Insulate our House?
Our home energy audit last fall told us that if we insulate our basement and our walls at 100 Prince Street (neither of which have any insulation at all), we can reduce our household energy use by 35 GJ/year.
The audit estimates that we use 188 GJ per year in oil to heat our house, producing 13.4 tonnes of CO2; lowering that to 153 GJ per year would lower our emissions to 10.9 tonnes, a savings of 2.5 tonnes per year.
We got an estimate from Greenfoot of $10,286 to insulate the walls (“drill and fill”) and basement (“2lb closed cell polyurethane foam insulation”); Efficiency PEI rebates would lower this to $8,036.
Put all this together, over a decade, and we’d save 25 tonnes of CO2, spending $321/tonne to do so.
Buy an Electric Car
Five months into 2019 we’ve spent $176 on gasoline for our 2000 VW Jetta, a total of about 160 litres; extrapolating over a year, assuming roughly the same consumption, 32 litres a month, we’ll use 384 litres of gasoline in 2019.
According to this conversion calculator, 384 litres of gasoline produces 0.93 tonnes of CO2.
We could replace our Jetta with a 2014 Nissan Leaf electric car for about $18,000 all-in, and we could charge it only from renewal energy
If we did that, we’d spend about $18,000 and, over a decade, we’d save 9.3 tonnes of CO2, spending $1935/tonne to do so.
So, which one?
There are several assumptions and missing parts built into my calculations (including the assumption that our 2000 Jetta will live forever), but as a gross calculation it’s helpful for making decisions about where money is best spent.
Buying an electric car is sexy and exciting and Jetsonian but, at least for people who drive as little as we do, it makes more sense, dollar-for-tonne, to put our money into our walls.