I listened with amusement last night to a CBC Ideas show featuring a story about an allegedly solar powered house in Toronto (the Ravina Project). I am always skeptical when I hear claims of how people have gone off the grid, especially when they live in cities. And for good reason: it takes a lot of energy to do ordinary household things like boil water for tea and make toast.
For example, let’s say you have friends over and want to make a pot of tea. Your teapot holds 1 liter, so you have to boil one liter of water. Well, it takes around 3.97 British Thermal Units (BTUs) to raise the temperature of one liter of liquid water by one degree celsius. Water boils at 100°C. So if you started with water that was at a temperature of say 15°C, you’d need around 337 BTUs to boil it (3.97 BTUs x 85°C).
What is the cleanest way to get those 337 BTUs? The Ravina Project house is, allegedly, now less dependent on grid electricity, so we can assume that its owners consider gas to be the better way.
Is it? Let’s compare the carbon dioxide (CO2) emissions involved in boiling one liter of water using natural gas versus those of using Ontario electricity.
According to the U.S. EPA, a million BTUs of natural gas will, when burned, emit 116.39 pounds of CO2. I’m Canadian, and use metric units. So a million BTU of gas will emit roughly 53 kilograms of CO2.
That works out to roughly 0.053 grams of CO2 per BTU. Remember from above that we need 337 BTUs to bring a liter of water from 15°C to 100°C. So if we got those 337 BTUs from natural gas, we would emit roughly 17.8 grams of CO2.
And if we got the 337 BTUs from an electric stove powered by electricity from the Ontario grid? Well, the grid’s CO2 intensity per kilowatt-hour tends to vary during the day, depending on the generators that make the electricity. Right now (ten a.m. on Saturday, August 4, 2012), CO2 intensity of Ontario electricity is roughly 140 grams of CO2 per kWh.
Our 337 BTUs work out to roughly 0.09 kWh. So 0.09 kWh of Ontario electricity at 140 grams CO2 per kWh comes to just over 13.83 grams of CO2.
So to get 337 BTU from gas and electricity, here’s the comparison:
|Natural gas||Ontario electricity|
|17.87 grams CO2||13.83 grams CO2|
The upshot: if you use a gas-fired stove to boil your tea, you’ll release slightly more CO2!
It turns out that the aforementioned house indeed uses a natural gas stove. And not just a gas stove. They heat their water and dry their clothes using natural gas as well.
Sorry, but that’s not green.
They would be greener if they just stayed on the grid.
More important is the fact that around 85 percent of the 140 grams of CO2 per kWh of Ontario electricity right now come out of natural gas-fired generating plants.
If there were less gas and more nuclear feeding the Ontario grid, the 140 grams of CO2 per kWh would drop.