Now that my rooftop solar is up and running, we have some data to analyze. One question, surrounds the environmental benefits, more specifically, how much carbon dixoide emissions have been avoided with the solar project. For that, we need two numbers, the amount of electricity produced (in kWh), and the carbon intensity of the grid here in Toronto. Unless you have a giant roof, or your grid is particularly dirty, rooftop solar is unlikely to be more than a break-even proposition, however investing in solar projects in norther communities is on par with tree planting.
Lets start with carbon intensity, on the average it takes about 100 g of CO2e to create 1 kWh, using the grid here in Ontario (source), the actual value fluctuates a fair bit, on a windy and sunny day, its is a lot less, while on a “dunkelflaut” day (e.g. one with no sun or wind), it is a lot more. But 100 g CO2e/kWh is a nice round number that falls within the average range here in Ontario (source).
This June I am on track to produce about 1 MWh of electricity. I suspect I could have produced a bit more than that, perhaps 1.5 MWh as I only got approval from my local utility to export to the grid mid way through the month, and there were times before, when solar production was curtailed as the energy had nowhere to go. This is inline with my solar installers estimate of about 12 MWh of production over the course of a year.
Thus, my 12 MWh produced, presumably saves 1.2 t of CO2 per year. Not bad, about the equivalent of carbon emissions created by an economy class passenger going across the continent to say Vancouver (source).
Granted, there is a bit of double accounting going on here, as my 12 MWh produced is about the same as my estimated annual electricity usage, but it is worth discussing the overall concept, can a solar project serve as a meaningful carbon sink?
For that to work, I run into two practical problems: Not enough solar potential, and cleanliness of the Toronto grid. Start with the solar potential, while I could add panels to my garage, and some shadier roof sections, production is very unlikely to get any higher than 16 MWh/year. Then there is grid cleanliness, 100 g/kWh of CO2 eq is pretty good, figures for Natural gas generation are about 500 g/kWh CO2 eq. (source) and Diesel generators go quite a bit higher sometimes even to 1 kq/kWh (source).
So, even with every square foot of roof covered in panels, I am more or less just treading water. Namely, my solar system generates the energy what my house consumes, and little more.
If the goal is carbon dioxide emissions, a community project might make a lot more sense. Particularly if the community mostly relies on Diesel generators, where the diesel is flown in. This happens in some parts of Canada’s North. I suppose it might take about 1l of Jet fuel to fly in 1l of Diesel, why that might push carbon intensity to 2 kG/kWh, 20 times more than the grid here in Toronto, while installation costs, and transport costs are likely to be a bit higher than the $3 or so I paid per W of installed capacity, it might overall be a good deal (source).
Now, my rooftop solar project, cost me about $3 per W installed, and that installed W could over the course of a year generate 1.2 kWh over 20 year life, thats 24 kWh, or at a Torontonian 100g/kWh, at the cost of $3, I have avoided 24 kWh x 0.1 kG/kWh = 2.4 kG of CO2. Per tonne, thats 1250 $ per tonne of CO2. Yikes, tree-planting gets us 20$-100$/tonne of CO2 (source).
Assuming that a fly-in-Diesel community would pay $4 per W installed, with similar solar radiance to Toronto (say 1kWh/W), 2 kG/kWh carbon intensity of electricity generation and 20 year solar life. All that gets us to 20 kWh generated per W installed of solar. Those $20 kWh avoid 40 kG of CO2 at a cost of $4, which is $100/tonne of CO2, on the upper end of what a tree-planting effort might yield.
Granted, wetlands restoration might be cheaper than tree-planting, with some suggesting as little as $5 per tonne of CO2 (source).
Electric car adventures 