Tesla Powerwall / Heat Battery / ASHP / Solar Installation


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New build installation, with a ‘No Gas’ aim

We first met these clients in 2016 when they were building a small ‘fabric-first’ wood-build annexe for a parent who needed the support of family around. Aspey Energy were able to add plenty of LED lighting, a small number of electric wall heaters, and assist with the installation of an MVHR system for the property.

Then, in 2019, the main property was replaced with a highly-insulated brick contruction, needing entirely new utilities that were appropriate for the time.

In order to achieve this, the architect had made provision for the south facing ridge roof to accommodate as many solar panels as possible. This would then, in time, power water heating, space heating and all household energy needs.

The array was installed in December 2019. Forty one panels were added in place of tiles on the south side. Further into 2020 once the build was progressed, the system was connected up to a SolarEdge inverter, and a Sunamp heat battery (with Eddi control panel) was added to provide hot water.

The family were keen to see how the various components would work out. Immediately the solar array did its job and both we and the family could monitor it via SolarEdge’s interface.

In June 2021 we were happy to return and add a Tesla PowerWall to the new build. The client was now enjoying up to 80kW in the sunny days of the summer, and the frustration was the wish to capture more of this energy rather than it returning to the grid.

Storage capability

The Heat Battery can hold around 13 kW and the Powerwall around 14kW. With the background use of the households (the annexe is also powered by the solar) we are now able to see around 50% self-power in the system on sunnier days. But as well as this, the tariff they are on will enable them to draw cheaper power at night once days shorten.

Next additions to the system

Currently we are busy completing the electrical aspects of a new ASHP using Mitsubishi Ecodan system. This heatpump should mop up more of the generated energy, and enable best use of the underfloor heating on two floors. With these acting as a heat sink (screed floor in the basement should hold the heat where it is most needed) the plan is to draw low levels of energy at night via the PowerWall and dissipate it as needed. Underfloor heating uses lower temperatures to warm the space, and the insulating value of the build makes it a perfect candidate for ASHP space heating.

Final additions to the system will be a second Heat Battery to add a further 13kW of stored energy and less need to monitor the bathroom use by the teens! And in time the family would like to replace their car with a EV, and we have made provision for this.

EV electric car pluged charging at a recharge station in the city

But what does the client think? Here’s how they described life with the new components:

“To be honest, we don’t really have to think about any of it at all, it all works perfectly. With a little initial tinkering, I managed to tell the PowerWall when to charge, when to discharge. The Heat Pump has priority after the household needs are satisfied, so there’s always hot water. If we have a grey day, its reassuring to know that the PowerWall will have recharged using energy from the early hours when its at its cheapest. Occasionally we even enjoy ‘positive pricing’ on this offpeak power!”

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