2015 Weather Statistics

I've recently finished my quick and dirty sun analysis for 2015 based on the Met Office data. Here I take the data for the Heathrow weather station and apply a few quick tricks to understand the amount of sun we've had in the years relative to previous years available on file. In this case there are now 59 years of data available.

I get the following results:

The Max, Min, Mean and Stdev stats are based on the last 59 years of data by month and are the numbers of hours of sun reported.

First, the good news. The year started well with fairly average Jan and Feb - Jan was actually quite good, but offset by a slower Feb. March and April were excellent, with April the 7th sunniest in the 59 year sample. April, it turned out was to be the sunniest of the year and my generation statistics back that up.

And then the averages started to bite. May, June and July were ok - but very average. I hope to have at least one monster month each summer when the sun comes out to play and stays there. In 2015 this did not happen, I suppose we were paying for April.

And then, the rot really set in. August was unseasonably dull the 55th sunniest out of 59 - pretty close to the bottom. Then September, which can often be a great month was dull and 57th out of 59. October was closer to average but without making a big contribution.

And then November. What can I say? The least sunny November in 59 years with only 41% of the average for the month, my lowest ever solar panel performance on record (in terms of % against model) and a grey 30-day period that never seemed to do anything. At least it kept unseasonably warm which kept the heating bills down.

Thankfully December was a little better and actually produced more kWh than November. But still there were too many dull days. 

Overall the year was not that sunny (45th out of 59) and 7% down on the average. Thankfully this was enough to hit the annual target. Although as expected not as much as the previous years.

Hopefully 2016 will be a bit better.

2014 in a nutshell

So, 2014 came and went -  a great year in theory for the PV system, but in reality it lacked any real outstanding performance.

On paper it was a very sunny year, but this was not the case in all months and in it failed to appear in the key months that mattered (April, May, August  and September for example). So whilst it was a good year, it wasn't a great year.

However there were a few milestones - November saw 10mWh appear on the meter. So just under three years since the system went in and the numbers look good. So, as a rule of thumb and subject to decent weather it looks like the system will create nearly one kWh of power per year for each watt of solar panels I have. So that's not a bad figure to aim for.

Money wise, the FIT payments keep coming in - £1600 a year is not to be sniffed at - and it looks like I'm using 70% of the power being produced. I've worked the latter out based on 2 methods:

1) the reduction in my electric bills

2) detailed analysis of the OWL data based on previous usage levels compared with the minute by minute data over a year (i.e. what amount of energy would be used vs exported each minute assuming a 1000w continual household consumption).

Both converged to the same number, so that's good enough for me.

Outlook for 2015... well hopefully more sun, more free power and I suspect a year end total close to 14mWh.

September 2013

September was dull.

It felt very grey from the start of the month and so it continued. I had to scrape back every last kWh to hit the target this month (this meant checking the generation meter under the stairs and finding my Owl estimates were a couple of units light).

101% of target achieved which was not bad given the we only had 81% of the average hours of sun during the month. September 2013 was the 47th sunniest in the last 57 years - you get the idea, it felt like Autumn all the way through and the PV system reflects this. Still, to continue generating under such conditions shouldn't be underestimated.

Unlike September 2012, I did not complete the year's generation target in September, falling about 20 kWh short by the end of the month. This will easily go during October, but the stats don't lie - I'm down on the previous year and the weather feels like that too. Maybe 2014 will give us a treat instead.

August 2013

August was good without being great - good kWh figures most days but what it lacked was the solid weeks of good weather that really help the numbers stack up when you hit 120+ kWh in seven days.

Still no complaints, 425 kWh produced, in what was a distinctly average month - we had 104% of normal hours of sun during August, with the months being the 23rd most sunny since 1957. Very average, but lots of watts anyway.

July 2013

Ok, I admit it, I'm late with the updates. It's been that type of summer - too much to do and not enough discipline to sit down and write some stuff up. 

But now, with a few hours to think and a load of data in Excel it's time to fill some gaps in.

July, well what can I say? Extraordinarily good weather, a severe drought that turned the lawn brown and lots of sun, although quite a bit of hazy weather that reduced the ultimate output of the PV system. According to the weather stats July 2013 was the 6th sunniest July since 1957 with 134% of usual hours of sunlight. The result was my best month ever with 499 kWh produced for 136% of target, that's over 130 kWh ahead. I could take that every month.

June

Well... June was a bit odd. It started well (as seems to be the pattern lately) but then the clouds descended and stayed put. 

At one point it looked like I'd just scrape home over the target, and then it looked like being a struggle. And then, a slight perk up towards the end of the month and all was well. 

So, still ahead of the cumulative target, but far behind where I was at the same time last year. But maybe the predictions for great weather in July will come true. Beating the target by 100kWh in a single month would be superb - but I really cant see that happening. Fingers crossed.

Mega time

So the latest from the meter under the stairs. Five megawatt hours of production have now been logged since the system was installed.

That's an awful lot of (energy efficient) lightbulbs run for free. With a good summer (unlikely, the way things are going) we could well exit the year close to 8 mWh. Well, maybe 7 (fingers crossed).