Solid biofuels

Energy coppice:

Energy coppices The technology of growing, harvesting and using an energy coppice is still developing and recent advances have been substantial. Poplars and willows appear to be the most promising species. When harvested, the wood has a rather high water content (approx. 55%) and drying is therefore necessary. The system is approaching economic viability, but currently still needs subsidization to be viable. (Spedding, 1996)

Fuel crops:

The main options currently appear to be whole-crop cereals and miscanthus. Fuel crops have the advantage of not requiring the development of different methods of production or machinery, and the harvested crops are relatively dry. Economically, however, they are similar to energy coppices and still need a subsidy.

Urban refuse:

Even though a larger part of urban waste is now recycled, particularly metals, paper and plastics, or composted (garden leaves), huge amounts of refuse are still dumped or incinerated. Incineration of refuse achieves its primary goal of reducing volume by 90 per cent, and the process can be extended, at extra cost, to provide energy in the form of electricity.

Wood:

Wood materials can be made to burn cleaner than most coals, but its use as a major source of fuel for power generation would necessitate the establishment of huge tree plantations. Almost all crop plants produce large amounts of biomass. Unfortunately, with a few exceptions such as sugar cane bagasse, which can be burned at the sugar refinery, costs of transportation do not justify using these biomass sources for fuel.

There are many routes by which biomass may be transformed into high energy products: these include combustion, fermentation, anaerobic digestion, distillation, biophotolysis, combustion, hydrogenation, gasification, partial oxidation, and pyrolysis.

Advantages of biofuels over other forms of energy

Biofuels have numerous advantages over other forms of energy (fossil fuels, nuclear, solar, wind, etc.) With regard to fossil fuels, the major advantage is that they are CO2 neutral, i.e. they do not increase the amount of carbon dioxide in the atmosphere when burned since growing biomass absorbs carbon dioxide from the atmosphere; this release and capture process is referred as closing the CO2 cycle. Both solar and wind power have limitations as to the amount of energy they can produce in the form of electricity, mechanical power or heat, as well as they types of energy that can be used. Biomass fuels are more versatile in that they can produce a gas to be burned, or a liquid that can be put in tanks, or converted into charcoal to be put in bags and exported. Also, biomass fuels are at this time the only alternative primary fuel to petrol for transportation needs. (FAO, 1997)

The constraints to using biomass fuels are mostly technical, but are also related to the availability of land, the difficulty in being economically competitive and the infrastructure necessary for processing and distribution. Also, it is important to keep in mind that the production of energy from biomass does not start to compete with food production, which obviously is a priority. It has been shown in many cases, however, that the combined production of energy and food enhances both in terms of the environment, economics, and infrastructure, so it can also be a benefit for food production (Brazil is a good example). In fact, the main constraint to the use of biomass fuels is the price. Fossil fuels are very cheap, so most of the renewable sources of energy have difficulty competing.

So are we looking to a future where biomass fuels would be a major source of energy?

They have great potential to be one of the main sources of energy. The future will probably use a greater variety of fuels for energy sources - biomass, solar, wind, geothermal, and even ocean power.

Many of these systems will be used to generate hydrogen, one of the most important energy fuels of the future but not available in its pure form in nature. Heat or electricity is required to produce it, and that energy could come from biomass, solar or wind energy. Hydrogen can be used for transportation among other things and there's already prototype cars and buses using the gas. It's all a matter of advancing the research and technology, and of society making the conditions for them to enter the market, the major constraint right now being price. More will be heard about such terms as biomass and solar energy as the supply and environmental effects of fossil fuels force a switch to alternatives (FAO, 1997).