UKH

Paging Wintertree and others who know a lot about this:

I'm making long term decisions about how to heat and power my home for the next few decades. 

Firstly, I'm making the assumption that at any moment, there is always some natural gas being burned in the UK fuel mix, via CCGT plants.  I think that's right, isn't it?  So every kWh of excess PV exported can be assumed to have displaced a unit of gas somewhere. 

I know that sometimes there's coal or diesel being used, and then the PV might be assumed to have displaced that instead, which would make the PV more valuable in terms of carbon savings.  Are there regular periods when there is no gas at all and the PV is therefore less valuable?  Even so, just assuming that it's displacing gas all year seems to be a good compromise?

Secondly, can I reasonably assume this will remain the case for some time to come?  It looks to me as if we're not going to remove gas from the fuel mix for decades yet, unless we start being much more serious about building renewable capacity, and even then gas will remain the preferred backup fuel.

I think gas will be part of the electricity generation mix for some decades more (coal and diesel though are already negligible).  As offshore wind is built out more, there may be more times when the gas contribution gets quite small, but very windy periods don't usually correspond with times when it's very sunny. And even if your PV just ends up displacing biomass (which is a large and possibly dubious contribution to renewable generation in the UK) that would still be valuable.

I read something somewhere the other week that heat pumps will be replacing gch boilers in the coming decades. While they are expensive I believe gov grants are available for their purchase and installation.

https://theswitch.co.uk/energy/guides/technology/air-source-heat-pump

I'm not sure what the long term plan for providing electricity during a cold still winter night. Nuclear seems to me the only current option. Perhaps the government is hoping that energy storage technology matures and becomes practical in the medium term.

Seems a shame that whilst I'm being offered 'heat source pump deals' with subsidies to retrofit my heating, they are busy installing gas heating systems in the new estate up the road. Why not subsidise the house builders and get them to fit in futuristic heating systems in new builds. Mad.

I think the main problem just now is who pays for the subsidies, usually added to all our energy bills, the more well off can afford green technology through government help, but it hits the poorest hardest in there energy bills, gas might well still be more environmentally friendly than air source heat pumps, as the electricity to power heat pumps won't all be coming from renewables, and if air source pumps are subsidied per unit of energy consumed again it's the poorest who are paying for this subsidy in there energy bills. But maybe it's would be sensible policy for all new built social housing as a starter to be heated from a central gas district heating system.

When thinking of climate change we should look at what provides most benefit to society, and for me just now would be looking at transportation, you can reduce emissions that will make no real difference to global climate change at end of century, but you have the benefit on society of reducing urban air pollution and making streets safer for active travel, net benefit for NHS and society.

Fossil fuels have fantastic storage technology - you can even leave them underground for millions of years then bring it to the surface to a coal heap, oil tank or gasometer for the consumption that screws the planet.

Maybe biomass is the nearest equivalent - leave it growing or in a wood pile.

Stuff you burn (chemical energy, see above) is great for storage. 

Renewable electricity to chemical energy looks like a good option but hydrogen not easy to store - high pressure or low temperature, too niche to power a nation when insufficient solar/wind/hydro/tidal generation for a week? 

Tidal flow is four times a day and can be predicted far into the future (thousand or millions of years) and reduces the storage timescale to a few hours if you have enough tidal (not possible?) and few enough outages.

Renewable electricity to liquid air is an interesting idea. 

https://www.theguardian.com/environment/2020/jun/18/worlds-biggest-liquid-a...

We could do with something closer to power station coal heaps which in the past stored enough energy to keep a nation going for weeks but nothing seems to be on that scale. 

Sure I'm aware of all that stuff but the amount of energy needed to be held in a store is daunting. The UK baseline electricity consumption is about 40 GW and will rise considerably if EVs become the default method of transport. Supplying say 50% of the UK's electricity from storage over a still winter night would require maybe 250 GWh of storage capacity.

