In his 2003 State of the Union speech, President Bush declared about hydrogen-fueled cars:
“With a new national commitment, our scientists and engineers will overcome obstacles to taking these cars from laboratory to showroom, so that the first car driven by a child born today could be powered by hydrogen, and pollution-free.”
Back in the early 2000s, the Hydrogen Economy had become all the rage in energy and environment discussions, and even the president caught the bug. The hydrogen car was going to be awesome because it was going to use a fuel cell that made emissions consisting of only water. While making a commercially-viable hydrogen fuel cell car a reality would be a major feat of engineering, government policy, and business, the real linchpin was where the hydrogen was going to come from. Getting it from natural gas would be a bummer because the whole point was that it should be a clean fuel! It needed to come from solar or wind power.
Today, people born in early 2003 may now be motorists, and there are indeed a few hydrogen fuel cell vehicles on the road, proving the technical feasibility. The solar industry is also big and growing, and wind power has definitely gone mainstream. These solar and wind projects nearly all make electricity though and not hydrogen for fuel cell vehicles. If we have the renewable energy and the fuel cell cars, why hasn’t renewable hydrogen fuel come to fruition at scale?
Two factors (among others) act to divert attention away from building capital projects to make renewable hydrogen. First, a solar plant (or wind or hydroelectric) is more competitive at generating electricity than making hydrogen. Second, if developers did want to build a solar hydrogen plant, they would likely find other applications more attractive than providing hydrogen fuel for cars. Neither of these are reasons why solar hydrogen for cars is a bad idea but just that this may not be the best option for those considering spending money on a renewable energy project. Finally, those set on delivering renewable hydrogen for cars may find that building a dedicated plant is not the easiest way to go.
How Hydrogen Is Made
First, let’s digress on how hydrogen is made. Three general methods exist at large scale:
- Electrolysis. In electrolysis, electricity is used to split water molecules into oxygen and hydrogen with an energy efficiency of approximately 70% to 75% for a large plant. (Santos 2012)
- Steam Methane Reforming (SMR). (or steam naphtha reforming of the light fraction of crude oil) Methane is reacted with water to make carbon monoxide and hydrogen. A second reaction between carbon monoxide and water produces more hydrogen. A large SMR hydrogen plant that is integrated into a chemical plant, like an oil refinery can achieve an efficiency of 80% to 85% on a higher heating value basis (process plant analysis).
- Gasification of coal (or biomass). Coal is reacted with water and a limited amount of oxygen to make carbon monoxide and hydrogen (used as “town gas” in the late 19th & early 20th centuries). A water-gas shift reaction is used to make more hydrogen from carbon monoxide and water.
The large majority of hydrogen produced in the world is from natural gas and from oil.
Why Not to Make Renewable Hydrogen
Of the three methods above, renewable hydrogen can be made at large scale by making electricity with a solar, wind, or hydroelectric plant and then using an electrolysis plant to make hydrogen. A rare example plant built in the 1980s is a 165MW-sized electrolysis plant located at the Aswan Dam in Egypt. Hydroelectric power is used to make hydrogen, which is used to make ammonia for fertilizer.
A good reason why lots of utility-scale solar electricity plants are being built but not solar hydrogen plants (or wind-hydrogen plants) is because solar is more competitive against natural gas for making electricity than for making hydrogen. Comparing efficiencies illustrates this. For solar, the efficiency to generate electricity is significantly higher than to make hydrogen. For natural gas, the efficiency to generate electricity is significantly lower than to make hydrogen. A solar electricity plant may be 16% efficient (sun to AC power under good conditions), and an electrolyzer can be 70% efficient. The overall sun-to-hydrogen energy efficiency would be 11% (0.16 * 0.7 = 0.11) versus 16% to only make electricity. A combined cycle natural gas plant can deliver power with a 50% efficiency (HHV); whereas, hydrogen can be made from natural gas with an efficiency of, say 80% in an SMR plant integrated in a large chemical plant complex. This comparison does not show that a solar hydrogen plant should not be built. It simply shows that a project developer will probably make a stronger economic case using the solar field to generate electricity.
|Making AC Power||Making Hydrogen|
|Solar||16% Efficiency||11% Efficiency|
|Natural Gas||50% Efficiency||80% Efficiency|
Suppose you did build a solar hydrogen plant
If a group of developers had a great plan to build a solar hydrogen plant to deliver low-cost hydrogen, they would likely find easier customers than a small, emerging fleet of fuel cell cars that needs a distrusted network of refueling stations. The bigger issue is that there are already major markets for hydrogen, totaling over $100 Bil. globally, and these existing applications are much easier to serve. First, oil refineries use a substantial amount of hydrogen to hydrocrack large hydrocarbons molecules into smaller ones and also to drive the sulfur out of refined products (hydrodesulfurization!). Second, hydrogen is a building block to make ammonia which is used in nitrogen fertilizer. In both cases, a substantial amount of hydrogen is used at a single process plant. Making these applications still easier to serve in two locations, the U.S. Gulf Coast and northern Europe, is that hundreds of miles of hydrogen pipelines have been built to move the stuff between producers and industrial consumers.
How can you get renewable hydrogen for fuel cell cars then? (not just trucking hydrogen from a steam-methane reformer plant)
Hydrogen refueling stations for cars may not attract investment for a large, dedicated plant. In a growing number of places, a business can contract for renewable electricity and use an electrolyzer to make the hydrogen. For example, here in the northern San Francisco Bay Area MCE (formerly Marin Clean Energy) provides different percentages of “green” electricity to its customers by contract and procures the power from wind farms, solar plants, and hydroelectric facilities. This may not look like a renewable fuels plant, but this method can enable small-scale hydrogen production with very low greenhouse gas footprint. That hydrogen from electrolysis is significantly more expensive than hydrogen from steam methane reforming serves as yet another hurdle toward this technology’s adoption. Though not impossible to deliver renewable hydrogen, it is no wonder investment money is flowing toward electricity plants or other applications.