golden boughs

The rising sun snuck round the side of the house and illuminated our neighbour's tree, whilst leaving out apple tree (on the left) still in shade.  A surprisingly beautiful contrast.

7:35 am GMT, looking north

sunrise

 

7:46am GMT, looking west

shepherds' heads-up

Looking west this morning, three minutes before sunrise (in the east, of course), a slightly frosty scene, with a pale pink sky.

7:39 GMT

Westward Ho!

I've finally got around to processing some of the data from our new garage roof mounted solar PV.

Because the house PV is facing south, and the garage is facing west, we expected the garage PV to start later, and finish later.  On the nice sunny 12th of May, that's exactly what we see:

blue = half the south facing house PV; orange = west facing garage PV; x-axis times in BST; y-axis production in Watts

We're getting nearly half as much again solar production from the new panels (the blue line is showing only one of the two banks of panels for house PV production, to make comparisons easier).  The new system peaks later, so we are extending the day to some degree.  But, the two systems actually start and stop generating at about the same times.  On 12th May where we are, sunrise was 5:07 BST, sunset was 20:44 BST.  So they both start generating just after sunrise (despite the garage panels facing west, directly away from the rising sun), and both stop just before sunset, albeit one generating much more than the other around these times.  

This is due to the panels generating a small amount from diffuse sunlight reflecting from the rest of the sky, in addition to generating the bulk from direct sunlight.

The effect of diffuse sunlight generation is even clearer on 16th May:

blue = half the south facing house PV; orange = west facing garage PV; x-axis times in BST; y-axis production in Watts

This was a cloudy day: note the different y-axis scale, here maximum production per bank of panels was around 1.4kW, as opposed to the 3.5kW on the sunny day.  On this day, sunrise was 5:01 BST, sunset was 20:55 BST, essentially the same as on the 12th.  There was no direct sunlight: it was cloudy all day.

Now the two curves are essentially identical, just tracking the thinning and thickening clouds: the different orientations of the panels has practically no effect.

More charts coming later!

red sky in the morning

7:56 GMT today

 Such beauty, but at what later cost?

view from a hotel window

I’m in Manchester for a meeting today.  So, another day, another hotel.

sunrise over Manchester: 8:15 GMT

view from a hotel window

I’m in Aberystwyth for a PhD viva.  I am reliably informed by the locals that Aber is most definitely not “the back of beyond”, nor even “the middle of nowhere”, but is rather “the edge of nowhere”.  It was a 7 hour train journey (with an expected stopover at Brimingham, and an unexpected stopover at Shrewsbury) to get here yesterday, and will be a 6 hour (hopefully) train journey back this afternoon.  It’s not that far, actually, it’s just that the local trains are so very slow.

But one advantage of being on the edge of nowhere is that I have a view over that edge: a lovely sea view from my hotel window (visible only after breakfast, once the sun had deigned to rise):

the view westward, out to sea

looking more to the south, along the bustling sea front (it is 8:40am, 25 minutes since sunrise)

full moon at sunrise

The sun has just risen; the full moon is just setting.

7:07 BST, looking west

autumn

I love autumn!

7:38am BST (and sunrise is 7:48 today)

sunrise

Just over half an hour after sunrise, the sunlight was hitting this tree horizontally, lighting it up against a dark background.  Spectacular.

8:21am BST

(re)discovering the year

We've had our solar PV system for over a year now.  One of the many plots we make is its output, measured every five minutes through the day, for each day:

(The horizontal time axis runs from 3:00am to 9:00pm GMT, and the vertical axis runs from January 2014 to February 2015.  The colour indicates the average production in kW in the five minute interval.)

Hey, there's a pattern!

We started generating in January last year, as the days were getting longer.  The changing day length is clearly visible.  Where we live, sunrise to sunset is a mere 7 hours 41 minutes on 21 December, and a whopping 16 hours 48 minutes on June 21.  I got those times from a website, not our generation data.  The system doesn't switch on exactly at sunrise and switch off exactly at sunset: it depends on clouds and scattering and stuff.  But the sinusoidal trend over the year is clear from the chart.

We get more power in June not only because the sun is up for longer, but it also generates more at peak, because the sun is higher in the sky, shining down fully onto the panels, not at an oblique angle.  So last June we saw this average over the month:

(Here the horizontal time axis runs from 3:00am to 9:00pm GMT, and the vertical axis runs from zero to 8kW.  The orange regions indicate the minimum, lower quartile, median, upper quartile, and maximum generation at that time, over the month. The black line indicates the monthly mean generation at that time.  The number is the average kWh production per day.)

The statistics show how variable the generation is.  On the best June day we got 53.63 kWh, but on the worst June day generated only 18.35 kWh.

Come December the generation plot looked like this, narrower and lower, with only a third the average generation:

There is still massive variation, from 27.63 kWh to a minuscule 0.34 kWh (it barely seemed to get light at all that day!)

But even an average of 12 kWh/day is a lot better than nothing!

a year in the sun

We’ve had our solar PV system for (nearly) a year now, so here’s a review of 2014.  We generated just shy of 9000 kWh: that’s 9 MWh!

daily power generation by month

violin plot of daily power generation, showing notched box plots of mean (dot), median, quartiles, and outliers, overlaid on a density plot

You can clearly see the effect of the year: much more in summer than winter.  Interestingly, December, containing the winter solstice, was better than November, which, as usual, was a miserable month; December has some lovely sunny days.

No sun – no moon!
No morn – no noon –
No dawn – no dusk – no proper time of day.
No warmth, no cheerfulness, no healthful ease,
No comfortable feel in any member –
No shade, no shine, no butterflies, no bees,
No fruits, no flowers, no leaves, no birds!
November!
     — Thomas Hood, 1844

We can look at the energy generation across each day for the whole year, and can clearly see the changing sunrise and sunset times, and the darkness near the end of November.

Each pixel represents the energy generation at the sample point, one every 5 minutes. Time is in GMT throughout. The colour indicates the energy generation in the relevant interval: darker colours indicate more energy.

It’s even easier to see the effect of the seasons looking at the generation through the day.  The curve gets higher and much broader.

Energy generation over the day, averaged per month. Data is gathered at 5 minute intervals. The horizontal time axis runs from 3:00am to 9:00pm GMT. The vertical axis runs from zero to 8kW. The orange regions indicate the minimum, lower quartile, median, upper quartile, and maximum generation at that time, over the month. The line indicates the monthly mean, The number in the top right is the monthly mean generation in kWh.

Of that power generated, we use some, and export the rest to the grid.  In March we got an extra device to measure this, too.  (March was anomalous in that our hot water boiler was out of action for about a week, so we were using more electricity than usual.)

Energy usage over the day, averaged per month. Data is gathered at half minute intervals from the Wattson meter (which we didn't get until mid March. The horizontal time axis runs from midnight to midnight GMT/BST. The vertical axis runs from -8kW to 8kW. The region above the axis represents our usage: orange is generated usage, red is imported from the grid. The green region below the line is surplus generation exported to the grid.

In the plot above, when the green area below the line is greater than the red area, we exported more than we imported, so are nett generators (month name shown in green). There are days where we import more than we export, taking more from the grid than giving back: on “orange” months we still generate more than we import, but use enough of it that we are not nett exporters; on “red” months we import more than we generate, but even so, may still export a little during the day.

The situation is actually even greener than this implies: some of the orange usage of generated power is being used to heat our water, thereby saving gas consumption, too.  That is why there is such a large oragnge lump in December: nearly all excess power is heating the water for the central heating.  In the summer, the only water heating is for hot water, as the central heating is off.

Next year we’ll have data to compare across years, not just months.  I’ll need to write more Python scripts for that.  Great fun!

sunrise

The view walking down from the car park this morning: tree in sunbeam.

8:02 GMT, Heslington East Campus, York

summer solstice

Hail solstice!  Where I live, today sunrise is (was!) 4:36 am, sunset will be 9:24 pm (BST). The sun is above the horizon for nearly 17 hours.  Bliss.  (Mind you, 21 December, it’s above the horizon for less than 8 hours: not so much fun.)

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cloudy afternoon

Here’s today’s solar PV electricity generation, from sunrise (8:05 GMT) to sunset (16:09 GMT), with data points every 5 minutes.  We generated 25.1 kWh in total.

vertical scale: kW; green line: total energy generated; blue line: energy generated from top row of 15 panels; brown line: energy generated from bottom row of 12 panels

Despite the weather forecast being for clear skies all day, there were large clouds this afternoon for the sun to hide behind.  So we were right to run the washing machine this morning.

