A hydrogen economy is often seen as a greener alternative to the current carbon economy. Hydrogen is the most common element found on earth and can be easily transported and burned as a fuel. However, the earth’s hydrogen is trapped in its vast seas and in other compounds. As such, before hydrogen gas can be utilized, it must be extracted and separated from its source. One method of generating hydrogen gas is by splitting water molecules into their oxygen and hydrogen components. The process involves running an electrical current through the water, which commonly requires the burning of fossil fuels, but the current needed to split water can be generated in another fashion—through photovoltaics. The combination of solar cell and hydrogen fuel technology solves a fundamental problem for solar energy: energy can now be stored for use even when the sun is absent. While widespread adoption of hydrogen fuel technology is currently economically infeasible, homes powered by photovoltaic generated hydrogen fuel are a possible future. Shah et al. (2011) describe and analyze a hypothetical hydrogen home built in Wallingford, Connecticut.
Shah, A., Mohan, V., Sheffield, J., Martin, K. 2011. Solar powered residential hydrogen fueling station. International Journal of Hydrogen Energy 36, 13132–13137.
Wallingford was chosen as the site of the hydrogen home due to its existing hydrogen infrastructure developed by Proton Energy Systems and Hydrogen Highway. It was also believed that due to the presence of existing infrastructure, there would be higher public acceptance of hydrogen homes. The home, in two levels, includes bedrooms, bathrooms, a closet, a kitchen, a dining room, a living room, and a garage. Built with the architectural heritage of the region in mind, the home has steeply sloped roofs.
The home is to be powered by a total of 60 PV panels arranged in two arrays. The first, containing 18 panels, is directed 19º off the East-west axis and is designed to capture maximum solar energy in the mornings. The second array, containing 42 cells, is pointed due south to maximize energy output in the afternoon and evenings. The specific orientation of the solar arrays can be adjusted to keep output high across different seasons. Researchers assumed 4.74 hours of daylight per day and an energy utilization of 32.8 MWh/yr.
The hydrogen system of the home comprises a high pressure hydrogen electrolyzer and three storage tanks. The electrolyzer turns on when the pressure inside the storage tanks drops below 138 bar and off when the pressure reaches 165 bar. Hydrogen fuel stored in the tanks is then piped to the hydrogen vehicle. The vehicle is assumed to commute 56 km per day at a fuel mileage of 71 km per kg hydrogen, thus requiring 0.8 kg of hydrogen per day.
Safety precautions of the hydrogen power system include the use of hydrogen detectors, an emergency shutoff button, fire extinguishers, remote emergency stops, and a pressure relief system. The power is disconnected to prevent ignition from electrical sources. Regular inspection is advised and warning signs are placed around the hydrogen fueling station. Significant failure scenarios such as the vehicle colliding with the storage tank, fueling nozzle, leakage of hydrogen gas, or hydrogen overfill are all taken into account.
The researchers developed a wheel-to-wheel analysis of the hydrogen home. The Wallingford hydrogen home is estimated to require 95 kWh per day assuming a house consumption rate of 21 kWh per day and a vehicle consumption rate of 74 kWh per day. The average daily output by the PV cells is 90 kWh per day which means that 5 kWh per day will need to be drawn from the power grid. A comparison of power consumption between the hydrogen car and a normal car shows that the hydrogen car produces 34.8 grams of carbon per mile whereas a normal vehicle produces 272.2 grams of carbon per mile.
The researchers calculate that 16.5 metric tons of carbon dioxide are saved each year with the use of the hydrogen home. The energy efficiency improvement for the Wallingford home is calculated to be 23% and the hydrogen vehicle uses 13% of the carbon of a normal vehicle.