Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    •  
      CommentAuthorfostertom
    • CommentTimeJun 18th 2020
     
    • CommentAuthorbhommels
    • CommentTimeJun 18th 2020
     
    At around 45% round trip I seem to remember - in same ballpark as other thermodynamic processes.

    It can be higher if the heat or cold from the compression & expansion is needed for something else, like an industrial process. The benefit being that it can be trucked/pumped to where the cooling needs to happen.
    • CommentAuthorLF
    • CommentTimeJun 18th 2020
     
    I had a number of 70% in my head not 45% ... googled it and it seems more like 60% according to this link.
    It is based on established technology from air separation process for making liquid oxygen, nitrogen and argon, so relatively low risk.

    Efficiency can be higher if heat and/or cold can be integrated from other processes.

    https://www.rechargenews.com/transition/liquid-air-storage-offers-cheapest-route-to-24-hour-wind-and-solar/2-1-635666
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    Posted By: bhommelsIt can be higher if the heat or cold from the compression & expansion is needed for something else, like an industrial process.
    The usual trick with this sort of thing is to store the heat from compression (e.g., in a phase-change material) then use that to re-warm the air on expansion. That article doesn't say whether they're doing that though I suspect not at 34p/Wh for what's essentially a prototype plant.
    • CommentAuthorLF
    • CommentTimeJun 18th 2020 edited
     
    Ed - This is not storing the compression heat but it is storing most of the compression energy in the form of liquified air at cryogenic temperatures. This is the stored with low losses until electricity is needed. This liquified air is then expanded and warmed driving the expander and the alternator, recreating electricity.

    Technology is based on very high efficiency heat exchangers and very high efficiency turbo compressors and expanders. The technology is well established it is just reusing it in a different way. I worked in it for 20 years in making oxygen and nitrogen.

    Waste heat from compression is likely low grade not steam and also not continuous so not easy to tie into another process.
    More interesting is linking with vapourising cryogenic LNG free cold would dramatically increase efficiency but how long will LNG be in play though ?
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    Posted By: LFEd - This is not storing the compression heat but it is storing most of the compression energy in the form of liquified air at cryogenic temperatures.
    Yep, understand that. But there have been projects in the US which try to improve the overall efficiency of the system by storing the heat separately.
    •  
      CommentAuthordjh
    • CommentTimeJun 18th 2020
     
    They do say they store both waste heat and waste cold, and that they use waste process heat to generate liquid air.

    See https://www.highviewpower.com/technology/
    •  
      CommentAuthorfostertom
    • CommentTimeJun 18th 2020
     
    Help me get it straight - do the strict Carnot limitations on max theoretical efficiency only apply where there is a mechanical stage in a thermodynamic process? i.e. compressors, turbines etc.

    But not where it's a non-mechanical i.e. chemical or photoelectric etc process e.g. maybe fuel cells?
    What about where food fuel is chemically 'burned' to liberate energy for animal use, a) mechanical for locomotion, pumping air/blood etc, b) for chemical processes, cell building etc? Is useless waste heat always inevitable?
    • CommentAuthorbhommels
    • CommentTimeJun 18th 2020
     
    Posted By: LFI had a number of 70% in my head not 45% ... googled it and it seems more like 60% according to this link.


    It looks like the efficiency can be anything between 25 and 100%, depending on how many bells and whistles you add to the process:
    https://en.wikipedia.org/wiki/Cryogenic_energy_storage
    • CommentAuthorbhommels
    • CommentTimeJun 18th 2020 edited
     
    Posted By: fostertomHelp me get it straight - do the strict Carnot limitations on max theoretical efficiency only apply where there is a mechanical stage in a thermodynamic process? i.e. compressors, turbines etc.

    But not where it's a non-mechanical i.e. chemical or photoelectric etc process e.g. maybe fuel cells?
    What about where food fuel is chemically 'burned' to liberate energy for animal use, a) mechanical for locomotion, pumping air/blood etc, b) for chemical processes, cell building etc? Is useless waste heat always inevitable?