Maybe it was hiding because of its spots.

Today’s sun, with its enormous spots. Image from NASA’s current solar images page

PV chart II

Here’s today’s solar PV electricity generation, from sunrise (8:06 GMT) to sunset (16:07 GMT), with data points every 5 minutes.  We were getting nearly 6kW at one point!  We generated 19.8 kWh in total, twice as much as yesterday.

vertical scale: kW; green line: total energy generated; blue line: energy generated from top row of 15 panels; brown line: energy generated from bottom row of 12 panels

The scaffolding was removed during the morning, and hence isn’t shadowing the lower row of panels in the afternoon.  So the brown line is closer to the blue one then.  It was sunny all morning, and a little hazy all afternoon.  We have a very sensitive sunshine detector!

Tomorrow’s weather forecast is for sun all day, so I’ll post one more chart, but that will be enough, as I suspect that they are really of interest only to us.  (There will probably be some monthly and annual stats, of course.)

PV chart

We downloaded today’s data from the inverters this evening, and we can see the electricity we generated, from sunrise (8:06 GMT) to sunset (16:06 GMT), with data points every 5 minutes.

vertical scale: kW; green line: total energy generated; blue line: energy generated from top row of 15 panels; brown line: energy generated from bottom row of 12 panels

The top row of panels didn’t start generating until later, as they need a bigger voltage to kick their inverter into life.  It was cloudy and gloomy in the morning, but around midday, the low winter sun came out, and generation leapt to 4kW.  The afternoon stayed sunny, and the curve is essentially tracking the setting sun, with occasional cloud.

The brown line is somewhat less than 12/15 = 80% of the blue one, partly from shading from the scaffolding poles (due to be removed tomorrow), and partly from being lower on the roof.

That’s a total of 9.5 kWh generated on a winter’s day, when the sun was above the horizon for a total of 8 hours, and it was cloudy until noon.  So that’s about £1.30 due from the feed-in tariff.  Not bad.  Now we have to replan our electricity usage patterns to coincide with when the sun shines.

windy

This morning:

7:52 GMT: sunrise over a millpond-calm lake

Yesterday:

a blustery day

au revoir, GMT

We're now into spring, and the days are getting longer. The vernal equinox (equal day and night, sunrise at 6am, sunset at 6pm, 12h of daylight), on 20 March this year, is past. (It's a bit more complicated than that, of course: according to The Weather Channel website in York UK on 20 March, sunrise was 6.08 GMT, sunset 18:17 GMT, with 12h 9min of daylight. And it's a bit light before sunrise and after sunset, during twilight.)

Yesterday sunrise was 5:53 GMT, sunset 18:28 GMT, with 12h 35min of daylight. Today, sunrise was 6:51 BST, sunset 19:30 BST, with 12h 39min of daylight.

Every year we hear this argument: "let's keep BST all year round, so we can have have more daylight in the evening!" Very few focus on the fact this means less daylight in the morning (very few except those pesky northerners with their later winter sunrises, of course).

Well, I think getting up in the dark is about as uncivilised as you can get. When I Rule the World, the second thing I will do is make it illegal to require anyone to get up in the dark. (The first thing I will do is outlaw lettuce.)

At the winter solstice in York, sunrise is 8:21 GMT, and sunset is 15:44 GMT, with 7h 23 min of daylight. So it's dark when I get up, still dark when I get to work, and dark again when I leave work. Ugh. (But the long summer evenings do make up for it. As I keep reminding myself in the depths of winter. Constantly.)

Those BST-all-year-rounders want me to wait for sunrise for an extra hour,
that's until 9:21 in the worst case, just so I can enjoy that extra hour of afternoon sunshine until ... wait for it ... 16:44. Well, no thanks. Dark mornings are bad enough, without making them longer! (I remember waiting in the pitch dark for the bus to school, back in the early 1970s, when this was last tried. It was not pleasant.)

If you want more sunshine, arrange flexible working times, and get up an hour earlier, in the dark, by yourself. Just don't force me to do it too.