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Gas or electric?

Discussion in 'Building' started by wilco88, 6 Jan 2021.

  1. IT Minion

    IT Minion

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    So as long as there's enough wind supply it works out better. Ignoring nuclear power and biomass etc.

    Heating with electricity is at least 100% efficient, heat pumps can get to 400% efficient after all.
     
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  3. Harry Bloomfield

    Harry Bloomfield

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    From the tiny amount of research I have read, it costs very little. It arrives as a liquid and mostly expansion to a gas is enough to propel it to where it is consumed. Happy to be corrected.
     
  4. Harry Bloomfield

    Harry Bloomfield

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    I have read 200% efficient, efficiency falls the lower the outdoor ambient becomes. The colder it is outside, the more heat input is actually needed.
     
  5. IT Minion

    IT Minion

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    I've seen claims of up to a COP of 5, but in bad weather and poor systems as low as 2. Which is 200% - 500%. (or is it 300% - 600%?)

    I haven't got a clue, but liquids need to be pumped and that isn't free.
     
  6. Captain Nemesis

    Captain Nemesis

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    That generic issue applies to all power generation.

    Nuclear is not "zero-carbon". Nor is wind power. Hydro doesnt always look too good if you look at emissions from reservoirs.
     
  7. Harry Bloomfield

    Harry Bloomfield

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    Yep, they are very short-sighted in what they include in the carbon count. Building a windmill involves carbon created to produce the massive amount of steel, the transport to site, erection - then the on going cost of maintaining them in widely scattered places, far from where people live or out at sea. Eventually they need to be dismantled and replaced with another unit, at great expense.

    Conventional generation is in power stations, in easily accessible locations for maintenance, much more easily maintained and unlike wind, they are not subject to the vagaries of the weather being just right for generation.
     
  8. mikeey84

    mikeey84

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    Well, as long as the
    I'm pretty sure most respected researchers will include those factors.

    These are low carbon electricity generation methods, not carbon free.

    Life cycle analysis of carbon footprints is a pretty mature field.

    Figures I have seen look like 11g per kwh for wind vs 400+ for gas. A pretty sizeable difference.
     
  9. endecotp

    endecotp

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    I thoroughly recommend the late David MacKay’s book, “Sustainable Energy - Without The Hot Air”, to anyone remotely interested in this subject. It’s available online free:

    https://www.withouthotair.com/

    David MacKay was a Cambridge academic. The book is full of pragmatic “let’s do a back-of-the-envelope calculation to see if that makes any sense” observations which I think would appeal to DIYnot readers. He died of cancer a few years ago: https://www.theguardian.com/environment/2016/apr/18/sir-david-mackay-obituary

    On this particular subject, see chapter 21 of the book. Here’s a quote:

    Let me spell this out. Heat pumps are superior in efficiency to condens-
    ing boilers, even if the heat pumps are powered by electricity from a
    power station burning natural gas. If you want to heat lots of buildings
    using natural gas, you could install condensing boilers, which are “90% ef-
    ficient,” or you could send the same gas to a new gas power station making
    electricity and install electricity-powered heat pumps in all the buildings;
    the second solution’s efficiency would be somewhere between 140% and
    185%.​
     
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  11. Captain Nemesis

    Captain Nemesis

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    How do (if they do??) CHP boilers affect calculations?
     
  12. endecotp

    endecotp

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    There’s a whole section on CHP in the book.
     
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  13. StephenOak

    StephenOak

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    Well, RL intervened and so I have only just done that! I did figures for all the sources for 2020 as that was hardly any more work.

    I have omitted the interconnectors (five external & two internal) and the small Other category. Notes on definitions can be found at https://gridwatch.org.uk/download.php by hovering over the white buttons.

    Gridwatch2020.png

    Adding up coal, gas & biomass, 47% was from CO2 emitting sources, all of which I would lump together as fossil fuels. Biomass is regarded as renewable but I don't think that is really true. If it is wood waste from quick growing trees that are planted for timber. toilet paper, etc then it is pretty close to being renewable. However (certainly AFAIUI) the wood chip at Drax is from mature (100 year old?) trees and they will not be replaced much if at all before the end of this century.

    NB, I suggested that biomass supplies >6% and the actual figure is >7%.

    I don't see that happening (gas disappearing) unless there is a fundamental change in technology or policy. It is not just that gas supplies c. twice as much as wind but that it (and coal) are reliable and wind is not.
    Wind delivers c. 30% of the nameplate figure, so a maximum wind figure of 48% means there is enough wind installed to theoretically supply well over 100% of our needs. If it was supplying it would be used as wind is given priority, but it only supplied more than 40% on 20 days whereas gas did that on 154 days. Gas supplied more than 50%/60% on 68/11 days, whereas the figures for wind are 0 & 0.

    "batteries for daily variations"
    I'm really not sure what you mean there. Batteries store enough power for some minutes and are used to cover for failing RE until a gas plant can be started. The largest battery in the world (might have been surpassed v. recently) is in South Australia and theoretically could supply the SA grid for less than 10 minutes.

    "Add in liquid air batteries"
    Are any significant ones of them operating commercially? If so what are the real efficiency figures? I have seen figures as low as 25% quoted for these.

    "interconnects"
    While other countries have reliable sources (e.g. nuclear in France) they will be useful but if wind is the main source for many countries then a static high-pressure system could render then useless.

    "flow batteries"
    I seem to recall that there is a significant problem with them. It might be that the discharge rate is not very high.

