PV panels powering geysers

I have a 8.8kw Sunsynk inverter with 2 x 3.5kw 3000 Pylontech batteries.

Jaco installing 8 x 545w panels.

Currently my 3 geysers and oven off inverter as non-essential.

The geysers are currently controlled ito times by 3 x CBI ASCs. I have one geyserwise lying around.


  1. Can I use the solar power to heat the 3 geysers?
  2. Should I install temperature sensors in the geysers (will need Tuya Smart Life) as I dont use Home Assistant?
  3. How many batteries and panels would supply my energy needs at night? 16Kw of panels and 4 or 6 Ă— 3.5 Pylontech batteries? Currently using about a 1000kw pm. Still busy measuring actual usage ito peaks.

Assuming that you have the CT clamp installed and the panels are producing enough power for the required load then yes it can be 100% from solar. You will probably have to schedule each geyser to have a turn to switch on(depending on what rating element was installed and the power produced on your PV)

The existing thermostat will regulate the temp. If you want to see the temp or add more intelligence when to switch on which geyser; then knowing the temperature could increase the efficiency of your system. If you want to automate the system to automatically schedule the heating of all geysers then HA would be the next logical step

Depends… if you boost the geysers temps to eg. 70 deg during the day using the sun, you might be able to get by by switching them off during the night. This should drastically reduce the amount of battery power you need.
How big are the geysers? What KW elements are installed? How much water do you use? All factors that could drastically change the amount of energy required.

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Are any geysers connected in series, and if not, can they be ?

Not linked and as for future to link in series might be too far away.

150kl all 3

Assume 3W elements

Not sure of water but catering to 1 person for 1 geyser

2 per other 2 geysers.

One geyser also services kitchen.

545W*8= 4360W max production

With some good sun you might be able to run 1 geyser at a time (assuming 3KW) and have something left to run the house (or charge the batteries).

Personally I would rather install more solar panels and store the excess energy as warm water than buying more batteries. At least double the solar production Jaco is installing. I would rather opt for 410-420W panels and parralel strings of 8 if you need more power.


If the geyser is connected to the non essential output of the inverter then this shouldn’t be necessary.

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My logic is to charge battery and then allow blending of grid and solar during day.

If geysers and oven on non-essential, will they get any solar power? I assume not?

Thus considering to reconnect them so they can use excess solar power.

Since the geyser stores energy (heat) it doesn’t require power when you use hot water. So it’s an ideal load for when solar power isn’t being used for anything else. And this happens a lot during sunny days…
However the oven needs to function when it’s switched on. I’ve noticed that often ovens are permanently connected to the grid due to their heavy essential loads.

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That does depend on how they are wired in and which system you use.

For instance if you have a Victron Multiplus it has an essential and non-essential output and it can blend power. So items on your non-essential output will be powered by the PV as well, but when the grid(input) fail it will only power the essential output from the batteries/PV.
If you use an external power meter like the ET112 you can even set it up that the Multi will puch power back through the input to power your non-essentials that is between the ET112 and your Multi (very cool, but most other inverters won’t do this)

Hmm have a super hybrid Sunsynk, so should be able to do this. Will check.

Yes the sunsynk can do this. It will feed power back into the non essential loads but not beyond the ct. this only happens if there is grid though. With no grid, non essentials will be off.

Unless you want to get complicated, the simple way is to monitor your loads and then just set the geyser on timers. It should work fine 90 % of the time.

I have 3 geysers. First is a 200l evacuated tube system that feeds into a 150l electric. The 200l has a “diy smart thermostat” connected to a sonoff with a relay that I can control if needed. However in summer, the tubes work fine to he’s the water to 60-70 degrees. The 150l is connected to a geyserwise control and only comes on at midday or if the water temperature drops below 50 degrees at night. At midday I heat it to 65 degrees. At night it’s set to heat to 52 degrees but it almost never comes on.

Then in the main bedroom I have a 200l geyser. This as well is connected to a sonoff via contactor. Element comes on between 1-2pm and is heated to the max of 65 degrees. I have a heatpump connected to this geyser and it comes on during specific times in the early morning and late afternoon.

Unless the weather is bad, I don’t use grid during the day… but I do have 11 kw of panels facing east, north and west.

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Yes the sunsync can be setup to first deliver all Solar power to the loads on the non-essential side (this will not work during loadshedding as there needs to be grid power connected to non-essentials).

Let us say all 3 geysers are on (9KW Load), and your PV is producing 4KW. Then 4KW will be delivered to the geysers via PV and the shortfall of 5KW will be fetched from the grid. Thus it will yield 4/9 = about 45% savings as we are still buying 55% from the grid. If the PV could meet 100% there would be no need to fetch from the grid. Hence the reason I suggested that you give each geyser a turn at heating.

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