We need to store surplus electricity as gas

(The comments underneath this article are particularly interesting. I recommend reading. Chris.)

Whatever renewable energy advocates say, the intermittent nature of solar, wind and marine energy production represents a difficult problem. Although we can adjust electricity demand to match supply to a far greater extent than we do today, the huge expected growth in UK offshore wind power is going to give the electricity grid major problems. When the gales blow, we’ll be dumping power but running short of electricity on cold, still days.

That’s why the recent contract win by ITM Power, the Sheffield hydrogen electrolysis company, is so interesting. ITM is supplying some of its units to a 360 kW hydrogen production plant in Germany that take surplus electricity, convert it into hydrogen and feed the gas into the national gas grid. (Please read the comments for discussion of some of the problems this might cause). In a second stage, hydrogen can be converted to methane, the main constituent of natural gas, and injected into the grid or into storage caverns. The Germans have been quicker to recognise than other countries that the gas network can store far more energy than any other media. Forget batteries, compressed air storage or pumped water: the national gas grid has a capacity several orders of magnitude greater. And the network and its storage sites already exist. No need to spend billions on new facilities. Complete reliability.

The problem

We can see the issue already. When the wind is strong the UK grid sometimes cannot cope with the electricity produced. Wind farms are paid to disconnect. We mustn’t exaggerate the current problem: the amounts are small and paying generators to shut down has long been a feature of all electricity grids. But as the capacity of working wind farms rises from 7 gigawatts now (providing – at peak – about 20- 25% of UK summer night demand) to thirty gigawatts and beyond we know the problem is going to get more and more severe. Electricity is wasted, increasing the long run cost.

And, of course, the reverse situation is also a problem. Cold December weather is often correlated with low wind speeds. Those thirty gigawatts of turbines might be only producing 1 or 2 gigawatts of power at times when electricity is really needed. Fossil fuel power stations will have to work instead. Most of the time these plants will stand ideal, and creating the right incentives to build them is proving one of DECC’s many challenging problems.

Most analysis of renewable energy deployment suggest that the UK and other countries need to invest heavily in energy storage and/or massive increases in the capacity to ship electricity around Europe. At the moment, we have very little storage of any form. The two large ‘pumped hydro’ plants provide a few gigawatts for a few hours. In Germany, the total amount of non-fossil energy that can be quickly converted into electric power is about one twenty fifth of one percent of annual electricity demand.

Some expansion of pumped hydro is possible; I’m told Japanese companies are pumping water up sea cliffs ready to be released when power demand rises. A few more large reservoirs are possible in the UK. But getting to the energy equivalent of more than a day’s supply of electricity is almost impossible to envisage. We could use a 100% electric car fleet to provide power but one German study suggested that this would provide, in total, only about a third of a day’s power. Other battery sources would be astronomically expensive.

Unfortunately, those periods of calm in mid-winter can last weeks or more in the UK, and longer elsewhere. The main potential sources of energy storage are insufficient.

The answer

This is why we need to consider the possible role of the gas grid. In the UK, total gas demand is very approximately 3 times total electricity use. (I’m using rounded figures only here).

Total demand Power source
Electricity 400 TWh
Gas 1100 TWh
   Of which, used for electricity c. 300 TWh

 

Most countries, but not the UK, have maintained substantial gas storage. Gas is bought when cheap, usually in the summer, and put into depleted hydrocarbon reservoirs and other storage reservoirs for use in winter and to meet unexpected needs. German has storage capacity of about 200 TWh. A gas power station is about 60% efficient, meaning that German gas storage could provide the energy to meet about 100 days of continuous UK electricity demand.

In the UK, the malfunctioning energy markets have held back investment in storage and we can only store about 18 days continuous gas use. But sites have been found, and planning permission often granted, to multiply this fourfold.[2] This is enough to overcome all the problems of intermittent renewables.

This, of course, is similar to what the government already intends. New gas-fired capacity will be given payments just for being ready to fire up when the wind stops blowing. The real innovation that the Germans are beginning to explore is to use the gas grid both as a back-up to wind in calm condition AND as storage for energy when the wind is too strong.

