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Solar Thermal an actual option in Ireland?

  • 12-01-2023 4:36pm
    Registered Users Posts: 5,517 ✭✭✭


    I bought a house recently that I am considering what renewables are feasible.

    The house has a 500L solar thermal store hot water tank (Joule Cyclone Thermal Store 1.0) with a 3Kw immersion, Oil Boiler, 11 kW back boiler in a stove (turf/wood) and under floor heating. Its walls were pumped but does need more attic insulation. It is approximately 135m2 3 bed single story detached bungalow.

    From what I've read I would probably have to replace the hot water tank (which is in an awkward location in the attic) in order to do a heat pump. So really my options when it comes to renewable energy are Solar - either Thermal or PV.

    Would Solar PV using an Eddi and immersion to fill the 500L thermal store with hot water be an option or is my only option really Solar Thermal?

    If my only option is Solar Thermal - is it worth it in Ireland?

    Thanks for any advice.



  • Registered Users Posts: 12,080 ✭✭✭✭Calahonda52

    Do you have the need for 500 litres of hot water.

    look at under sink heaters providing water where needed.

    An eddi on 500 litres is not practical

    you can do the math here

    “I can’t pay my staff or mortgage with instagram likes”.

  • Registered Users Posts: 5,517 ✭✭✭axer

    No, I can't imagine a situation where I need 500 litres but unfortunately that is what the previous owner installed. Is Solar Thermal our only option really then?

    Just trying to figure out the best thing to do if I had to keep the 500L tank or whether in reality I am just going to have to change the tank at some stage.

  • Registered Users Posts: 20,976 ✭✭✭✭ELM327

    Whether you use an Eddi or a solar thermal, 500l of water will take a long ass time to heat and will be impractical.

  • Registered Users Posts: 1,368 ✭✭✭DC999

    Stepping back, what are you looking to achieve? Cut down on water heating costs, get more hot water, reduce electricity costs, get a heatpump…..something else… Then you can get a steer on the best option.

    Solar thermals are best for houses that use a lot of hot water and work perfectly well in Ireland. So say teens that take long showers.

    Solar PV is best for electricity. If there’s excess you can either get paid ~20c per unit. Or ‘dump’ to the hot water tank (HWT). But it’s much less efficient at heating water. Or charge an EV if in the driveway during the day from March to Sept (with a Zappi type car charger that is solar aware). Houses will be going more electric (EVs, heatpumps…) so solar PV helps there. Which we really just call ‘solar’ on this site

    Both compete for roof space, though solar thermals can be wall or ground mounted so can keep the roof space for solar PV.

    That Joule is a good HWT with low energy loses (in cooling water, so lost as heat) -  spec says 115w ‘standing losses’. I’d assume that means a full heated tank loses 115w constantly at some temp they measured it at. So it’s also a mini heater for the area it’s in – good in winter. I wouldn’t be changing that unless it’s needed. And you could flog it if needed to change it.

  • Registered Users Posts: 5,517 ✭✭✭axer

    I'm trying to lower costs for heating the house/water as much as possible - making it as efficient as possible so am willing to invest in that. Given that the house has under floor heating and is relatively well insulated it feels ripe for using renewables.

    At the moment I use only oil. I use the stove with mostly turf on cold days. Turf is going to get harder and harder to get plus its terrible for the environment. Also the oil tank is a really old homemade steel tank with an unknown life left so may need to be replaced in the next few years.

    The hot water tank is in the attic so any heat loss from it is going straight out the roof. I've no idea why they out in such a big hot water tank.

    To change the water tank would involve removing the ceiling of one of the rooms to drop it down to the ground - then figure out how to get it out of the house. Or else cutting up the tank in the attic into smaller pieces. To me it seems like a huge job that's unlikely to be feasible unless there is actually an issue with it forcing me to replace it thus I'm trying to see if it's possible to use it in a way that saves me money.

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  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Back up a Bit.

    What is the tank connected to? Domestic hot water or heating system? Is it just a massive buffer for the stove? Ie Heating only.

    I have a 500L tank plumbed into my heating. Heating with excess solar PV, Stove, & Night rate electricity.

    Having the tank in the attic is quite interesting. Heat it up at night from the back boiler and let it slowly come out as needed.

    What sort of heating controls do you have?

    yeah.. takes a good 9 hrs to heat it. Doable though, Maybe a second immersion.

  • Registered Users Posts: 5,517 ✭✭✭axer

    The tank is for both domestic hot water and under floor heating.

