Recently, various studies and memes express a peculiar distortion of reality, heavily supported by oil and gas industry lobbying and PR groups. It is claimed that gas pipelines carry much more energy and much more cheaply than high voltage direct current (HVDC) transmission.
To be clear, this does indeed apply under specific circumstances. In any real decarbonized world, this is simply completely untrue. What are these specific circumstances? You need an existing pipeline between the existing concentrated supply of natural gas and the energy demand market that uses that natural gas. In other words, if the world doesn’t need to change at all, then the movement of molecules makes a lot of sense. Unfortunately, it doesn’t stand up to the slightest scrutiny.
Authors of the articles — Saadi et al. in 2018 and deSantis et al. in 2021 — they seem to have their hearts in the right places, they’re just drawing system boundaries around their studies in such an arbitrary way that leads to misleading results. Saadi et al. they are probably more useful and less easy to distort, but they still have problems. And these misleading results are being amplified by the same organizations that have been amplifying climate misinformation and solutions for decades.
Let’s break down the problem.
First, I mentioned system boundaries. Both studies assume a 1,000-mile power transmission distance and are limited to the movement of energy over that distance as gas, liquid, or electricity. For natural gas flowing through pipelines from a natural gas extraction operation, this is a reasonable choice. But it breaks down quickly for hydrogen vs electricity. There are no natural reserves of hydrogen to mine unless you make it from natural gas or coal, and the people who own the gas reserves and the pipelines that lead from them really want to do that.
But the comparison with HVDC immediately becomes problematic. Both articles assume that there is a concentrated source of hydrogen to be introduced into the pipeline. However, producing green hydrogen at a cost of just under $1.00 per kg, which is only twice the price of natural gas per unit of energy before the surge in the last year, requires $0.01 per kWh of electricity delivered 24/7/365 to dirt cheap electrolysers on a large industrial scale. hydrogen production facilities that do not exist. To achieve steady electricity 24/7/365, the facility needs to build a lot of new wind and solar farms, build a lot of transmission from renewables to the facility, and build storage on top of that.
In other words, all the HVDC needed to move power from renewable sources to power demand centers would be needed, as well as hydrogen pipelines. It is systemically much cheaper to cut the middle man out of the hydrogen pipeline, something the studies completely miss.
Second, that hydrogen still won’t be cheap. While my estimate is that the massive increase in renewables, transmission and storage will lead to electricity prices of roughly $0.02 per kWh in 2020 dollars by 2100 or so, that’s pretty much the end game with a fully decarbonized grid. And it’s still twice as expensive per kWh as the sub-$1/kg estimates call for, so energy per unit of energy is 4 times more expensive than natural gas. In the real world of the next two decades, fixed 24/7/365 electricity will be much closer to $0.10 per kWh, or ten times the $1 per kg requirement.
Third, there is another issue, exergy. DeSantis paper at least acknowledges this, but then dismisses it. Exergy is the amount of useful work that can be done by an energy-carrying substance, be it electricity, hydrogen, or gas. Electricity has a very high exergy. If you have a MWh or 3,600 megajoules or 3.4 mmbtu of electricity, then you have the ability to work MWh. But if you use the same units for natural gas or hydrogen, it breaks down quickly.
The largest use of natural gas is for electricity generation, about 40%. The new hydrogen production and storage facility in Utah will combine gas generators initially with natural gas, then a mixture of natural gas and hydrogen, and sometime in the mythical future, hydrogen alone. But combined cycle gas generators are about 50% efficient at converting natural gas into electricity. Hydrogen fuel cells are about 60% efficient at converting hydrogen into electricity. That 3,600 megajoules, or 3.4 mmbtu of gas, in other words, equates to only about 0.5 to 0.6 MWh in the real world.
Fourth, it is worth pointing out that when you produce green hydrogen, you waste about 20% of the energy in electricity. We’re going to make it a bit more efficient, but it’s small and incremental steps with a likely hard ceiling of 86% efficiency. So we throw away high-exergy electricity when we make green hydrogen, and we throw away 40% to 50% of the energy in the hydrogen when we convert it back to high-exergy electricity that we can use for something.
Finally, there is the transmission itself. HVDC lines from wind and solar farms to demand centers have energy losses of 3.5% per 600 miles or less, while hydrogen requires three times more energy to compress and pipe than natural gas. Even that energy has to come from somewhere.
By drawing the system boundaries narrowly and ignoring exergy, the comparisons become deeply misleading and make it seem like putting hydrogen in the pipeline is pointless when anything else is involved.
And it leads to people like Lion Hirth, PhD, energy economist, and otherwise sensible climate action wink on LinkedIn, posting misguided memes, which led me to write this article. He claimed the following:
“A pipeline (say Nord Stream 1) can transport 540 TWh worth of gas per year. That’s 30 times the power you can put into an HVDC line. Thirty.”
It has a bar chart with no reference to the underlying data, which shows. Nord Stream 1, by the way, is a 4-foot-diameter, 1.6-inch-wall steel pipe that runs about 1,000 miles.
But it falls apart when you start counting. According to the rating above, when you add up all the losses, it doesn’t deliver 540 TWh, it delivers half of that when exergy is taken into account. And when you add up all the extra infrastructure and losses, it throws off a lot more.
The size of the HVDC line is also misleading. It’s not a single strand HVDC that no one would build, but a small HVDC transmission line capable of delivering about 18 TWh per year that was chosen for comparison to make pipeline power look better. For better comparison, the 6,400 MW HVDC link from the Xiangjiaba Dam to Shanghai, China delivers 56 TWh per year with 5% energy losses per 1,000 miles.
Make the pipe energy much smaller and the HVDC line is actually real size, and suddenly it drops by an order of magnitude 30x. And that’s before you build all the HVDC infrastructure to bring solid electricity to the pipe head and build a massive hydrogen factory to make molecules.
All of this is to say that in the future where hydrogen as a molecule is needed – and again this is a declining market, not a growth market as we eliminate most oil refining and reduce our reliance on fossil fuel derived fertilizers – we will produce hydrogen on site with solid, high-energy electricity that also powers the rest of the industrial equipment, not building a massive hydrogen distribution system that is also massively redundant with only moving electrons.
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