Photovoltaic solar, with its range of complementing technologies and uses, is expected to be integral in another process of decarbonizing the grid: creating a carbon-free fuel source.
Hydrogen cells are an energy source that, when expended, release no carbon, just heat and water vapor. They’re commonly used in food and fertilizer production, treating metals and refining petroleum, but hydrogen has the potential to be used as both a source of electricity and a fuel cell. The driving concern with hydrogen fuel production is that most of it is created with fossil fuels, about 95% worldwide.
However, there are many ways to produce hydrogen fuel, and each production source is color-coded. Using natural gas as the energy source is designated as blue or grey hydrogen; using nuclear energy is called pink, purple or red hydrogen; black and brown hydrogen are produced using coal; and, of course, using carbon-free energy sources like solar makes green hydrogen.
Hydrogen fuel cells are created by splitting water molecules (H2O) to form separate hydrogen and oxygen molecules. This process is called electrolysis and is conducted by an electrolyzer. The material makeup of electrolyzers varies, but the general idea is a water molecule passes between an electrified cathode and anode, is split into the two elements and the positively charged hydrogen and oxygen molecules are expelled, producing energy.
With greater deployment of hydrogen production operations alongside renewable energy projects, there’s the possibility of producing a carbon-free fuel source that has some applications beyond what PV solar is currently capable of powering.
Solar’s application with green hydrogen
As the name suggests, the process of electrolysis requires a lot of electricity, so renewable energy resources like solar are a possible source of production. A hurdle for widespread green hydrogen production is that electrolyzers (the systems that use electricity to split the H2O molecules) are still quite expensive. Analysts expect the cost of an electrolyzer to be cut in half by 2040.
A recently published study from the Carnegie Institution for Science found that regions with high curtailment rates of solar, wind and hydropower could instead use that excess energy to produce green hydrogen. A once “wasted” electricity bank could be redirected to aid electrolyzers.
Like storage technologies coupled with solar projects, hydrogen fuel can be used as energy backup. It can be stored as a gas or liquid and expended when required in different applications, like grid backup and transportation. There is potential for pairing solar with hydrogen electrolyzers and storage units to provide direct backup where that electrical load is needed.
A challenge to properly storing backup hydrogen is that it requires large tanks when it is in gaseous form. In scenarios like grid backup, where there is ample space for tanks to be placed or buried, that is less of a concern than in transportation and even small-scale distributed generation applications.
But another appeal of hydrogen fuel, especially in vehicles, is that it has three times the energy density of gasoline. Cars can drive much further on one gallon of hydrogen than on gas — and it’s cleaner. Electric vehicles are a solution to decarbonizing transportation and are certainly leading that effort, but the technology exists to power vehicles with hydrogen. Where a vehicle owner can directly power their electric car with solar panels installed on their home, solar could indirectly power hydrogen fuel-based vehicles just by producing the fuel itself.
Electric vehicle manufacturers are trying to crack the code of electrifying heavy transport vehicles, like semi-trucks, ocean freighters and airplanes. Hydrogen fuel cells, however, are a more feasible solution to carbon-free vehicles at that scale, experts say, and this could apply to industrial uses as well. Like conventional EVs, hydrogen fuel cell vehicles also use an electric motor but have a fuel tank for carrying hydrogen gas.
There’s significant infrastructure buildout required before hydrogen vehicles are as widely available as even electric cars. As of mid-2020, there were only 43 public hydrogen fuel cell refilling stations in the United States.
Green hydrogen is still a nascent fuel source in the United States, but development is on the horizon. The Biden Administration has included it as a solution to greenhouse gas reduction goals, and solar will undoubtedly be part of its production.