    I've thermostats on the wall in nearly every room that will call for heat when needed.

    Very interesting what you are doing with your tank. That is exactly what I am looking for i.e. A way to wisely use the 500L tank - supplementing it with renewable options make sense. Would I be better off to give the tank a blast of heating to heat the whole tank and somewhat then keep it hot with top ups instead of doing what I am doing which is heating it with oil 2 times a day?

    The other thing you are doing which I would love to have in place is a way to know how much the thermal store is heated up because if it is already hot there is no point sending heat to it.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    How does it do both?

    Is there thermopockets that you can put temperature sensors in it?

    So your heating it via oil right now,

    And then the thermostats in the rooms call for heat from the tank?

    What water is actually in the tank?

    How many coils?

  • Registered Users Posts: 5,517 ✭✭✭axer

    I might have a wrong understanding but from what I know the hot water doesn't come directly from the tank but the domestic cold water travels through heat exchangers in the tank to pick up the heat from the 500 litres of potentially hot water in it, same for the underfloor heating.

    The thermostats in the rooms just open valves and receive whatever hot water is being produced through the tank. Because there is both a stove back boiler and an oil boiler there is no connection between the underfloor heating controller and the boiler so while the UFH thermostats can open their valves for more hot water when they need it, if the tank doesn't have heat in it then UFH doesn't heat anything.

    I need to look to see if there are thermopockets in the tank. I see there is the emonPI that I can look into using.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Im Gonna need photos to get my head around this properly. Either DM or here I dont mind.

    It is making sense to me though, your DWH is heated "on demand" per say A bit like a combi boiler, If that tank is cold you have no heat correct?

    You essentially have a massive battery. For heat. And there isnt much heat loss from them tanks, they are really well insulated.

    You dont even need a emonpi. .. although would recommend it for energy monitoring.

    Im using ds18b20 temperature sensors on a esp8266 running tasmota.

    They all report back to home assistant.

    When you say there is no connection, do you mean electrically? Or is the UFH also running through a heat exchanger?

    Tank + oil+ Back boiler is on a Vented system, (because of back boiler,) and Underfloor heating and DHW is on a sealed/pressurised system?

    I assume the DHW and underfloor are on some sort of thermostatic mixing valves too? as UFH tends to run at a cooler temperature vs what could be in the tank.

    Its very clever, I like it.

    You could slap a pile of PV on, run the immersion (s)? with an eddi maybe a willis type added onto it so you can heat the bottom of the tank..

    For instance, It sounds mad, My night rate is now 7.9c. which per kwh is half the price of oil. I heat the tank with the immersion on night rate now in the winter, house is warm in the morning, so when i stoke the stove, I'm not heating a cold house.

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  • Registered Users Posts: 5,517 ✭✭✭axer

    I'm still trying to figure out the system and understand all of this. I'm still not sure if this is a vented or unvented system but reading places like this it seems to say that a thermal store is a sealed vented system so is safe to attach solid fuel sources to. Here a link to which one I think it is:

    If the tank is cold I neither have hot water nor heating.

    It looks like the tank is really made for solar thermal along with the other sources but for now it sounds like your method of day/night meter plus using immersion is a great idea to do in the short term assuming I can get that low of a night rate.

    In relation to the UFH and using a mixer, I don't know enough yet if that is the case. According to this page a mixer is not used, instead stratification is used with UFH comes from a coil lower down and hot water comes from a coil at top of the cylinder.

    Having learned a lot through all the help from everyone in this thread I'll go through the system again to work it out more and take photos.

    Thanks everyone.

  • Registered Users Posts: 6,768 ✭✭✭Alkers

    You don't necessarily need to take it out if your replacing it, just disconnect it and bypass it. Might simplify things.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    The stove will be vented. It has to be as it's a "uncontrolled" heat source. So a small header tank somewhere.

    How it's connected into the thermal store will determine the layout.

    Two likely options

    Stove and oil together, water in the tank is the water that comes from the stove or oil, Ufh is a sealed system being heated via a coil.


    Stove on a coil, oil and dhw on the water in the tank.

    Should be fairly obvious when you start figuring out where pipes go.

    DHW, is likely to be in that big coil, or at least the top coil.

    Take photos and start sketching out where everything goes. Even get a sharpie out and label pipes to stop confusion.

    I wouldn't be taking out that tank, you have a 20-30kwh battery, (and for sure not cutting it up! New they are about 1.5-2k!).

