Over the years, we have heard considerable rhetoric about investing in "clean energy" but what, exactly, does that mean?
Like most terms in common usage, it means different things to different people at different times.
The first time I heard the term "clean" applied to an energy generating system was about 25 years ago. At the time, we were still suffering the ravages of acid rain which was devastating the hardwood forests in the Maritimes, Quebec and the northeastern United States.
Acid rain results from the combustion of sulphur during the production of electricity by coal-fired power plants.
The American utilities relied extensively on such power plants - over 50 per cent of the electricity generated in the U.S. at the time.
The emissions from these plants, in combination with other gases, resulted in sulphur oxides which combined with rain droplets to produce rain with very low pH - very acidic precipitation.
The chemical reactions producing the acids take time and so the rain did not fall back down on the power plants. Rather, it fell hundreds or even thousands of kilometres away.
For a long time, both the American administration and the power producers denied responsibility. Eventually, better emission controls on newer power plants cleaned up most of the problem. The new coal powered plants have been deemed to be clean.
In this case, though, it was a relative term. They still emitted acidic gases - just not as many or at high concentrations.
They were clean in the same way your kid's bedroom is clean after they have stuffed everything on the floor into the closet. Not gone - just out of sight.
Indeed, it is actually impossible to have truly clean energy.
Further, coal-powered electricity generation is not particularly efficient. It is estimated that even with the new plants only 30 per cent of the energy obtained from combusting the coal ends up as electricity. The rest is wasted.
This inefficiency spawned a new wave of electricity generating power plants based on natural gas instead of coal.
The advantage, in this case, is natural gas is desulphurized at its source and does not produce the acid emissions a coal-powered plant generates. Natural gas power plants are also much more efficient with the new ones able to harvest as much as 43 per cent of the energy as electricity.
Hence, if the new coal-power plants are labeled as clean then the natural gas plants must be even cleaner, right?
Except it depends on what you mean by clean energy.
Both coal and natural gas power plants depend upon the combustion of carbon compounds for their energy and both produce carbon dioxide as an output. Carbon dioxide emissions are a major contributor to climate change.
To put things in perspective, a
kilogram of natural gas produces
10.8 kWh of electricity but generates 2.45 kilograms of carbon dioxide or
4.4 kWh per kilogram of carbon dioxide emitted. Not a particularly favourable ratio but better than brown coal, which generates only 2.8 kWh of electricity for every 2.93 kilograms of carbon dioxide or 0.95 kWh per kilogram of carbon dioxide.
Comparatively, natural gas is the cleaner alternative, but if you are worried about carbon dioxide emissions, then you can't say natural gas is clean.
How do these compare to generating electricity from other sources?
In British Columbia, with our mountainous terrain and abundance of rivers, we generate much of our electricity by hydroelectric dams. Once completed, these have very, very low emissions.
They do not rely on the combustion of carbon for energy.
Indeed, some would argue we get all of our electricity for free since the natural water cycle fills the reservoirs behind the dams.
This is not quite true, as both the dams and the reservoirs require maintenance and there are some greenhouse gases generated as a consequence of flooding valleys. However, the amount of carbon dioxide or any other emission produced by a hydroelectric dam once it has been built is a tiny fraction of the amount generated by combusting carbon-based compounds.
That said, it is the "once it has been built" part that leads to questions about the relative emissions. The Site C dam, for example, if it were built out of concrete would result in huge carbon dioxide emissions. Every tonne of concrete generates 1.25 tonnes of carbon dioxide just to manufacture, and not taking into account the energy spent on construction.
But even so, if you work out the carbon dioxide emitted per kWh of electricity generated, the number for hydroelectric dams is tiny - about 1/100th of the value for natural gas. In B.C., it is approximately 24 grams per kWh or 42 kWh per kilogram of carbon dioxide. In Quebec electricity is almost exclusively hydroelectric and generates only two grams per kWh or 500 kWh per kilogram of carbon dioxide.
By any measure, that is what I would call clean energy.