    Looking through the figures, there are plenty of instances of wind supplying less than 10% for 3, 4, 5, 6 or more days on the trot. Compared to an average of 22%, you are talking about having available (from storage) a minimum of 100% of a days consumption (15% shortfall times 7 = 105%) which (if I have calculated this correctly) is c. 850 GWh. And that is available, no storage is close to 100% efficient so quite a bit more than 850GWh needs to be put in.

    So in winter when most heating is needed these are at their least efficient.

    Oh sure. It is just, as I said above, Drax is supposed to be green.

    I have no idea if this is true but I have read that wind turbine contracts do not require their owners to remediate the sites afterwards.
     
  14. IT Minion

    IT Minion

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    It has been surpassed. Hornsdale is a mere 194MWh, your numbers are probably low since It was so successful they increased it by 50%. The Gateway battery is 250MWh (active now), Vistra Moss is 1.6GWh (due Q2), Ravenswood is 2.5GWh (due Q1).

    In the next few years the batteries will be undercutting leaker plants and bridging the gap until slower gas turbines can spin up. They've already undercut the business case for peaked plants entirely as they're too expensive and slow to make sense. As the batteries continue to get cheaper and bigger they'll force out more of the gas plants as they soak up the nuclear power overnight from our nukes and surplus wind.

    The gas plants will end up needing to be subsidised to keep the reserve for when the wind doesn't blow. I can live with firing up a gas plant for a week once a year, we'll just have to redesign them to operate in an economic manner.

    By the way, saying they could only carry the entire grid for X minutes is absurd, the quickest discharging grid batteries can discharge in an hour, no faster. Or they explode. Just like trying to release all the power contained in a nuclear power reactor at once, albeit with less fallout.

    Not in operation yet, under construction. The economics seem to make sense but I don't own a LAES company. The advantage is that you can keep that power for a long time at minimal cost.

    That's not a problem, that's a feature. Flow batteries provide potential for economic storage for greater than 8 hours. In other words to provide protection for low renewable supply.

    Also, this is all assuming business as usual, in a market economy the cost of power will rise as the supply contracts. In turn the amount actually used will decrease. That happens now, although most don't see it, something similar will inevitably continue into the wonderful new world of not destroying the environment.
     
    Last edited: 17 Jan 2021
  15. StephenOak

    StephenOak

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    Not really sure what you mean. That is already what they do.

    Really? Any numbers to back that up? CCGT plants are close to being the cheapest source of electricity. Batteries are expensive, only store spare power and return maybe 90% of what goes into them. The figures I have seen, albeit not for a couple of years, show them as being c. 10 times as expensive as gas.

    The primary reason that people use them is that a grid with a significant %age of RE is inherently unreliable. To cope with that (without interruptions) you need some sort of storage or a gas plant spinning but not generating. The latter is literally wasted money so that is the only way that batteries 'save' money.

    And, AFAIUI, none have been built in this country. If they were so cheap surely they could displace some of the less efficient sources now. But last year we used OOGT (half as efficient as CCGT?) on 363 days and even coal on 185 days.

    You have that the wrong way round. As batteries get bigger they get more expensive. Economies of scale may help a bit (so price per MWh is less) but I cannot see any reason to think it will change dramatically, lithium extraction is not cheap.

    Except the amount of nuclear power available is expected to go down. And surplus wing cannot be relied upon. 121 days last year when it was less than 15% of demand, 73 days less than 10%. When that happens for several days in a row there will be demand on batteries but no replenishment

    Not at all. It is just an indication that these batteries are anything but grid-scale.

    This is why I asked for real world figures. If you really do get out only 25% of what goes in then I doubt that many will be built.

    How does that compare to storing the equivalent amount of energy as natural gas?

    Except low discharge rates mean that you need a huge number of them to supply power at the rate needed. That in turn puts up the capital cost. Spending, say, £10 billion on power plants that work 90+% of the time makes a lot more sense than spending that on something that only works 10% of the time and only supplies 10% as much power.

    Not really relevant, in a market economy no power company would buy wind or solar.

    And old people have to choose between heating & eating.

    If we wanted to protect the environment we would never have built any wind farms and would have built a load of nuclear plants.
     
  16. mikeey84

    mikeey84

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    My understanding of the issue here is that reactor design hasnt really moved on, and still produce lots of waste.

    I know there are a number of programmes globally looking to address this with safer, low waste reactor designs.

    Happy to be corrected...
     
  17. IT Minion

    IT Minion

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    Actually you've got that the wrong way around, as batteries get cheaper they also can be used in larger installations. Cheaper leads to bigger. The price of batteries dropped by 87% in 2010-2020, they dropped 13% last year. They will continue to drop in price.

    Also, Lithium is cheap. It costs around 10 times what methane does per kg. But methane you burn once and lithium you use for 20 years then recycle it.

    Not quite, instant grid balancing is provided by inertia, in recent years it has been suggested that plants would run just to do it but it's a niche market. For short term peaks you have the incredibly expensive, polluting peaker plants that can spin up in minutes rather than hours or days like the big cheap gas plants.

    You don't need artificial inertia when you've got a decent volume of batteries, even if it's only enough to power the grid for a matter of minutes :rolleyes:, Hornsdale has demonstrated that already. Short term stability isn't going to be an issue for much longer.

    And the reason they're used at the moment is to make money, Hornsdale has done better than it was predicted for both it's investors and the SA public.

    Why don't we have any in the UK? Good question, apparently we've got around a GW of installed grid batteries, but very few big ones. The first >100MW one I've heard of for the UK is due to go live in 2024, that's a decent 320MW/640MWh one though.
     
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