I can't imagine we're less than a decade away, if ever, of being able to provide that.

It’s about 3 years since I looked in to solar storage with batteries and concluded that all it does is load shift CCGT and waste net energy in round trip inefficiencies.

Gridwatch shows CCGT remains a continuous source of power.

I can’t see CCGT going away any time soon as is it can spool up/down way faster than other combustion plants which is a key part of a renewables heavy grid until there is way more battery storage - which I don’t think can happen for at least a decade as that level of storage needs to move beyond lithium batteries to not be an environmental disaster, and aluminium isn’t market ready and won’t be for some time.

One possibility for seasonal storage of renewables is large Sabatier reactor plants converting excess solar/wind in to methane storage, then a shift towards CCGT in mid winter.  There’s a lot of infrastructure already there for that.   Another reason I think gas has a big role for some decades.

One thing to consider - a gas CHP generator.  These generate electricity from the gas, powering the grid, and use the waste heat from the generator as the domestic heat.  So it gets exceptionally high net efficiency from the gas - it’s sort of like embracing district heat but without needing the central planning that’s seen the UK mostly waste that energy for decades.  No idea what the feed in situation is like.

Lots of wild cards on the horizon.  Plummeting space launch costs could make orbital solar arrays viable in 15 years time I think, and whilst these got a bad rep from Sim City 2000, they can be made intrinsically safe and could deliver solar power 24x7 to the UK.

Why not just ban all new individual gas boilers in new housing tomorrow, end of. There are plenty alternatives. At the same time increase the insulation specs massively. 

Air sourced heat pumps really aren't very expensive and you don't need to pipe gas to every house, there are infrastructure savings to be made. 

That’s about 2.5 million BEVs which doesn’t seem unrealistic for a decade hence.  The problem is we will need to cope with several weeks of winter lull...

Thanks, all.

I'm almost certainly going for an ASHP; in the medium term, at least, these seem to be the best we're going to get.  I'd love to install an enormous WSHP driven from the Thames for the estate I live on, but realistically it's never going to happen.  Obviously the subsidy is what makes ASHP currently viable, but I do believe that subsidy for early adopters is what drives pricing down so that tech becomes viable for all.   Solar PV shows how that can work - it's halved in price since I bought my array.

The tricky one for me is about deciding between direct feed to the UFH or a thermal store, and/or including battery storage.  Both are ways to deal with the fact that over a 24 hour period, the time when it's cheapest to run the AHSP and the time you need the heating are poorly aligned.  

If we're confident that there will be a CCGT running continuously pretty much every day of the year, then that simplifies things for me.  It means that a battery can't ever be better than carbon neutral, as it's only ever shifting CCGT power from one time to another.  

I've seen some estimates suggesting that there's enough storage for hydrogen in old salt mines near Deeside and Teeside to make some impact to seasonal storage; no point taking the losses involved in making methane if you can just burn hydrogen directly.  I think if you're going to the trouble of using hydrogen to reduce carbon dioxide you might as well make a liquid fuel as it's easier to store.  In any case, I think the big push here will be in making synthetic zero carbon aviation fuel as I don't see how without that there's going to be any long-haul aviation.

A 200L domestic hot water tank heated to 80C could power your heating for a few hours and takes a day or two to cool down.

If the primary concern is to lower CO2 emissions, I think there are more issues to take into consideration. My house is centrally heated from a gas boiler, and I am told that an ASHP does not produce as much heat as my current boiler. If I were to install one I would have the choice of either digging up my concrete slab and quarry tile floors to install underfloor heating or getting rid of my current radiators and replacing them with substantially larger ones. The CO2 emissions created by installing underfloor heating with a new concrete slab would probably take more than the rest of my lifespan to offset with an ASHP, and although the new radiator option would not create so much CO2 I do have a limited amount of wall space to mount them on.