This is why the ITM Power contract is so intriguing. Its units will be employed to turn surplus electricity into hydrogen through simple electrolysis, the splitting of water into its components, hydrogen and oxygen. The intention is then to put the hydrogen into the gas grid, mixing it with the methane already there. (I didn’t know this, but it seems that 1 or 2 percent concentrations are safe). This means we’ve potentially got energy storage from surplus wind in the gas grid. At times when wind is over-abundant, and usually this means wholesale electricity is cheap, the wind farm output can be diverted to electrolysis in a process that is about 80% efficient. (This means that 100 kilowatt hours of electricity can be converted into hydrogen that when combusted produces 80 kilowatt hours of heat). We’ve got some storage, and energy that would otherwise have been dumped or sold for less than nothing.

But, you might say, adding 1 or 2 percent hydrogen into the gas grid doesn’t provide enough storage for more than a few days. The logical next step is even more interesting, and just beginning to be explored in the Germany and Austria. Hydrogen can easily be converted to methane using a well-understood process. Find a source of CO2 (not scarce) and hydrogen be turned into conventional natural gas. Except that, in effect, it is ‘renewable’ because it is sourced from water and CO2.

2H2 + CO2 = CH4+O2

Very roughly, this methanation process is also 80% efficient . That is, 100 units of chemical energy in the hydrogen turn into 80 units of chemical energy in methane. Conceivably the lost heat could be reused, possibly in a simple Organic Rankine Cycle (ORC) plant to produce electricity. More about all this here.

The storage process is complete. When the wind is blowing, the surplus electricity gets converted into hydrogen and then methane. The total efficiency is about 64% (80% times 80%).This isn’t great, but the wind farms’ power might otherwise be wasted. And it is not much worse than other conceivable large scale energy storage mechanism.

If the UK wants thirty gigawatts of wind (equal to total UK demand on a summer night), we have to find a way to enable electricity to gas conversion to happen at a very large scale. It seems to me that there is no alternative if we want to use renewables, decarbonise the power supply and keep the lights on as well. Electricity-to-gas hugely increases the capacity of the electricity grid to cope with intermittent renewables and provides ‘zero-carbon’ gas to power stations in times of low wind. Perhaps critically, it also helps stabilise the price of gas and reduces the UK’s increasing dependency on imports. We can engineer the market so that gas-fired power stations can work most of the time on ‘zero-carbon’ methane, reducing the overall cost of renewable power.

Electrolysis and methanation are relatively cheap. I can’t see a good reason not to go down this route. Am I missing something?

 

 

 

 

 

 

http://www.oxfordenergy.org/wpcms/wp-content/uploads/2011/08/NG-54.pdf

UK storage estimates

http://www.uni-kassel.de/upress/online/frei/978-3-89958-798-2.volltext.frei.pdf

 

 



[1] http://www.itm-power.com/news-item/first-sale-of-power-to-gas-plant-in-germany/

 

  1. Mark Brinkley’s avatar

    It sounds v clever but it still leaves us burning methane as an end product which produces Co2, reversing the reaction we have striven so hard to produce (i.e. CH4 + 2O2 -> CO2 + 2H2O) . Or have I missed something? Using hydrogen to create methane seems a strange way of going about things, esp when hydrogen itself can be burned in a fuel cell in a completely clean way.

  2. Chris Goodall’s avatar

    Mark,

    The CO2 in the gas network would extracted from exhaust streams, so the net result is no increase in CO2 from burning the methane. At least I think this is right.

    Yes, the hydrogen can be used in a fuel cell, but only to generate electricity. Doesn’t solve the storage problem, which is the critical issue.

    Chris

  3. John’s avatar

    At last – intelligent use of over capacity. When are we likely to see a similar scheme up and running in the UK?

  4. Mike Lloyd’s avatar

    I agree with you that this looks worth pursuing further development, particularly using the gas grid for storage.

    I looked up the German reference but it was still sparse on details. I couldn’t see what the actual energy efficiency (or losses) over the whole process were. Neither could I find reference to the chemical reaction efficiencies, i.e. the percentage of required product of the actual reaction. Whilst, the starting reactants could be fed back in to improve yields, the conversion rate needs to be high or there will be further energy costs.

    BTW, your chemical equation (which isn’t an equation – no equals sign required) does not balance, and is different to the chemical equations quoted in the German reference. I am happier with their chemical equations because the by-product is water which can be easily separated out from the gaseous products.

  5. Chris Goodall’s avatar

    I’ll put up some more links. Apologies about the chemistry. Will change.

  6. Michael Knowles CEng MIMechE’s avatar

    This is all like the air to petrol demonstration.

    Questions –

    i) how come efficiency of electricity to H2 and H2 to CH4 is as high as 64%?

    ii) what is the likley total cost?

    if IT thinks it can do this offshore, sea water contains salt and electrolysis will produce chlorine as well!

    When RWE NPower had the Regenysis 12 MW electrolyte flow storage demo at Didcot they found it was too costly. i.e., much higher than their target figure of £1000/kW It was then sold off to a Canadian firm.

    Mike CEng

  7. Markbrinkley’s avatar

    It seems to get us to a place similar to the burning biomass debate. Yes there may be no new CO2 net, because the source is from combining hydrogen with CO2 to create methane. So the extracted CO2 is later released (less all the inefficiencies involved). But it is inelegant because it still involved releasing CO2 as its end product.

    How much better it would be if we burned the hydrogen directly as a fuel source for transport. Whatever happened to the hydrogen economy, a phrase not much heard these days.

  8. Chris Goodall’s avatar

    Mark,

    This doesn’t stop the hydrogen economy. Far from it. We can still have fuel cells, mobile or static. This is just about storing ‘electricity’ so that wind and solar power can be more easily accommodated on the grid and surpluses are actually used rather than thrown away.

    Chris

  9. Markbrinkley’s avatar

    My point is having gone to the trouble to turn electricity in hydrogen, why then convert it to methane just so you can store it? Why not store the hydrogen and use that as a fuel in its own right?

    Or is it just that its cheap to store in the gas grid? It may be, but it doesn’t seem like a very elegant solution because all its doing is displacing fossil methane, not lowering CO2 emissions. It might score on fuel security, but not on climate mitigation.

  10. Oliver Tickell’s avatar

    The other key technology is conversion of the renewable hydrogen to ammonia. This is a valuable feedstock for the fertiliser industry, currently produced by burning gas or coal, so it has an immediate market. It can also be burnt as a fuel, best done in a mixture with hydrocarbons as it is hard to ignite on its own. It has the advantage over H2 that it is much more compressible and easily and more safely stored.

  11. Markbrinkley’s avatar

    Lets face it, they are using wind power (part of the solution) to create methane (part of the problem). The more you think about it, the more bizarre it seems.

  12. Tom’s avatar

    Mark,

    But even using the hydrogen directly and not converting it into methane, just displaces fossil methane. Both have no impact on the climate. The methane converted from the hydrogen is simply releasing CO2 that was already in the atmosphere, so no net effect on the climate.

    I see your point that burning the hydrogen directly would be more efficient than converting it into methane and then burning, but I think Chris’ point is that the efficiency losses are outweighed by the scale of the energy storage potential if it is converted to methane so we can use the existing gas grid.

  13. Douglas Haigh fidhe’s avatar

    existing power stations have large amounts of land around them, use it to site wind turbines, electrolysers and storage vessels. Then I’m sure our engineers could manage to convert the gas or oil burners to burn hydrogen to raise the steam required to drive the turbines. It may not be super efficient but it is a hell of a lot better than what the government are forcing Drax to do in East Yorkshire! And burning Hydrogen only produces water vapour as a product of combustion.
    We all know that water electrolysis is not cost effective, but if the energy input is free what does it matter?

  14. Michael Knowles CEng MIMechE’s avatar

    Douglas – re your ‘We all know that water electrolysis is not cost effective, but if the energy input is free what does it matter?’ The energy input is not free it costs anywhere from £97/MWh for onshore wind to£148/MWh for for R1 & 2 offshore wind and £160/MWh solar pv 2 to 4 times the current wholesale cost of generation. Or even if you don’t like it Drax co-fired biomass at £75/MWh. The foregoing based on the Renewable Obligation payments 1ROC; 2ROCs and 0.5ROC respectively plus the wholesale cost of generation last year £44/MWh average for the year.

