Tuesday, October 21, 2008

Measuring Energy

The first step in saving energy is to measure how much energy one uses. You might think that your utility company already does that, and you would be right, but I am talking about taking control here. If you were to ask yourself how much energy you use a year, it is possible that you know how much you paid for that energy but it is unlikely that you know how much energy you have used and this is what is important, the amount of energy that you use, if you don't know how much you use you'll never know how much energy you are saving. It seems unlikely that prices will be coming down soon or ever for that matter (I'll rant about that in another occasion), therefore any savings are going to have to be made by you, but before you make any savings you need to know how much energy you have used.

In a country like the UK, heating during winter is essential, particularly given the age of the housing stock, and air conditioning in the summer is a luxury. If you, like me, heat your house using gas (LNG) then your gas bill is going to be determined to a large extent by the weather. If you don't use gas, your electricity bill will be affected by the weather, but there is plenty of scope for reducing it.

At any rate, grab your old utility bills and get counting. Go back as far back as possible and look at the kWh figures. You want to compare like for like, therefore if you have made substantial changes to your house, e.g. doubled glazed windows, insulation or added an extension or conservatory, get your bills from after the change, that way you can measure exactly how much energy you use in your house as it is now. What you want to arrive is at a yearly usage figure for both electricity and gas. This will be your baseline energy use, your target as it were.

This is all well and good, but I appreciate that with utility companies relying more and more on estimates, the figure you arrive at might not be very accurate, that's true, you could try going back a couple of years and calculate the average energy use per year, that should iron out inaccuracies due to poor estimates.

Armed with this figure(s) (My figures below)

7500 kWh for gas
1900 kWh for electricity

You are ready to start saving.

It might be due to my scientific background but I like talking of energy use in kWh rather than how much it costs. This approach is more transparent as the savings or otherwise are not dependent on the whims of the utility companies. It is also fiendishly hard to calculate how much you are actually paying because of the many discounts and tariff tiers, kudos to EbiCo for having a simple tariff.

In order to simplify the calculation of how much energy you pay for during a year, I suggest you do the following:
  • Ignore discounts (Dual fuel, online, special rates, etc)
  • Calculate an average electricity and gas price tariff.
In order to calculate an average tariff one needs to calculate the relative weight of each tariff, so in my case my supplier (Scottish Power) charges anything above 4572 kWh p.a. at a lower rate, talk about madness, the more you use the less expensive it is, comparatively. Anyway back to my calculations:

4572/7500 ~ 0.61

So 60% is at the higher rate (4.860p per kWh), 40% at the lower rate (3.837p per kWh)

My average gas tariff = 0.6*4.860 + 0.4*3.837 = 4.497p per kWh

Doing the same for electricity I get an average rate of:

11.57p per kWh

(The cut-off for higher rate is 900 kWh p.a. for electricity)

Just bear in mind that the lower your energy use the higher your average rate will be. However, do not be deceived into thinking that you are not saving money, you are. Think about it this way, If I were to use 4000 kWh of gas a year, it would cost me £194.4, however if I were to use 5000 kWh I would pay £238.6.

So armed with these figures on to the energy saving sunset we ride

No comments: