Immersion heater automation

[Andrea C]

Good morning,

I have solar panels in my roof, installed 12 years ago.

I would like to automate the production of hot water from the immersion heater, when the sun is out, without spending too much money.

My idea is to use a IFTTT applet and couple it with a sunlight sensor and a wi-fi operated fused spur.

I found the sensor (https://cablematic.com/en/products/smart-wifi-light-sensor-compatible-with-google-home-alexa-and-ifttt-AN13500/?utm_source=pocket_saves)

I am not sure of which fused spur to use - I find wi-fi swithces, but not a fused spur adapted to an immersion heater.

Any idea?

Thanks in advance

[TonyT]

You generally need current transformers to determine power generated and consumed.

 

I wouldn’t be using a spur on an immersion, normally it’s a 20 amp double pole switch, so you would be better switching a contactor on and off.

 

Edited November 16, 2022 by jack
Changed "contractor" to "contactor"

[JohnMo]

I would keep it simple either

 

A simple immersion timer or an immersion diverter.  The advantage of the diverter is if you have 0.1kW it goes to the immersion, nothing more or less - not the full 3kW demand you would get from a simple sunlight sensor.

[Marvin]

10 minutes ago, JohnMo said:

I would keep it simple either

 

A simple immersion timer or an immersion diverter.  The advantage of the diverter is if you have 0.1kW it goes to the immersion, nothing more or less - not the full 3kW demand you would get from a simple sunlight sensor.

Yes our diverter to the immersion is still heating our hot water tank. There are several systems out there which you can buy, we use a Solic 200.

[BotusBuild]

1 hour ago, TonyT said:

switching a contactor on and off.

 

Edited 1 hour ago by jack
Changed "contractor" to "contactor"

I'd like the original switch for some contractors 🤣

[Radian]

Now I don't think the electricians around here would be very impressed, but this is what you asked for:

 

wifitu-wi-fi-controlled-fused-spur-tuya-edition

 

Switch Rating	13A (3kW) resistive, 1000W Incandescent/Halogen lighting, 500W Fluorescent lighting/LED, 100W CFL lighting

 

 Here's a reddit discussion about the kind of thing you want to do that might be worth a read through

[ProDave]

You don't just want to turn the immersion on or off with a remote switch like that.  That will only be any use then there is 3kW of power spare from the PV.  Most of the time there will be very much less than 3kW spare.

 

Install an ordinary solar PV dump controller, that usually burst fires the immersion heater so the power sent to the heater matches the surplus from the PV.  There are a few different ones to choose from, and a few of us have built our own.

 

They operate completely on their own, they just monitor current flow and as soon as they detect power being exported start turning on the immersion heater.

 

 

[Radian]

10 minutes ago, ProDave said:

Install an ordinary solar PV dump controller,

6 hours ago, Andrea C said:

without spending too much money.

 

Certainly the diverter is the ideal solution but £200 is about the minimum you have to pay for one, and it might prove difficult to install unless the immersion is near the main meter tails where the current clamp goes. If the water is normally heated by gas and the idea is to drop the tank stat to a slightly lower temperature (say 50^oC instead of 60^oC) and let excess PV top it up now and then, a simpler scheme like @Andrea C is considering might be worth doing.

 

Going full Eddi with wireless communication to allow the CT to be placed remotely is a ~£600 proposition and displacing gas at £0.11/kWh means running an immersion at full power for almost 2000 hours with it before breaking even. 

 

[Andrea C]

Thank you all for the answers and ideas.

Yes, I did ask a Solar PV company about systems that use the excess production from the panel (I suppose what here you call dump controller and diverter) - They quoted 800£.

I checked the Solic 200 diverter (thanks @Marvin) - 200 £ on ebay. My immersion heater is far from the PV switch, so it needs to be wireless communication.

As @Radian said, I was trying to find a cheaper solution. My idea was: create a rule that says: if the light sensor detects lights over a threshold, then switch on the immersion heater; this would work even below the 3 Kw demand level.

Still not sure which switch to use and I do not know if this one (https://www.timeguard.com/products/wifi/wi-fi-switches/fstwifitu-wi-fi-controlled-fused-spur-tuya-edition) is compatible with IFTTT.

@TonyT you suggest a switch-bot right?

 

[Marvin]

Hi @Andrea C

 

Not sure what you mean by PV switch but anyway.

 

Our Solic box is connected along the cable supplying power to the immersion. The CT clamp that is used to monitor the PV supply is clamped to the positive cable going from the main meter to our our consumer unit. No cable is required to connect to any of the PV system.

 

When installed in this way, as soon as excess power is produced, rather than delivering it to the main grid (if the hot water requires heating) the Solic will divert, whatever amount it is, to the immersion.

 

2 hours ago, Andrea C said:

As @Radian said, I was trying to find a cheaper solution. My idea was: create a rule that says: if the light sensor detects lights over a threshold, then switch on the immersion heater; this would work even below the 3 Kw demand level.

We use a similar system to charge the EV (Electric Vehicle). The main difference being that the EV charger requires an inductive load and must have the full wattage to operate. This means we have set up a CT relay on the PV positive cable which only switches when a certain power level is reached; from 2kW during winter to 3kW in the summer. 

 

Whereas the immersion heater uses a resistive load and the diverter will divert only excess power be it 3000 watts or 20 watts, but only excess unless you over-ride it.

 

Our car charging system supplies about 80-90% power from the PV unless overridden.

The immersion diverter supplies 100% PV excess power to the immersion unless overridden. Today was quite bright and our hot water tank reads 72.5C all from PV. We have only heated the hot water tank using mains power once since about June.

 

I assume other diverter makes work the same way as the Solic.

 

Good luck 

 

Marvin.

 

 

[Radian]

4 hours ago, Andrea C said:

till not sure which switch to use and I do not know if this one (https://www.timeguard.com/products/wifi/wi-fi-switches/fstwifitu-wi-fi-controlled-fused-spur-tuya-edition) is compatible with IFTTT.

The switch uses Tuya as the control app and that has IFTTT integration:

https://support.tuya.com/en/help/_detail/K9t5tqp8132gg

It should be accessible as a regular smart socket but I've not used this particular product.

 

Tuya devices are also hackable using Tuya-convert to load an alternative open-source firmware. This provides another means to control the switch using a Raspberry Pi or other computer running an MQTT broker. It would basically cut out the Chinese cloud (Tuya) and the (now paid for) IFTTT cloud and give someone who enjoys tinkering with code hours of fun. 😀