    EDF looks like getting £95/MWh for Hinkley C.

    This is all La La Land energy.

  15. Dominic Hofstetter’s avatar

    Hi All,

    I would like to add a few comments from the perspective of a power-to-gas technology developer (disclosure: my view is biased).

    Using the natural gas grid as a storage buffer makes sense for a number of reasons. First and foremost, the gas grid has a practically unlimited storage capacity. Whilst pumped hydro stations, compressed air storage facilities, and batteries reach their storage capacity after a few hours (and have to discharge before they can charge again), a power-to-gas facility can “charge” during hours and days at a time without ever having to discharge. Second, only power-to-gas offers the ability to provide seasonal storage. In the UK, the load factor of wind turbines in January (40%) is about double that of July and August (20%; Source: Sinden, in press). Shifting some of that wind energy from the winter months to the summer months smoothens the seasonal supply pattern. Third, only power-to-gas allows for a complete dissociation of charging/discharging in terms of geography and power rating. Not only can you transport energy from the wind-rich North to the energy-hungry South, but you can also defer investment in new electricity transmission lines. And finally, by converting electricity into methane, the versatility of wind and marine power is increased, as the methane can be used in long-range transportation (CNG trucks) or industrial processes.

    I would also like to comment on a few specific issues raised:

    - The efficiency chain can be approximated as such: electrolysis 75-80% x methanation ~82%. The methanation efficiency of 82% is obtained by dividing the HHV of a molecule of CH4 by the sum of the HHV of 4 molecules of H2. Some processes (e.g., ours) operate very close to the 82%. Also bear in mind that both electrolysis and methanation produce heat that can be harnessed and used in district heating grids or industrial processes, which further increases the energy efficiency-

    - The gas produced is in fact renewable and it has the same carbon footprint as biogas. Think about power-to-gas as “accelerated photosynthesis”. Instead of waiting for atmospheric carbon to be bound in biomass (which is then digested anaerobically to produce biogas), power-to-gas captures the CO2 molecule at the smoke stack before it reaches the atmosphere. Also bear in mind that as a society we won’t have reduce our carbon emissions to zero, as the Earth has an inherent CO2 absorption capacity and we just need to ensure we keep a balance.

    - The reasons why direct hydrogen injection can be problematic are manifold: risk of leakage, risk of pipeline embrittlement, end-use appliances are very sensitive to heat value variations and flame properties (which change with H2 injection), 1/3 energy density of methane (you can get less in the grid), etc. Slim (2006) provides a good overview. That said, hydrogen injection regulations are under review in many countries.

    Best,
    Dominic

  16. Tom’s avatar

    Re:Michael Knowles
    It is almost free because this discussion is not about using all wind/renewable generated electricity to create hydrogen/methane for the grid, it is about using the wasted or dumped electricity that is generated when it is not needed. In theory, all you would have to pay for this electricity is what is currently paid to generators to disconnect from the grid when there is oversupply.

  17. J. M. Korhonen’s avatar

    Excellent news and valuable commentary, particularly from Dominic – very nice to hear from An Actual Expert :).

    One problem I’ve rarely seen discussed with energy storage is that unless backed with right politics, it may not be the savior of renewable energy it’s often made to be. Remember that there’s also a range of power plants and their owners who would benefit enormously from being able to shift production: coal-fired (and nuclear) baseload plants.

    If energy storage is affordable, it also greatly improves the competitiveness of additional baseload plants. As (in particular) coal power is still very much cheaper than renewable energy, I see a great danger in that what renewables gain from storage is offset by what is gained by coal.

    Cheap storage also means that nuclear would become quite attractive: if one could cheaply store excess electricity into methane, the technically (though not politically) simplest way of decarbonising a society would seem to be to build enough nuclear plants and energy storage to do the trick. As an added benefit, cheap, CO2 neutral methane could be used for transport fuel, either directly or after conversion to liquids (e.g. methanol).

