Hydrogen as a Battery

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Enough sunlight falls, on average, on an area the size of Delaware to have supplied all the United States’ electrical power needs for 2019. Delaware is our second-smallest state. Since Texas is over one hundred times as big, a solar array one-hundredth of the area of Texas could have done the job.

So sunlight is more than enough, even without the wind it helps power, to provide all the electricity we need to run our advanced civilization. And it gives us that gift without pollution, greenhouse gases or global warming.

We know how to use sunlight and wind. We have for years. We know how to make solar arrays and windmills, how to install them, and how to connect them to our electrical grid. Texas, for example, leads our nation in wind-energy capacity while it’s also mired in fracking for fossils. And the energy solar arrays produce is cheap compared to nuclear and fossil energy.

If we put our minds to it and exercised worldwide discipline, we could probably convert our entire energy infrastructure to renewables in a decade, certainly in a generation. So what’s stopping us? Mainly political and social interia. We’ve got too many stranded assets tied up in extracting, refining and using fossil fuels, and too many powerful people and corporations invested in them. The problem is mostly historical and political, not practical or technical.

If there are any real practical problems left, they all relate to energy storage. Sunlight and wind at the Earth’s surface are intermittent. They’re not always perfectly matched to electrical load. We can match energy production to load better by building regional and even national electrical grids. But we can’t match production and usage perfectly without energy storage.

Storage is difficult for some applications. They include things like aircraft, locomotives, big ships, long-haul trucks and heavy construction machinery. The batteries we have now are mostly too heavy for these applications—even batteries using lithium, the lightest we have.

Enter hydrogen. Although it’s a gas at normal temperatures, you can think of this lightest of all elements as a big battery. It’s a flexible battery precisely because it’s not solid. You can put it in a tank of any shape. You can compress it. You can send it through pipelines. If you’re willing to spend the energy and cost, you can even compress and cool it until it becomes a liquid.

So hydrogen used as a battery is simple and flexible. Unlike solid batteries, it doesn’t require electrodes with complex chemistry involving other elements. It never degenerates or wears out. All it requires is a storage container.

We can use the energy stored in hydrogen in two ways. The most elegant is in fuel cells, which can produce electricity from elemental hydrogen at will. A less elegant way is in rotating internal-combustion engines, such as gas turbines or even piston engines.

Even in this crude “burn it up” application, hydrogen batteries have two key advantages over fossil fuels. First, they produce no carbon. If hydrogen burns in oxygen, the result is pure water and nothing else. If hydrogen burns in air, which is mostly nitrogen, the result may include oxides of nitrogen, but no carbon and therefore no greenhouse gases. (Carbon dioxide, CO₂, and methane, CH₄, are the principal greenhouse gases created by burning and extracting fossil fuels.)

Our fossil-fuel industries already know how to produce hydrogen from methane, a component of natural gas. But there’s a much easier, simpler, cheaper and less polluting way of producing hydrogen: electrolyzing water. Put a little salt in water to increase its conductivity, run electricity through it, and you get hydrogen and oxygen, water’s atomic components, and nothing else.

You can use the hydrogen as a formless battery. You can use the oxygen for medicine, as in helping Covid-19 patients breathe, or for numerous industrial processes. Or you can burn it with hydrogen, in the exact same proportion as electrolyzing water produces, in the same way you use fossil fuels. The only relevant difference is that the combustion product, pure water, contains no pollutants and no Earth-heating carbon.

This is not theory. It’s practice. As a recent New York Times story reports, California is already doing it. It’s spending close to a quarter-billion dollars on hydrogen storage and pumps—to replace gas stations for cars—by 2023. Most of this effort will support hydrogen fuel-cell cars and light trucks, which work about the same, with about the same performance, as lithium-battery electric cars.

From a practical perspective, there are only three differences between these hydrogen-fuel-cell vehicles and their lithium-battery counterparts. First, the fuel-cells cars “fill up” with compressed hydrogen much faster than lithium batteries in cars can recharge. Second, the fuel-cell cars have a longer range than the electric cars, about 50% more. Third, the fuel-cell cars now cost at least 50% more than a high-quality electric car, such as a low-end Tesla (the Model 3).

The popular press has reported the development of fuel-cell cars as an epic battle between Elon Musk of Tesla and the foreign car makers (principally Toyota, Hyundai and Daimler) that are now developing fuel-cell vehicles full speed ahead. Musk has taken the bait and has blasted the fuel-cell cars as expensive, overly complex and perhaps dangerous, due to the special flammability of hydrogen.

But this “battle of the industrial Titans” totally misses the point. When properly used in the applications for which they are most suited, lithium batteries and hydrogen batteries are apples and oranges. They will be complementary, not competitive. Each has special, if not unique, preferred uses. Both will be absolutely necessary if we are to convert our entire energy infrastructure into a carbon-free one, let alone before positive global-warming feedback drives global warming to run away.

Lithium-battery technology works well in short-haul, light vehicle transport, where it already has a huge head start. Its problem, as outlined below, is that lithium batteries are quite heavy in relation to the energy they store. Lithium-battery cars get even heavier the longer their range. They work best for drivers who drive less than 100 miles a day, who can charge them from zero, without special equipment, in only a few hours.

Drivers like that not only waste their money buying more expensive cars with 250 mile ranges. They also about double the weight/mass of their cars. That’s why, with my limited retired-person driving range, a Chevy Volt’s 50-mile range was perfect for me, even living out in the country 17 miles south of Santa Fe.

For long-range vehicles, including heavy trucks, trains and aircraft, these disadvantages of lithium-battery technology are decisive. The batteries are just too heavy in these applications for the energy they store. They also take far too long to recharge fully. In these applications, and also probably for heavy construction equipment, lithium batteries are just not appropriate for the job. That’s why several companies are reportedly developing long-haul trucks that run on hydrogen and fuel cells.

