Volume 3 - Program & Project Ideas (PDF - 4.5 - Natural Life Network

Natural Resources Canada – Community Energy Systems
ALTERNATIVE ENERGY SUPPLY OPPORTUNITIES
(See also the buildings, land use and transportation sections.)
Renewable energy systems use resources that are constantly replaced and are usually less
polluting than fossil fuels. For the purposes of sustainability, these resources never run
out. Examples of renewable energy systems include solar, wind, and geothermal energy
(energy from the heat in the earth). We also get renewable energy from trees and plants,
rivers, and even garbage.
Resources: http://www.newenergy.org/links.html.
http://www.sustainable.doe.gov/municipal/sstoc.shtml This provides good case studies on
alternative energy supply from the US.
A.1 Cogeneration
Generation of electricity has traditionally been undertaken using the Rankine
thermodynamic cycle (see below), and often with steam as the generating medium.
Overall electrical generating system efficiency lies between 30 and 36 per cent depending
on the fuel and other factors. Even with the use of gas turbines and supplementary steam
generation, barely 50 per cent of the input fuel creates electricity. The remaining energy
is rejected to the atmosphere or to a nearby water source.
Modern thinking makes use of the reject heat, possibly for space heating, and thereby
reduces the fossil fuel requirements that would otherwise have been required for that
heating purpose. The process of efficient generation of electricity followed by the use of
reject heat is known as cogeneration or Combined Heat and Power and is fast becoming
the starting point for community energy or district heating systems. Through the use of
both electricity and heat, efficiencies of up to 85% are possible.
Draft 4/11/2005 107