Trieste sunset

After a long day of great talks and discussions, a small group of us went out to dinner.  It was still hot, but not as hot as it has been.  We found a nice fish restaurant, and I had a marvellous herb salmon and green bean dish.  Walking back to the hotel via a gellato shop, we stopped to admire the sunset.  

Happy New Year

 Presumably, there are lots of delighted shepherds celebrating this New Year's sunset.

16:10 GMT, looking west

sunset with a bonus

Gorgeous sunset, with a bonus Venus -- can you spot it?  (You will probably need to click on the image to make it full size.)

18:30GMT, looking west

Here's a clue:

sunset

 Another lovely sunset this evening.

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!

Porto bookshop and station

I'm visiting some friends near Porto, Portugal for a couple of days before going down to Lisbon for a conference.  They came to pick me up from the airport, so we could do a bit of tourism before going to their place.

First lunch, then a walk around a park, with great views.

a view over the river

Then to a famous bookshop (they know me so well), the Livraria Lello.  It is such a tourist attraction that you have to buy a ticket to go in!  I bought a book about the bookshop.

the staircase at the Livraria Lello; the place was packed

Then afternoon tea, a bit more walking around, then off to the train station with its amazing tiles.

A short train ride later, and a short walk, we arrive at their place.  They have a fantastic view over the sea:

Then dinner and lots of good conversation.

moon and sun

 A lovely full moon close to the horizon (overexposed, because phone camera)

17:30 GMT, looking east

And, because it’s a full moon near the horizon, there’s a lovely setting sun 180 degrees away:

17:30 GMT, looking west

cloud shadow

 A glorious sunset tonight:

sunset, looking west, 16:25 GMT

Towards the lower left edge of the coud, there’s a diagonal dark band: it’s a shadow of part of the cloud cast by the setting sun on the cloud!  Here it is in an expanded view:

sunset

16:15 GMT, looking west

sunset

Usually it takes clouds to help produce a spectacular sunset.  But tonight, a cloud-free sky exhibited a beautiful gradient from gorgeous indigo to glorious orange.

7:29pm, BST

shadows of clouds

A spectacular sunset this evening, with clouds casting shadows on other clouds:

21:30 BST.  The picture is a bit washed out on the horizon: reality was darker and redder.

Zooming in on the base of the shadow, to show the setting sun shining between two bands of coulds:

chimneys in the sun

The setting sun lit up a line of golden chimneys:

View of sunlit chimneys, 21:16 BST.  They are not normally golden, but are “white” brick, which reflects more than the red.

View in the other direction, of the sunset lighting up the chimneys, 21:18 BST

clouds at sunset

I love this kind of interplay of clouds and sun at sunset.

16:17 GMT

sunset

A glorious sunset this evening:

18:58 BST

delight

Sunset

18:28 BST

falling, stars

Today was quite relaxed, staying with friends.  In the morning I looked round their smallholding, with its bees, chickens, ducks, and cows.  In the afternoon we took a short trip out to Bridal Veil Falls.

We walked down a staircase by the 55m drop, stopping half way to take a panorama view:

Bridal Veil Falls, from half way down: panorama view

Then we went on down to the bottom.

Bridal Veil Falls creating rainbows

The noise was tremendous:

Yes, another portrait mode video, but it’s a portrait mode waterfall!

Then we had to walk back up the 55m of staircase…

After that, we drove up to Raglan, to wait and watch the sunset, while drinking hot chocolate.

sunset at Raglan

The reason for this wait, apart from good hot chocolate, was that I had yet to see the southern night sky, due to clouds.  Even my earlier sighting of the full inverted moon had been after dawn.  But tonight was forecast clear, so we waited for sunset, then post twilight, and drove to an unlit place.

The sky!  Full of stars!  Alien stars!!  It was a most peculiar experience, seeing a sky full of completely unfamiliar star patterns.  Oh yes, I identified the Southern Cross, but wasn’t the same seeing it for real as seeing a picture.  For one thing, it’s tiny!

The Milky Way towards the galactic centre is splendid: broad and structured.  I stayed looking up and around for quite a while.

a short round trip of about 140 km

flaming July

The end of a hot July day.

21:06 BST (sunset is 21:39 – there’s a small hill hiding the horizon)

Tomorrow is supposed to be cooler.

(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!

delighted shepherds, with Venus

There was a deep red sunset tonight.

17:32 GMT

The horizon clouds were a rich deep red, much redder than the photo shows; I need a better camera than my phone!

I didn’t notice Venus when I was admiring the sunset, although it is just visible in the photo above (click to embiggen).

However, a few minutes later, once the overwhelming redness had diminished, Venus was brilliantly visible, so much so that it’s easily visible even in a grainy photo:

17:51 GMT

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!