Looks like the party is over....

[Dillsue]

8 hours ago, ProDave said:

And if you have PV on your roof, you can pretty much guarantee when you need to run your cooling system, there will be enough power from the PV to power it, so no demand on the grid.

If youve got AC isn't one of the prime times to run it in the evening and overnight to help with sleeping?

[Oz07]

33 minutes ago, Dillsue said:

If youve got AC isn't one of the prime times to run it in the evening and overnight to help with sleeping?

Assume with well insulated house you bring temp down during day when sun shining?

[JohnMo]

1 hour ago, Dillsue said:

If youve got AC isn't one of the prime times to run it in the evening and overnight to help with sleeping?

That isn't how you run a heat pump so why do that with A2A (which is a heat pump)? You keep on top of the temps and run low and slow. So when sun is out, the house starts to heat up and cooling starts then. You can always add a battery then it's still powered by solar overnight as well.

[Beelbeebub]

Batteries. 

[JohnMo]

24 minutes ago, Beelbeebub said:

Batteries. 

if you want

[sharpener]

3 hours ago, Beelbeebub said:

Batteries. 

 

It's still not a costless option. If you can sell all you generate at 15p/unit then that is what it is costing you for domestic consumption of every kind.

[Beelbeebub]

20 minutes ago, sharpener said:

 

It's still not a costless option. If you can sell all you generate at 15p/unit then that is what it is costing you for domestic consumption of every kind.

But batteries allow you power your air con in the evening/night with solar from thr day atow cost (4p/kwh assuming 4.5k cost for 14kwh usable over 8k cycles)

 

And crucially at zero extra load on the grid. 

[sharpener]

18 minutes ago, Beelbeebub said:

But batteries allow you power your air con in the evening/night with solar from thr day atow cost (4p/kwh assuming 4.5k cost for 14kwh usable over 8k cycles)

 

Yes I get the depreciation calc which is often forgotten, but to arrive at the true cost of night-time usage you still have to add the cost of exports foregone which (with Octopus) is 15p/unit, and also divide that by the charge/discharge efficiency which might be as low as 0.8.

[Beelbeebub]

But your import rate is likely to be higher - at least outside of night rate. 

 

So exporting at 15p and importing at 25p makes the financial efficency 60%. 

 

Say you produce 10kwh during day and over the same 24h use 10kwh 

 

During the generation period you use 5kwh and export 5kwh (earning 75p) 

 

Then after suunset you use 5kwh, buying it all from the grid at a cost of 125p

 

Net loss of 50p

 

If you stored the 5kwh you would forego 75p but not spend 125p.  And lose 20p in depreciation. 

 

Overall a difference of 5p - chicken feed really, though it does widen if your power requirement is higher or if the imoort/export gap widens (eg the 15p rate is cut or price of day rate elec Rises) 

 

*but* the battery option has zero impact on the grid - there is no import or export 

 

 

[sharpener]

3 hours ago, Beelbeebub said:

If you stored the 5kwh you would forego 75p but not spend 125p.  And lose 20p in depreciation. 

 

Overall a difference of 5p

 

Don't quite understand where your 5p comes from, 125 - 75 - 20 = 30 not 5 which is an appreciable saving.

 

But in the real world you might need to sacrifice more like 6 or 7 kWh in exports to get 5 kWh out of the battery again which is starting to make it a very close run thing.

[JamesPa]

15 minutes ago, sharpener said:

 

Don't quite understand where your 5p comes from, 125 - 75 - 20 = 30 not 5 which is an appreciable saving.

 

But in the real world you might need to sacrifice more like 6 or 7 kWh in exports to get 5 kWh out of the battery again which is starting to make it a very close run thing.

I run the numbers for batteries at least every 3 months and can never quite get it to work out after accounting for cost of capital (even if I allow for tax on savings).  I want them to and its close, but they don't for me.  A decent nighttime tarrif, doing washing and charging ev overnight, and running the heat pump 24x7 without setback still works out the best bet.  Drop the price by 20% and it changes, but the installers don't drop the prices.  Even factoring in arbitrage doesn't tip the balance.

Edited Wednesday at 23:18 by JamesPa

[sharpener]

26 minutes ago, JamesPa said:

A decent nighttime tarrif, doing washing and charging ev overnight, and running the heat pump 24x7 without setback still works out the best bet. 

 

Battery is now a sunk cost and depreciation not a consideration as it will probably outlast me! 

 

I cannot be doing with chopping and changing e.g. to milk Octopus Agile (even though I have an EV). So am on Cosy and charge battery to 100% every cheap period. This means I do not have to guess what the next day's PV will bring in order to leave enough room for it. (Havenwise might do a better job of this but is not compatible.) Also means we can do laundry/dishwasher at any time without penalty.