The most difficult application of stored electricity is aircraft. No one has even thought of replacing jet engines with electric fans. That’s in part because of the huge weight/mass disadvantage of lithium batteries, and in part because jet engines use the heat of burning fuel directly to develop thrust. (The turbines’ rotary motion mostly controls combustion and its natural thrust.)

But here’s the thing. The specific energy (energy per weight/mass) of hydrogen is about three times that of jet fuel. Thus compressed hydrogen is actually a better fuel per weight than fossil-fuel-based alternatives. We can use it in place of jet fuel to avoid carbon pollution, and we can make it (by electrolysis) to maintain air travel after fossil fuels run out. (Hydrogen may require some additives to increase the ejected mass and thus thrust, and the turbines may require modification to withstand higher temperatures. So some R&D maybe be necessary here. But the concept worked in early rocket engines and could be made to work in jet engines.)

As for ships, the specific-energy advantage of hydrogen can be exploited either with hydrogen turbines or with fuel cells, as the extra weight of the fuel cells is not of much a problem for ships. Some ships might even use on-board solar arrays and windmills to augment their electricity or produce additional hydrogen fuel by electrolysis as they sailed.

It’s thus entirely possible, while using hydrogen as a battery, to replace fossil fuels in virtually all of their uses today. We could even modify blast furnaces and other sources of industrial heat to burn hydrogen without carbon release. We can then make enough hydrogen, by electrolyzing water with electricity from renewables, to replace fossil fuels in every application.

Unlike burning fossil fuels, an energy infrastructure based on hydrogen will leave no stranded assets. When new sources of carbon-free electric power develop—whether they be safer nuclear fission plants or the still-elusive better-than-break-even nuclear fusion plants—we can just put them to work electrolyzing water to make hydrogen. They can replace solar and wind farms whenever economically advantageous. Then the hydrogen their electricity produces can serve as non-polluting battery/fuel in all forms of transportation and in all industrial processes that require heating, with renewables providing the rest of our electricity and electrolyzed hydrogen smoothing their intermittency.

Using hydrogen as a battery has one final advantage. As global warming accelerates, the globe's equatorial and tropical regions may become even more sparsely populated than they already are. They could be used for massive solar farms and wind farms, which could supply hydrogen fuel to the rest of the world by electrolyzing water in autonomous or semi-autonomous plants. The resulting hydrogen could power the temperate zones, supplementing their own renewables. It could also help heat the temperate zones, with their warmer but still uncomfortable winters, after natural gas runs out.

Footnote 1: Solar Power per land area. According to this report of the National Renewable Energy Laboratory [Scroll down to Page v, Table ES-1], the average land use for a large-scale commercial solar photovoltaic array using fixed panels is 2.8 acres for each gigawatt-hour of power per year. In 2019, total US electricity consumption was 3.99 trillion kilowatt hours, or 3,990,000 gigawatt hours. The equivalent land area is thus 3,990,000/2.8 = 1,425,000 acres, or 2,227 square miles. That’s less than the 2008 land area of Delaware. In other words, if Delaware were paved with solar panels, it could, on average, power the entire nation.

Footnote 2: Battery Weight, Range and the Electric Car Conundrum. In a previous post, I had criticized Tesla and the whole electric-car industry for offering electric cars with 250+ mile ranges, which few, if any, drivers need regularly. That sort of range adds something like 2,000 pounds to the car’s weight/mass—all in the battery—while inflating the price by $10,000-$20,000. The massive battery improves the car’s performance somewhat, but not nearly proportionally. For me, it would have meant driving a 5,000 pound car to drag my 150 pound body around.

What I failed to realize in my earlier post was that a small internal combustion engine (ICE) is a superior, if somewhat inelegant, solution to the problem of range anxiety. Instead of carrying around 2,000 pounds of extra battery everywhere it goes, the Chevy Volt has a small ICE and a gas tank, which probably weigh no more than 350 pounds together.

The Volt’s ICE needs no transmission, transaxle or differential because, in a serial hybrid, it merely drives the same generator used to charge the battery while braking. The same electric motor drives the wheels whether the electric energy comes from the battery or the ICE and connected generator. The ICE also suffers far less wear than the engine in a gasoline car because it runs at constant RPM, optimized for conditions; it never has to lug the car’s whole mass directly from a standing start.

Now gasoline weighs only six pounds per gallon. So for eighteen additional pounds in the tank, at 30 miles per gallon I get an additional 90 miles of range. If I wanted to fill the tank, I could, according to GM, get an additional 480 miles of range. But why bother, when I rarely, if ever, drive more than 50 miles a day?

After “repositioning” the car from the state in which I leased it, I typically drive for six months or more without adding gasoline. Occasionally I burn 0.06 gallons or so when I overestimate the car’s electric range.

This arrangement has only one tiny downside. After six months, the car’s computer forced it to burn a little gasoline to keep what’s left from getting stale. Yet all this is far preferable to adding 2,000 pounds of weight/mass to the car, which it has to drag around everywhere, even up the big mountain from my home to Santa Fe.

I’m sorry that my own electrical “purism” kept me from appreciating GM’s effective and efficient solution to the range anxiety problem. I’m even sorrier that GM decided to drop the entire model/line rather than to educate the public on its advantages. The Volt is a superb car, and I love mine.

Footnote 3: Comparative specific energies of hydrogen gas and (liquid) jet fuel. The specific energy of jet fuel is 11.99 kWh/kg. The specific energy of hydrogen gas is 36 kWh/kg, about three times as high.

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