I'm guessing having an electric boiler say alongside and existing gas boiler installation is possible? Thinking during the months when excess solar is generated (April to Sept for me) that we could switch from gas water heating to electric and potentially save a bit more should gas prices keep increasing. Thoughts?
Do you have a tank? It’s possible, use a Mixergy, Sunamp type cylinder in the system.
Mal-Givenergy Yeah hot water tank, traditional gas boiler set-up.
most hot water tanks have an immersion element / heater. There are a number of devices such as immersun, iboost+ that will divert excess solar to the immersion. During the summer months it heats our water with no use of gas. On days which are forecast to be cloudy I'll also heat the water with the immersion during cheap rate times. It has been mooted that givenergy have such a device on the way but its been mooted for some time
I have an immersun diverter - and works along side my gas boiler. I have the Hot water set to come on in the morning for about 90minutes on gas and then again for an hour at about 5pm - but that will only come on if the temperature is below setpoint - I'm using the stat just for the solar diverter which is set for 60'C the boiler uses a sensor in the same place but controlled via software, hence the different set points.
Yes...our Gas boiler is off for central heating or hot water - usually between May and September. There's usually just the odd day where a boost might be needed if it's particularly dull.
I use both evacuated tubes (bought well before any solar PV and divert was installed) and diversion of excess PV power using an iBoost+ (once the batteries are full).
It does get quite hot! (weather syste has stopped working - it wasn't 0)
Here's a good sunny day heating the hot water tank (the "willis" is the temperature of the pipework being heated via an immersion heater. The panel is the evacuated tube panel temperature).
That looks good. Interesting graphic. What’s the package?
Is the hot water in your tank 85’c?
The stat on the hws cylinder is on max on ours which is 60’c. The top of the tank is higher though. About 68’c.
The graph (and the dashboard) is generated by Emocms
https://guide.openenergymonitor.org/emoncms/coreconcepts/
Yes - the water is a bit (too) hot - but I do that, so it lasts longer via mixing with cold, as it's not the largest of tanks.
The cylinder stat doesn't get involved - it only controls the gas boiler. The immersion is set to 80C I think; but the panels tend to push the cylinder higher. It's a vented cylinder, so pressure wise safe, and it will dump hot water if it gets to 90. I wouldn't recommend running a cylinder this hot - it's my personal choice.
Ours is pressurised so wouldn’t want to run as high as 80 - and I wouldn’t want to run the diverter without a stat either. I could run an interlock into the diverter from my controller to turn it off (it does have programmable inputs on the diverter) but I would still want to have a high limit stat to turn it off if it was too high
To be fair it does work well as is. Only on really sunny days / not much house load that it tops out.
Like today as it happens. Though we have put some washing on this evening to use some of the solar. 🤣
My hot water tank can be heated by either the gas boiler or an immersion heater. When the central heating is active I use the boiler for hot water also, at the same time the heating comes on in the early morning. In the summer, when the boiler is off, I use the immersion heater - via a 16A LightwaveRF relay that is timed to be on from 1pm to 3pm. So on a dull day it will pull some power from the batteries (2x8.4 +AC3), but the PV soon refills the batteries. But the hot water tank is well insulated and will stay hot for 24 hours, so one bout of heating a day works fine.
Baychattan I'm sure ours would last 24hrs - if it wasn't for the kids - when they shower they can be in for bloody ages and have been known to empty the tank! Then moan they have no hot water!
In the winter I did have a lunchtime boost set for an hour on the weekend, but have disabled that now as it either keeps going of is topped up by solar during the afternoon. (Battery is almost never full before about 2pm as our solar production is bias towards the afternoon.)
Ok, feeling a bit dumb here now... Moved into this house just over 2 years ago and not even realised that our hot water tank has an electric immersion heater already built in! So I guess all I need is something like a Solar iBoost fitted and away we go?!
chris_p that will indeed work. For info, I have an immersun from before they went bust. It has worked well for the last 7 or so years. The resurrected model is expensive particularly if you app connectivity option is added. There are a few threads that have mentioned options - iboost plus and solic are 2 with a decent price tag.
anglefire if you can live with importing occasionally on a grey day, a simple timeswitch for the immersion, set for midday, works well for £30.
Nice. As the immersion hasn't been used for a while (at least two years), should I have it looked at before switching on? Will it have gone rusty?
chris_p Nah shouldn't be an issue - there is nothing really to see - mine hadn't been used for several years before I turned it on.
stevelewis I've an immersun one - after trying a switch controlled by HA and excess solar - proved concept but too crude to be economic as unless its a really good day (Or several reasonable ones) we don't get the battery full until about 2pm as our solar is west bias and often see the biggest overall generation in the afternoon and can still be pulling in over 3kw early evening (2 strings each of 6 395w panels one south one west)
chris_p id just check what its set to temp wise before you turn it on and find out its been set well below your boiler.
Also may be a good idea to check if it has a thermal cutout (a little button thay says push to reset normally)
They became mandatory a fair few years ago after one got stuck on and well...I don't need to explain other than Google "immersion overheat child"...
hoggy Can't see a reset button. The temp is set to 65ish. I didn't realise that thermostat was for the immersion, what controls the temp when it is the gas boiler heating the water, is it the dial on the boiler? That has no temp at all, just like a low > high, similar to a volume control.
chris_p its usually behind the plastic cap of the immersion. (One bolt sticking out the top and it exposes the immersion head and dial)
The thermostat i suspect your describing (i bit like a house thermostat - sqaure?) Is the one that the boiler runs off.
