Most of the fuel we use today to run our cars and to generate power, such as electricity, comes from fossil fuels. This is the name given to coal, petroleum (or crude oil) and natural gas which are extracted from the rocks of the Earth’s crust.
Fossil fuels come from animal and plant remains from many millions of years ago that formed fossils. Natural gas and oil are fossil fuels that are often found together. South Africa is rich in coal, but poor in crude oil and natural gas.
Running out?
For the past 150 years oil and coal have been the main energy sources used in industrialised countries. There is more energy stored in fossil fuels than in any other available energy source. No other source of energy is as cheap and powerful.
Fossil fuels have been providing an “easy” energy source for man, but there is a limited amount of fossil fuel on Earth. It is not “renewable” and there is no known way to make more.
Dirty fuels
Apart from the fact that fossil fuels may run out in time, they are also very “dirty” fuels. When we burn them a lot of greenhouse gases (GHG), especially carbon dioxide, are released into the atmosphere. These gases trap the sun’s heat in the atmosphere close to the Earth’s surface, with the result that the Earth’s temperature keeps rising. This is called global warming.
All over the world there is agreement that we need to reduce the levels of gasses in the atmosphere. One way to do this is by reducing the amount of fossil fuel we use.
But then we will need alternative sources of energy. Alternative forms of energy are nuclear energy, solar power, wind power, hydrogen and biomass. Governments all over the world, including South Africa, are looking into producing more biofuel from biomass.
What is biomass?
Biomass is organic material from living plants or organic waste. Biomass contains stored energy from the sun. Some examples of biomass fuels are wood, plants such as agricultural crops, manure and even some rubbish. When burned the chemical energy in biomass (the stored energy from the sun) is released as heat. When you make a fire for a braai the wood you burn is a biomass fuel. Wood waste (or rubbish) can be burned to produce steam for making electricity, or to provide heat to industries and homes.
Biofuels
Biofuels are energy sources that are produced from biomass. These fuels are usually blended with the petroleum fuels – petrol and diesel – but they can also be used on their own.
The two main types of biofuels in use are:
Plant sugars or starches that come from biofuel crops, such as sugar cane, rice, wheat and maize. These crops are fermented to produce ethanol. Ethanol, an alcohol fuel, can be blended in small amounts with the petrol we use in our cars.
Biodiesel that comes from vegetable oils, such as rapeseed or soybean. Even fats or greases, such as recycled restaurant grease, can be used to produce biodiesel.
New sources of biofuels still being researched and developed include:
Non-edible plants and plant parts. Scientists are working on cheaper ways to make ethanol by using all parts of plants and trees. Farmers are experimenting with other sources, such as small trees and grass, to see if they can grow them cheaply and abundantly. Scientists and farmers are doing research on new biodiesel crops such as jatropha, a non-edible plant with oil-rich seeds that grows on land where nothing else will.
Algae that are easy to grow and that can carry up to 50% oil content and good candidates for making biodiesel.
Why consider using biofuels?
Biomass is a renewable energy source because we can always grow more trees and crops and waste will always exist. Using biofuels means we don’t burn quite as much fossil fuel. Ethanol and biodiesel are still more expensive than fossil fuels but they are cleaner burning fuels, producing fewer air Âpollutants.
Biodiesel fuels can be used in diesel engines without changing them. Biodiesel, a renewable fuel, is safe, biodegradable, and reduces the emissions of most air pollutants.
Biofuel crops recycle carbon dioxide by absorbing it when they grow and
then releasing it back into the atmosphere when they are burned. So in theory crops grown for biofuels should not add to the total amount of carbon dioxide in the atmosphere.
Most farmers, however, use fossil fuels to work the land and for many other purposes. This amount varies from crop to crop. So in practice one cannot say that the production of biofuels do not add to GHG emissions at all.
What are the issues around biofuels?
We need new technology and better farming practices before biomass can replace fossil fuels. These technologies should increase the production of biofuels, minimise the negative effect on the environment or food supply and use less energy to grow, extract and burn the fuels than the total energy they supply.
Food supply
Countries are using the crops they grow best (because of factors such as climate and agricultural practices) to produce biofuels. This means they use mostly food crops, which can drive up food prices.
Farmers would rather plant biofuel crops than food crops if they can get a better price for the former. This puts pressure on the limited land available for agriculture and on water supplies.
Fortunately it seems that new crops, such as inedible plants that can thrive under harsh conditions, such as jatropha, can be developed to replace food crops as sources of biofuels.
Energy balance
The production of ethanol from maize now consumes about the same amount of fossil fuel as the ethanol itself replaces.
Environment
Some biofuel crops harm the environment. They need lots of fertiliser, pesticides and water to grow and can cause soil erosion.
If not biofuels, then what is the solution?
Biofuels are one tool of many. The production of biofuels is only one of a number of energy options that can eventually replace fossil fuels. These include nuclear energy, solar energy and wind power. Fossil fuels, especially coal, will, however, remain an important part of the energy mix for the foreseeable future.
This resource for science teachers is brought to you by the Public Understanding of Biotechnology project of the South African Agency for Science and Technology Advancement