7.1 Introduction

Biological energy production begins with the photosynthetic fixation of CO₂ into biomass (starches, lignocellulosics, etc.) and is followed by conversion of biomass via various microbial processes to fuels (ethanol, methane, hydrogen, oils), as discussed in previous chapters. In the case of algal production of hydrogen and vegetable oils, both processes are conducted by a single organism. Even in these cases there is a clear differentiation between the photosynthetic processes of CO₂ fixation (and oxygen production) and the subsequent conversion of the fixation products to renewable fuels. The production of the waste biomass is of little concern in the conversion of waste materials, such as in methane fermentations. Still, ultimately, the source of all biological fuels is photosynthesis, carried out by plants and algae. The efficiency of photosynthesis (Chapter 2) is, thus, a central issue in the future development of these renewable biological energy sources.

Other overriding issues in the future of biological energy systems are the overall efficiencies of converting biomass to useful fuels, the economics of such processes, their environmental impacts, their competitiveness with thermochemical conversion processes for biomass (combustion, gasification), their resource potential, and, perhaps most important, their compatibility with evolving economic and political structures. Biofuels would for example, complement solar electricity in the renewable energy mix of the future. This chapter presents some projections on the development of renewable biological energy systems in the 21st Century.

The human race is already, directly and indirectly, exploiting a large fraction, almost half (1) of the total primary production of the planet - through agriculture, fisheries, forestry, and other activities. Indeed, few productive ecosystems around the world remain in their natural state, not diminished by the actions of mankind. As global ecosystem exploitation and destruction reaches its end-point sometime in the first half of the next century, and natural environments cease to exist outside a few more-or-less protected enclaves, our reliance on the bounties of nature will end. We will then depend entirely on how well we can manage the remaining biological and physical assets of our planet, to sustain the existence of a human population whose current growth rate is only exceeded by its accelerating consumption of natural resources. In addition, we will need to manage these resources within the context of a rapidly changing global environment, with unpredictable climate, ever scarcer raw materials, and diminishing productive land, which is being covered by settlements or devastated by exploitative practices. To mention just a few of the challenges we are leaving for the next generations.

If catastrophe - economic and population collapse - is to be avoided, we must not only curb populations and consumption, but must also develop and implement more efficient and environmentally benign technologies, more available to the large populations currently not enjoying the benefits of our technological economy. Biological energy systems can play an important role in this transformation of the human economy and condition, necessary for our survival through the 21st Century.