What about pumped-storage hydro-electric plants, which are effectively hydro-electric plant that can be run backwards when there's spare electricity generation?  There are a coouple in Snowdonia already and several in Scotland.  The Dinorwig scheme can deliver 1728MW and stores around 9.1GWh according to Wikipedia.

You’re right about there being less losses in producing H2 than methane from electricity, although most of the extra losses in CH4 production come I think from the heat required and the need to extract CO2 from the atmosphere - which is an area of active and growing research.   It’s also possible that the CO2 could be sequestered from the CCGT plant in winter then recycled in to CH4 come the summer.

Methane can be liquified for storage and has a much higher boiling point than H2 so is easier to liquify.  I’m not sure which needs more energy given the heat capacities and different refrigerant cycles.

The heat needed for the sabatier reactor can recovered from liquifying the methane for long term storage with a heat pump I’d imagine, lowering the energy needed.

Liquid H2 or CH4 storage for seasonal energy shifting has a thermal problem - lots of waste heat in summer when nobody needs it, and a heavy demand for heat in the winter; I suppose the waste heat from the CCGT plant can be used.  I’m sure I’ve read an article on a clever approach to this when storing energy in compressed air; perhaps with a big aquifer involved?

As well as being instantly comparable with our existing infrastructure, atmospheric LNG production can be used to sequester carbon by pyrolysis of the methane.  Then we can shove that solid carbon back in to a hole in the ground somewhere.  

Yup.  Most of the PR around electric aviation is beyond wishful thinking when it comes to the next 20-30 years.  You can make a solar / battery plane.  You can also make a pedal powered plane.  That doesn’t mean they can do general aviation...  It doesn’t seem like it’s going to be difficult to convert to Fischer‐Tropsch fuels, just expensive.  But I don’t think BAESystems’ but in to Reaction Engines is driven by space access; air breathing hypersonic H2 engines are going to transform the upper end of long distance general aviation and give the yank military an alternative to their scramjet reeearch which isn’t m delivering much.

Pumped hydro is very limited in what it can store - a fully renewable grid might need 3 weeks of storage, and U.K. pumped storage can do maybe an hour of electricity.   Building more needs quite specific geography and a lot of water.

There are plans to do gravity storage with solid objects - robotically shunting blocks up a mountain railway or building/unbuilding a tower with a crane.

https://www.google.co.uk/amp/s/www.wired.com/2016/05/forget-elons-batteries...

https://arstechnica.com/science/2018/11/battery-idea-hydroelectric-pumped-s...

That's where my thinking is headed.  If battery storage is unlikely to become financially viable for a few years, and also unlikely to become carbon saving for many years after that, then thermal storage is the way to go.  Working on whether it's actually financially sensible given the increased system cost.

Of course, once you have a thermal store then tying a boiler stove in becomes a possibility, but that then screws the RHI over.  Difficult.

In reply to John2:

An ASHP can easily produce as much heat (energy), but it does so best at a lower temperature - that's why bigger rad areas are needed.  We've just had low profile wet UFH fitted as part of a renovation - it only raises the floor by about 15mm overall.

Agree that digging out and re-pouring a concrete slab is unlikely to become carbon neutral within a lifetime.

I think the plan for storing hydrogen in old salt mines would be to do it in the gaseous state, under pressure.  If you want an easily liquified fuel made from hydrogen, I think you're better off with ammonia (I suspect this will end up the solution for maritime transport).  I'm all in favour of pyrolising your synthetic hydrocarbons and burying them.  You could even use them as a feedstock to make very non-biodegradable plastics and put them in landfills (only half-joking...)

We moved in to a big drafty old house with limited central heating and an ancient boiler last year. We needed to extend the central heating extensively and replace the boiler but I wanted to be more environmentally friendly so I did a lot of research in to heat pumps. I even considered matching with a few solar panels to provide the electric to run the pump. I was willing to spend quite a bit of my own cash on top of the max £7k grant if necessary, and willing to have them dig a huge trench in the garden.  However, after speaking to two different engineers from companies whose business was to sell me a ground source heat pump (one by phone and one in the house) they were both adamant it was a bad idea, would prove incapable of heating the house adequately and I should get a new efficient gas boiler instead (not through them.) So that's what I did.

