ling the current push toward a hydrogen economy, namely, reducing CO2 emissions and reducing the need for hydrocarbon imports. In addition, it is the most affordable renewable technology deployed today, with expectations that costs will continue to decline. Since renewable technologies effectively address two of the major public benefits of a move to a hydrogen energy system, and wind energy is the closest to practical utilization with the technical potential to produce a sizable percentage of future hydrogen, it deserves continued, focused attention in the DOE’s hydrogen program.
Although wind technology is the most commercially developed of the renewable technologies, it still faces many barriers to deployment as a hydrogen production system. There is a need to develop optimized wind-to-hydrogen systems. Partnerships with industry are essential in identifying the R&D needed to help advance these systems to the next level.
There is little mention of hydrogen production from wind throughout the entire June 2003 draft of “Hydrogen, Fuel Cells and Infrastructure Technologies Program: Multi-Year Research, Development and Demonstration Plan” (DOE, 2003b) or in the July 2003 Hydrogen Posture Plan: An Integrated Research, Development, and Demonstration Plan (DOE, 2003a). An RD&D plan for hydrogen production from wind power needs to be developed and integrated into the overall hydrogen strategic RD&D plan.
Energy security and environmental quality, including reduction of CO2 emissions, are strong factors motivating a hydrogen economy. These goals can both be fulfilled by wind-hydrogen systems. Thus, wind has the potential to play a significant role in a future hydrogen economy, both during the transition and in the long term. Since wind is currently the renewable technology that is most developed and lowest cost, wind-electrolysis-hydrogen systems merit serious attention.
Wind-electrolysis-hydrogen systems have yet to be fully optimized. There are integration opportunities and issues with respect to wind machines and electrolyzers and hydrogen storage that need to be explored. For example, coproduction of electricity and hydrogen can potentially reduce costs and increase the function of the wind-hydrogen system. This could facilitate the development of wind energy systems that are more cost-effective and have broader utility, thereby assisting their development and deployment.
Two basic avenues for molecular hydrogen production by biological processes are currently being considered: (1) via photosynthetically produced biomass followed by subsequent thermochemical processing, and (2) via direct photobiological processes without biomass as intermediate. The first process is well known and intensely researched, while the second is still in the early research stage. These processes have in common the capturing and conversion of solar energy into chemical energy mediated by photosynthetic processes. In both cases, solar energy serves ultimately as the primary energy source for the production of molecular hydrogen by biological processes. In contrast to processes using fossil fuels as primary energy sources, biological processes do not involve net production of CO2.
In photosynthesis as carried out by plants, cyanobacteria, and microalgae, solar energy is converted into biomass in commonly occurring ecosystems at an overall thermodynamic efficiency of about 0.4 percent (see Figure G-13; Hall and Rao, 1999). This low efficiency is due to the molecular properties of the photosynthetic and biochemical machinery, as well as to the ecological and physical-chemical properties of the environment. Of the incident light energy, only about 50 percent is photosynthetically useful. This light energy is used at an efficiency of about 70 percent by the photosynthetic reaction center and is converted into chemical energy, which is converted further into glucose as the primary CO2 fixation end product at an efficiency of about 30 percent. Of this energy, about 40 percent is lost due to dark respiration. Because of the photo inhibition effect and the nonoptimal conditions in nature, a further significant loss in efficiency is observed when growing plants in natural ecosystems. Therefore, the energy content of common biomass collected from natural ecosystems contains only on the order of 0.4 percent of the primary incoming energy (see Figure G-13). Although higher yields (in the 1 to 5 percent range) have been reported for some crops (e.g., sugarcane), the theoretical maximal efficiency is about 11 percent.
Generally, two types of biomass resources can be considered in the discussion on renewable energy feedstock: (1) primary biomass, such as energy crops, including switchgrass, poplar, and willow, and (2) biomass residues (primary when derived from wood or processed agricultural biomass; secondary when derived from food or fiber processing by-products, or animal waste; and tertiary when derived from urban residues).21
Today about 4 percent of total energy use in the United States is based on the use of biomass, mainly in the form of