It’s time to look over the spreadsheet and see what our energy consumption looks like for the year 2010. As both the end of last winter and the start of this one were very cold I guess one would expect to see that reflected in the numbers. This may have been very slightly offset by the fact that we put in about 5 cms of foam and foil-backed plasterboard onto the ceiling the main bedroom to try to reduce losses through our butterfly roof. I also insulated the loft hatches properly with two layers of the same.
Anyway, on to the numbers.
First up, plots of estimated total emissions. The numbers are either based on meter readings or calculations of distances travelled (more on that later), or they are based on national averages sourced originally from COIN – there are separate values for food, meat, and consumption (Things). I’d love to imagine that my consumption is less than average, but I doubt it. Although we’re a reasonably frugal household, we are definitely above average in terms of income (thanks to that amazing Where do you fit in? calculator produced by the Institute for Fiscal Studies – if you haven’t tried it yet – the result may surprise you). As there are two children that have come on stream since 2004, I’ve have used a completely empirical taper to increase their contribution to consumption and food with the assumption that by age 4 they are pretty well up there at adult levels. No doubt one can argue about this, but it should ensure that I’m over- rather than underestimating. So here are the bar charts since 2006 (2011 consumption numbers are already in there and notice that they’ve gone up further as our kids now count as two adults):2010 is well below 2009 and the reason is not hard to find – we didn’t fly at all this year and if you now look at the week-by-week plot of CO2 you can see that the increase is smooth rather than step-like.
In 2009 we flew to Switzerland, to Turkey, and one of us went to the US. In my spreadsheet I use a radiative forcing factor of 2.0 to account for the effects of aircraft emissions on the edge of the stratosphere (NOx, contrails, soot, etc.). The value I use is less than that listed in the IPCC’s Aviation and the Global Atmosphere (2.7-ish) because of more recent work that suggests that it may be lower. But as before I’d rather over- rather than underestimate our contributions. But even without that factor, flying really bumps our emissions totals up and that is a key and easy place where we can cut things, as shown by this year’s numbers.
The cold winter however, has had a significant impact on our gas usage which is up by almost 500 kgs this year – that’s about 20% compared to the year before. And there is precious little one can do about that with a Victorian house. We will double glaze the large bay windows at the front; replacing the panes there should cut heat losses through that room by about 50% and should make that room warmer than it is at the moment without needing an additional radiator.
But ultimately, my feeling is that this is likely to be as low as we’re likely to go without starting to clad the walls and that starts getting very very complicated, expensive and unpopular.
The final thing to mention is solar panels. We’ve now had these for 3 1/2 years. This is just past the expected energy payback time at 40 degrees north according to a number of studies (see for example: Vasilis Fthenakis and Erik Alsema, Prog. Photovolt: Res. Appl. 2006; 14:275–280). In June we got a Smart Meter and this finally allows me to see on a week by week basis how much we generate, import, and export.
What I find interesting is that we can expect the intersection of the electricity generation curve (orange) and our total consumption curve (pink) to occur in the next ten days or so almost exactly six months after I started recording the numbers. In other words, our sixteen panels look like they produce pretty well exactly the amount of electricity we use averaged over a whole year.
If in fact the UK used net metering, then we wouldn’t pay anything for our electricity. In practice that isn’t the case and our import tariff is about twice the export. But that’s another story.
Conclusions? There are clear ways of reducing emissions further – they are all no brainers, but they come up against all manner of difficulties. No flying and travelling less – can one really do that with relatives, collaborators, and experiments to visit abroad? Eat less meat? Yes, of course. But like St Augustine, “not yet”. And start cladding the house? Maybe I should sell up and buy something less Victorian……..
I guess the best thing I can do is to focus on where I work. More on that over the next few months.