    Thus, I see that advances in energy storage mean that we need to redouble our efforts to block the construction of new coal plants and shutting down the existing ones, before coal power producers gain even more power from cheap storage. There also needs to be an alternative to cheap baseload, and the way I see it the only one fitting the CO2 requirement is nuclear.

    I was also about to remark on the problems with pure hydrogen – embrittlement, problems with certain types of seals, sealants and lubrication, and leakage issues (H2 is a very small molecule that has a nasty tendency to go through even rolled steel plates). I haven’t run the numbers nor have seen anybody do it, but I have a nasty suspicion that pure hydrogen-based systems would cost far more and be more energy intensive than methane-based systems, even when considering conversion losses et cetera. But that is covered pretty well in Smil 2006, as mentioned.

  18. Dominic Hofstetter’s avatar

    J.M., you are correct in saying that in most countries the market design (i.e., policies) is not yet in place to make storage attractive. This is called the “split incentive” problem and it’s well known and researched. The nature of the problem is not that storage doesn’t create enough value compared to its cost, but that storage facility operators can’t internalize (i.e., capture on their profit & loss statement) enough of that value. For instance, deferral of investment in transmission and distribution lines is a recognized and easily quantifiable benefit of storage. Yet in most countries that benefit is reaped by the rate payers (indirectly through lower costs passed on to them by the TSO/DSO). So the challenge is for policy makers to redesign the market in a way that allows the entity incurring the cost (storage facility owner) to reap the benefits of its technology.

    On your comment regarding potential feedback effects on coal: Like most thermal generators, coal plants have rather long ramp times, typically up to 8 hours. This low degree of dispatchibility means that they are not well suited for intermittent operation. As a result, coal plants are usually run at steady state, and other, more flexible generation assets – such as wind turbines – are shut off instead (so-called “curtailment”). See, for instance: http://uk.reuters.com/article/2012/01/25/uk-britain-wind-cost-idUKTRE80O1LR20120125

    And yes, from a climate change perspective, shutting off nuclear power plants is nonsense. But of course there are many other dimensions to the nuclear debate than just climate (security, inter-generational equity and nuclear waste, true cost of nuclear electricity, etc.). You are, however, correct in pointing out that using nuclear electricity during off-peak hours to produce renewable gas is one way to decarbonize the gas sector.

  19. J. M. Korhonen’s avatar

    Dominic,

    as you say, as of now the slow ramp-up/down of coal plants makes them poorly suited for intermittent operation (although newer plants, such as those built in Germany, are somewhat better in this regard). But that’s precisely the issue I’m trying to raise awareness of: if large-scale energy storage becomes cheap – as it should – then, unless backed with right policies i.e. ones that make burning difficult and/or costly, these coal plants become much more competitive and may very well lengthen our dependence on coal.

    A real danger is if the plants + energy storage become so competitive that it’s financially attractive to build them even in excess of baseload requirements; in my mind, there is little doubt that without markedly higher-than-current carbon prices such investment would be easily cheaper than any combination of storage and renewables. The worst case in my mind is probably an energy storage breakthrough under current business as usual policies: financial logic would then dictate that renewables would remain niche players while major earnings are made by burning cheap lignite and storing the energy for periods of high demand. The results to health and environment are ghastly to contemplate.

    Even if renewables achieve high penetrations and baseload becomes an outdated concept, as many seem ready to predict, cheap storage will still make fossil fuel “baseload” plants useful and – absent strict carbon pricing – competitive, for obvious reasons. Thus, there will be little incentive to run them down, and the danger of fossil fuel lock-in at levels in excess of climate requirements seems to be very real. As it is, we’re already very close to a dangerous and probably irreversible fossil fuel lock-in, with coal even increasing its share of world energy generation, which in itself is growing, year from year.

    I’m not arguing against energy storage, far from it, and methane storage seems to me one of the best ways of doing it after pumped hydro sites are used up. I’m only trying to raise this issue into discussion and perhaps analysis before the fact.

  20. Dominic Hofstetter’s avatar

    Janne,

    A few brief observations:

    - I agree that lock-in is a major problem, not only in Europe but also in Asia (China and India in particular) and the United States.

    - Also bear in mind that a price on carbon isn’t the only policy mechanism to reduce coal consumption. Outright bans (e.g., through the EU’s Large Combustion Plant Directive) as well as binding legal targets for emissions reductions (as stipulated in the National Renewable Energy Action Plans NRAPs) are also working to that effect.

    - In analyzing perverse feedback effects of storage, bear in mind that with growing deployment of storage capacity, the spread between peak prices and off-peak prices starts eroding, as the storage facilities act to increase the supply of electricity during peak hours (and prices in the power market are set by supply and demand). In a theoretical model of the world where storage is essentially free (or at least very cheap), this spread would erode to a level equal to the marginal cost of production (ie, marginal cost of providing a stored unit of energy). The winners in this ‘race to the bottom’ will be the electricity generation technologies with the least marginal cost of production, namely wind, solar, and marine energy.

    Dominic

  21. John Goldsbrough’s avatar

    On the problem of renewable energy intermittency.

    I have calculated the usage capacity factors of some of the items I own that use energy:

    Car 1.9%
    Engine that powers car 0.44%
    Gas Boiler 5.5%
    Kettle 1.4%
    Bicycle 1.1%
    Oven 0.68%
    Toaster 0.15%
    TV 6.3%
    Vacuum cleaner 1.0%

    Why do I own all these things yet use them so little? The answer, of course, is simply convenience. They are sitting there idle, and are ready and waiting for when the I wish to use them.

    No company is going to build a CCGT power plant and run it at a 5.5% capacity factor for the times a windless high pressure moves in.
    But I run my gas boiler at 5.5% so I can have a warm house and hot water when I want.

    I think that we should use this acceptance of households to purchase items that will have low capacity factors as a way to solve the intermittency problem.

    Gas boilers are replaced every 15 years, so replace it with a chp fuel cell. The grid can operate the fuel cell either as Short Term Operating Reserve or as Long Term Operating Reserve. Totally flexible. 23million 1kW chp plants. That’s 23GW for starters, and fits in with biogas and power to gas.

    Replace the ice car with an BEV with fuel cell range extender. Say 10kW per car. 40% of the fleet, at 25% availability and there is another 26GW of operating reserve.

    Add a smart electrolyser (for heat as well as hydrogen) to the house/office, smart battery charging of ev’s, hot water tanks, washing machines and freezers to mop up on windy/sunny days.

    Thanks to nano technology are we seeing a revolution about to take place in the price of batteries, electrolysers, fuel cells, and hydrogen storage? Could we have of tens of millions of smart mini\micro energy storage and generation solutions, with each and every energy user doing their bit to balance the grid?
    It is bringing the systems of companies like Flexitricty from the company scale down to the householder scale.

    La la land? Maybe. Home computers and smart phones were la la land not so many years ago.

  22. Proteos’s avatar

    I do not think that the lack of gas storage capacity in Britain has been caused by a bad market design or bad policy. As a gas producer thanks to the North Sea, Britain had natural gas storage facilities named gas fields. Britain has been a net exporter throughout the 80s and the 90s, I think (and maybe the 2000s). So no need for special storage facilities. The french and german case are very different: they have no gas field worth mentionning now, and have always had a low production capacity. So storage was the natural thing to do.

    On the core subject, the problem of storage facilities is that they have to compete against fossil fuels as you mention. Fossil fuels are essentially the same as dammed lake: a store of energy. So long it’s cheaper to pump gas out of the ground, storage in the form of gas makes no economical sense. And the price of stored gas from renewables sources like wind is severely constrained.

    First, wind is reckoned to have a price of €80/MWh on the mainland, so it must be around £70/MWh in Britain. With a yield of about 2/3, like you mentioned, it puts the price of gas at more than £100/MWh, just with the energy input!
    Second, the facility has to be built and operated: the fixed costs will be incurred on top of the cost of the energy inputs. As wind has a lowish capacity factor (~25-30% in Britain), the storage facility can only expect to run an equivalent of 15% of the year at best, if it must run on wind. It’s fairly low for an industrial facility, and fixed costs will certainly matter here. Even with a baseload source of power available, it does not run that much. The french pumping stations have a capacity factor of only 12-15% (~6TWh for 5GW). So storage is dear.

