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Discussion Starter #1
Yesterday I deliberately ran the battery down so the car went into ER mode and I plugged it in to charge the car consumption meter read 51.8 to start with and after the charge was complete it was 64.9 so it took 13.1 kWh to charge from flat. The energy usage popup showed 10.5 kWh had been used from the battery. That is a 2.6kWh overhead to charge from flat as far as I can see.

Now at the moment I am still working on the best way/rate to charge the car from my current supplier but given whatever tariff you are on, as far as I am aware there are two rates.

1). for the first x units per year you pay a higher rate
2). for all subsequent units you pay a lower rate

The way this seems to be calculated is:

date of current bill - date of last bill = days between bills
higher rate units for this period = Round(x units per year / 365) * days between bills
lower rate units for this period = units used in this period - higher rate units for this period

Then using the reading from the car consumption meter:

car units used in this period / units used in this period = percentage used by the car

I then use that percentage to calculate the cost of each type of unit used and over 218 miles this gives me a figure of £0.05 / mile so far, but it's early days.

What results are you getting?
 

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The Higher-rate/lower-rate tariffs are the alternative to the old standing charge + units used. (the higher rate will generate the value of the old standing charge, then swap over to the lower rate) If you go to a tariff with a standing charge you will just pay the lower rate for all units.

Also it is likely that your domestic usage will use all of the higher rate units anyway, unless you are exceptionally frugal, so just run your calcs on the lower rate.

There are some companies that offer only one tariff for all units (https://www.ebico.org.uk/products-and-p ... and-prices), Whilst these are beneficial if you have relatively low usage, ie if you have gas heating and cooking, they may not be so good for ev users, Because they recoup the standing charge section across all their users, so if you use above average you pay above average. (do the maths to find out!)

P.

PS EBICo (that I linked above as a flat rate supplier) are very fair with their pricing and are also 'not for profit' they may be a good solution for you, as always find out by doing the sums..
 

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Discussion Starter #3
When not cooking (electric oven/microwave) the house consumes a max of around 600w even with the lights on (LED or low energy) and the central heating running. for the last two months that is approx 300 units but I also have a 4kWh solar array which complicates things a bit.
 

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Was that 300 just domestic usage? if so 300 units in 2 months would put you at 1800 units per annum. the High rate from Eon (http://www.eonenergy.com/At-Home/Produc ... counts.htm) is for the first 900kWh (units) So your usage is way over the high rate in this case. Any additional (ie a new ampera) would be based on the low rate only.

Check your own supplier rates though!

P.
 

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Discussion Starter #5
Yes that was domestic usage only I subtracted the Ampera meter reading. Your right of course but to be pedantic about it the Ampera should take its fair share of the higher rate. In order to calculate the true cost one should consider the Ampera as being the only load on the electricity supply, would you not agree?
 

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No, the true cost is the extra you have to pay over what you would have paid without it. So ignore the standing charge/higher tariff as that is already all used up.
 

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As Duncan Said^

Owning the Ampera does not make your microwave cheaper to run. So you can't take funds that you currently account to the microwave and move them to the Ampera.

Just accept the standing charge part of the rates (treat it as you would with BT line rental) and use the low rate for all your calcs.

To calculate the standing charge part use: ([High Rate] - [Low rate]) * [number of units at high rate]

P.

(Or move to a flat rate provider.)
 

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I did the full charge and took meter readings before and after. My meter is a kWh meter on the Home charging unit so I am certain it is only recording the car charge.

These are the readings:

Before charge: 2495.81
After charge: 2508.66

Total: 12.85 kWh


20120711_114354.jpg by Paul Churchley, on Flickr


20120712_080359.jpg by Paul Churchley, on Flickr

Using the accepted caculation of 9 kWh being equivalent to 1 litre of petrol and given I usually get about 45 miles per full charge this puts my Ampera as using the energy equivalent of 1.43 litres per 45 miles or 143 MPGe.

Combine that together with my normal petrol only fuel use of about 60 mpg and a lifetime of 90mpg.

Not bad eh?
 
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