How do I automatically switch DHW Gas to Electric as tariffs change?

TheTwillows

I have a 250L pressurised DHW cylinder. At present it is heated by a loop from the gas boiler which is controlled very accuratly by a Heat Genius controller. When on cycle it stays within 0.5C of target so all is well. It costs about £1 a day in the summer for the boiler to keep the DHW at temp.

What I want to do is take advantage of the cheap electricity I get from 20 PV pannels, two batteries and sometimes cheap electricity I get from Agile Octopus. In the summer it seems to me that the free or low cost electricity from PV and Octopus should on occasions be switched to the immersion heater of the DHW cylinder, and the gas boiler turned off, thus reducing costs.

Is this pie in the sky or is there a formal way of doing it?

theboylard

Do you have an immersion heater element in your cylinder?

Cheapest way is when the sun is shining (not literally, but when you are generating!), turn on the immersion heater. Stick a timer on though so you don't forget about it, that could get very expensive!

Solar diverter.

Range in price from self build kits to expensive.

Ours is a solarimmersion, fitted by the sparky who did the electrical  work on our install 9 years ago.

From April to October, no boiler use at all, so just standing charge for gas.

No brainer.

Batteries add something to the equation, also if you get a higher rate export messes with the numbers.

Beyond my simple means, I defer to others on here for the 'they did the math' stuff!!

paul991

just use a solar imersion controller or a shelly em to  do it over wifi

QrizB

TheTwillows said:

What I want to do is take advantage of the cheap electricity I get from 20 PV panels, two batteries and sometimes cheap electricity I get from Agile Octopus.

Is this pie in the sky or is there a formal way of doing it?

There are a number of options, from simple to less-simple.

• A solar diverter would deal with the excess PV generation. A diverter is likely to cost around £300 and, unless you're on a FIT with deemed export, the loss of export payments could make the payback period quite lengthy. If you only have a solar diverter, you're then looking to manually switch the immersion heater on and off to take advantage of plunge pricing on Agile - easy today, less easy when it's the wee small hours!
• You could use a timed immersion heater switch to make plung pricing switching easier. This could be a dumb timer like the ones used with E7, or a smart switch controlled by eg. WiFi or Zigbee. Prices start at about £10 for a dumb switch; a smart switch could be £50 or so.
• If you choose a smart switch, that then opens up various Home Automation options, which could eventually leave you wih a fully automated system that monitors Agile prices and the temperature of your tank, then applies the right amount of heat at the cheapest time of day. But Im' not going down that particular rabbit hole today!
  

michaels

We have an iBoost solar diverter fitted with our solar for £250 as we were on deemed export and a 200l tank.  Currently we set the gas boiler DHW temp to 45 and the iBoost controlled immersion to 75. the idea being we always have hot water but mostly heat with PV, we also have 4.5p off peak electricity so again use the iBoost to as a timer to heat the tank overnight with the boiler set not to heat at all after 9pm.

Not used for this but I managed to purchase a 15A wifi switch for just over a tenner from eBay but this is obviously on/off unlike the iBoost that is variable load matching the PV generation.

yp70479

You really need to do some calculations before taking the leap to all electric water heating. How much do you export and how much do you get paid for it? How much do you pay for your gas per KW? I have an iboost and last year when on a poor export tariff  with British Gas it made sense to use the excess solar to heat my water - turned the boiler off all summer. This year I'm on the Octopus Flux tariff - get paid 19-31p/KW depending on the time of day I export, but my gas cost has dropped to 7.6p/kw. So it makes sense for me to continue to use gas to heat my hot water, and export the solar. Although solar hasn't been great this summer I've covered the cost of my standing charge and any gas I've used from my export tariff, and I'm stockpiling credit for use when I put the gas heating on in the winter. Although Flux is supposed to be for PV owners with batteries they don't check up, and with 20KW PV you could be quids in if you export a lot.

holywoodhouse

This might help you @TheTwillows.

I've replaced all my timer switches on my heating system with wireless switches that are app-controlled. If you google 'holywoodhouse wireless heating', I've written a post on how I did it.

You can create 'scenes' for the controllers that turn the switches on/off for a specific period based on various inputs.  For mine I've used the weather forecast - so the heating only comes on if the weather outside is cold enough.

They only cost about £20 each and are rated 13 amp - so might suit your needs (although I'm not a spark!).

Cheers