 |
Electricity in Your Home |
|
Electricity in Your Home |
All electrical energy that we use in our homes, (except for a few small battery-operated applications), is energy that is extracted from other sources. These sources are primarily:
Both nuclear and hydro sources of electricity are clean energy sources in terms of greenhouse gases, acid rain producing gases, and soot.
The environmental issues related to hydro electricity concern land use, water quality and resource (water) management. The really big advantage of hydro electricity is that, in addition to being considered the most environmentally friendly source of energy, it is relatively inexpensive and 100% renewable.
The environmental issues related to nuclear energy are related to the safe disposal of used nuclear fuel, and reactor safety. For a wide range of technical and design reasons, Canadian built CANDU reactors are the safest in the world, but the public perception of the nuclear industry is one of slightly nervous skepticism in view of some international nuclear disasters such as Three-Mile Island and Chernobal. Nevertheless, nuclear energy is quite safe and very environmentally friendly.
GAS:
|
Transparency Master |
Gas is the cleanest fossil fuel. Only electrical energy from hydro and nuclear sources are cleaner sources of electrical energy. If it were possible to do so, we would get 14kWh of electrical energy from every kilogram of natural gas burned, however the laws of thermodynamics make this impossible. We can only get, at best, 3-4 kWh of electrical energy from each kilogram of natural gas burned. |
A major component of natural gas is methane (CH4). Natural gas is a common fossil fuel used in the production of electricity and is burned to produce steam, which is in turn pumped to turbines which drive electric generators.
The process of extracting energy from natural gas is not 100% efficient. Energy is lost, (mostly as heat to the environment), during the conversion from chemical potential energy in the gas molecules to electrical energy in your home.
The diagrams below outline the major steps in the energy conversion process. If we suppose that we start with 10 joules of chemical potential energy in a sample of natural gas, we only end up with 2 - 3 joules of electrical energy in our home.
Typical efficiencies for fossil burning power plants (gas,coal, and oil),
|
To understand the impact of using electrical energy in our homes it is necessary to look at the greenhouse gases produced by burning fossil fuels. In this example we will consider natural gas since it is a widely used fuel for the production of electricity and because its CO2 production rate is similar to that of other fossil fuels.
There are three reactions shown below, all representing the combustion of methane, but describing the process differently. For our purposes, the third (mass) equation is the most important.
|
One molecule of methane plus two molecules of oxygen will burn to produce two molecules of water, one molecule of carbon dioxide, and heat.
|
|
Due to energy losses in the energy conversion process, the energy available as electricity to the consumer is 2-3 kWh per kilogram of fuel.
For convenience we will adopt a value of 3.5kWh per kilogram of methane. To determine the amount of natural gas needed to extract electrical energy, between 0 and 100kWh, one can use the graph shown below.
For arbitrarily large amounts of electrical energy one can use increments of 100kWh.
For the mass equation (above) for the combustion of methane, one can also determine the amount of carbon dioxide produced from natural gas to extract electrical energy. This is shown in the graph below.
From this graph one can determine the total CO2 produced for an arbitrarily large amount of electrical energy by using increments of 100kWh.
|
1 kW· h = 3.6 MJ |
OIL:
|
 Transparency Master |
Oil is easily transported, relatively inexpensive and widely available.
Actual energy available as electricity to the consumer is 3-4 kWh per kilogram of fuel. |
|
Two (-CH2-) hydrocarbon components (of a longer molecular chain) plus
three molecules of oxygen will burn to produce two molecules of water, two molecules of carbon dioxide, and heat.
|
|
COAL:
|
 Transparency Master |
Coal is the cheapest and most abundant fossil fuel.
Unfortunately coal is also a major source of sulphur dioxide, (which causes acid rain and soot). Actual energy available as electricity to the consumer is 3-4 kWh per kilogram of fuel. |
|
Four (-CH-) hydrocarbon components (of a longer molecular chain) plus
five molecules of oxygen will burn to produce two molecules of water, four molecules of carbon dioxide, and heat.
|
|
Molecular equation
