Lowering Energy Spending Together With Compression, Storage, and Transportation Costs for Hydrogen Distribution in the Early Market

This chapter is dedicated to the optimization of cost and energy consumption for compression, transportation, and storage of hydrogen for vehicle refueling in the current hydrogen emerging market. Thus, it considers only small refueling stations (20–200 kg/day) and current costs. It considers two cases: the case of a refueling station on the site of the hydrogen production and the case of a production unit supplying hydrogen to several distant refueling stations. In the case of production and distribution located on the same site, no transportation has to be considered, and the energy consumption is mainly due to hydrogen compression and cooling. In a reference case corresponding to good current practice, the study calculates an energy need of 3.5 or 4.4 kWh per kg of hydrogen transferred to a car tank at 35 or 70 MPa, respectively. It then shows that this need can be reduced by > 25% through judicious use of four or five stages of buffers organized in a pressure cascade for the filling of a tank at 70 MPa. Whereas the total volume of the staged buffers is higher than the volume of a single very-high-pressure buffer (VHPB), the investment cost is only slightly higher; then the energy saving results in short payback times for the extra investment in staged buffers. In the case of a production unit supplying hydrogen to several distant hydrogen refueling stations, energy for transportation by truck and for re-compression on the distribution site must be added. Current off-site distribution practices are used as a reference case; it considers the transportation of hydrogen in 20 MPa steel bottle bundles or trailer tubes and the re-compression of all the hydrogen to the VHPB. To lower the energy spend, solutions are proposed and quantified, such as using small transportable containers of higher pressure light composite bottles and bypassing the compressor as much as possible. Energy needs and CO2 emissions are estimated and compared for the reference case and the innovative cases. The study shows that, even if the investment in composite bottles is high, the resulting overall cost is definitely lower and CO2 emissions can largely be decreased. The size effect appears very important; cost decreases by 60% from 20 to 200 kg/day.