May's solar generation stats and quarterly feed in tariff results

Here's the graph for May's generation from our array of solar panels. This is for our 2kW 8 panel solar array (Panasonic HIT panels), mounted on our south-facing roof at approximately 35-40° angle from the horizontal.

The turquoise line is May - the orange line is December (the lowest solar generating month) by way of comparison.

May has not quite hit the forecast target for the month.  The forecast suggested 228.85kWh would be generated in May, and the panels actually generated 221.8kWh, which is 7.05kWh down on the monthly forecast.  

This works out at an actual average of 7.15kWh generated per day.  I put this down to May being more-than-averagely cloudy this year.  Although we have hit another daily record this month - on the 6th May, the panels generated a total of 13.7kWh.

Here's the yearly forecast chart:

And the yearly sun-strength chart:

The June value is for the first 3 days of June only and so is not accurate.

Feed-in Tariff
One thing I have completely overlooked in my financial projections is the fact that the amount we get paid for our solar generated electricity under the feed in tariff is index-linked.  The pence-per-kWh increases every quarter, and this quarter it's gone up by a monumental 0.277p per kWh generated, and 0.1p per kWh exported. At the end of the first year I'm going to factor this into our 20-year projections and see how much it brings down the time-to-repay figures.

The spring feed-in tariff is in. For the months March - April - May the panels generated a total of 638.8kWh, for a total of £112.26 (100% generation at 15.1577p/kWh + 50% exported at 4.731p/kWh).

We also benefit financially by using our own solar-generated electricity, as this is electricity we're not having to buy from the grid.  Our electricity meter only measures how much electricity we use in total (solar + grid), and the solar meter only measures how much electricity the panels have generated, and trying to estimate how much of it we've used ourselves is getting tricky. The sun is shining more often, and I can't keep ducking into the under-the-stairs cupboard to see if the electricity meter has stopped counting up.  Having my office at home means we are using a lot more electricity during the day than normally would be expected, but I'm going to hedge my bets and say we have used 75% of our solar-generated electricity this quarter.  This equates to an additional saving of £71.43 of electricity we've not bought from the grid.  This brings the total benefit to £183.50 for the quarter.
Here's a graph showing how much electricity we've bought from the grid over the last 12 months:

The panels were commissioned on the 28th August 2013, which was when I started taking regular readings. The first reading (June 2013) is an average of the previous 5 months.  Still, we're approximately 10kWh per day lower compared to this time last year.  Unfortunately, I can't put this all down to the solar panels, because I've also been fitting low-energy lights throughout the house (and insisting the boys turn the TV off when they've all left the room!) which will also have contributed, but by how much I can't tell.

This has also got me thinking again about energy storage - for every kWh I export to the grid, I get only 4.731p. Whereas if we can use all that energy ourselves, we save 15p/kWh not buying it from the grid. Depending on the set-up costs, it sounds sensible to have small short-term storage (up to a maximum of say 5kWh for 8-10 hours), so that excess generated during the day is used in the evening for lighting/TV etc. -  but I'll save that for another blog!