Thursday, 4 August 2011

Another way to cut CO2 and save money

While I had been focusing on the house as a way to cut our CO2 emissions, it was becoming apparent that there would be little we could do to find any more significant reductions in usage.

But, there was something we could change lurking outside of the house.  The cars!

We drive an average amount, and had a Renault Alliance convertible that was 25 years old, and got about 22 mpg in town (though it only drove 3000 miles) and a Chrysler Grand Voyager that got about 30 mpg, that was 10 years old, and starting to cost us quite a bit after we had its gearbox refurbished.

Rather than continue to fret about these two cars, I put my foot down and decided we needed to do something about it.

Now the UK has a scheme where cars that put out less than 100 g/km pay £0 road tax, less than 110 g/km pay £20, less than 120 g/km pay £30, and less than 130 g/km pay £90.

Older cars pay £180 per year.  So, right there, a potential savings of £360 a year, if I an get two cars in the lowest band.

Well, that didn’t happen, but we did manage to get a Citroen C1 (or Toyota Aygo/Peugot 107 depending on which brand you went with) that attracts only £20 road tax, and a Kia Cee’d SW 2 that attracts £90 road tax.  We had tried to buy a Skoda Octavia that is in the £30 bracket, but unfortunately had to cancel the order as delivery slipped.

The C1 has now done 4400 miles since we bought it (and with my son learning to drive in it), and averaged 48 mpg, more than double the 22 mpg car it replaced.

The Kia has been travelling all over the country with a boat on top for my daughters sailing, and despite that, has averaged 47.6 mpg over the 7000 miles it has travelled.

So, the Chrysler generated 58% more CO2 than the Kia and the Renault generated 118% more than the Citroen.

How much CO2 have we saved?  A ton!

On the Kia, 647 l * 2.7 kg / l * .58 = 1013 kg
On the C1, 416 l * 2.3 kg/l * 1.18 = 1129 kg

That’s a 55% reduction in CO2 caused by travelling, and that’s assuming we had the same cars.  In fact we’re actually driving less now too.

And how much money since last October?

Kia: £871.26 * .58 = £505 + £90
C1: £519.46 * 1.18 = £612 + £160

Grand total: £1367 in the 10 months we’ve had the cars.

An update on energy use

I haven’t updated the blog for 2 years, so here are the last two years worth of figures and the previous year for reference.

Season Degree Days @17.5C Average Per Day
2008-2009 2134 10.51
2009-2010 2121 10.45
2010-2011 2072 10.21

Our energy usage appears to have stabilized; here’s the daily average usage in kWh.

  Low Rate
High Rate Electricity
Per Degree Day
08-09 7.20 16.30 71.90 95.40 9.08
09-10 7.09 16.18 62.52 85.79 8.21
10-11 7.14 18.46 60.73 86.33 8.46

What happened in 09-10?  My wife was away skiing, and it was also very cold.  I took the opportunity to tape over the open fire in the lounge with cardboard and duct tape.  I had planned to stick a picture of some flames on top too, but never got around to that part.

That simple measure dropped our usage by over 10%.

In November 2010 we replaced our open fire with a balanced flue system, installed additional installation over another part of the loft, and installed new double glazed french doors.  Despite this, it appears that our usage actually increased, though that may have been caused by a large family Christmas last year.  We also actually used the fireplace, and the loung was a little warmer.

It certainly felt like a colder winter last year, despite the number of degree days being lower, and we had long period of snow and sub zero temperatures.

Alas, because of the balanced flue, we began to have some problems with condensation, because air wasn’t being sucked out of the chimney, so we also began using a dehumidifier for some of the year to prevent condensation.  It turned out reorganizing the loft to add additional insulation had blocked the airflow, and that was actually the cause, so we now rarely use the dehumidifier.

Again, I also tracked our neighbours usage (with their permission of course)

  Average Daily
Total kWh
Per Degree Day @ 19.5
08-09 106.70 8.50
09-10 98.93 7.95
10-11 94.74 7.76

This autumn, we install Solar PV, as I mentioned earlier today.  Fingers crossed we can bring down the energy usage even more.  I’ve also started a campaign to hibernate off PC’s when you’re not actually sitting at them.

Solar PV

Earlier this year I wrote:

I keep hearing people tell me that it's crazy not to install PV on our house, especially with feed in tariffs that pay back almost 40 pence for each kWh generated, so I thought I'd look into it at bit.

So, start with the assumption that we fit about 2.1 kWp to the house, that means that on a perfect day, the solar grid would produce 2.1 kW of power. It turns out that where we are, the expected output of that panel would be around 1750 kWh per year. That currently costs us about £150 for that amount. Now, the feed-in-tariff would also pay an additional £720 per year (tax free? maybe let's assume it is).

Now, the installed cost for this system is £8700, which the solar websites tell me would make me £29,000 better off after 25 years, and that I break even after 8 years and 6 months. Really? Where do I sign up, and do you have a bridge you want to sell me too?

Sure, the government currently promises that we'll get the subsidies over 25 years, but I'm not sure I trust promises from governments.

Now, what's the real payoff time?

Well, first of all, the opportunity cost on the money is missing. Let's say that you take your savings out of a nice safe bank account to pay for it, and that it's currently paying you 1% interest.

The lost interest costs you £87 per year, so that now takes you 13 1/2 years to break even.

But I know you manage your money better than that. You can get 3% really easily here in the UK, and interest rates are soon to rise. At that rate it's 13.5 years, but if you think you can pull off 4.5%, it goes all the way out to 18.5 years. Don't even think about taking out a loan at 7.5% to pay for this; if you do, payback goes out to 31.5 years!

If you instead ignore the government subsidy, even at a paltry interest rate of 2% on your money, you're losing £24 a year every year.

Never mind you've invested your capital so if it breaks, you lose your investment, unless you insure which costs you money, making payback worse.

So, for me, I've decided to put this on the back burner again, until something else changes.

What’s Changed?

My old college roommate installed the panels on his house, and they are producing electricity as expected.  Based on the quotes he received I did the above calculations.

However, when I actually came to have someone quote me, the installed system price was just over £6500, giving me a payback time of shortly over 7 years.

The parts are guaranteed for 10, so even if it all goes wrong, it looks like the system should pay for itself, so we’ve given the go ahead, and in just over 4 weeks time, we should be generating a quarter of our electricity.