Cloudy days and Sunspots

I had a chuckle the other day when my son opined that it had been a really dismal summer. "Yeah," I said, "the units from the panels are way down on last year."

"Typical," he laughed. "It's funny how, for me, it's just a feeling and you have the figures to back it up!"

My obsession with logging things on spreadsheets is becoming legendary and, right enough, our poor summer has been reflected in an increasing difference in the generation from the panels between the first and second year of operation. This first graph illustrates the difference between the two summers.

It started well but we did have a ridiculously awful late May and June. We even had a storm that would not have been out of place in the middle of January. A lovely spell in July meant that this summer almost caught up with last, but since August and right through autumn, there has been no shortage of cloud over west central Scotland and the declining orange line on the graph shows the result in my generation.

As of today, the second year of the panels' operation has yielded 170 fewer units of power compared to last year which represents an income drop of about £73. So are there any reasons why this summer has been so bad?

It is next to impossible to treat a single summer as a statistically valid data point so I'll throw a health warning over the following but it does seem that, over the short term at least, the Sun's variability has an effect on the weather in the northern hemisphere.

Now, of course, the Sun's output is the basic energy source for all weather on Earth but scientists were loathed to make a connection between the slight variability we see on our local star with more profound changes in weather, despite a number of interesting coincidences. For example, many of our recent hot summers in the UK do coincide with the peak of the Sun's sunspot cycle. In 2003, we were soaking up the Sun in Kirkwall on the Orkney Isles when they had their hottest day ever recorded at 26 degrees. (Orkney is quite far north and surrounded by sea which means that although it can be a wild and stormy place, it never really experiences extreme temperature changes.) At the same time, the heatwave caused the deaths of many old folk in France which became a national issue for them.

My mum tells me that the summer I was born (1959) was a very hot one and she was glad to get me out. The following graph, which shows monthly sunspot numbers, indicates that for both these years, the Sun was at the maximum part of its 11-year sunspot cycle.

However, a counter to that is the summer of 1976 which was very long and very sunny yet which coincides with the sunspot cycle being at its minimum. Yet it has long been noticed that major periods of low sunspot activity coincide with depressed temperatures in the northern hemisphere. The most notable of these is a period in the late 17th century called the Maunder Minimum which also saw normally ice-free rivers becoming fully frozen on regular occasions. A smaller dip around 1800 also seemed to be associated with famously cold winters.

Now new research by the Met Office and others based on measurements from NASA's SORCE satellite begins to hint at a possible mechanism for these coincidences. From this BBC article, it seems that the Sun's UV output is much more variable than previously thought. Its effect on the atmosphere is theorised to affect our jetstream, the high-speed airflow that dictates the run of low-pressure systems that feed up the Atlantic Ocean towards the UK

Essentially, the quality of the Scottish summer is dramatically affected by how far south the jetstream runs and it seems that the absorption of energy from UV sunlight may be a major factor in that. If the jetstream is north of the UK, we sit in the same high pressure system that dominates the weather of southern Europe and we get more sunlight. If the jetstream comes south, it brings with it the frontal systems that mean cloud and rain.

The research is mostly concerned with how cold our winters get and it suggests they may be milder over the next few years as the Sun's cycle builds to a peak. Right enough, we've just had two very cold winters and they coincide with the longest period of no sunspots for a couple of hundred years. If so, I might have fewer days when snow on the panels blocks their ability to generate anything. I'd like to think that in the near future, there might be a summer to compare with those of years gone by. That is something that would transform the return from the panels.

Back to the generation graphs.

This graph represents my generation since installation and the patterns are becoming clearer. Of note is the truncated summer peak. As the Sun gains altitude towards midsummer, one would expect the average figure to display a rounded curve that is roughly the inverse of the winter dip. instead, for both summers, there is a pronounced clipping of the curve. My favoured explanation for this is the tall trees to the northwest of the house. As the setting Sun of summer goes towards the northwest, it begins to hit these large trees which cut off the last hour or so of sunlight.

Another figure of note from the spreadsheet is the average generation across the year. It stands at 6.69 units per day, slightly below the 6.79 figure that had been my original target and it represents 2,441 units over the last year. Given that I am 170 units down over the summer, this low figure is hardly surprising. Let's see what the winter brings.

A Feast of Figures

At last, it's one year on for my solar panel installation and time to give an overview of its operation. When I was given a quote for the work, Installation Company told me I should expect 2,480 units annually. The actual number was 2,613, a decent amount, given that my system is not ideally aligned. The panels are on a 30-degree roof pitch that faces WSW. I think performance has been good knowing that Glasgow is not a part of the world known for sunshine. Anyone who is more southerly aligned than I am is going to do substantially better.

Not all of those 2,613 units attracted the Feed-in Tariff (FiT) payments. I lost a week's worth at the start while the bureaucracy surrounding FiT application worked it's way through. Nevertheless, the FIT's earnings for the year have been about £1,044. I say 'about' for two reasons. Half of my eligible units, 1,250 of them attracted an additional Export Tariff of 3 pence which adds £37. Also, both the Export Tariff and the FiT were increased by the inflation rate on 1 April. However, the people looking after the payments have no way of knowing what my reading was on that day so I guess they will apply the higher rate for my next reading which means that a few units from before April will attract the higher rate. Note that not only are these payments index-linked, they are also tax exempt.

Average generation per day was 7.16 units across the course of the year, pleasantly clear of the 6.79 target I was hoping to exceed.

The year prior to the panels, we used 8,816 units of electricity in our house - sons have a habit of leaving their stuff powered up! This year, primarily due to the power provided by the panels, our consumption has fallen by 2,180 units to 6,636 units which represents a saving of about £220 pounds at current rates. Adding that to the income above, we ought to have realised £1,300 by virtue of having the panels. Three major factors will affect that in future years. The price of retail electricity is bound to rise, increasing the savings that can be made by using power when the panels make it available; for example, coaxing the family to run items like the dishwasher when the Sun is out. The FiT payments will rise along with the Retail Prices Index. The panels are expected to deteriorate at about 0.9 per cent annually.

Now for the big, important chart from my spreadsheet:


When I first started this, I tried to guess what shape this graph would have. I thought that mid-winter would still yield a couple of units daily. The effect of weeks of snow on the panels was not expected, essentially turning them off for days on end. I suppose I expected an approximation to a sinusoid waveform but I now think that, over and above the snow, the alignment of my roof amplifies the effect of the lowering of the Sun's passage over the sky. Now I really understand why life goes to sleep over the winter. The prime source of energy for life, the Sun, basically all but disappears.

For the future, I am going to keep track of my panels' performance. My overall average figure will now become an annual average. A new figure I will be generating is a comparison of current generation with the previous year with a running total of whether I've generated more or less this year. Everything else being the same, I should see a very slight decline. However, given the variability of the Scottish cloud cover and a good summer, figures could easily be higher.

Nearly there

The Sun is out in west Scotland with a vengeance and the units are clocking up with gusto. It's been gladdening to see generation return to high levels and there ought to be no impediment to exceeding my target amount. With the current sunny weather, the panels have been achieving over 19 units a day.

A week ago, I had a visit from the chap who installed the system. I pointed out a long flow of bird pooh that had run halfway down one of the panels and up he went to clean it off. Apparently, tests done by his colleagues showed that even small areas of shading have a profound effect on the entire string of cells. Since they are connected in series, the shaded cell acts like a resistor and impedes the flow of power. He gave the panels a quick once-over while he was up.

Now to the figures.

My annual average is 7.02 units, having passed the 6.79 figure required to hit target a week ago. 30-day average is a healthy 12.19 units. Here's the graph that covers the life of the panels.

To see better the recent improvements, here's the last two months. Remember, red is the 30-day average and yellow is the overall average.

I'll report on the first year's generation in two weeks time.

Easter rising

To the blog follower who wondered if I'd fallen off the end of the Earth, I haven't. You know who you are! :-)

I have skipped a month and re-engaged with the turn-of-the-month blogs. Boy is it good to see the Sun. There was a sharp upturn in the insolation and subsequent generation of the panels which was presumably due entirely to the change in the weather. Another nice piece of news is that from 1 April, the Feed-in Tariff has been raised from 41.3p to 43.3p, a rise of 4.8 percent, in line with the RPI. So to figures and graphs. This is the overall generation since installation. The orange line is the 30-day average while the yellow line is the overall average:

The change in illumination is clear and the 30-day average has a very steep rise as we get out of winter and into spring. It's no wonder that life shuts down in the cold months given the lack of light and therefore energy. To give a little more detail, here's the last three months of that graph:

In last few days, there has been a reestablishment of the usual Atlantic sequence of weather fronts and their associated blankets of cloud which has put a brake on the springtime improvement in generation. So where does the system stand with respect to predictions? I've just passed 2,080 units so would like to gain another 400 before 18 May to match initial expectations. There are 47 days to go so I'd need to average 8.5 between now and then. For a prediction, lets look at the same period on the opposite side of the winter solstice - 24 July to 9 September. Then I gained 506 units which is a good omen because, if that performance is repeated, I should be 100 units over my target and £43 better off.

30-day average is currently 6.04 and the overall average is 6.52, gently up from its low of 6.46 in mid-March. It should pass the 6.79 target I want to reach before May 18 if the above predictions hold out.

Finally, to the chap who I met in Ossett, Yorkshire yesterday who took much interest in my panel stories, I hope you find this blog interesting. It was written for folk like you. You also know who you are.

Turning the corner

Thanks to other things happening in life, this entry is late - nothing new then, but its timely too. The coalition government in the UK has announced a review of the Feed-in Tariffs scheme and I learned about it when a friend sent me a link. The site he sent me to was none too informative, primarily because it wanted me to cough up cash to learn more than the headline. A Google search yielded more and brought a little relief. Articles here and here indicated that the core of the review would be to drop subsidies for systems rated at over 50 kW-peak. My little system is only 3.5 kWp so hopefully I will not be affected.