I think until technology can provide reasonably equivalent outputs  we shouldn't be banning anything, at least in older houses that can't manage without. However I'm very much hoping that I'll be able to replace the gas boiler with something clean in another decade.

Ground sourced is a different fish to air sourced, in terms of logistics and installation. 

Your problem wasn't the price or efficiency of the air/ground sourced unit, but the insulation level of the housing stock. 

Note. My original comment said in any new house. But really they need phasing out in general. 

I run a thermal store (1000l) but they are a requirement anyway for both my heating plants (pellet and wood gasifier) but it's BIG. Mine's in my workshop building along with the heating plant  but in a normal house it's going to be a problem. On a night at 0°C it starts at 80+° and in the morning it's at 20°. Getting it (and the rest of the system) back up to temp takes hours! While it's selectively heated there's still no concept of quickly warming the house up so not everyone's cup of tea.

One thing I don't get is why ASHP are suddenly such a theme in the UK, is there some massive advertising campaign on TV? I know 5 people with GWHP and one with ASHP and that's only because couldn't go for ground water, for us in Bavaria ground water is so vastly better the ASHP is a non-starter (and probably what I'll add to my system next with the wood fired system to bring the temperature up the last 20°).

It is utterly batsh1t that you're allowed to build a new house with insulation as poor as the regs will permit, and with a gas boiler.  The building regs should require much better insulation and heat pumps only for new builds.  It's not even as if insulation is expensive, if it's planned from the start.  It's retrofitting it that is difficult!

That's a drop of 70kWh.  What are you heating with that?  My three-bed and not brilliantly insulated semi takes 35kWh on the coldest day of the year.

I think the problem is that most people don't have the opportunity for GSHP or WSHP.  You need enough garden to provide the heat source, and the willingness to dig it up.  ASHP is a comparatively simple swap for the boiler.  I'd be getting GSHP if the garden were large enough.

I live in an old farmhouse with 260m2 living area and also heat 60m2 workshop with "some" insulation, the total nominal heating load is 11kW normally. When it gets cold (-12 or lower) it's a challenge to my wallet!  If I run the pellet heating on 7kW it's not enough (it never cycles off) and on 15kW it can cope).

I know one guy with a ground array but he's got a new-build on 1000m2 so it was easy (his garden starts growing 2 weeks after everyone elses though), everyone else I know has boreholes. I live beside a river so my neighbours only had to do a single bore 30m deep which is cheap enough. I wanted to use my well but measured the temperatures over the winter but it drops to 2°, its filling with surface runoff not groundwater.

The answer to the aviation industry's dilemma seems to be hydrogen.

https://www.airbus.com/newsroom/press-releases/en/2020/09/airbus-reveals-ne...

Fair enough - you're heating about twice the area I am, and in colder ambient conditions.  This probably says something about how much more improvement I need to make to my insulation, really. 

By boreholes - do you mean they're running WSHP from the constantly replenishing (and relatively warm) groundwater?  That's neat.

Absolutely. Tragic that the political system won't allow for such obvious solutions. These house will be mostly detached, 1/2 garages. They could be a really neat new build development of terraced affordable housing with shared heating system. Anything would be better than more of the same.   

Fair enough, I agree about new houses. Also the rest of your post, but ashp capacity is more limited than gshp as I understand it, so I think the problem then with larger (especially very high-ceilinged) or poorly insulated houses is greater still.

They go down until the ground water is around 13-16° and use brine filled coils for heat transfer, the ones I've seen are maybe 30 cm in diameter and 10ft long ( I drive past a guys yard who installs them). Being by a river the shallow water just isn't warm enough as the surface melt water just perculates through the gravel layers, the river freezes pretty often.  Constant 13° water makes GWH plants a lot more efficient than air, that's for sure!

