UPDATE - Photo-voltaic cells: free money

I wrote with conceit about a year ago about our PV cells. It is now two years since their installation and the pictures they generate begin to stabilise.

The average daily generation and usage look like this (click to enlarge)

(recall that "usage" is not a clearly defined quantity).

The best fit sine waves to generation and usage, plotted on the graphs, are (click to enlarge):

The waves are (again) reassuringly homed on the spring equinox. The average daily generation in 2011-12 was 9.8KWh, and in 2012-13 was 11.3KWh - yes, the weather really was better!

Out of interest, remember especially that June 2012 was awful, and July 2013 was pretty good - here are the pictures for those months against the best fit - no prizes for guessing which is which:

Well, the upfront money-in-pocket from the FIT is now over £5/day. What we save from using free rather than costed power, and pushing surplus into the grid, is as ever secondary and difficult to pinpoint, but is certainly another positive quantity.

We're not regretting this purchase.