Download daily data since installation of my 3·29kW system

A Guide to the use of the Excel Spreadsheet

Most of the headings should be self explanatory.

Column B is the total power output on the day in question. Column C is the total power output since installation date. D is the number of kWh needed to fulfill the annual (supplier provided) prediction and E is the ‘profit or loss’ on that prediction.

F is the average daily output for the month, G is the accumulated total for the month. H is power generated against the prediction for the month expressed as a percentage.

I is the cumulative annual achieved output as a percentage of the annual predicted output.

K and K are calculated from the current Feed in Tariff plus the deemed 50% export.

Columns D, F, G and H are reset on the 1st day of each month to reflect the new monthly prediction as necessary.

The interest and profit columns compare the FiT plus 50% deemed exported with the daily compounded interest which may have been gained had the money been invested and the interest taxed. 3% is chosen because that is what I was getting from the instant access account from which the money was taken. The rate will be adjusted if the instant rates I might have earned are changed. The higher rates are given solely for illustrative purposes. My inclination would not be to put money into a five year bond at the present time and so for me the figures are academic but may be of interest to others. If long term bond rates are changed the figures used here will not be, at least not in the first five years as that would be unrealistic.

Column O can only be regarded as a guess at this early stage of the system’s life. It is my savings on the electricity bill at my current tariff if I use half the generated power. In Winter with a pond pump and computer gear running constantly that may be possible but in Summer could be optimistic. An adjustment may be made in the light of experience.

I hope the spreadsheets will be of assistance to anyone contemplating a similar installation. Feel free to modify if you wish.