The Boy That Cried PV Extension

[Krill]

I've been wondering recently on the benefit, and frankly feasibility, of having the output from a DHW cylinder run through an electric boiler (I think nowty still has his cylinder plumbed to go through a gas boiler). The point being all the benefits of the normal cylinder and ToU tariffs with the potential to turbo boost the output if needed for flexibility.

This would mean a smaller EB but the running costs (as heating from a higher starting point) should be far smaller still, only use the EB when absolutely needed. With thermostatic mixers and running the DHW temp higher during higher use periods ie visitors even a 125l volume could be stretched quite far IMO.

The problems are one of space and wiring though, and additional costs, but it does provide the flexibility most people demand with a gas combi boiler

[Stinsy]

I've been wondering recently on the benefit, and frankly feasibility, of having the output from a DHW cylinder run through an electric boiler (I think nowty still has his cylinder plumbed to go through a gas boiler). The point being all the benefits of the normal cylinder and ToU tariffs with the potential to turbo boost the output if needed for flexibility.

This would mean a smaller EB but the running costs (as heating from a higher starting point) should be far smaller still, only use the EB when absolutely needed. With thermostatic mixers and running the DHW temp higher during higher use periods ie visitors even a 125l volume could be stretched quite far IMO.

The problems are one of space and wiring though, and additional costs, but it does provide the flexibility most people demand with a gas combi boiler

Even a 30kW gas combi is pretty slow to fill a bath. This is precisely why we have DHW tanks. A 3kW immersion can heat 250L of water from 10-60℃ in about 5hrs, this puts very little strain on your max demand and is perfectly reliable with zero maintenance for decades, and is economically viable on ToU. But is no good for “on demand”, you can’t expect the Mrs to wait 5hrs for a bath.

Electric boilers still require a DHW cylinder, but can reheat it much quicker because of their 10-14kW rating. On the other hand they’re very noisy, more complex and therefore likely to be unreliable, they cause big problems with max demand (particularly if you also charge an EV). You could therefore make use of a much smaller cylinder and rely on it being quick to reheat but you lose out on ToU.

[Mart]

Quick update on the upgraded system, and the unplanned decision to not use the GCH this year ..... well, hope to not use the GCH.

The recent cold spell, took Cardiff down to -1C for a day or two, plus a lovely snowstorm, but too brief to stay long.

I appreciate that -1C isn't impressive, but that's probably a fair figure for low winter temps here. The 'Cardiff bowl' is a temp control here, with rising hills/mountains on most sides inland, and the sea on the other. So the water temp tends to dampen temp extremes.

So, whilst we could well see -5C on occassions, and a week of cold may drain warmth from the house, I still think it was a decent test for average Dec-Feb conditions for the improvised leccy heating system. And it did fine. The two A2A units merrily pumped heat through the downstairs, and then some warming of the upstairs. I was running them a degree or two higher at night when going to bed, and opening the room doors wide to leak/spread heat as much as possible. During the day they run a bit lower (as rooms get too hot).

Batteries (20kWh) went down to 10-15% on the coldest day with next to zero PV, and down to about 20-25% on a sunnier day, with ~6kWh of gen. That 6kWh fig is interesting/important, as that's roughly what I expect in Dec, before gen rising in Jan. Dec forecast 175kWh, Jan 200kWh.

So looks like the basics might work. I have bought two oil rads, ....

[As posted earlier, I realised that a leccy boiler was resistive heating to the rads in the rooms, so why not cut out the middleman.]

.... just a very small in size 600W (£25), and a larger 2000W (800W/1,200W) with timer (£40). I had an idea of maybe getting 5 or 6 of the ickle ones, and they would pack away lovely in a tub, or on a shelf. But I may not need anymore, not sure. I'm only running the big one (at 800W), and an old 1,100W (400W/700W at 400W) through the night to warm two rooms that get a bit cold upstairs.

Problem areas as expected, and lots of questions:

1. Bathroom definitely cold, unless door left open for leaked heat to reach, but I'm thinking(?) this is easily solved with the planned leccy towel radiator. The room is tiny 1.8m by 2m, so I'm thinking of a towel rad immersion this is just an example. Has anyone used something like this, are they OK?