 

With a buy price now 14.xx p and sell price at 15.00 I am still probably losing a bit bc of the round trip inefficiency but it is totally set and forget.

 

 

Edited Wednesday at 23:44 by sharpener

[Gus Potter]

Hi all.

 

The party is over indeed. I'm going to lay this on thick as it's time.

 

I've picked UFH first but will turn to PV in another post.  But to wet your aptetite! 

 

I've argued on this forum for a long time that underfloor heating is the bees knees. I've done this and worn the tee shirt. Long before most of you were in short pants. So if any of you can tell me how you installed and designed an UFH 22 years ago on a self build then I'm all ears! I would love to hear from you how we all flew by the seat of our pants at that time. I do hope that there may be one person. Many think they have invented the UFH wheel.. well you have not! The Scandinavians were at long time before the Brits..

 

I've made the case for simplicity and the need for UFH (the pipes in the slabs) to last the lifetime of the building, the cost of maintenance, reacting to how technology will evolve in terms of boilers etc. BUT what is in the concrete floor is a FIXED ASSET! Just like the walls and the roof!

 

I also happen to be an SE who has actually been designing these slabs, insulated rafts to work with UFH for decades. So If there are any on BH that want to have a serious structural discussion with me then I would welcome that.

 

You can ponce about with your weather compensation as much as you like, the flow rates.. your controls and buffering.. but see.. your heating has to work for 50 years so until you can make that arguement fdor life time performance, then I'll write down the value of your house if the pipes in the floor are not designed to adapt. SO GET A GRIP!

 

I can and estate agents will also take a dim viw on a house value!

 

Now some may just want to have a house that is a hobby, that is fine and I'm ok with that. But actually that may also make your house unsellable! Seriously.. you need to WAKE UP and smell the coffee, surveyors et al are clocking this so your hobby might come at an unexpected expense! Don't trust me. maybe ask a valuer?

 

What I'm not OK with-  if your house gets a loss of value as you have played with (and it is playing) home automation / complex UFH controls then that is a price you pay.  But if you try and sell your house to some unexpecting young couple.. you can f...  off., and I'm going to go hard on you! You are  not  going to sell your house to my kids!

 

Advance Foundation technolgy have grasped some of it, Tanners in Ireland are competant SE's but no one has actually put all the bits together!

 

The thing for me is that I want to design and build stuff that lasts, that delivers profit for self builders and that encourages young folk to enter the market,  that benefits society. It's not a big ask? 

 

But as a designer with lots of real life experience I want to help young folk see the wood for the trees. I want them to get on the self build ladder on the self build ladder, I did it on a shoe string and that is why I keep pushing the simple stupid... as that means you can get a wider coice of Contractors.. which drives cost down.

 

That is why I often push against the UFH complex thing and other stuff. It's also basically bonkers, but a lot of tecky folk on BH can'r see beyond 5 years.. 

 

So in summary I would like to see a lot of experienced folk on BH saying.. this works and if you are young folk embarking on a self build, on a limited budget this can work for you to.

 

OK this is not going to go down well. But the life and future of BH is in the young folk, that are strapped for cash..

 

This for me and is why I'm still here.. I want to help and this is my hobby. To enthuse young folk, we need to solve problems, use our experience to say this can be not as hard as you think, if you take our advice, but at the same time give a bit of tough love if need be.

 

PV is following much the same cycle.. 

 

 

 

 

 

 

 

 

Edited Wednesday at 23:54 by Gus Potter

[Gus Potter]

I wish BH had a spell checker. I just can't be arsed checking my dyslexia bit and spelling when I'm writing about stuff as a hobby. 

 

For all, my grammer and spelling may be a bit off when I'm off duty.. but neglect what I'm saying at your peril.

Edited yesterday at 00:36 by Gus Potter

[SteamyTea]

4 hours ago, Gus Potter said:

I wish BH had a spell checker

Most web browsers have them built in

 

[Dillsue]

14 hours ago, Beelbeebub said:

And crucially at zero extra load on the grid. 

If you've already got PV then in most instances any surplus goes to the grid and powers your neighbours. If you then start using the surplus or put it into batteries to power AC then your neighbours are deprived of your surplus so have to increase their draw on the grid.

 

Obviously it's up to the PV owner what they do with the PV they generate, but I don't think that adding AC has no effect on the grid.

[JohnMo]

8 hours ago, sharpener said:

cannot be doing with chopping and changing e.g. to milk Octopus Agile (even though I have an EV). So am on Cosy and charge battery to 100% every cheap period. This means I do not have to guess what the next day's PV will bring in order to leave enough room for it. (Havenwise might do a better job of this but is not compatible.) Also means we can do laundry/dishwasher at any time without penalty

I followed your lead on this, exact same, fill battery over each cheap cosy slot, if there is excess PV it just gets exported. Doing a predictive charge may save a few pence here and there, but life's too short. The batteries own control does all the work.

