Reposted from NOT A LOT OF PEOPLE KNOW THAT
JANUARY 9, 2021
Guest Post By Joe Public
Drax’s latest Quarterly Bulletin has a section on storing excess wind power:
I have picked out these particular claims for observation:
1. Why no mention of those electricity storage systems’ capacity and discharge rates? Britain’s 4x pumped hydro stations have a total storage capacity of 26.7 GWh and discharge rate of 2.86GW.
http://www.withouthotair.com/c26/page_191.shtml
2. “…28 TWh of storage … comparable to the total natural gas storage the UK has in the form of underground salt caverns.”
2.1 Not quite correct. It is comparable to the total natural gas storage Gt Britain has in the form of underground salt caverns plus LNG storage facilities. We have ~18,000GWh of conventional storage plus ~13,000GWh of LNG storage.
https://mip-prd-web.azurewebsites.net/DailySummaryReport
2.2 The Gross Calorific Value of hydrogen is just 3.3kWh/m^3 vs approx 11.1kWh/m^3 for Nat Gas, so low energy-density H2 has less than 30% the energy content of Nat Gas per unit volume at STP.
Consequently our energy storage capacity for hydrogen is not 28TWh, but just 8.4TWh at the same pressures.
3. “….Perhaps some of these wind farms should produce something other than electricity. Electrolysers can be used to turn electricity and water into hydrogen. The excess electricity production in 2030 could be used to make 670 million kg of hydrogen. That would be enough to fill 133 million fuel tanks in fuel cell vehicles such as the Toyota Mirai, or to heat nearly 2 million homes.”
3.1 It’s disappointing to see the deliberate obfuscation caused by mixing units – (the weight of hydrogen produced) denying readers the opportunity to easily compare relative figures. Why did the report’s authors not continue to use electricity-industry units of TWh/GWh they’ve already used in their article?
1 kg of hydrogen contains 33.33 kWh of usable energy.
3.2 The “37 TWh of excess electricity” production in 2030 could be used to make 670 million kg of hydrogen.”
So the “37 TWh of excess electricity” produces 670,000,000 kg hydrogen. But that mass of hydrogen has only 22.3 TWh of usable energy. i.e. it takes 66% more electrical energy input to make one unit of energy available via hydrogen output.
3.3 We’re told “…. (670,000 tonnes of H2) would be enough to fill 133 million fuel tanks in fuel cell vehicles…”
No mention is made of the energy needed to compress low energy-density H2 into those 133 million fuel tanks.
Approx 4kWh of energy would needed to compress 1 kg (33.3kWh) of H2 to 700bar.
https://www.hydrogen.energy.gov/pdfs/9013_energy_requirements_for_hydrogen_gas_compression.pdf
This means (4/33.3) 12% of the available “37 TWh of excess electricity” is needed simply to compress the H2 into those 133 million fuel tanks. That then means that just 33TWh available to produce the H2, so only (22.3 TWh x 88% =) 19.6TWh of useable H2 is available when stored at 700bar.
Consequently, 37TWh of initial electrical energy input results in just 19.6TWh of hydrogen being available at the input of the vehicles’ fuel cells.
1.89 units of energy input to obtain 1 unit of energy into the fuel cell.
The fuel cell is then only 40% – 60% electrically efficient. This means end-to-end process efficiency requires approx 3.78 units of energy input to obtain 1 unit of energy OUTPUT from the fuel cell.
https://www.energy.gov/sites/prod/files/2015/11/f27/fcto_fuel_cells_fact_sheet.pdf
4. The authors consider “Hydrogen could potentially be hauled to shore at lower cost, piggy backing off the existing oil and gas pipelines, which will see limited use as the North Sea fields start to wind down.” yet don’t explain what they consider to be ‘piggy-backing’.
4.1 Do they consider it to be feasible to inject hydrogen into an operational oil pipeline? Do they realise that natural gas imports have to comply with National Grid’s strict quality-control standards that hydrogen doesn’t meet?
https://www.nationalgrid.com/uk/gas-transmission/data-and-operations/quality
4.2 Regarding steel pipelines – both those to be ‘piggy-backed’ undersea, and on land – the authors might not be aware of hydrogen’s chemical effect:
“Conversion of the UK gas system to transport hydrogen” explains:
“At ambient temperature and pressures below 100 bar, the principal integrity concern for high-strength steel is hydrogen embrittlement. Hydrogen will diffuse into any surface flaws that occur due to material defects, construction defects or corrosion, resulting in a loss of ductility, increased crack growth or initiation of new cracks. These will ultimately lead to material failure. Higher pressures are thought to increase the likelihood of material failure although no threshold value has been defined independently of other factors …”
https://www.sciencedirect.com/science/article/pii/S0360319913006800
Paul’s Additional Comments.
- Their calculation that we need 1000 times more storage than we currently have sums up why storage can never be the answer to long term intermittency ( as opposed to intra-day needs), particularly since pumped storage accounts for about 95% of current storage, something which cannot be easily increased.
- These projections are based on 40 GW of offshore wind, so the problem of surpluses will become much more acute as more wind capacity is added later.
