The main advantage of biohydrogen is that it is a clean, CO2 neutral energy source, which can be used in fuel cells to produce electricity efficiently and water as a by-product, compared to other fossil fuels, the oxidation of which is accompanied by CO2, NOx, particulate and other emissions. Moreover, the high efficiency of electricity generation in fuel cells that utilize hydrogen is independent of the scale of the fuel cell. This feature allows the application of fuel cells (and consequently, the use of hydrogen) at both large scale (e. g. industrial plants) and small scale (e. g. vehicles) (Gosselink, 2002). In biohydrogen processes, the energy of sunlight is first captured in the plant biomass and then transferred to H2 as an energy carrier or is directly harvested in the form of H2. The chain of sunlight energy to hydrogen production and then hydrogen storage and distribution to the ultimate electricity generation comprises a sustainable energy scheme, which can be applied to replace gradually the fossil fuel economy. Technological advances reducing the limitations of biohydrogen processes could render the hydrogen economy easier to implement.

There are few economic analyses in the literature about hydrogen production. Most studies have been conducted at lab scale, while problems related with scaling up have not yet identified. Ressnick (2004) performed a comparative economic analysis applying a series of economic models to predict the capital and operating costs of the various approaches having been tested at a lab scale. The estimation has been based on a capacity of 50 million SCFD (standard cubic feet per day) and, based on the specific hydrogen production rate reported in the literature for the various biohydrogen processes considered, the size of the plant was assessed (Table 13.7).

The capital cost is mostly affected by the land area required in every approach. The annual sunshine limitations have not been taken into account in this analysis, and this has an impact on all photo-dependent processes. The specific rate of hydrogen production is also crucial in the above analysis. Any increase or decrease of these values would dramatically affect the economic analysis. As a result, more efficient bioreactor designs that could improve the rate and decrease the reactor volume, shrinking the capital cost further.

The operating costs also vary significantly depending on the biotechnology used. The high operating costs of direct biophotolysis are attributed to the labour costs associated with the large land area involved. In the case of the water-gas shift and the photo and dark fermentation technologies, the cost of the feedstock is crucial. If the cost of CO and glucose is excluded from the analysis, the operating costs of these technologies would decrease to 17.44, 5.60, 4.43 $/GJ respectively.