I'm in the middle of a re-think of the whole system, for the last ten years I had the forest rights for a wood across the road and a fair amount of free time so pulled out about 15 tons of wood for free but old age and more business means time for another plan.

'One thing I don't get is why ASHP are suddenly such a theme in the UK'

I quite agree. I have started to think about what I will do when my current very efficient combi boiler gives up the ghost, and I have yet to see a viable alternative. The media pressure in the UK to install ASHPs is currently immense, and the protagonists never mention the noise problems or the expense of installing either underfloor heating or larger radiators.

You could look into a limecrete floor? There’s less embodied carbon in it than concrete. It’s worth doing the sums on your options if you can, a conclusion we’ve come to after various wrong decisions!

I've already fitted my wet UHF. We were remodeling the entire ground floor of the house, and rather than dig up the floor slab we fitted a low profile system and then tiled over the top.

Limecrete does look like an interesting alternative.

I live in a 150 year old house with low ceilings and door heights. If I installed a low profile system I would have to duck every time I walked through a doorway.

One of my fears in life is next door installing an ASHP that is too noisy.

LG do a dual-cycle unit that achieves a high enough temperature for conventional radiators.  Now I think about it, I wonder if it’s possible to do a single compressor high temperature heat pump using a zeotropic mixture as is used for auto cascade refrigeration...

AHSP is not for every property, and no-one is really saying it is.  In a poorly insulated 150 year old house with no easy way to install UFH or oversize rads, it would be a very poor choice.

The house is not poorly insulated. 

So what do you think I should replace my gas boiler with?

In all likelihood, a new gas boiler.  Gas is really cheap, and unless you a) want to take pretty extreme measures to improve your insulation and b) fit oversize rads, then the high grade heat from gas is what you'll need. Gas boilers aren't being withdrawn from sale any time soon - with the state of the UK's housing stock they can't be.

Having just watched an Icelandic crime drama, I remembered they store hot water (geothermal) for the winter when it is used for district heating and domestic hot water (all year). Taking a shower or doing washing up stinks - it's full of hydrogen sulphide.

https://en.m.wikipedia.org/wiki/Perlan

District heating - too socialist for UK?

I think all new developments of flats over a certain size have to use district heating - but it has it's own problems - not so much with the actual heating & hot water - more with the ignorant people who inhabit the flats not realising how all the energy/utilities they use (district heating, electricity, gas - less usual, cold water/waste) is supplied and paid for - this applies to tenants more than owner-occupiers - I deal with billing for some of these developments and I can tell you that there are a lot of people out there who you would not describe as "smart".

To be fair some of the blame is due to site managing agents not disseminating information, and property/letting agents not realising what's going on with district heating so they fail to inform prospective tenants, etc.

I'm not aware of district heating being used in houses in the UK (not saying there aren't any) but who would own the heating plant and therefore supply (and bill) the houses?

Pyrolysis of methane is pretty energy intensive, but producing solid C is attractive, especially if it were not shoved back in the ground but made into something (very) useful like graphene.

Not really anything to add re energy sources but if you are looking at long term investment make sure you've got your energy storage/insulation as good as it can be. Triple glazing, draft proofing, decent loft insulation etc.  Probably the best way to spend your cash. 

This is an interesting page to bookmark. Live U.K. energy usage dashboard. 
 

https://www.gridwatch.templar.co.uk

Yes, there's probably a less energy intensive way of disposing of the carbon.  Polymer production as Richard J said would probably pay for itself, just so long as the plastics aren't burnt.  I can see a point in 30 years where we use energy to pull net carbon out of the atmosphere one way or another.  

You can also google "prevailing view" to see the state of the gas transmission system. The units in mcm mean millions of cubic metres (of gas at STP). 1mcm is approx. 720 tons of gas.