Board logo

Maths help needed
Jasper - 12/12/09 at 06:36 PM

Ok, my brain is already muddled with beer, so I need some help. I bought one of those electricity meter that tells you how much you're using. Trouble is, there is a single value for kWh, and our bills have two amounts. So what I need you cleaevr chaps to do is to work out my arevage price per kWh:

242 kWh at 18.66 each used: £45.16
2004 kWh at 9.71 each used: £194.59

So, on a regualr period, what would my average kWh rate be?


big-vee-twin - 12/12/09 at 06:43 PM

9.36p/KWh


matt_gsxr - 12/12/09 at 06:43 PM

average price = total price / total kwh

239.75/2246

~11p

Matt


big-vee-twin - 12/12/09 at 07:01 PM

Matt is right I am wrong


Jasper - 12/12/09 at 07:25 PM

Cheers Matt


craig1410 - 13/12/09 at 01:42 AM

I'd tend to keep the equivalent of the standing charge separate and then just track usage based on the actual £/kwh cost. Otherwise it will be inaccurate and will only be accurate if you continue to use the same energy you have been using up until now which I presume you hope to reduce. To visualise this, think of a graph with a steep initial line of 18.66 followed by a reduced slope of 9.71. By averaging this out you are replacing two lines with a single line so it will not be accurate except if your energy consumption is the same as last time.

Assuming the figure you quoted are quarterly figures then you are paying a standing charge of 23.7p / day. This worked out as follows:

Premium on first 242 kwh = 18.66-9.71 = 8.95p
Multiply by 242 to get charge per quarter = £21.66
Multiply by 4 to get charge per annum = £86.64
Divide by 365 to get charge per day = 23.7p

So, what is really happening is that the energy is costing you 9.71p per kwh and you also get charged 23.7p/day standing charge.

So, if your aim is reduce energy consumption then use the 9.71p per kwh figure to gauge your savings and accept that you will have to pay 23.7p per day for the privilege of being connected to the grid.

I don't like these dual rate schemes because nobody ever reduces consumption below the threshold between rate 1 and rate 2. It's a bit like BT changing their billing to absorb the line rental into the call charges by having two different rates for calls.

I hope this helps and doesn't just confuse you.
Craig.