already hosted seven Tesla Powerwalls; we have now added twelve expansion packs, bringing total battery capacity to a staggering 305 kWh, a figure that places it among the largest residential battery installations in the UK.
In the basement of the main manor we had already installed four Tesla Powerwalls. We have fitted twelve expansion packs, three behind each unit. Because of a current software limitation, we have split the work into two phases: in phase one we attached three expansion packs to the lead Powerwall; once Tesla releases its multi-Powerwall update, we will return for phase two to install the remaining nine. the customer, Nigel, has ordered all twelve packs in advance, so as to avoided any delays. We should be able to install these as soon as the software limitation is lifted.
Earlier this year we installed thirty JA 440 W bifacial panels on the hay barn, orientated 45° east of south with a 10° pitch. They generate around 11,550 kWh each year. We have also fitted three Powerwalls there, each paired to ten panels via its own MPPT channel. We have not added expansion packs at this location, as the existing 40.5 kWh capacity meets the barn’s load. The Tesla Gateway has been configured to provide single-phase backup for essential circuits while Tesla develops a three-phase solution.
On the barn’s exterior we have mounted a Tesla Wall Connector, wired across all three phases and capable of 22 kW output. In the Tesla app Nigel can choose whether the Powerwalls should supply the EV charger. Although most owners use off-peak tariffs rather than battery power for EV charging, this setup lets him “drive on sunshine” whenever he wishes.
Across the courtyard we have relocated a 49.2 kWh Alpha Smile T10 battery, originally in the manor’s basement, into the larger barn. That barn had already been equipped with two 20 kW SMA inverters feeding an older solar array (~12-15 years old). We have left the Alpha unit in place because Nigel’s main house now benefits from a 216 kWh Powerwall bank, vastly improving both storage capacity and inverter throughput.
Many ask how a single-phase battery supports a three-phase supply. We have configured the Powerwall to discharge into its phase to meet local load and export any surplus to the grid. A vector-sum smart meter then offsets imports across all three phases, so exports from one phase effectively reduce import charges on the others. Nigel therefore saves on his entire three-phase bill without needing batteries on every phase.
The estate comprises three sections: the main manor, a stud farm (stables, horse walker and vet) and a separate cottage. The manor alone draws roughly 90,000-100,000 kWh per year, driven by three heat pumps, a swimming pool and general use. With eight solar installations on roofs and ground mounts, plus the 15 kW wind turbine, we have designed the renewables to offset as much of that demand as possible.
We have dubbed the largest outbuilding the “horse-walker barn”. It hosts a substantial older solar array and three-phase distribution powering stable equipment. The 15 kW wind turbine, installed in 2008, connects through three 7 kW SMA Windy Boy inverters. Its autumn-and-winter output complements the summer-peaking solar, smoothing the estate’s energy profile. We note that domestic wind turbines rarely pay back in the UK unless sited high above obstructions on a substantial mast, conditions this property uniquely meets.
Back in the manor’s basement, we unmounted each Powerwall, stacked its three expansion packs on the same wall bracket and reconnected the assembly. We used 0.5 m expansion harness cables for neat stacking and ensured floor support for the entire battery weight. Although most distributors limit three Powerwalls on a three-phase supply, Nigel secured permission for two on phase 1 (with one on each of the other phases), giving him four in total.
At the end of April we reviewed system data. The previous day the house consumed 175.5 kWh; solar and wind supplied 28 per cent directly, but combined with off-peak charging the renewables covered 71 per cent of use. Over the first four months of the year grid imports accounted for 60 per cent of the 26 000 kWh total, with solar and wind supplying 18 per cent. This shortfall validated Nigel’s decision to expand battery capacity. We have configured the Powerwalls to maximise the seven-hour overnight off-peak window on his E.ON Next Drive tariff, ensuring a full charge each night.
All twelve Tesla expansion packs have now been installed and commissioned, working seamlessly alongside the existing solar, wind and Alpha ESS systems. Tesla UK’s case-study team has filmed interviews with our crew and Nigel to document the upgrade. We await Tesla’s multi-Powerwall expansion-pack update so we can complete phase two, while this estate already enjoys one of the largest residential battery installations in Britain.