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Sustainable Energy

Plants are Really, Really Amazing
As with all other forms of renewable energy we have been discussing, biomass gets its energy from the sun. Plants convert light energy into chemical energy in a process called photosynthesis, which means, “putting together with light.” They accomplish this by taking six molecules of carbon dioxide from the air and combining it with six molecules of water. The result is one molecule of sugar and six molecules of oxygen (6H2O + 6CO2 = C6H12O6 + 6O2, if you want to be technical). In this way, the plant turns sunlight (which we cannot use directly) into the food we need in the form of sugar, and the air we breathe in the form of oxygen, two things necessary for survival.

Photosynthesis is a vital part of the carbon cycle. The carbon cycle, like the water cycle, explains how carbon is moved and used on earth. Plants are considered to be carbon “sinks” because they are one of a very few things that take carbon out of the atmosphere.

The carbon cycle is in balance if the amount of carbon being released equals the amount of carbon being absorbed by plants. However, many scientists believe that the cycle is no longer balanced. This is problematic because carbon is a greenhouse gas and contributes to climate change.

There are lots of sources of carbon. When animals breathe in the air, their bodies remove the oxygen for their own use. The left over carbon dioxide is then breathed back out. When biomass is burned, carbon is also released.

Although the use of biomass to create heat energy or electricity does result in the release of carbon, which is a greenhouse gas, biomass is still considered a renewable technology. This is because the fuel source, the plants, are renewable, and many of the other harmful pollutants associated with fossil fuels are not present in plants. Think back to the carbon cycle again. The plants (biomass) that are burned release carbon into the air, but those plants can be very quickly and easily replaced. The replaced plants serve as a way to remove the carbon from the atmosphere and a source of fuel for the future, keeping the carbon cycle in balance. This is different from fossil fuels because they took thousands of years to form. The carbon in those fossil fuel deposits are now being released suddenly and the existing plants can’t remove the carbon released fast enough from the atmosphere. This throws the carbon cycle off balance.

For more information on photosynthesis and the carbon cycle, see Safe Climate, NASA's Earth Observatory or Estrella Mountain Community College.

How is Biomass Harnessed?
Biomass can be harnessed most usefully to create heat and electricity, and there are several very different technologies that make the production of heat and electricity possible.

One form of electricity generation being explored and even used for several different applications is to burn biomass directly in a similar way to how coal plants work. In fact, one of the benefits to this form is that old coal plants can be converted to burn biomass without too much trouble.

The biomass is burned to create heat energy, which produces steam, which drives the turbine, which turns the generator, which creates electricity.

The combustion of waste is not the only technology. Other technologies have been adapted to make use of the methane emissions that result from the decay of biomass, for example, from municipal waste and manure.

Methane is also a greenhouse gas and by reducing and using it to generate electricity, we can limit its release into the atmosphere. The methane in landfills can be captured and used to generate electricity. Methane is carried by pipes to a central point, where it is filtered, cleaned and then burned to power a turbine and produce electricity.

One of the most promising technologies for applications in Ontario is an anaerobic digester. Both sewage and manure can be used as fuel. In the absence of oxygen, certain strains of bacteria are able to decompose organic matter and produce a combustible gas. The gas produced is made up of mostly methane and carbon dioxide, which can be cleaned and used instead of natural gas for electricity generation. The leftover waste can also be used as an excellent compost.

How Can Biomass be Used?
Humans have been using biomass for heat energy since the invention of fire. Wood has been used to cook food and warm our homes, and manure is still burned for the same purpose in places around the world where wood is scarce.

Directly burning biomass has many larger-scale applications and benefits. For example, much of the wood waste from the forestry and paper industries can be burned at the site of the mills to produce the power for the factories.

Similar applications are possible and indeed being used in the sugar industry. The juice of sugar cane is extracted and used to make refined sugar, but the leftover pulp is normally thrown out. Increasingly, however, the pulp (known as “bagasse”) is being seen as a source of power, since it can be burned to produce electricity for the sugar mill and surrounding area.

There are already several landfill gas generators in Ontario, and three in operation under the Renewable Energy Standard Offer Program (RESOP). One is a 5 MW project that began operation at the end of January, 2007 at the Trail Road Waste Facility Landfill Site and the adjacent closed Nepean Landfill Site in Ottawa. For more information on landfill gas generation projects under the RESOP, see the Ontario Power Authority (OPA) website.

Anaerobic digesters have huge potential for farmers and rural communities in Ontario. The technology is well placed to make a significant contribution to electricity generation and Community Power in the province.

What to do with farm waste, particularly manure, has been a challenge facing farmers in recent years.  After the Walkerton incident, increased attention has been paid to manure storage and handling. Anaerobic digesters offer a solution for what to do with excess manure and a way to make manure safer to use as a compost.

The digestion process produces a gas that can be burned to produce electricity. Depending on the size of installation, the electricity can be used on site, or sold back to the grid. Once the manure has gone through the digestion process, up to 99.9% of pathogens found naturally in the manure, such as E. coli, Salmonella, Cryptosporidium, and Giardia, are removed, which makes the manure safe to use as a fertilizer, and helps reduce water source contamination.

Biogas digesters are beneficial because they convert the sunk costs for manure handling into a revenue generating opportunity for farmers. A great resource for more information on anaerobic digesters can be found on the Powerbase website.

Benefits of Biomass
One of the greatest benefits of energy from biomass is that most of the technologies are making use of waste products. Digesters can process manure and sewage, landfill gases can be captured and used, and the waste wood and cane from the forestry and sugar industries can be burned.

Anaerobic digesters can be used to produce energy from manure on farms. Benefits include electricity production, a more distributed generation system, and reduced pressure on the transmission system associated with large-scale installations. 

Another environmental benefit is the reduction of pathogens within the manure, making it safer to use as a fertilizer, and a reducing groundwater contamination. There are also the economic benefits for rural landowners and farmers associated with Community Power.

Landfill gases can be captured and converted into electricity, which reduces the amount of methane being released directly into the atmosphere.  Methane is a potent greenhouse gas, with 21 times the effect of carbon dioxide.  Using landfill gas in this way helps combat global warming.

Burning landfill gases also has other benefits including reduced odours, reduced release of harmful substances in the landfill, and reduced chance of explosion from the build-up of landfill gases in nearby structures.

These generation technologies are also beneficial because they can be used locally at the site where the waste is produced, reducing the need for fuel transportation and bringing economic and environmental benefits to the local community.

Did You Know?
Think back to the discussion on the main Renewable Energy webpage about Hermann Scheer’s ideas in The Solar Economy, on the complexity of different generation technologies. According to his argument, Biomass is as complex as fossil fuel generation. You have to plant, harvest and ship the biomass you are using, and some forms of biomass must be processed (i.e. made into pellets) before being burned. Some of the generation plants work on the same principles as coal or gas plants as well, so the fuel is burned, the heat is converted to steam, the steam to mechanical energy and mechanical into electricity.


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