The wall the tall towel rad we have is on, is a lathe and plaster wall, and the rad lines up well with a socket on the other side. I'm thinking of maybe using a timer socket. Again, any thoughts? This seems simple and obvious, but I appreciate life is rarely that simple. I have a great plumber/builder friend, who actually installed our bathroom. He's who I'll be asking to do the work.


2. Next is the kitchen, here's some pics of the new heating system:






So, this is the A2A unit in the 'conservatory' (in reality a small room, just 2.4m cube), and it heats really easily as the unit is overpowered at 3.5kW, but that's to cope with heat (if we need A/C) and to ensure plenty of spare heat for its real purpose. The door leads to the main room/living room and with the conservatory at 23/24C the living room is about 20C with door to hallway wide open.

The kitchen is heated via blind optimism, and that small window from the conservatory. Surprisingly it's reaching around 17.5C on the opposite side of the kitchen, and outside wall. I'm pondering placing a fan on the windowsill, to see if it will pull the heat through better. I have tried a blow heater (with heat off), but it's very noisy, and doesn't excell at blowing. Heat will also enter the kitchen from the hallway where the heat from both A2A units travels, on its way up the stairs.

The original plan, was to put a simple hot air blower somewhere on a wall, but I'm pondering another of those towel rad heaters. Any reason why I can't put one in a 'normal' rad, as there's a lovely big double rad in place? So just some gentle heating through the night on cheap rate, and maybe timed to come on for evening cooking.


3. Not really a problem, but the spare room / gym / Cookie's room, is warming well with the 400W heater. It seems to modulate on and off roughly the same amount of time, so ~200W heating. So that's around 5kWh a day. May be better with door wide open (but Cookie foster cat is in there now), but I've mentioned a HW tank before, and that's where it will go ....... so, silly question, I'm expecting it to leak 1-2kWh of heat, which may top up the room, but could I deliberately set it for a higher temp in the winter, so it leaks a bit more. It would then effectively be a storage heater, leaking a bit of cheap rate leccy heat 24/7. Am I going mad? Two birds, one stone and all that. (In the 6/7 warmer months, we will have loads of PV, so it can heat a bit lower, as and when needed, from PV/batts.)


4. Lastly, not the end of the world if heating comes up short at times, as I can then just turn up the oil rads, turn on the blower etc. But I'm trying to aim for close to zero day-rate leccy consumption. Also, because my batts are DC side, then charging them winds my TGM backwards, and reduces FiT earnings. So all battery losses have a small cost. So another 2 birds / 1 stone, I've ordered a small portable battery system. Only 3kWh for £927. I hope to plug it in between the mains and one of the A2A units. Charge at night and power the unit during the day. That top up may be all I need taking me to 23kWh storage, or if it works well, I could get another for the other A2A unit.

I'm hoping during the summer, my friend who's getting my old PV panels, can use them (and the panels) to reduce their leccy bill, as they are struggling a bit.

So, anyone want to bet if I've found a good deal, or wasted the better part of a grand on some Chinese units ..... from a US based company ..... via a UK distributor ..... via Fed Ex delivery on Monday .... what can go wrong?

This is what I bought. have I made a mistake?

Apologies for the numerous spelling errors I'm sure I've made and missed.

[Countrypaul]

We have some bathroom towel immersion radiators controlled by similar to :
https://www.heatandplumb.com/acatalog/w ... gJ4avD_BwE

They were fitted a few years back but have no temperature control and unfortunately one overheated and had steam blasting out the top. I would definitely go with ones that ha a temperature limit (and looking at changing ours).

[Mart]

We have some bathroom towel immersion radiators controlled by similar to :
https://www.heatandplumb.com/acatalog/w ... gJ4avD_BwE

They were fitted a few years back but have no temperature control and unfortunately one overheated and had steam blasting out the top. I would definitely go with ones that ha a temperature limit (and looking at changing ours).

Thanks, do you have any suggestions, as this is totally new to me, and would rather not have steam related problems?

[Stinsy]

I've been wondering recently on the benefit, and frankly feasibility, of having the output from a DHW cylinder run through an electric boiler (I think nowty still has his cylinder plumbed to go through a gas boiler). The point being all the benefits of the normal cylinder and ToU tariffs with the potential to turbo boost the output if needed for flexibility.

