You can imagine a very long 'black box' with one end touching the surface of the sun, and the other end enclosing your solar panel, with its cable sticking out of the side. Heat enters the black box from the sun at extreme temperature, and leaves the box from the back of the PV panels at ambient temperature.

The maximum theoretical Carnot conversion of sun's heat into electricity is given by the temperature ratio of (sun minus ambient) to (sun), **irrespective of whatever types of technology or physics happen inside the box**.

The good news is the ratio works out at nearly 100%. The bad news is our current technology is far short of the theoretical Carnot limit, although with plenty of room to improve.

Now imagine moving the black box so the hot end touches the warm waste air coming from an aircon condenser. The maximum Carnot efficiency is now low, close to 1%.

The good news is if the waste heat is free and plentiful, you might not care if you only recovered 1% of it as electricity or hydrogen. The better news is you could use all 100% of the warm air to heat a house, if you didn't involve electricity or hydrogen.

Posted By: WillInAberdeenIf there was a supermarket with freezers, it could sell their extracted heat into the ground loop.

Since the heat being extracted from inside the freeezer ultimately comes from the freezer's surroundings, exactly the same amount of heat needs to be supplied to maintain the temperature of the surroundings. So it's more efficient to put the extracted heat into the surroundings.

I used to be really into this kind of closing-the-loop thinking - now it just hurts my head!

Treasury have confirmed that new homes will not be gas heated after 2025, as per CCC recommendations. Can't find much detail. Eg does this include hot water heaters where heat pumps struggle. Does it include LPG or oil heating.

How will it be legislated, a building regs change? Does it apply in Scotland? A "Future Homes Standard" is promised as well as incentives for small businesses to save energy.

https://www.gov.uk/government/publications/spring-statement-2019-written-ministerial-statement

https://www.theguardian.com/environment/2019/mar/13/hammond-says-gas-heating-will-be-replaced-by-low-carbon-systems

Well, no, the bottom of page 4 talks about the decarbonisation of gas supplies by increasing green gas. The bit above about the Future Homes Standard talks about low carbon heating, which gas might be considered if it is 'green' gas. There is no statement about banning gas in houses.

The Guardian article similarly says 'Hammond appeared to row back on implementing the full recommendations from the government’s advisory committee on climate change last month, which called for new homes to have no gas for cooking or heating from 2025'. So they seem to agree with me.

Seeing as sustainability building codes were abandoned as a result of pressure from the house builders, who suggested that volumes of houses built would be reduced and cost per unit increased, is it really feasible that gas heating in its entirety can be phased out from 2025. Can’t see it.

Developments with some sort of district heating schemes based around ground source heat pumps working from comunal open space rather than individual gardens, may work but then it leaves hoseholders reliant on and tied to service contracts etc.
Borehole gshp in each garden would probably be preferrable and with sufficient demand perhaps costs would reduce considerably.
But surely it would make sense first to have a housebuilding industry that can build tight well insulated homes requiring minimal gas to heat them would be a good first step, plus look at encouraging/subsidising improvements in pre 1970’s housing stock in terms of energy efficiency.
Just a lot of hot air and guff to fill out a spring statement at the moment.

What Artiglio said +1 Plus the point I already made about electricity generation capacity.

Posted By: WillInAberdeenPosted By: WillInAberdeenTreasury have confirmed that new homes will not be gas heated after 2025, as per CCC recommendations.

Yes, that bit. Where is that confirmation stated?

You posted that statement together with a link to the chancellor's statement, which makes no such statement. So where does make that statement?

I don't think it's unreasonable to be asked to back up claims you make about what has been said.

Posted By: WillInAberdeenI am not 'claiming' anything.

Yes you are. You have claimed that "Treasury have confirmed that new homes will not be gas heated after 2025" and I have asked you repeatedly to explain where that statement was made, and you have repeatedly dodged the question. Either you have actually seen evidence that the chancellor/Treasury made that statement or you haven't. i.e. not third-party reports in doubtful newspapers. Which is it? Have you or have you not got evidence for your claim?

And in the written ministerial statement at https://www.gov.uk/government/publications/spring-statement-2019-written-ministerial-statement

Clean Growth
The government is determined that we will be the first generation to leave the environment in a better
state than we found it. The UK leads the world in tackling climate change and delivering clean growth,
preserving the planet for future generations. In the coming months the government will set out further
detail on the following:
...
Future Homes Standard – A Future Homes Standard, to be introduced by 2025, future-proofing new build homes with low carbon heating and world-leading levels of energy efficiency. The new standard will build on the Prime Minister’s Industrial Strategy Grand Challenge mission to at least halve the energy use of new buildings by 2030.

They’re talking in a manner expelling massive quantities of male bovine excreta, the UK economy needs to be able to generate enough wealth to make such goals even vaguely likely. Really can’t see the construction industry and their suppliers being able to achieve this in 6 years even if all the detail was available today, but it makes for good sound bites and punts the need for any action well into the next parliament.
With a bit of care developers could turn out properties with solid A ratings on an EPC, ensuring this happens might be a better target for 2025, in the meantime why doesn’t the govt. invest in genuine construction training/ apprenticeships which highlight the skills and attitudes required , plus investment into developing a broad knowledge and research base into affordable ground source heating technology.
All alongside efforts to improve the efficiency of existing stock, most of us remember the days of Ă‚ÂŁ1 insulation from the diy sheds, always seemed far more sensible than posting low voltage lamps to people that just went to land fill.

Ok, yep i suppose if you inject 5% green gas into the supply and new houses only use 5% of gas used you’ve got round the language, but its not the headline that the statement was wanting to create. Just the usual weasle words politicians like to spout.
Probably a target we’ve already met statistically.

For anyone who missed it, there's a thread on how the Government hopes to achieve this for existing homes - 'Govt consultation on low carbon heat' at http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16542

And for new homes 'The Future Homes Standard' at http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16273

District heating - a new generation of disaster.
I’lol have passed on by the time they do this but let me predict. They get the capex approved and then it cost twice as much, it runs, unreliably for a while. About ten years in due to failure to maintain the boilers and pipe network and failure to thoroughly demineralise the water the whole system turns into a awful mess of breakdowns, leaks, boiling mud geysers.
I have lived on a small place of about 10 units with biomass fired district heating. It was always going off. The original designer and supplier had gone bust leaving the operator up sh#t creek.
Also worked on two sites with gas fired district heating. Constant problems and I mean problems like boiling mud geysers. Only one of the three boilers running. Client giving up and installing individual boilers in all the buildings. The pipe network had been replaced with best Danish kit just eight year earlier.
Other site splashing Ă‚ÂŁ2m up the wall on replacing their cracked up pipe network. Some of the new towns where I grew up had district heating, none survived.
It sounds great in the text books though.