Solar diverter options...

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Kraven

738 posts

Ultimate Geek
+1 received by user: 190

#3436086 19-Nov-2025 21:43

kangaroo13:

That's why I'm interested in diverters, and I'm particularly curious to hear of experiences with the SunStash diverter (from Ashburton, NZ), as it is a simlar price to the Catch Relay, about half the price of other diverters, and it promises full diverter functionality. If it says what it claims, then I would expect RoI to be quite good.

I have the SunStash, installed alongside our solar in May this year. It does what it's supposed to do. Bernard (owner/creator) is great and will respond quickly to any queries. We have ours set to boost from 2pm-6pm and this saw us through the worst generation days during winter.

The web interface is really basic but (mostly) functional. I had trouble with the initial setup webpage, where you enter in the size of your element and the export threshold. It was throwing an error on save and I wasn't sure it was saving the settings because reloading the initial setup page always shows the default settings. Turns out it was saving despite the error. Not a biggie as once it's setup you don't really need to ever look at the web interface again.

You can get data into Home Assistant via MQTT which is useful if you have this.

Bewildered

107 posts

Master Geek
+1 received by user: 31

#3436093 20-Nov-2025 02:39

Hey @kangaroo13!

I'm using a Shelly 3EM to monitor my power and am using its built-in relay to drive a contactor which in turn switches the HWC on/off, and that in turn is controlled by Home Assistant. This is the broadly the same as others have replied. Where I'm perhaps a little different is that I time the HWC based on the solar forecast using NodeRed.

In short:

HA provides me with a solar forecast that includes an indication of when the maximum generation is expected
I have a 300L HWC, it only needs to be heated once and then that is more than enough to last 24 hours.
Heating typically takes 3 hours
I use the forecast solar peak as the midpoint of my heating cycle - so 90 minutes before the peak the HWC is activated
I then monitor the HWC power use and once that has been at zero for 5 minutes (after activation) it will turn off the contactor until the following day.

This approach means it is minimal switching, and the heating time is optimised, regardless of the actual solar production. Once activated a shift in the forecast peak time will not disengage the HWC, and there is some logic to deal with any forecast change that pushes the peak into the past.

It's not perfect, but the RoI on a contactor is good, whereas a diverter will not pay for itself at the current rates.

---------------------------------------------
Why does this always happen to me?

timmmay

20858 posts

Uber Geek
+1 received by user: 5350

Trusted

Lifetime subscriber

#3436100 20-Nov-2025 07:07

I don't use a forecast to drive the HWC contactor, I use actual solar output / export which I have integrated with Home Assistant. The logic is roughly:

Once there's enough export the HWC turns on, no earlier than (from memory) 10am
If the Met Service forecast says it's a cloudy / rainy day the threshold for turning on is lower. For example the HWC takes 3.3kw to heat, on a cloudy day in winter I know we won't get that so I think we turn it on when there's 1.5kw which is better than nothing
If we start importing power for 5 mins, HWC turns off
The HWC always turns on at 1pm
If HWC turns off at 5pm
If the Met Service says it's a very windy day it turns on as early as 8am in case there's a power cut. Cuts are rare but happen. I set the threshold at some value I picked on a very windy day

michelangelonz

125 posts

Master Geek
+1 received by user: 40

#3436241 20-Nov-2025 17:35

timmmay:

I don't use a forecast to drive the HWC contactor, I use actual solar output / export which I have integrated with Home Assistant. The logic is roughly:

Once there's enough export the HWC turns on, no earlier than (from memory) 10am
If the Met Service forecast says it's a cloudy / rainy day the threshold for turning on is lower. For example the HWC takes 3.3kw to heat, on a cloudy day in winter I know we won't get that so I think we turn it on when there's 1.5kw which is better than nothing
If we start importing power for 5 mins, HWC turns off
The HWC always turns on at 1pm
If HWC turns off at 5pm
If the Met Service says it's a very windy day it turns on as early as 8am in case there's a power cut. Cuts are rare but happen. I set the threshold at some value I picked on a very windy day

My solar control is very similar. I do like the logic with weather great idea.

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