Earth Notes: Heat Battery Experience So Far - EcoHome Lab (2022-06-09)

Updated 2022-10-02.
Some brief notes on my Thermino/Eddi experience for a Manchester Carbon Co-op virtual meeting. #cutCarbon #heat #storage
The heat battery works, hugely reducing gas demand for DHW so far.


At home I have off-grid and grid-coupled electric storage already, ~1kWh and ~5kWh respectively.

I had considered thermal storage of some sort, up to buried milk tanks for interseasonal, for years.

I was about ready to finally actually do something when coronavirus landed, but I finally had a Sunamp Thermino 150 and myenergi eddi diverter in place.

The Thermino 150 (was UniQ 6 when I originally planned it) was chosen to carry slightly more than one day's average consumption of ~4kWh, and to be able to fit in the space underneath our combi.

Since it has gone live, we have only drawn a fraction of usual gas at a bit over 0.5kWh/d of ~4kWh/d DHW demand, even though we have had some strings of fairly poor solar generation days.

Diversion pushes up electricity self-consumption, not imports.


The eddi was chosen over other possible diverter solutions in part because I can control it remotely from my (Raspberry Pi) servers to 'boost' the stored heat when grid intensity is low.

For about half the year I expect the Thermino to be kept topped up from solar PV diversion, eliminating ~4kWh/d * 180d = ~720kWh of our total yearly ~3MWh gas consumption.

During winter, I expect to boost it many windy mights in the wee hours from the grid, making our DHW less carbon-intense than burning gas directly, and maybe saving (depending on many many factors) as much gas as diversion.

20220512 heatBatTarget
2022-05-21 heat battery target percentage and GB grid intensity.
202205 heatBatteryInputDailyRecent
2022-05 eddi PV divert and mains boost to the Thermino.

So this boost may enable us to get our residual gas consumption down to well under 2MWh/year, mainly for space heat. We shall see!

Boost pushes up electricity imports.

Note that if boost (or divert) do not inject enough heat, the demand simply falls back to the combi, so no sudden cold showers!

Synthetic "heat" Dataset

So that I can track overall heat demand even as some of it shifts from gas, I have created a new synthetic dataset which is gas consumption (back to the dawn of time, ie 2007) plus the total divert and boost from the eddi. (Yes, another set of stats logged!)

I don't like mixing kWh of electricity and gas as they are very different animals, but this value reflects heat demand/output. If (say) I did put in a heat pump I would then add in its delivered heat also (not its input electricity).