Although I have seen some systems with two of those cylinder stats fitted - one for immersion and one for boiler.
My only have a single stat with two contacts one for the boiler and one for the immersion heater. It’s not got a high temp stat (that I can see anyway) and it’s not that old.
hoggy Yeah sqaure thing with 50, 60, 70, 80 on. So that tells the boiler when to stop heating? What tells the immersion what temp to heat to?
chris_p same thing usually.
anglefire Ah ok, thanks.
Ours isn’t, (Kingspan Cylinder): square stat does the boiler, immersion does the immersion.
Rather than start a whole thing about this, just switch it on and adjust the stat up and down and see if the immersion comes on and off via watching the load on the app. If it stays on or doesn’t come on at all then it’s either dead or not controlled by it.
AFAIK, if the cylinder is unvented then the immersion thermostat will also be the boiler thermostat. You'll identify an unvented cylinder as it will have some form of expansion tank (either externally or in some cases like Megaflo, internally). There will also be a tundish plumbed into it where you can see if the pressure valve is venting water.
" if the cylinder is unvented then the immersion thermostat will also be the boiler thermostat." not always the case, our megaflo has 2 thermostats, one for the boiler and one for the immersion. I have the boiler thermostat set lower than immersion which works nicely with the immersun. As long as there is enough sun the boiler does not cut in.
chris_p I tried using (the never used) immersion in our water tank - fitted in the top of the tank (normally the CH heats it).
It sounded alarmingly like an electric kettle boiling, and it only seemed to heat the very top of the tank? Are there different types of immersion heater elements, and mine is the wrong sort?
I'd love to know if anyone knows, as I have surplus daytime power to spare!
It may be that the immersion heater is designed to only heat the top of the tank and is for emergency use. Or there may be a circulation pump that mixes the water in the cylinder so doesn’t really matter where the element is located. Might be a case of space.
But yes they can make a bit of noise as you get localised boiling on the element.
pjb904 no expert but I believe most immersion elements are 3kwh elements. Due to difference in density of hot and cold water it tends to sit in layers with hot towards the top. Immersion elements can be top or bottom or both. Bottom should provide a better overall impact as the hot water will tend to to rise allowing more to be heated than a top element.
A little odd that it sounds like a kettle, it should heat the water up to the temp set on the immersion thermostat which should also have a safety cut out. My immersion state is set to just aroun 65 degrees and the stat for boiler supplied heat around 55.
As I say mine makes a bit of a noise. But it’s not like a roaring kettle. Just some noise.
a quick look shows multiple different lengths up to 3 feet, for instance https://www.screwfix.com/c/heating-plumbing/immersion-heaters/cat830986?productlength=36__#category=cat830986
Is the tank quite old? Live in a hard water area?
it might be that the immersion has a lot of scale built up on it. That'd certainly make it noisier than normal.
At the end of the day an immersion is the same technology as old electric kettles- a resistive heating element immersed in water. It's bound to sound similar.
It's also a long shot, but has someone in the past by-passed the immersion thermostat?
Can only comment on the iboost+ (bought last month), but have practically turned off gas at the moment as the iboost tracks the excess solar output with tolerance of 100kw to 500kw (currently set to 100). Water is hot by 10am ish with no gas.
Obviously overcast days a longer, but only uses what excess is available, but never the 3kw hit by just turning emersion on !
Waiting for battery, which should take solar first before water - well that is the aim.
Iboost tracking
Zakalwe thanks, it's old, certainly. Might get a plumber to have a look.
For a standard vented tank it should have a data plate with a recommended element length.
I've got an Eddi wired into my hot water cylinder (had to fit a new one as the old one died pretty much straight away). As most traditional hot water tanks have an electrical element as a back up alongside a power supply this stuff is relatively easy to install.
Elements can come with either a fixed thermal cut out or a variable one, this time of year I've cranked the gas boiler temp output down to minimum and the element is set higher.
With gas prices being what they are I think it's going to be cheaper heating using electricity over winter on Go instead.
Today we have just started to get some decent excess after two miserable days, so I turned on the immersion. I could hear it start to heat up, had the app open to see the live inverter data, house demand rose by 3kWh as expected. I switched down the Honeywell thermostat as far down as it would go (heard a 'click' as it went below 50c) but the demand from the immersion remained. So guessing that thermostat just controls the gas boiler?
As this wire just goes straight to the switch, I guess it has no interaction with the thermostat on the bottom of the tank? How do I control how hot the immersion should get?
chris_p Switch it off at the fused spur and take the top cover off the immersion (the grey/silver round thing) the cable goes into.
There will be a dial on the immersion - it may or may not have a temperature (mine just have dots which correlate to temperatures from the instruction manual if you can work out the make)
You can hear/feel it click on and off though so you can always get the boiler to warm the tank to whatever you normally have it and get the immersion to click off around the same.
hoggy Well would you believe it, ha! Excellent, thank you so much for your help:
with the two thermostats you can set the immersion to be higher than boiler so boiler is only needed if there is not enough sun (or boost)
locked Yep, that is one thing in this whole fact finding mission that I actually figured out for myself, ha! Thanks anyway though 😃
locked that’s how mine works. And there is a high limit stat with a manual reset which is nice to have.