question

tailele avatar image
tailele asked

Management of electric resistance for water accumulation

Good morning,

I am asking for community support for an application that I am installing inside my home.

I have currently finished installing 12 kW of photovoltaic panels, connected to an RS 450/200 charger and a Multi plus II 48 - 70A GX inverter. Both input and withdraw energy from a 15 kWh battery storage system.

I'm completing the installation, I expect it to be operational by the end of the week.

At this point, considering that in summer and winter I will have a surplus of energy, I would like to use the surplus to heat an 800 L technical water boiler for domestic hot water and heating using a 3kW resistor. My question is whether there is a Victron product that can manage the resistance, perhaps through a Canbus or RS485 connection. Considering that the tank is 10 meters away and possibly I would like to control it via a solid state relay wirelessly.


Thank you for the support

VE.Canmultplus 2 gxrs 450
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6 Answers
sean avatar image
sean answered ·

https://www.victronenergy.com/live/actor_ess

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sean avatar image sean commented ·

I've no experience of a shelly switch, but I suspect its output will simply be on/off rather than the elegance of an output that is proportional to the surplus.

The Thor only needs a ethernet or RS485 connection to your Venus device, along with a grid connection to feed the load.

Whilst the Thor is not a Victron product is does work seamlessly within a Victron system.

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tailele avatar image tailele commented ·

Sean you are a phenomenon, always ready and fast..congratulations. So in summary it would be enough to just install this AC Thor in my system. However, I see that it is not from Victron, does it work well with the GX communication protocol?

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tailele avatar image tailele commented ·

I ask you for a suggestion. Reading carefully, I notice that I must be connected both electrically and via ethernet to the multiplus II GX. In your opinion, instead of using this Thor AC, can I use the relay output of the Multi plus to control a shelly switch?

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sharpener avatar image
sharpener answered ·

You can certainly use the aux relay to control your water heater via a suitable contactor e.g. on SoC.

There are many other PV diverters available on the market e.g. Myenergi Eddi, these mostly use a current transformer on the grid connection to monitor the surplus and control the heater to balance it at ~100W export. I built my own before they were commercially available. No interface to the Venus device is required.

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sean avatar image sean commented ·

I've previously used an Eddi, it just fights with the ESS wanting to make use of any "surplus".

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sharpener avatar image
sharpener answered ·

I think there is a programmable offset which may help.

I have got my (own) diverter adjusted so that it requires about 125W export to turn it up to the full 3kW. Normally ESS is set to a grid balance of 50W to avoid any metered import in summer and this combo works OK for me.

Zappi EV charger similar so I have to choose which to use. Annoying as today the sun keeps going in and out - the minimum for the Zappi is 1.4kW so some generation is wasted when it dips below 1.4kW but the HW diverter is switched off.

Dynamic ESS is hopeless though, it just oscillates back and forth if I try to use it with the diverter.

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tailele avatar image
tailele answered ·

Sorry to get back to the issue of stamina management, but I've checked both Thor Ac and Myenergy. Probably with the Thor system connecting via Lan and DHCP protocol, it should be able to do what I ask, I haven't yet understood if Myenergi does it. Let me explain better, I am connected to the electricity grid via multiplus II but I cannot input energy, so I don't understand how it understands what surplus energy needs to be managed. Am I doing something wrong maybe?

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sharpener avatar image sharpener commented ·

As upthread most of the products on the UK market including the Myenergi use a current transformer to measure a small export to the grid typically 100W or so and use this to control the current to the heater.

If follows that if there is no physical grid connection or as in your case you are not allowed to export then this method will not work. Assuming that your utility will be able to detect an export as small as 100W in the first place or will do anything about it if they do.

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tailele avatar image
tailele answered ·

So should I give up? Isn't there a way to do what I think? in reality even the thor AC I can't understand for sure if it does what I need, and spending €900 for a test would annoy me a lot

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sharpener avatar image sharpener commented ·

Will your utility company be able to detect a small export like 100W and what will they do if they find you are exporting this tiny amount?

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tailele avatar image tailele commented ·

In my opinion absolutely yes, you can understand, as there is an exchange counter with internet connection. the thing it can do is make you pay the 100W as consumption, I assume.

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sharpener avatar image
sharpener answered ·

If that is the worst thing than can happen I would try it.

The Myenergi Eddi is a lot cheaper than the Thor and they have a good forum here. I have their Zappi EV charger; it works on the same principle and my Multiplus II is happy with it.

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