    In thermodynamic cycles generally, the molecules stay intact, i.e. no chemical reactions or such like. It is just the cycling of a medium through thermodynamic states (by compression & expansion and possibly a phase change) by whatever means you fancy.

    In practice there will always be losses since you can fight but can't win against the second law of thermodynamics.
    • CommentAuthorLF
    • CommentTimeJun 18th 2020
     
    In practice there will always be losses since you can fight but can't win against the second law of thermodynamics.</blockquote>

    Agreed, there are losses on shafts, inverter drives, motor losses etc. There are losses on imperfect heat recovery on heat exchanges. You can then add extra processes and heat recovery systems to lower losses and increase insulation levels etc.

    Agree with points above the move that is spent(capital invested) the higher the efficiency and I guess the 60% efficiency is a current sweet spot to get a commercial plant into operation.
  1.  
    +1, and also more generally - you can't make eg an electrical or biochemical process that does better than the Carnot limit at extracting work from a flow of heat.

    But fortunately the Carnot limit applies when heat flows from a hot source to a cold sink and does work. When the air is liquified and later regassified, it only exchanges heat with the atmosphere, there's no separate hot and cold source/sink and no net work is done. You can devise a theoretical cycle that is 100% efficient, though in practice there will be many losses. As was mentioned, any available source of 'free' heat or cold will make the efficiency better.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 18th 2020
     
    Ah - that's the answer Will, thanks.
    • CommentAuthorphiledge
    • CommentTimeJun 18th 2020
     
    If, in the not to distant future, were all going to be heating our houses/water and charging EV's with off peak green electricty, how much surplus is there going to be for this sort of battery? I hope someone has run the figures!
    • CommentAuthorbarney
    • CommentTimeJun 18th 2020
     
    Overall, there won't be much surplus - the whole point of storage is to max out the generation when it's favourable so we can make a demand on it when generation is not so favourable - and that storage is likely to be significant and varied - everything from a lagoon to an EV battery

    Regards

    Barney
    • CommentAuthorEd Davies
    • CommentTimeJun 18th 2020
     
    Replacing electricity generation with renewables is only the beginning. We need to replace other fossil fuel uses too so we should finish up with renewables producing, on average, some 6 to 10 times the current electricity generation.

    E.g., the average European (EU28) uses about 2.8 kW of final energy [¹] but UK electricity production is typically something of the order of 30 GW so roughly 0.5 kW/peep.

    [¹] plus embodied energy in imports from other continents less embodied energy in exports to other continents.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 19th 2020 edited
     
    Posted By: Ed DaviesWe need to replace other fossil fuel uses too so we should finish up with renewables producing, on average, some 6 to 10 times the current electricity generation
    That's assuming that all energy use doesn't get very much more efficient e.g. building insulation, re-use of waste heat from hi-grade processes by a chain of lower grade uses, etc. That's already happening at quite a pace.

    Against that is growth in total of processes, albeit at improved efficiency.

    And the energy use that's hardly got going yet - near-100% recycling of all materials, which will involve breaking chemically lo-grade compounds and 'pumping' them back up (with energy input) to hi-grade virgin feedstock - that will take a lot of energy, but that's OK if renewable, and will largely put an end to new mining/extraction incl all the toxic process chemicals involved.

    Also distilling fresh water from sea water, and breakling atmospheric CO2 into C and O.
    • CommentAuthorEd Davies
    • CommentTimeJun 19th 2020
     
    Agreed, there's lots of scope for reducing energy use, too, to meet the excess over current electricity use somewhere in the middle, perhaps finishing up at 2 or 3 times the current electricity generation. Still, that's a bit hard to quantify so for simple proof-of-concept calculations it's probably more convincing to ignore those reductions and show that it is, at least in principle, possible to duplicate current final energy production with renewables.
    • CommentAuthorLF
    • CommentTimeJun 19th 2020
     
    Do we agree this UK liquid air battery is a good thing?

