ABSTRACT
This chapter addresses the challenges facing the evolving biogas sector and integration into electricity grids fed with increasing amounts of energy generated by intermittent wind and solar sources. Biogas is a readily storable gas which can be used to generate electricity, when needed, and therefore to make up for periods of time when the wind is not blowing or the sun is not shining. Various options for biogas storage are considered, both locally at the site of biogas plants and in centralized locations where bigger and more efficient gas engines can be used for electricity generation. Upgrading to biomethane allows gas storage in the natural gas grid and later use for conversion to electricity. Additional biomethane can also be produced by a range of power-to-gas concepts, which also allow storage. Finally, while biogas plants are normally operated
under constant conditions, recent research has shown the anaerobic digestion process may not be adversely affected by substantial changes in operating conditions over a period of a few hours or days, and therefore biogas production could in principle be regulated and used on demand when the electricity grid is needed from the power. 17.1 Introduction
It has been known for centuries that a flammable gas, nowadays referred to as biogas, is formed naturally under anaerobic conditions from the decomposition of organic matter. The first biogas plant built to capture biogas was in Mumbai, India, around 1859. The technology was transferred to the United Kingdom toward the end of the 19th century and the gas used to light street lamps. Subsequently, in the 20th century the technology was developed firstly for sewage treatment at a time when urban drainage systems were being built. By the time of the Second World War biogas was being used as a vehicle fuel produced at sewage treatment plants. Extension of biogas plant technology to other feedstocks started in the 1930s, again in India, as a way of providing rural areas with fuel for domestic use. China followed a similar route to build millions of small-scale biogas plants based on septic tanks by the 1980s. Since that time the biogas sector has expanded in many ways in terms of technologies employed, feedstocks used, size of installations, and utilization of the biogas. And of course all kinds of legislation have been introduced to ensure minimum health and safety standards and quality. Nowadays, biogas plants are built to address a range of environmental, economic, and social needs. From the environmental side, treatment of wastes and residues is necessary to avoid health problems, contamination of the ground and of ground water, infestation by insects and rodents, and air pollution. Environmentally acceptable treatment of waste also avoids unsightly waste dumps and associated odors. In recent times, biogas has also come to be seen as a source of renewable energy which can contribute to reducing fossil-derived carbon emissions. The economic side of the biogas sector has always been an economic challenge and remains
the case to the present time. In many cases some kind of government support, or support from local taxes, is needed for biogas plants to be economically viable. All the time, industry and researchers are working to improve biogas plant performance in order to improve economic performance. From early in the 21st century renewable energy from biogas has become recognized as a significant contributor to reducing fossil emissions through use as bioheat, bioelectricity, and biofuel. For this reason in many developed countries biogas plants are set up to be as energy efficient as possible and export energy to heat, electricity, and gas distribution grids. A range of feed-in tariffs, quotas, and green certificates have been put in place to meet targets and compensate operators for relatively high production costs compared to equivalent fossil energy generators. Over time, substantial renewable energy markets have emerged. In most developed countries biogas plants are therefore operating in markets where there is competition with other energy providers, both renewable and nonrenewable. This introduces both constraints and opportunities and possibly additional responsibilities. This also brings us to the next challenge in the history of the biogas sector so far-full integration in complex energy supply infrastructures. Whereas biogas is widely used as fuel for electricity generation, and the electricity is fed into power grids as base load, the rapidly increasing contribution of intermittent wind and solar electricity to power grids has led to increasing demand for a flexible power supply which is controllable so that grids can both meet electricity demand and remain stable. In principle, the biogas sector has the ability to export energy in a flexible manner, because gas can be stored and used when needed, but how this can be done in a costeffective and efficient manner still has to be established. At the time of making this publication, various options were being considered for managing biogas plants in integrated energy systems. This high-tech demand for biogas plant operation of course does not mean that small-scale biogas plants in developing countries will change in any significant way. The scope of biogas production will simply become ever more diverse.
