Pop the Hydrogen bubble
transitionengineering.org
OK that is a really kick-ass article right there, but I’m going to go on and explain why hydrogen is a really dumb thing for a government to be saying is part of their vision for a national strategy.
EROIDiatomic hydrogen (H2) does not exist except in the sun, or as a short-lived part of catalytic processing such as crude oil cracking or methanol reformation. Thus, it is not a resource. Hydrogen is a manufactured product with energy density at atmospheric pressure of 120 MJ/kg (or 0.012 MJ/lit). It is not anything like extracting and refining a barrel of free energy in the form of crude oil into 0.8 barrels of transport liquid fuels, 0.15 barrels of petrochemicals, and 0.05 barrels of bitumen. In the hydrogen economy, you start with the kg of fuel product (say diesel) you have already got which is not free and which you could use to drive a vehicle without building a new vehicle. You need to generate superheated steam at over 800C which is about twice the temperature as a steam power plant which is very high pressure so needs expensive equipment and you need to use catalysts that can survive this temperature to make it work – and the by product is CO (a poisonous gas). So if you were going to burn diesel to produce that type of steam (4 MJ/kg x 5 for reforming), you could generate power through a steam power plant or directly through a diesel engine, then you would have electricity to use. But our story is that we want a green fuel for vehicles?
It isn’t really clear at this point how to separate the H2 from the other reforming products of excess steam, CO and CO2, but it would definitely require cooling energy to condense the steam and bring the H2 back to room temperature to begin compression for storage in a tank.
Then of course is the compression energy to take the H2 to 700 bar is about 25 MJ/kg.
The embedded energy in the plant to reform and compress diesel into H2 isn’t exactly known because these reformers and compressors are rather specialist or research scale (e.g. don’t exist for the hydrogen economy) but let’s estimate given the types of materials that they are like the Methanex plant, then we get about 2 MJ/kg of H2.
So the energetic profit so far, from what is considered the “most promising route” for getting hydrogen into filling stations for vehicles is:
To Produce 0.07 kg H2 8.4 MJ
Invest 1 kg of Diesel (-45 MJ)
Invest 5 kg superheated steam (-20 MJ)
Invest 25 MJ/kg H2 for compression. (-1.75 MJ)
Invest in cooling and separation (not counted in the calculation but probably at least -10 MJ/kg)
So whereas in the Diesel Fuel System, the investment of 4 MJ of energy returned 80 MJ of fuel (EROI = 80/4 = 20) and some useful other products…
In the Hydrogen Fuel System, the investment of 66.75 MJ of energy returned 8.4 MJ of fuel (EROI = 8.4/66.75 = 0.126) and some toxic by-product CO and as much GHG CO2 after the CO is hopefully combusted as diesel fuel system PLUS the GHG CO2 emissions from the energy input.
EROI is the easiest way to burst the hydrogen bubble.
BUT WHAT ABOUT GREEN HYDROGEN?If you have an idea that GREEN Hydrogen generated from "extra" renewable electricity could work. Then let's do the EROI on that.
First, let's be clear, there is no "unused" or "extra" electricity - that isn't how power grids work. There is spare capacity, but that is designed in for reliability. The grid is using the spare capacity for spinning reserve, for meeting peak loads, and to take up the loads if power plants trip out or are out for maintenance.
We all agree that the BEST energy engineering of solar PV is direct load reduction. This means installing the PV directly on the flat, unobstructed roof of a commercial, educational or industrial facility with large mid day loads that could be partly supplied by the solar. No solar PV goes back into the grid. The grid does not get strained it gets peak demand relief which directly reduces peak capacity margin. Good Good. Thus, if we do our jobs right, and policy incentives don't result in sub-optimal outcomes, then we would not have any "extra" solar PV.
Wind is the renewable resource that is like a bad boyfriend. It randomly gets excited and puts it in whether you want it or not.
Wind definitely has some periods of generation when the demand is already met by other assets in the grid. You can tell how often this happens by looking at the node price data for wind - when the price falls to zero or near zero then probably the wind generation will be spilled. So we don't really know how much wind could be available for electrolysis. What we do know is the electrolysis really should be a steady operation, not intermittent. That is a spanner in the works of the whole story of "when there is extra wind energy..." But let's not let technical feasibility stop us from calculating the EROI.
Wind EROI is about 20. Electrolysis energetic efficiency from electricity to H2 at atmospheric pressure is about 70%. So 1kg of H2 requires 200 MJ of electricity. To produce the 200 MJ of wind energy we have to invest 10 MJ in wind turbines. And we definitely have to compress the H2 to 700 bar at 25 MJ/kg.
To generate 1 kg of H2. 120 MJ
Invest Wind Energy. (-200 MJ)
Invest Wind Production (-10 MJ)
Invest Compression. (-25 MJ)
And the EROI = 120/235 = 0.51 That's a Deal Breaker! Recall EROI must be greater than 10 for it to be an Energy Supply System of Merit
So Green Hydrogen is obviously not an energy production system it is an energy consumption system. The CO2 emissions in this system are from the wind farm construction and compression, so yes much lower than the diesel reforming. But the whole thing is not a energy supply technology that can support any kind of an economy. It is a Biophysical Economics Fail.
But if we were going to build the wind turbines anyway, isn't it better to store the extra energy and use it later than to just waste it?
The engineering answer is "No". We don't run the wind turbine when the windspeed is below the cut-in because operating hours are not free, each rotation of the wind turbine incurs maintenance and expends lifetime. So come on - Renewable energy is not free. Think like engineers.
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