    It seems good to me, it allows MW of power to be be pumped into grid quickly on the peak times of usage during the day in middle of winter on a windless dark cold late afternoon.
  2.  
    AiUI the liquified air systems are good for storing energy week-to-week. They complement the lithium batteries that store energy hour-to-hour. I don't know what systems will emerge to store energy season-to-season, possibly hydrogen.

    If renewable generation continues to get cheaper quicker than storage does (as has been the case) then it might be more economic to have excess capacity of generators, so there's enough generation to supply most demands even on cloudy calm days. Then on sunny windy days there will be excess energy which might be cheaper to dump than to store! The price would then go negative sometimes and be more volatile than we are used to. That's a complete change of attitude from even a few years ago when the idea of dumping energy seemed ridiculously wasteful.

    The other promising idea is to store up demand instead of storing energy - IE hold back consumption until energy is available - including hourly time-of-use tariffs, but also seasonal demand strategies such as smelting aluminium in cold countries in the summer when electricity will be cheaper.

    I'm not sure if this big change in economics and attitudes could be enacted only by price signals or if some central planning will be required.
    • CommentAuthorbarney
    • CommentTimeJun 19th 2020
     
    A liquid air battery is essentially no more of a "good" thing than simply pumping water back up to an upper reservoir when you have a lot of "spare" energy available - or by freezing or heating some mass as alternatives.

    Regards

    Barney
    •  
      CommentAuthordjh
    • CommentTimeJun 19th 2020
     
    Posted By: barneyA liquid air battery is essentially no more of a "good" thing than simply pumping water back up to an upper reservoir when you have a lot of "spare" energy available - or by freezing or heating some mass as alternatives.

    That's true, but it is possible to build liquid air storage in places where it's difficult to build reservoir storage, and in smaller scale units too. It can be more effective to build storage that uses phase changes, such as this, than those that simply store thermal energy as temperature differences, because the energy density is typically greater. And finally, a system like this one that apparently reuses waste process heat from nearby sites can be more efficient than other systems built remote from such opportunities.

    So I'd say that I think this project does appear to be a "good" thing.
    •  
      CommentAuthordjh
    • CommentTimeJun 19th 2020
     
    Posted By: WillInAberdeenThe price would then go negative sometimes and be more volatile than we are used to.

    Energy too cheap to meter! Now where have I heard that before ???

    seasonal demand strategies such as smelting aluminium in cold countries in the summer when electricity will be cheaper

    One problem with all such seasonal operations is that it effectively increases the cost of capital, making them more difficult to build and operate economically. It would make more sense to place the smelter in a hot (sunny) country and operate it year-round. Or in a country with large hydro resources and again operate year-round.
    • CommentAuthorbarney
    • CommentTimeJun 19th 2020
     
    Wylfa Nuclear station and Anglesey aluminium as an example ?

    Regards

    Barney
    •  
      CommentAuthordjh
    • CommentTimeJun 19th 2020
     
    Posted By: barneyWylfa Nuclear station and Anglesey aluminium as an example ?

    Of what? Sorry Barney, I can't be bothered to think too hard tonight.
  3.  
    Wasn't Barney just answering DJH's question?

    Posted By: djh
    Posted By: WillInAberdeenThe price would then go negative sometimes and be more volatile than we are used to.

    Energy too cheap to meter! Now where have I heard that before ???

    No, negative electricity prices are not the same as cheap or unmetered prices - somebody is still getting paid (the consumer) so it still needs to be metered (what smart meters are for). And the 'more volatile' bit means the occasional low or negative prices are accompanied by spikes to high prices at peak times.

    European electricity prices have gone negative many times the last few years, including before Covid. UK electricity prices have gone negative several times this year. International oil prices went negative briefly this year.

    Electricity prices are not the same as energy prices, the inability of many folks to distinguish between electricity and energy is part of the problem that Ed raised.

    Incidentally, the majority of the worlds aluminium is smelted in China.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press