This would mean a smaller EB but the running costs (as heating from a higher starting point) should be far smaller still, only use the EB when absolutely needed. With thermostatic mixers and running the DHW temp higher during higher use periods ie visitors even a 125l volume could be stretched quite far IMO.

The problems are one of space and wiring though, and additional costs, but it does provide the flexibility most people demand with a gas combi boiler

Even a 30kW gas combi is pretty slow to fill a bath. This is precisely why we have DHW tanks. A 3kW immersion can heat 250L of water from 10-60℃ in about 5hrs, this puts very little strain on your max demand and is perfectly reliable with zero maintenance for decades, and is economically viable on ToU. But is no good for “on demand”, you can’t expect the Mrs to wait 5hrs for a bath.

Electric boilers still require a DHW cylinder, but can reheat it much quicker because of their 10-14kW rating. On the other hand they’re very noisy, more complex and therefore likely to be unreliable, they cause big problems with max demand (particularly if you also charge an EV). You could therefore make use of a much smaller cylinder and rely on it being quick to reheat but you lose out on ToU.

Great post!

I too no longer use my GCH. It's been a few years since we used it. No DHW tank so rely on the combi (I was planning to swap combi for immersion and cylinder but life got in the way). My single "7kW" A2A unit on the upstairs landing and resistive heaters do the whole job. And I only have a 3.6kW inverter and 12kWh battery.

My main bathroom is pretty cool. We have a mahoosive towel rad and I've bought a heating element for it. We too have a convenient socket on the other side of the wall. But I haven't gotten around to fitting it yet and we get by with the situation as is. You could fit one of these: https://www.tlc-direct.co.uk/Main_Index ... index.html or have a standard FCU and a shelly (or similar).

I fitted a "silent" bathroom extractor-style fan with some insulated ducting in the attic to transfer some of the warm air from the hallway to the one bedroom that the A2A couldn't reach. This worked really well. I would imagine that a small "desk fan" such as this one: https://amzn.eu/d/6QpRF76 would do a good job of moving warm air from your conservatory into your kitchen.

You absolutely could set your DHW tank to heat to 80℃ in winter and allow the heat leaking out to heat that room. Is there a piece of pipe lagging you could remove to very-slightly speed up the rate at which heat is lost?

I'm not familiar with any FiT solar/battery system where the batteries are behind the generation meter. Usually when adding batteries to a FiT system: the solar has its own inverter providing power through the meter and there is a separate AC-coupled inverter connected to the batteries that doesn't go through the meter.

Those battery units seem to be pretty expensive! You could build a mahoosive battery from LF280k cells for cheaper.

[Mart]

Thanks Stinsy, those smart fused sockets look good. That would hopefully give me all the control I need.

Funny you should mention the small fan, I was looking at those, but was very disappointed at the poor air flow from the hot air blower, on fan mode, so couldn't decide. But that could just be that the heater is crap. I'm leaning towards getting a classic 9" fan. We have/had one, but damned if I can find it. Suspect I lent it to someone, or the cat rescue. Did find our tower fan, but too big for the little window.


Thanks for advice on HW tank. I know it may sound weird, especially on a site like this to design in heat loss, but it dawned on me, that that's what a storage heater is, after all.

Love the idea of removable insulation. We don't have a tank yet, so all new to me, but exposing some pipework for the winter sounds like a possible and dare I say 'simple' solution, if designed in.

Speaking of HW tanks, do you, or anyone know much about top, bottom or vertical immersion elements? I was wondering if say a 2 or 3kW element at the top, would work for summer, with it simply re-heating (off the battery/PV) when needed. And a low 2 or 3kW element for the winter, which would better heat the tank from cheap rate (no daytime re-heating, unless really needed). I'm totally guessing that heating from the bottom, would result in more total heat/energy in the tank, from of course more input, and perhaps more heat loss too?


