Various recent studies and memes express a strange distortion of reality, strongly supported by lobbying and PR groups in the oil and gas industry. The claim is that gas pipelines move energy much more cheaply than high-voltage direct current (HVDC) transmission.
To be clear, this is actually true under certain circumstances. In any realistic decarbonized world, it is completely false. What are these specific cases? You need an existing pipeline between the existing concentrated natural gas supply and the energy demand market that uses that natural gas. In other words, if the world doesn’t need to change at all, moving molecules makes a lot of sense. Unfortunately, it does not stand up to the slightest scrutiny.
The authors of the articles — Saadi et al. in 2018 and deSantis et al. In 2021 – their hearts seem to be in the right places, they simply draw system boundaries around their research in ways that lead to the wrong conclusions. Saadi et al. it’s probably more useful and less easy to distort, but it still has its challenges. And these false conclusions are fueled by the same organizations that have fueled climate and solution disinformation for decades.
Let’s break the problem down.
First, I referred to system boundaries. Both studies assume a power transmission distance of 1,000 miles and limit energy to moving over that distance as gas, liquid, or electricity. For natural gas flowing through a pipeline from a natural gas extraction operation, this is a reasonable choice. But it breaks down rapidly for hydrogen and electricity. Unless you get it from natural gas or coal, there are no natural reserves of hydrogen to produce, and of course the people who own the gas reserves and the pipelines that run from them want to do so.
But comparing this to HVDC immediately becomes problematic. Both documents assume a concentrated source of hydrogen to be piped. However, producing green hydrogen for just under $1.00 a kg, delivered 24/7/365 to pollute-cheap electrolyzers in big industry, which was just twice the cost of natural gas per unit of energy before last year’s spikes requires $0.01 in electricity. non-existent hydrogen production facilities. To achieve robust 24/7/365 electricity, the facility will need to build a large number of new wind farms and solar farms, build a lot of transmission from renewable sources to the facility, and build storage on top of that.
In other words, all HVDC as well as hydrogen pipelines will be required to transfer energy from renewable production sites to energy demand centers. It’s systematically cheaper to cut the hydrogen pipeline, something the studies completely miss.
Second, this hydrogen still won’t be cheap. Although my assessment is that mass deployment, transmission and storage of renewables will lead to an electricity price of about $0.02 per kWh in 2020 by 2100, this is the end game of a fully decarbonized grid. And that’s twice as much as the sub-$1/kWh asking price, and 4 times more expensive to run than natural gas. In the real world of the next two decades, 24/7/365 electricity will cost $0.10 per kWh, or about ten times the $1 per kg required.
Third, there is the next problem, exergy. The DeSantis paper at least acknowledges this, but then denies 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 MW or 3,600 megajoules or 3.4 mmbtu of electricity, then you have the capacity to do one MWh. But if you use the same facilities for natural gas or hydrogen, it dissipates rapidly.
The largest use of natural gas is for electricity generation, about 40%. The new Utah hydrogen production and storage facility will combine cycled gas generators first with natural gas, then with a mixture of natural gas and hydrogen, and at some mythical future date with just hydrogen. But combined cycle gas generators are about 50% efficient at converting natural gas to 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, is only about 0.5-0.6 MWh in the real world.
Fourth, it is worth noting that when you produce green hydrogen, you throw away about 20% of the electricity. We’ll make it a little more efficient, but it’s small and incremental steps with an 86% probability of efficiency. So when we make green hydrogen, we throw away high-exergy electricity, and when we convert hydrogen into high-exergy electricity that we can use for something, we throw away 40% to 50% of the energy in it.
Finally, there is the transmission itself. HVDC lines from wind and solar farms to demand centers have an energy loss of 3.5% over 600 miles or less, while hydrogen requires three times as much energy to compress and transport as natural gas. That energy has to come from somewhere.
By narrowly drawing system boundaries and ignoring exergy, the comparisons are deeply misleading and make it seem like a no-brainer to put hydrogen in pipelines.
And it leads to people like energy economist Lion Hirth, PhD, posting misleading memes on LinkedIn and otherwise climate action, which eventually led me to write this article. He confirmed the following:
“One pipeline (for example, “North Stream 1″) can transport 540 TWt/h of gas per year. This is 30 times more than the power you can deliver with an HVDC line. Thirty.”
It has a bar chart with no reference to the underlying data that shows this. Nord Stream 1, by the way, is a 4-foot-diameter, 1.6-inch-wall steel pipe that stretches about 1,000 miles.
But when you start doing math, it falls apart. According to the estimate above, adding up all the losses, it gives not 540 TWh, but half that after exergy is taken into account. If you add up all the extra infrastructure and losses, it throws up a lot more.
The size of the HVDC line is also misleading. This is not a single-wire HVDC that no one will build, but it is a small HVDC transmission line capable of transmitting about 18 TWh per year, selected for comparison to give the pipeline energy a better look. As a better comparison, China’s 6,400 MW HVDC link from Xiangjiaba Dam to Shanghai delivers 56 TWh per year with 5% energy loss over 1,000 miles.
Make the pipeline energy very small and make the HVDC line actually real-size and suddenly drop by 30x orders of magnitude. And that’s before building all the HVDC infrastructure to bring solid electricity to the top of the pipeline and build a giant hydrogen plant to make molecules.
All of this suggests that where hydrogen is needed as a molecule in the future—and again, it’s not a shrinking market as we phase out much of our petroleum refining and reduce our dependence on fossil fuel-derived fertilizers—we’re looking for a robust, robust, yet powerful, industrial facility that powers the rest of the industry. produce hydrogen on site with high exergy electricity, don’t build a massive hydrogen distribution system that is massively redundant with only moving electrons.
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