components needed to charge batteries and then go to hot water heater

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davidervin asked Feb 20, '21

components needed to charge batteries and then go to hot water heater

Good day all.

I am new to this technology and am getting conflicting answers in the "retail world".

I would like to set up a solar system (2x350 Watts) to charge 4x100aH LiFePo4 Batteries and when those are topped up to switch over to start a hot water heater (Bosch or Rheem) to heat the water. Of course at a set temperature I would want to switch off the heater and not have it switch on again until it dropped several degrees so it is not cycling on and off too often.

What components do I need (and what specs) to make this work efficiently. I am thinking I would like to use the Cerbo GX to monitor all of these (and more) devices.

I would appreciate the solution details and any things I should be concerned about that could go wrong.

Many thanks,

MPPT SmartSolar Hot Water Diversion

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shaneyake commented · Aug 30, 2021 at 12:39 AM

What voltage is your DC bus?

Are those hot water heaters DC or AC?

How much power do they use?

If AC do you have an inverter?

Info will help us gave you suggestions.

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Modifications Space

Node Red Space

Answer 1 · 2021-08-29T22:50:46Z

taylortops answered · Aug 29, 2021 at 10:50 PM

How did you go with tis? I'm setting a similar system. I'm using either Load Output or Relay of the MPPT to initiate the switch over. I'm experimenting with feeding PV DC current direct to heater element, currently via a MOSFET.

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shaneyake commented · Aug 30, 2021 at 01:09 AM

I have 4x 1kw 48V elements being switched by these mosfets, going through fues and then onto the DC bus. I have a PLC with Temperature probes be the the thermostat. You could use a normal thermostat with a 24V supply to switch these units on and off.
https://www.newark.com/celduc/som040200/mosfet-relay-110-vdc-40-a-0-046/dp/23M7350

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taylortops shaneyake commented · Jun 20, 2022 at 11:02 AM

I'm proceeding with: https://community.victronenergy.com/questions/140765/hot-water-power-diversion-idea.html

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Answer 2 · 2022-06-27T13:52:06Z

fHey folks, judging by the comments I'm far less technical than you guys but my planned solution to the above (with limitations) is below. Bit of background, for me goals are ease of install and ease of removal if i move house. I also dont really want a system so DIY/bespoke that a local plumber will panic if he ever comes to service the hot water system.

Use Node-red and a raspi with venus os.

Node red sudo code:

if (battery SOC > defined limit) & (solar power > 3kw) //(mine was going to be 90% SOC).

Send http get request to smart switch connected to immersion heater. My prefered smart switch being from the brand shelly as allows for physical switching and smart.

The pros of the solution.

Relatively easy setup and install with off the shelf parts if you already have an immersion heater. Few lines of code in node red and wiring one smart switch into immersion heater assuming you have on already installed.

Limitations:

16a is the highest off the shelf smart light switch I've seen so not appropriate for larger immersion heaters. Although i imagine for some folk making a higher rated relay controlled via http get requests is easy but for me the effort vs gain isnt worth it give my immersion heater is rated for less than 16a anyway

The above is an inefficient use of power in the sense that DC solar is inverted to AC and then back to DC in immersion heater element. For me this isn't too big a deal because my inverter is in a shed 90m from hot water heater, and i have no intensions of trenching new DC wires in just for heating.

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