Incorporating of how to work out your generation from solar panels used in your own home?

[Oscargrouch]

I am trying to incorporate the amount of Solar generation used in my own home.
I know the figures for how many kWh I imported prior to having panels installed, and have worked out approximately what kWh were used during each quarter. The date of installation was Nov 22nd 2011. So my spread sheet starts from this date. My attempts start from row 23 -27, could anyone help in sorting these out so that they calculate properly please? If year 'Stats 2013' is done, I can probably sort out the other years...Thanks
Example I have of how to work it out is:-

Calculating what you export

If you want to do a rough calculation of how much electricity you export over a year you
can carry out a very rough estimate by:
calculating the amount of electricity you used in the year before your PV system
was installed in kWh (import year 0). You can get this from previous electricity
bills
•
calculate the electricity you've imported in the year since your solar PV system
was installed (import year 1). Again using electricity bills
•
make a note from your generation meter of the amount of electricity your solar PV
system generated in year 1 (total generation). This should be over the exact same period as bullet above.
•
For example, if you imported 4,000kWh in year 0, imported 3,400kWh in year 1 and your total generation in year 1
was 1800kWh then you will be exporting 67% rounded to the nearest decimal point. This has been calculated
using the following formula:
Total % exported = (1 – change in import over two periods (kWh)/total generation (kWh)) x 100
67% = (1 – (4,000 – 3,400)kWh/1,800kWh) x 100)
In this example, the fact that you’re exporting 67% of the electricity generated also implies that 33% is used on
site which is the saving you make from import.

Sample.xlsx