Here in the State of Hawaii, much attention has been directed to our future energy demands, and where it will come from. Currently, through renewable energy initiatives, we have lowered our dependence on imported fossil fuels below 90 percent, but this is just the beginning (HECO 2010). One proposed alternative for fossil fuel consumption is Hydrogen. Much research has gone into hydrogen because compared to gasoline, is an environmentally friendly fuel which can be incorporated into internal combustion engines, (automobiles), as well as integrated into fuel cells, such as in electric motors. When integrated into electric motors, it produces no air pollutants, and when burned, in replacement for gasoline, only produces nitrogen oxides, a prominent greenhouse gas which is produced by any combustion. So far, many renewable energy technologies have proven to have a bright future in supplying commercial, industrial, and residential environments with clean and affordable energy, but that still leaves one of the largest energy consuming sectors, transportation.
The diminishing resources of fossil fuels, as well as the pollutions associated with fossil fuels have lead to discussion of a “Hydrogen Based” economy. This is an extremely interesting idea as using hydrogen in fuel cells, (batteries), creates only a byproduct of water, and if electrolysis is used for the production of hydrogen, there is no pollution associated with the splitting, and recombining of water molecules, compared to the environmentally harmful production of gasoline. The main question that people have been asking is where and how do we produce hydrogen? There are two well-developed processes, one is the splitting of water, known as electrolysis, and the second is done by using fossil fuels. The electrolysis of water is the main interest in the future, but is energy intensive, and can only be economical if coupled with a renewable energy source.
Geothermal energy has a strong potential to create hydrogen as a byproduct compared to other renewables because of its consistent nature. As I stated before, the electrolysis of water for hydrogen production is extremely energy intensive, and combining the heat of the geothermal plant with energy created at the plant, through a process known as a hybrid, or integrated cycle, is a very feasible situation. Conveniently, in some regions of the world, hydrogen steam is vented directly out of the geothermal reservoirs. This hydrogen may be pure, or hydrogen sulfide, where it can be separated and concentrated for production, given the technology is economically available. Such an example is the Bjarnarflag geothermal field in northern Iceland, where it’s estimated that 50 tonnes of hydrogen are released to the atmosphere annually. (Arnason)
Assuming that a large geothermal plant is developed on the island of Hawai’i, three pathways have been presented as a method for the production and distribution of the hydrogen produced at the geothermal site. The first is called the Central gaseous pathway, where hydrogen is produced through electrolysis at the plant, where it is then compressed, and stored on site. It can then be delivered through pressurized vessels for consumption. The second is called the Central liquefied pathway, where hydrogen is produced through electrolysis, then is liquefied, and transported through cryogenic tankers, as liquefied hydrogen must stay at a lower temperature than in the gaseous state. The last is known as the forecourt gaseous pathway, where hydrogen is produced at the refueling station, with energy supplied by the geothermal plant, where it can then be compressed, stored and distributed on site. These pathways were run through economical modeling, and the liquefaction pathway was found to be uneconomical, while the central gaseous pathway is the most economical, and the forecourt gaseous pathway was slightly less efficient, as the electrolysis is done offsite with respect to the geothermal plant. The specific method of hydrogen production, with association with a geothermal plant depends heavily on the type of geothermal plant being used.
The Hawaii Natural Energy Institute, part of the University of Hawaii has been done research into the feasibility of using hydrogen for transportation purposes. (Sentech, Inc, 2008) A main concern with the investments into hydrogen research is, as with many alternative fuel sources, the economics behind the fuel source. Can it be, or when will it be cost competitive with fossil fuels? A combined report that is cited above, prepared by Sentech Inc, gives some economic driving factors with the combined production of hydrogen and geothermal energy. All conclusions have been based around the year 2025. It’s stated that Hydrogen as a transportation fuel can compete with diesel fuel, if the price of diesel rises above $5.30 a gallon, and if the electricity from the geothermal plant is being produced at less than $0.10/kWh.
This is a possible scenario for Hawai’i Island, and the main costs associated with this modeling were the cost of producing the energy, and the capital cost of buying the electrolysis machinery. This is specifically for using hydrogen as a direct fuel, but there are also many other scenarios as hydrogen fuel cells can be incorporated into electric vehicles to have hybrid power trains, and cost-effectively moving our transportation off of fossil fuels. It is assumed also that state incentives will be passed as to expand the renewable energy industry locally, and to support the production and use of hydrogen as an alternative fuel. This has already started to happen, and an example of this forward thinking is the Hawaii Legislature act 240, or Hawaii Renewable Hydrogen Program, of 2006.
Geothermal in Hawaii is a large point of interest for renewable energy as it is a clean, and steady source of renewable energy. In association with the geothermal potential on the island of Hawai’i, is the production of hydrogen through hybrid, or integrated systems. The processes used to create the hydrogen are still improving, and electrolysis is expensive with the available technology. However, this switch to hydrogen could ultimately fill the gap between renewable energies and transportation. According to the paper in the International Journal of Hydrogen Energy, using geothermal energy would be more sustainable and efficient to use for hydrogen production, than nuclear energy, the next best source. The thermodynamic calculations, or the theoretical efficiency of the process, give results between 86% and 87% for electrolysis, using energy derived from geothermal.