Hot Water Cylinder Questions

Reed_Richards

The iBoost seems to be a very popular option on this forum. It seems to me to be a great idea if:

• You have solar PV
• The solar PV is not so old that you get a really good deal on exported electricity
• You already have a tank with an immersion heater

I, like SolarChaser have a combi boiler with no hot water tank at present. As I am starting from scratch I wondered if a solar water heating panel was the way to go (as I have space left on my roof). My reasoning is that solar thermal panels are much more efficient than solar PV. Otherwise I was thinking along the same lines i.e. pre-heating the water input to my combi boiler when the hot water tank is only tepid.

EricMears

Reed_Richards wrote: »

The iBoost seems to be a very popular option on this forum. It seems to me to be a great idea if:

• You have solar PV
• The solar PV is not so old that you get a really good deal on exported electricity
• You already have a tank with an immersion heater

I, like SolarChaser have a combi boiler with no hot water tank at present. As I am starting from scratch I wondered if a solar water heating panel was the way to go (as I have space left on my roof). My reasoning is that solar thermal panels are much more efficient than solar PV. Otherwise I was thinking along the same lines i.e. pre-heating the water input to my combi boiler when the hot water tank is only tepid.

'Modern' solar PV installations get an almost reasonable payment for exported units. Although the actual FIT payments for older are generous, export payments are derisory.

Zarch

Reed_Richards wrote: »

The iBoost seems to be a very popular option on this forum. It seems to me to be a great idea if:

• You have solar PV
• The solar PV is not so old that you get a really good deal on exported electricity
• You already have a tank with an immersion heater

I, like SolarChaser have a combi boiler with no hot water tank at present. As I am starting from scratch I wondered if a solar water heating panel was the way to go (as I have space left on my roof). My reasoning is that solar thermal panels are much more efficient than solar PV. Otherwise I was thinking along the same lines i.e. pre-heating the water input to my combi boiler when the hot water tank is only tepid.

Interested in thoughts on this too...... what are the options for those of us with PV, combis but currently no tank. Is there any way we can use the PV / iBoost to help the combi along? For both central heating and hot water?

joefizz

Another upvote here for the willis type of immersion heaters but they may be predominantly an NI only thing?


One other thing from NI, as of last July the export payments moved to an actual export figure rather than fixed percentage. We are usually a test bed for this type of thing and the rollout was based on installing export meters (with every new solar installation) instead of smart meters.
Wouldnt like to have based iboost return/profitability on the life of an iboost or similar only to find out it was being cut, worth keeping an eye on.

mmmmikey

Hi all, my understanding if you want to go down the route of adding a hot water cylinder.....

1. A combi boiler is more or less a bog standard boiler with extra bits that it allows it to provide instant hot water as well as heat radiators. The provision of hot water avoids the need for a hot water cylinder.

2. There is no reason (space permitting) why you can't install a hot water cylinder (be it direct, indirect or thermal store), and use the radiator-heating bit of the combi boiler to heat the water in the cylinder just like you would do with a standard non-combi boiler. This isn't trivial, and needs the appropriate controls, but certainly do-able.

3. As long as the cylinder has an electric immersion heater (whether it's a bog-standard internal one or NI-style Willis heater that goes on the outside) you can then heat your water with a combination of gas, surplus PV or paid for electricity, whatever you choose.

4. Costs would vary quite a lot depending on your existing system, but I'd anticipate the costs for the cylinder, controls, plumbing & electrical work to be in the £1,000 to £2,000 range, and then you'd have the cost of the iBoost (or Solic 200, etc.). So whether this would be worth it would depend on how much you're spending on hot water. Reading these forums, it's not uncommon for spare solar PV to provide all your hot water for 10 or 11 months of the year, so I wouldn't be surprised if you could see a payback in a reasonable time (but this is shooting from the hip a bit!)

5. Installing a hot water cylinder can have other benefits, such as not freezing in the shower when someone turns the hot tap on in the kitchen.

These are just thoughts coming from someone who's done a fair bit of research on hot water systems recently - my experience is limited to the 2 or 3 houses I've lived in so I certainly wouldn't take this as definitive, I'm not claiming to be an expert

Hopefully there's something here that helps someone, Mike

mmmmikey

Reed_Richards wrote: »

I wondered if a solar water heating panel was the way to go (as I have space left on my roof). My reasoning is that solar thermal panels are much more efficient than solar PV. Otherwise I was thinking along the same lines i.e. pre-heating the water input to my combi boiler when the hot water tank is only tepid.

Hi - when I looked into this recently, the economics for me made solar hot water a non-starter, even given that the hot water cylinder needed was effectively free (I needed that anyway). That might just be because of my low usage.

zeupater

mmmmikey wrote: »

Hi - when I looked into this recently, the economics for me made solar hot water a non-starter, even given that the hot water cylinder needed was effectively free (I needed that anyway). That might just be because of my low usage.

Hi

Solar thermal used to make sense at the beginning of the current decade, but as PV prices fell the economics of thermal faded away ...

We have both thermal & PV on our roof, with the thermal taking the space of approx 4 PV panels, although likely providing the thermal energy delivered by ~8, and that normally provides all of our DHW from March 'till November, with the GCH providing support in the winter gap with top-ups (maybe 1 or 2 per week) only when MrsZ starts to complain about not being able to scald herself in the shower (talk about pain threshold! ... ).

There are really two main elements to the success in using solar DHW, whether thermal or proportional diversion .. firstly is to reduce overall hot water usage, particularly in the shower, so moving away from pumped pressure systems or 'tropical downpour' type heads is key, else your energy is simply running down the drain ... and secondly, to have larger than 'normal' storage capacity to buffer against normal periods of poor weather ...

As mentioned, solar thermal probably doesn't suit many on cost grounds these days, but where roof space is at a premium, it certainly warrants consideration, especially to anyone looking at a DIY project as there are a number of decent suppliers which supply complete installation kits (including Navitron which operates a long-standing forum full of information regarding thermal installation) ...

HTH
Z

mmmmikey

In answer to question raised by Coastalwatch elsewhere, re: cylinder sizing....

I have limited data but based on my research before I bought I'm confident the 160litre Advanced thermal store would provide enough hot water for 2 if heated daily (with obvious caveats about normal usage) - not sure beyond that.

A big part of the reasoning for the 210litre version for me was my e7 tarrif - I pay 3.5 times as much for a kWh during the day as overnight so there's a big penalty if the sun doesn't come out enough to heat the water via the immersion controller. Not such a big deal if you're on a single rate tarriff.

I've just switched both immersion heaters off so I can see how my battery system is working without them getting in the way. Thinking about it, if I leave it off until I run out of hot water, that will give some clues about how much spare capacity I have. Won't answer 160litre / 210litre question directly but may help inform the decision. Will post back here in a couple of days when I have some more info.

Incidentally, I suspect that I could reduce standing heat losses a fair bit by running the store below the recommended 75 degrees and still have enough headroom for cloudy days. Also scope for better insualtion of pipework, and I need to check flow rates at the shower as although the mains pressure water is great as Z points out I'm running energy down the drain. At the moment I'm wasting "free" power so not a big cost incentive to reduce the standing losses most of the year, but it will make it easier to manage the immersion controller alongside the battery.

HTH Mike.

Solarchaser

What I need is a priority based system.
Solar goes first to the batteries, 2nd to the ev and lastly to the hit water cylinder.
I think it's got to be one system to avoid the problems with cross talk. Hmmmmm

mmmmikey

Solarchaser wrote: »

What I need is a priority based system.
Solar goes first to the batteries, 2nd to the ev and lastly to the hit water cylinder.
I think it's got to be one system to avoid the problems with cross talk. Hmmmmm

As I understand it, solutions here (expensive?) would take care of prioritising the EV and hot water, but not sure where batteries fit in:

https://myenergi.com/

Been thinking about interaction between my PowerVault and Solic 200 following a suggestion from 1961Nick on another thread, and come to the conclusion that with a bit of thought I can make something myself mostly using bits I already have that will simply disable water heating when the battery is doing anything to stop the battery heating the water. Haven't thought too much about prioritising charging the battery as most of the time there's plenty of power for both, and it's 6 and two 3's whether I top up the water or the battery overnight on e7. Something to ponder on, probably an autumn/winter project for me as I've a few jobs lined up for friends which I really need to get on with.

(Plenty of hot water this evening for piping hot shower from thermal store despite having immersion switched off all day - proper update on this tomorrow or Saturday).