Why are gas meters read in cubic metres but bills calculated in KwH?

Suffolk_lass

Is there a good reason why the Gas meter reading unit cannot be converted into a chargeable unit on a one-for-one basis when you are on a fixed price deal?

I do try to help my aged Mum and had set up a fixed price deal for her but was aghast to find my calculations were nowhere near the figures on the first bill. Mine were based on her meter readings for the first six months that we have used to track her consumption against the stated unit cost and multiplied by the daily standing charge, and then adding 5% VAT).

It was only when the first bill arrived and I looked into it that I realised the gas algorithm is not transparent, not straightforward, and despite the deal being fixed price for standing daily charge and per unit cost, the supplier can and still does change variables within the calculation of the unit.

These are:

1. Volume correction factor (seems to be 1.02264 currently) which allows for seasonal variation - is this because gas more dense in cold weather?

2. Calorific value - On various calculator sites this is shown as about 40 (always between 37.5 and 43, apparently) but on my Mum's bills it is 39.5 in the summer bill (last one on the old deal) and 39.4 on the bill she has just received. Apparently Transco monitor this and pass the values to the supplier daily (is it that volatile?) and it is based on megajoules per cubic metre.

This begs the question - if the supplier has this daily, why are we seeing this shown as a single unexplained figure for each meter-reading interval?

Worse than this is the calculation:

1) Number of units used (e.g.) 100 based on gas meter
2) Multiply by volume correction factor (1.022640) = 102.264
3) Multiply by calorific value (39.4) 4029.2016
4) Divide by kWh conversion factor (3.6) 1119.2226

Given the gamble element in fixing the tariff, couldn't the supplier also use historical calorific value data to determine an average CV and correction factor values and provide the tariff as a price per cubic metre so that customers can calculate costs on a consistent basis and budget properly?

I have posted this for two reasons:

To establish the basis for this convoluted and opaque calculation and to share with others why it is so difficult to calculate and predict your domestic energy consumption.

Back to the spreadsheet now…

SL

C_Mababejive

Simply because the gas supplied is volumetric but the mechanism by which you are charged is by heat/energy value. I do tend to agree that the cv doesnt vary all that much and it would make sense to simply change to volumetric direct charging. I'd be more conerned about the purity of gas supplied in particular how much foreign substance and water vapour is contained therein.

molerat

The only one that varies between bills is calorific value. When estimating multiply the meter units by 11.2 to get the rough kWh value.

Ryune

Gas is affected by things like temperature and pressure so there needs to be allowances for this. For smaller supplies the variation on CV doesn't make a huge difference. For large supplies (i.e. factories) though it can make a difference of hundreds of thousands of kWh. For that reason the calculation is done and it would be awkward to do it separate ways based on supply size.


For calculating all you need to do is use 11.2 for a Metric meter and around 32 for an Imperial meter and not worry about the detail.

macman

Because the meter can only measure volume, not energy. Since the billing is in kWh's, and the conversion factor is not a constant, it can't be done on the meter.
In reality, the changing calorific value makes no more than a few pence difference per year.
Also, remember that there are still many imperial meters installed, so a conversion on the volume side has to be done for them anyway.

SwanJon

Gas is a natural product and varies in quality.
Some days it has more energy than others, and so a smaller volume is needed for the same amount of heat.
National grid monitor this at stations around the country - you can find the figures on their site.
You can't see a daily value on your bill as you aren't billed daily - the suppliers use an average for all the days in the bill.

I think calling the four steps an algorithm is a bit much, and the way you set it out seems fairly transparent. While the numbers aren't round, multiplication and division are primary school maths, so quite simple, especially with a calculator or spreadsheet.

I do agree that the explanation for the figures and calculation is poor.

macman

This makes the job even easier:
http://www.energylinx.co.uk/gas_meter_conversion.html

C_Mababejive

Indeed..though one thing that is no longer monitored to any great extent is the amount of water vapour in the gas sold to you via your meter and so no one knows least of all the punters, how much heat energy they are being done out of. This used to be closely monitored but now isnt as OFGEM decided that it was no longer required. They had their reasons for doing this which i shall not go into here..! If you went down the petrol station and bought 10 litres of unleaded and then the lady in the office came and tipped 250ml of water into your tank and asked you to pay for it,how would you feel about that?

[Deleted User]

I agree with the OP about the terms kwhrs. Hardly anyone I meet actually understands what it is , or means. It just confuses every one. I can never understand why the big suppliers dont set about some basic customer bill awareness programs, or even TV ads like the clunk click seat belt adverts we all got in the 70 s. BBC Watchdog once did a little story a few years back where the winner of "Mastermind " tried to understand an energy bill and struggled. Getting rid of the two tier standing charge s will help, but surely a few mailshots explaning what it all means would help

silverwhistle

Funnily enough I was doing a similar exercise earlier this afternoon. As Npower don't seem to want to send me bills (none in 5 months since I moved in and changed to credit) I've been keeping a weekly watch on my usage. I think I was using a rough overall conversion rate (units to kWh) of 11.5. I wanted to check as that was only a figure that had stuck in my mind from gawd knows where. It actually needed a fair bit of rummaging around to find the appropriate figures. I'm not too bothered about the full calculation, although I'm perfectly capable of working things out. But for rough domestic consumption estimating purposes it would be quite good if they could publish an appropriate figure somewhere, (11.5, 11.15, 11.2 or whatever) with a decent explanation - as suggested by sacsquacco - for those who know even less than I do!