[Roger440]

On 18/11/2025 at 21:35, Michael_S said:

Logically I think you are right but in reality people seem to be very short-sighted and only look at the up front cost - se for example EVs.

 

I dont think they are short sighted. The vast majority of the population simply cant afford to drop a 5 figure sum on heating, an EV etc, no matter how good it looks finanicially over the long term

 

If electricity was free for heat pump use, thay still cant fund the heat pump in the first place. Running costs are acedemic if you dont have the capital.

 

You have demonstrated, once again, that BH members are not representative of society at large.

 

[sharpener]

38 minutes ago, Roger440 said:

 

I dont think they are short sighted. The vast majority of the population simply cant afford to drop a 5 figure sum on heating, an EV etc, no matter how good it looks finanicially over the long term

 

If electricity was free for heat pump use, thay still cant fund the heat pump in the first place. Running costs are acedemic if you dont have the capital.

 

You have demonstrated, once again, that BH members are not representative of society at large.

 

 

Loans/2nd mortgages for home improvements are long established (think double glazing and conservatories).

 

There are also dedicated finance schemes for solar panels (we receive the junk mail as they seem to be able to get our details from some public register). And for HPs as well, IIRC some installers have links on their web sites.

 

So you don't actually have to have the capital. And plenty of ppl seem to blow what they do have on expensive holidays and weddings, it's largely a matter of personal choice. 

 

 

 

[JamesPa]

28 minutes ago, sharpener said:

So you don't actually have to have the capital. And plenty of ppl seem to blow what they do have on expensive holidays and weddings, it's largely a matter of personal choice

Now you are expecting people to take responsibility for their own actions.  How dare you, don't you realise that everything is the fault of the Government/the Council, the EU/immigrants/whatever other target for hate somebody chooses to invent.

 

If course there definitely are people who can afford neither home improvements nor 'expensive holidays and weddings'.   Assuming that they are trying to improve things for themselves then they deserve help with improvements to make their houses more efficient IMHO.

 

Here are some stats from ABTA.  Nearly 60% of people in the UK (according to ABTA) take one or more foreign holidays in any given year (allowing for Covid recovery).

Edited yesterday at 10:39 by JamesPa

[-rick-]

11 hours ago, Gus Potter said:

You can ponce about with your weather compensation as much as you like, the flow rates.. your controls and buffering.. but see.. your heating has to work for 50 years so until you can make that arguement fdor life time performance, then I'll write down the value of your house if the pipes in the floor are not designed to adapt. SO GET A GRIP!

 

You've said stuff like this a few times and everytime I try to understand what you are getting at but I'm afriad I'm not really getting your point. In case it doesn't come across in the way I indend, the below is not having a go, just trying to understand your argument.

 

The pipes buried in concrete (at least in low energy houses) are going to be able to cope with almost anything thrown at them and will last a very very long time.* A lot of what we discuss here is how to get the maximum efficiency out of a system and the theme here to achieve that is minimum controls, low water temperature, system on most of the time with weather compensation (a technology that has been standard in all heating systems in other countries for literally decades).

 

Even if you add lots of fancy controls on top of the basic system, the fundamentals of the system are such that you should be able to remove those controls and still get a very functional system. Similarly, if the heat demand of the house increases then worst case you need to up the flow temperature in the pipes to compensate. Again, most of the designs talked about here for new builds are based on very low temperature heating. If you can output sufficient heat with the water in the pipes flowing at less than 30oC then if some cataclysimic climate change happened and suddenly we were all living in -20C then upping the temperature in the pipes to 40-45C should still be able to adequately heat the house.

 

Obviously if people want to extend the house then any extension would need work, but thats no real difference to any other system. If you have a low and slow design the system shouldn't care too much where the walls are if they needed to be moved.

 

I do think that any 'smart' stuff added to a house should always be removable while maintaining the basic function of the house. Maybe you lose convenience or a little efficiency, but things should still work. Again, in the vast majority of cases, the systems discussed here are of the type that could be removed without significantly reducing the basic function of the house. Therefore, it is easy to offer any future buyer of the property the option to have all smart systems removed before they complete any purchase. So these shouldn't have a negative impact on the price of the property.

 

* Plastic pipes don't corrode and UFH systems should have much less metal in them overall reducing corrosion of other parts and build up of gunk. They can be flushed if there is a problem. Even in the unlikely event of the pipes developing a problem, retro fitting radiators or even electric heating to affected rooms would be unlikely to dramatically change the sale price of the house.

 

I do see a concern about whether rafts can be relied on to last as long as traditional foundations, but this has nothing to do with UFH.

Edited yesterday at 11:21 by -rick-

[sharpener]

1 hour ago, JamesPa said:

If course there definitely are people who can afford neither home improvements nor 'expensive holidays and weddings'. 

 

Housing Associations seem to be very active in putting in HPs for their tenants. Accounts for a large proportion of my installers business.

And to judge by what is written on the Arotherm plus FB forum their contractors are amongst the worst for bodged installations, poor configuration and abysmal handovers (luckily was all OK in my case though).

[Roger440]

4 hours ago, sharpener said:

 

Loans/2nd mortgages for home improvements are long established (think double glazing and conservatories).

 

There are also dedicated finance schemes for solar panels (we receive the junk mail as they seem to be able to get our details from some public register). And for HPs as well, IIRC some installers have links on their web sites.

 

So you don't actually have to have the capital. And plenty of ppl seem to blow what they do have on expensive holidays and weddings, it's largely a matter of personal choice. 

 

 

 

 

Not sure finance is an answer for people with no money or an inability to manage money. That doesnt normally end well.

 

I forget the number of people that dont even have £200 in savings, but its substantial. They live month to month. They dont have any capital, and borrowing money in that circumstance would be foolish.

 

Wasnt really debating if all those people needed to be in that postion. Just observing that they are, be it through circumstance or the choices they make. 

 

Related, though not directly is the very long payback periods on some of this stuff. If you can see a return in 2 or 3 years, if you have the capital its a no brainer. But 10 years, not so much. Might make good sense on paper, but 10 years is a long time, lots could happen. Could even be dead. But a half resonable you chance that you may not benefit as you might die, move house or whatever.

Edited yesterday at 14:24 by Roger440

[Beelbeebub]

15 hours ago, sharpener said:

 

Don't quite understand where your 5p comes from, 125 - 75 - 20 = 30 not 5 which is an appreciable saving.

 

But in the real world you might need to sacrifice more like 6 or 7 kWh in exports to get 5 kWh out of the battery again which is starting to make it a very close run thing.

You're right, 30p saving by using a battery. 

 

Given the sun doesn't sine 24h a day at some point we cannot use the panels directly. 

 

Our options are use the grid or use a battery. 

 

The viability of using the grid as your battery (ie exporting when you have excess and then importing when you have shortfall ) is critically dependant on the price ratio between import and export. Without a battery the best you are likely to get is 15p all day, and the best import you can get is 25p because you can't time shift without a battery.  This is equivalent to a storage efficiency of 60% and is unlikely to stay as good. The SEG rate is a better long term metric which is around 5p IIRC (could be more but it's nowhere near 15p). This drops the efficency really low. 

 

For a battery, your estimate of 6 to 7kwh in to get 5kwh out implies a round trip efficency of 70-80% which I think is too low it's more likely 80-90% or better. 

 

 

To be fair panels are so cheap now that *if you could get a really high export limit*, like 10kw or something you could have a huge array, big enough to export so much elecreicty in the day and summer months that you could build up enough credit to import "off sun" and still end up ahead. 

 

But you would need the space for the panel and the high export limit. 

 

[Beelbeebub]

6 hours ago, Dillsue said:

If you've already got PV then in most instances any surplus goes to the grid and powers your neighbours. If you then start using the surplus or put it into batteries to power AC then your neighbours are deprived of your surplus so have to increase their draw on the grid.

 

Obviously it's up to the PV owner what they do with the PV they generate, but I don't think that adding AC has no effect on the grid.

The grid is already sized and set up for all the houses on it. 

 

If you have enough PV and battery that you never export or import you essentially dissappear from the grid in the same way as if you disconnected. 

 

Yes your neighbours can't use your solar but there is now more headroom in the infrastructure for increaced demands from them.

 

Your contribution to the local grid will not be as stable, when thry are charging an EV and your panels are cutting in and out because of clouds the grid is having to take up the slack. They may not even be charging at that time and your lower might be effectively powering a factory across town - which requires the grid to carry the current. 

 

If I installed a 2Mw solar farm, more than enough to run all the houses in thr area, the grid would still prob be overloaded because it couldn't carry the current from me out.

 

Imagine a block of flats with water pipes, a big water main splitting into smaller pipes for each floor and then smaller ones for each flat before even smaller ones for individual taps. 

 

If I had a magic water fountain, that produced free water from nothing, I still couldn't provide water for the entire block just by plugging the fountain into my kitchen tap. 

 

On the other hand, if I (and some other tenants) used our magic water fountains to satisfy all our individual water needs, the remaining tenants without magic water fountains would have better flow and pressure. 

Edited yesterday at 14:38 by Beelbeebub