Regarding 'FiT batteries', my system is DC side. So from PV, the inverter redirects unneeded generation straight into the batts, and only outputs the required AC. Then draws DC from the batts when needed. So all the generation goes through the inverter/TGM when needed. But this also means, that when I charge them from the grid, it's the PV inverter (not a separate AC side battery inverter) that stores it in the DC side batteries. The beauty of this, is that my batts utilise the PV inverter and DNO permissions. Since they've told me, they regret giving me my 5.9kW limit - I'm avoiding anything that would give them a chance to re-assess, when they may be minded/able to rescind my higher permission.

To avoid fraud, I had to replace the old TGM with a bi-directional meter, so that future readings are 'net'. So when I mentioned FiT losses, that would be for example, I charge the batts with 10kWh from the grid, and that winds my TGM backwards 10kWh*, but when I draw on that energy, there will be losses on the inverter side from AC to DC, and back to AC, so let's say only 9kWh comes out, winding the TGM forwards* with a net loss of 1kWh.

*In reality, the import reading goes up 10, the export reading goes up 9, and the net reading would be 1 less.


I did look at cheap(ish) batts, such as Fogstar, perhaps 15kWh for less than £2.5k, even the kits for less again, but I'm a tad intimidated. But I'd also need an inverter, and possibly, perhaps, maybe, would need to tell the DNO, which is something I need to avoid. So it seemed to work out ~£1k ish for 5kWh of battery storage, and I paid £927 for 3.1kWh which I thought wasn't too far off.

That's why I went for the all-in powerstation, and also the idea of loaning it too a friend in the summer. Also, could be used to recharge a BEV (slightly) if me or wifey run out, and call home for the other to come out. So far Wifey has refused to let me 'explore' the reserve tank in the Tesla. It seems that a LR model can run for 20-25 miles after zero ..... if you have the guts to try?

May have now found a flaw in that particular powerstation. It says it can charge at 400W, and I hoped/assumed that it would be higher with the add on batt. But I've looked at the on-line manual and that suggests 180W, which isn't much use over 6hrs of cheap rate, for a 3.1kWh battery. Who'd have thought a Chinese product would have differing information. The FAQ's contain highlights such as "Why can not my equipment be used?"


{Would have helped if I'd posted this hours ago, instead of just leaving it. Doh!]

[Stinsy]

Lots to think about re DHW tanks.

The traditional way to manage a 2-element DHW tank is to have the top element powered all the time set to 45℃ and the bottom element powered only in the cheap period and set to 80℃.

Devices such as the Eddi can be set to use the top element until its thermostat kicks in and then use the bottom one.

External “Willis” immersion heaters have their fans too. These are the standard way of doing things in NI. They heat the water in the tank from the top down giving you precise control of how much water you heat, they also heat every last drop of water allowing a smaller tank to store more hot water.

Destraifying pumps are popular nowadays to increase the amount water being heated.

[Mart]

Many thanks again Stinsy. As you say, lots to think about regarding the tank.

Does suggest to me that going a bit bigger with the tank, as costs don't increase much, is sensible, especially if I want to factor in some heat loss for the winter.


Regarding the big picture, the original plan was to operate a hybrid system, and see how much less GCH I'd use this winter (2024/25), and then ponder next steps. But things are going well, and the oil rads seem to displace the GCH need (and leccy boiler idea). So might as well start with some of the next steps earlier than planned.

Couldn't have done all this without knowledgable folk and a site like Camelot to provide ideas, suggestions and encouragement .... but mainly to hold my hand when doubts kick in.


Edit - Just to add, if any/all think I'm overthinking this, and being a bit paranoid, that's fine I am - I'm just trying more as a fun challenge to find a way where I can meet needs from cheap rate leccy, but it's absolutely not the end of the world if I have to use day-rate at times. It's just nice to think of ways of operating without it. So already looks like meeting our needs with leccy mainly via the 2 A2A units, is a winner. And 'failure' won't be a lack of heating or hot water, just some minimal day rate import.

So far this month we've imported about 550kWh of leccy, with less than 10kWh being day rate (that sneaks in at times), so around £40. And that includes BEV charging. Gas is on course this month to be ~100kWh (~£6), as it typically is through the non-heating months. Very happy with that, especially given poor Nov PV gen, I'm down at least 100kWh so far, off average target.

[Stinsy]

Funny you mention it but my bill just dropped: