HiPoppy,
I think I have exactly what you are looking for.
We have Geothermal in since last December. When researching it I could find no detailed cost of running only estimates. So I got my electrician to put a meter on it so I could calculate the daily running costs to prove to myself I had made a good decision, and so I could pass these on to other people considering putting it in (and prove many doubters wrong). I have the daily breakdown if you would be interested in seeing them.
In short here are the average daily running costs per month since I started recording the meter.
February€4.53
March€4.02
April€4.10
May€2.67
June€1.23
July€1.01
August€1.38
Total Daily Average€2.71
This does not include nightsaver, which roughly means taking off a 1/4 of the price, so at the moment it's costing 2.03 / day = €741 a year, for constant heat and hot water in a 3500 sq foot house. However I expect October, November, December and January costs to be high say €4-5/day still only = €850/year.
Thats for 24/7 heat and hotwater. People have argued that a fill or 2 of oil sees them through a year, but not without occasional use of the imersion heater, and certainly not without occassionally finding the house freezing when they get up in the middle of the night, or get home late etc etc.