- The surplus wind power, 37 TWh, equates to about a quarter of total wind power. If this excess had to be thrown away, it would effectively increase the costs of wind power by a third.
- As Joe rightly points out, the capacity of salt caverns is not 28 TWh, as far as hydrogen is concerned. It is less than 8 TWh, meaning that most of the surplus cannot electricity cannot converted to hydrogen and stored.
- Claims of enough hydrogen to fill 133m fuel tanks, would imply maybe 3 million hydrogen cars. In reality, there are unlikely to be more than a few thousand on the road in 2030, and little prospect of many more in 2050. There may be a market for fuel cells in lorries and buses, but that will in all likelihood be decades away. (Apart from anything else, where will cars and lorries get their hydrogen from in winter, when there is no surplus wind power?)
- It is good to see they confirm that when wind power is in surplus here, it will also be on the continent, and equally so when wind power is low.
But I’ll leave the final comment to Drax!
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A big problem with the Drax analysis is that it fails to account for the intermittency and duration curve of surplus wind production.
It is easy to see that the instantaneous amount of surplus varies as the wind strengthens and weakens, and as the level of demand changes. Thus overnight in the small hours when demand is low you are likely to see the highest surpluses – but only when it is also particularly windy. But you will also see much lower surpluses, and also plenty of nights with no surplus at all. As the level of wind capacity installed increases, surpluses will also start to appear during the day at weekends, again when it is windy. They will tend to be smaller, but the overnight surpluses will be come larger because of the extra capacity. Yet still most of the time there will be no surplus at all, which means that any power used for electrolysis has to be replaced by other backup during those times – backup that will become increasingly expensive as it hours of use reduce. Of course, Drax do partly acknowledge that in reality in these circumstances electrolysis would be halted as completely uneconomic.
But that still leaves a problem: to utilise the surpluses you must have the instantaneous capacity to do so (and the ability to feed it via a grid beefed up for the purpose – another layer of cost). Now, a record surplus from a windy night is a rare event, occurring perhaps 1% of the hours of the year. You are not going to build capacity in order to capture the full extent of that surplus, remaining 99% unused. In fact, you are probably not going to build capacity that doesn’t achieve a rather higher rate of utilisation – say at least 20%, which would normally be way below what would make economic sense for plant that operates at its best in continuous operation.
I have produced a series of surplus duration curves for different levels of wind capacity on top of an assumed baseload of “nuclear” that is largely there to provide inertia (National Grid have recently announced they are suggesting that they should maintain a minimum of 140GVAs in response to the blackout of August 9th 2019, where inadequate inertia contributed to the problems), based on hourly demand and wind generation data, scaled up to reflect different additional capacities. I expressed the time dimension in percent of a year, or equivalently capacity factor for the electrolysis plant. When I did this, the installed capacity was about 22GW, so the factor multiples are relative to that level. Adding 40GW of offshore wind takes us roughly to the Factor 3 level.
https://datawrapper.dwcdn.net/jpImX/2/
If we read off the maximum amount of capacity that could be sure of 20% utilisation, it’s about 4GW. But none of it gets much more than 25% utilisation, which means the average plant utilisation is about 22.5%, or about 0.9GW, which works out to less than 8TWh a year – and that is as input to the process. The rest of the surplus is still wasted.
Hydrogen is a road to nowhere.
With some deadly and expensive accidents on the way.
You could much easier and more cheaply resolve the problem. Start an education program , like a detoxifying program for the brainwashed population. Explain how the global warming hysteria has been grossly exaggerated and that renewables just won’t cut it. Explain that the transition being forced upon people will be extremely costly and make the electricity supply much less reliable. Then you can create a huge competitive advantage helping local industry and creating jobs. It’s the false premise upon which the policies are based which is the problem. What needs to be explained is that Renewables is a solution being pushed by a global elite that’s looking for a problem to solve and because they didn’t have one they made up global warming.
…670 million kg of hydrogen…would be enough to fill 133 million fuel tanks in fuel cell vehicles…
What? 5 Kg of hydrogen per tank? Are they joking?
Just like an EV, plans are you’ll be range limited!
The UK site Gridwatch provides a download of hourly figures of electricity demand and contributions from the various sources. A summary of wind contributions for 2020 (up to end Nov – Dec not available yet).
Average wind contribution – 22% of demand
Minimum contribution – 0.4% on one hour during the year
Max contribution – 61%
Sorting the table from the lowest – 10% of the time, the contribution is less than 5.2%; 20% of the time, less than 8.3%; 30% of the time, less than 12%.
So, if offshore capacity is increased 13.5 to 40GW by 2030 and assuming that onshore increases from 10.5 to 27.5GW (some plans exist), then capacity will increase by a factor of three. So the minimum will now be 1.2%, 10% = 15.6%, 20% = 25% and 30% = 36%.
So, for a third of the time, wind will account for less than 36%. (Demand is due to grow by 2030, of course, so the numbers will be less than this by some way.) All coal will be gone by then, most nuclear still (we may have some new nuclear on the drawing boards). Stuffed.