    It was likely put in to have a stove and run under floor heating. And have the ufh on a sealed & pressurised system. Taking it out isn't really an option unless the stove goes too.

  • Registered Users Posts: 5,517 ✭✭✭axer

    So according to the installation guide for the cylinder it is an indirect unvented system but can be setup to have a boiler, solid fuel and solar thermal (and I guess this could be also OR Solar PV using the immersion).

    One thing I did come across though is that it is supposed to be serviced annually - which from what I can see hasn't been done since it was installed like 10 years ago so need to find someone who can service such a system.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    What's to service?(maybe a mag filter?) As long as it's holding pressure and working it's fine

    It's a bit of a get out for the warranty and you'll be out of warranty too.

    And the installation manual is more of a guide than a rule.

    But you do have sensor pockets! Time to get some sensors in!

  • Registered Users Posts: 5,517 ✭✭✭axer

    I think the servicing is to ensure the escape valves are working properly in the event of it over heating.

    A lot of the sensor pockets are being used, can you double them up? I see being able to determine how much water is in the tank to be the key to being able to use it efficiently.

    It doesn't look like using the immersion at night time to load the tank up with hot water is a runner because its about 26c a KWh at night rate at the moment on a day/night meter from what I can see and as you said its about 13c a KWh using oil.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Ah Unlikely to be able double up, Depends on the hole!

    Yeah, 13c if hitting 100% efficiency, but all depends on your boiler, but with that big store, and if you have a condensing boiler 90% is maybe achievable. Still, at 26c (OOOF) that's nearly as high as my day rate. my old boiler, would be lucky to hit 70 id say!

    What is using the sensor pockets then?

    PS photos! Then I can have a good figure out of what goes where!

  • Registered Users Posts: 5,517 ✭✭✭axer

  • Registered Users Posts: 5,517 ✭✭✭axer

  • Registered Users Posts: 5,517 ✭✭✭axer

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  • Registered Users Posts: 5,517 ✭✭✭axer

    Its quite complex to work out what's going on with the above because of the spaghetti of pipes covering.

    The pipes by the radiator go down to the solid fuel stove. This has a thermostat on the I'd imagine pipe carrying the hot water back to the tank but not sure what that's used for. The radiator is a heat release for I think if the thermostat on the tank called "high limit stove stat" is reached.

  • Registered Users Posts: 5,517 ✭✭✭axer

    The top of the tank has two pipes, one is for direct hot water coil out (and has a small silver expansion vessel) and the other at the top is expansion output of the tank that goes back to the two red expansion vessels before connecting on elsewhere. There is a pressure gauge on the pipe after the expansion vessels that shows zero which I am assuming is good in that the pipe is currently not in use.

    I noticed that the thermopockets and pipe connections of the tank don't exactly match up with what it shows in the mechanic diagram in the manual so I've emailed joule to see if they have a more exact manual or diagram.

  • Registered Users Posts: 5,517 ✭✭✭axer

    Still working out the rest

  • Registered Users Posts: 6,768 ✭✭✭Alkers

    Why is there rads in your attic?

  • Registered Users Posts: 5,517 ✭✭✭axer

    In the first photo you can see 2 dark dots on the left side of the tank - one at the top and one at the bottom. They seem to have a small plastic/rubbery cap in them that seem like they can be pulled out (they are not very tight in) . There might be one lower down too. Are they likely to be thermopockets safe to be pulled off? I'll take some more photos of them.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Looks like a sealed system.

    Yep there is a normally open valve on the radiator. when powered it is closed. It can "fail" open, It acts as a heat dump when the tank gets up to temperature/too hot.

    I can see the sensor pockets here :

    Thats the sensor pocket, you dont need to do anything it will fit a temperature sensor directly

    Fits one of these easily, DS18B20 for example

    Is this mixer valve on the under floor heating circuit?

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Its a heat dump/overheat protection for the stove, if the tank was hot, its somewhere for the excess heat to go, safely.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Oh that mixer is for your HW.. Nevermind.

    Its all making sense.

    Immersion is half way up, at the same level of the flow from the UFH.

    The top half of the tank is dedicated for DHW. Bottom half for heating.

    Immersion cant heat the water for UFH.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Also, your DHW is pumped from the header tank? I wonder why they didnt take it straight off the mains.

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  • Moderators, Sports Moderators Posts: 18,446 Mod ✭✭✭✭slave1

    Respect to installer for lagging all that pipe work so well