    The price is so high, that at first, the interest will be to expand the grid to be able to export and import. Britain may have some difficulties here, because it’s an island, but at least, fishes do not stage demonstrations against HV lines.

    And a second point of note: As I have said, pumping stations produce ~6TWh in France, but water heating consumes 17TWh, mainly by night, and running mainly on nuclear power. The issue here for wind is its intermittency: where nuclear power is here every night, it’s not true of wind thus needs larger tanks or a more long term medium of storage. That’s why baseload power can have an edge over wind (and solar for that matter) for storage facilities: it’s entirely predictable.

  23. Steve Dove’s avatar

    Batteries in in our own homes seems a simple solution. Our home is run on a couple of batteries which happen to be charged by solar panels but why not charge batteries from the grid?
    Seems obvious to me and as I have lived here on batteries for five years without ever wishing we were connected to the grid.
    It would help though if technology could reduce the amount of electricity fridges, hair dryers and kettles use.

  24. Paul D’s avatar

    Finding a use for surplus wind power.

    Chris Goodall asks :-
    ‘Electrolysis and methanation are relatively cheap. I can’t see a good reason not to go down this route. Am I missing something?’

    First time that I have read this debate; things have gone a bit quiet over at heat pumps.

    The fundamentals of this appear to be that wind turbines alone could end up supporting the whole grid system on a windy night in summer, with power to spare. What to do with the surplus?

    My first thought is that the interconnector to/from France seems to import continuously. I thought it was built because the 24 hour demand peaks in France and Britain were not coincident and power flows would be two-way. If the marginal price of electricity in the UK falls to zero, would the continentals not like to buy some at a bargain price?

    If the price of electricity is so low in the UK, then can someone turn a profit by electrolysing water and collecting the hydrogen? Up to a concentration limit this can be directly injected into a gas flow in a pipeline. The amount that can be injected depends on the concentration limit and the gas flow. That suggests that small multiple units on multiple pipelines with good steady gas flows would be needed.

    When the concentration limits on all pipelines are reached, then what to do next? Methanate the hydrogen and inject that? Injection of methane would not need a gas flow in the pipe, so any pipeline with stagnant flow but connected to the gas grid would do.

    What I do not get, is why the subject of storage was ever raised. To the extent that the hydrolysis and methanation plants inject, the gas supply from anywhere else can reduce. The injection is never going to reach the levels of the overall supply, surely?

    If anyone can make a profit from the low utilisation factors, but almost free electricity, with hydrogen first and then methane, then good luck to them.

  25. bill watts’s avatar

    As a heating engineer my concern is how to provide heating from renewable electricity that seems to be the only way to get our carbon emissions down.

    The received DECC wisdom is to make use of heat pumps that can give you 2 to 4 kWh of heat for a kWh of electricity [the COP]. However for air source heat pumps the performance goes down as it gets colder and the greatest amount of energy is required. At -10oC you may get 1 to 1.5 units of heat per kWh of electricity. As such you need to have the national generating capacity to deal with this.

    As an illustration the current maximum gas heating load peaks at 300 GW. With an aggressive insulation program you could get this down to say 150 GW. With a COP of 1.5 you would need 100GW of electrical storage or new generation capacity that would be needed for a few days every few years. This compares to our current electrical generation capacity of some 50 GW.

    Meeting this peak at the moment is no problem at all for gas. Methane gas is a marvellous fuel that allows you to store the energy through the year and move it around with little loss and can be used by other energy users such as transport if you compress it. Hydrogen is very elegant but it does need a carbon or two to make it manageable.

    Producing the gas from renewable electricity seems to be a perfect solution to keep the gas infrastructure and decarbonise it. The heat that you get from methane produced in this way would be low – like 0.5 kWh of heat for every kWh of electricity. While this could be improved in time with local fuel cells linked to heat pumps, it would still be lower than a heat pump driven directly.

    However I maintain that the fact that it make better use of our renewable energy assets over the year, and not having to treble the capacity of the electricity grid would make up for it. How much it will cost is another matter but I think that is a bit academic for the next 10 to 20 years while we make hay with shale gas. The main task currently is to reduce the heating loads in our buildings.

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