I understand the concept (not the details) of PV Diverters for 1:1 electrical boilers that follow the PV production very nicely to avoid PV injection into the grid.
But nowadays a lot of heat pump manufactures advertise with things like smart grid ready, SG Ready, PV diverter, solar pv ready, … (eg. Solar PV Ready Heat Pumps by Stiebel Eltron). But can they do the same so nicely as a 1:1 electrical boiler? I don’t think it is a good idea for the lifetime to just interrupt the process of a heat pump?
As an example my heatpump (in red), PV production (blue) and my situation to the grid (yellow: + is import ; - is export). The only thing I do is programming to heat water starting from 13:00 as the chance is bigger there is sun. As you can see: it fails big at avoiding export or import…
Here’s the strategy that I use with my PV + battery + heat pump: forecast how much solar generation is expected today, and check how much energy in stored in the battery. I’ve setup the heat pump to start the water cycle at 12:00, or when the battery reaches 90%. On cloudy days, it only heats up to 45C, but on days that are forecasted to have an excess of PV, it will heat up to higher temperature.
Of course, this does rely on having a storage battery to even out the fluctuation in generated power. It’s much harder to have a heat pump respond in real-time to PV.
Something that might work for you is to look at the current generation & the forecast for the next half-an-hour. When you’re generating (say) more than 500W and the forecast suggests that you might generate at least 500W for the next half-hour, then turn on the heat pump. Looking at your chart, and assuming the forecasts are reasonably accurate, this would have the HP running from 10am until 1:30pm. (You’ll want to adjust the threshold to include your house load too).
Running in 30 minute cycles will probably work okay, without being too detrimental to the heat pump, but do check the manufacturers recommendations for minimum run time.
I don’t think any heat pump will be able to do load matching as closely as a resistive heating PV divert or battery inverter. HP compressors are not designed to be controlled in this way.
My Samsung Gen6 ASHP has got a solar PV input and a Smart Grid Input, it’s quite simplistic: when solar PV input is active the ASHP will run a DHW cycle and bump up the indoorT set-point by a couple of degrees for heating for couple of degrees less for cooling:
Sorry for the late answer! Thank you @Timbones and @glyn.hudson. We don’t have a home battery, because financially it doesn’t seem that interesting (at least in Belgium). We also don’t have the “normal” central heating: our passive house does reasonably well without. We use a simple electric heater during some colder days/hours (consumed about 125 kWh last winter in our living room). This means that our heatpump is for domestic hot water only (and ventilation).
So I guess it is possible that a cloud passes by and that electricity is imported from the grid during it heatpump cycle.
Our heatpump consumes about 600 Watt during its cycle. Would it be possible to produce a heatpump that can have different ‘levels’. Eg. 300 Watt cycle if there is not much sun (of course it takes double as long) and 600 Watt cycle if there is more sun. If this could be possible: are they on the market already?