Numerical fun.

Since the panels were brought online, I've been hoping that their output over the year will beat the predicted value of 2,480 units. Throughout these blogs I've stated that this would represent an average generation of 6.85 units daily. Duh! Checking it now, I find that 6.79 units is the true daily average and I think I got 6.85 by having divided 2,500 by the number of days in the year. The following discussion is based on my erroneous belief that 6.85 was my predicted generation average.

As my spreadsheet containing my data has grown, I've kept a track of my 30-day average and, more importantly for my number fixation, a total average. By 18 May, I hope this latter figure will be over 6.85. A couple of weeks ago, I tried to predict this with an experiment on the spreadsheet.

On the assumption that the average amount of sunlight (a quantity known as insolation) between the summer and winter solstices would be the same as between the winter solstice and the subsequent summer solstice, I took my historic data from the autumnal side of 21 December and plotted it into the appropriate spring days leading up to the 18 May anniversary. Each data point would keep the same time from the solstice and, clouds willing, would represent the same insolation.

I'll admit it is a shaky assumption but it is fun. The results of this exercise were as follows: It predicted that my total average would descend to 6.85 on 11 February - today! So what actually happened? It is currently at 6.79, having passed the higher waypoint three days ago. So there is less power being generated this side of the solstice, presumably due to the very poor weather we've had recently. Other predictions that came from my exercise were that the average would bottom out at 6.55 on 18 March as lengthening days would turn it around; that it would rise back above 6.85 on 21 April, four weeks before the anniversary; and that it would show an average of 7.18 units average on the anniversary which would represent 2,621 units overall, a decent enough figure, though reality is already slightly behind this prediction.

So to graphs and figures:

A number of interesting things are apparent. First, the 30-day average (orange line) has made a definite upturn and that's great to see. Second, yesterday, we had the first really clear day in quite a while and a thumping 7.5 units were generated, the highest since 24 October. I had hoped that the spikes produced by occasional clear days would show an obvious curve nicely symmetrical about the winter solstice but the Scottish weather seems to have interfered too much and I cannot discern it. Finally, the decline in the total average (yellow line) is slowly being arrested.

Meanwhile, I bought myself a toy!

I was in B&Q (a DIY store) where they had wireless energy monitors available. I had thought about these before the panels were installed and had decided not to bother when I saw that it would be easy to gather readings from under the stair. Nevertheless, I had hankered after a way of being able to watch the rise and fall in generation as the Sun rose and fell, and as clouds came and went. My family were known to giggle as I would dive under the stairs to satisfy an instantaneous craving to know how much power was being generated. Now with this toy I can watch all day if I want.

The unit I went for is an Owl CM160+USB model that I got from an Amazon third party seller. These units are meant to tell householders how much power they are using either in terms of kWh (units) or in monetary terms. It comes in three major parts. A sensor goes around the live cable feeding power into the house. This connects to a unit that turns its output into a digital signal that is wirelessly transmitted to a display unit sat somewhere handy to view - in my case, on my desktop beside me here. Users can enter details of their tariff for accurate cost displays and it will also inform the user of how many grams of carbon their electricity usage is causing to enter the atmosphere. Neither of these latter two features were of much interest to me but one that did make me go for this model was a USB connection that would allow minute-by-minute readings to be displayed on the computer as a graph.

All I'm really interested in is the power display and I want to use it for the solar panels so instead of the incoming mains, I place the sensor around the live feed that comes from the inverter to the mains. Happily, the unit arrived on the beautiful sunny day we had yesterday and there was plenty of power to exercise its abilities. I left it set to assume our voltage was 230 volts. I think the setting of this will have an effect on its reading of power as I guess it is essentially reading the current in the cable and multiplying the value by the voltage to determine the power. Later, I set it to 240V as I think that is nearer the mark.

The unit works a treat, its displayed kW value going up and down as the occasional cloud gets in the way of the Sun. A reading of 1.8 kW from the inverter was about 1.75 kW on the monitor and I'm assuming the low reading can be blame on the voltage setting.

The one shortcoming I've found is that after the Sun has gone down and the inverter has switched off for the night, I continue to get a reading. Despite no power coming from the panels, it still shows 50 or 34 watts passing through. Is this an inherent offset in the unit's calibration? Does it instead represent a current draw by the system to power the inverter in its sleep mode and keep the meter going? First I'll try taking the sensor off and see what reading I get... (goes off to carry out experiment). When taken off the cable, the unit says zero. Good. Next, I'll place the unit next to the cables but not clamped around the live to see if a stray magnetic field is to blame... (goes off to carry out second experiment). Still zero.

I think this shows that the solar power systems themselves require about 40 watts to operate, even at night. Taken over a day, this represents (40 x 24 = 960 watts) a full kWh or one unit of electricity! Wow! If half of that time, the power comes from light on the panels, then I have to 'buy' 175 units annually to operate the panels. That's about £17. What it needs is a light-operated switch that completely disconnects the panels and inverter from the mains when it's dark outside.

I like this unit.

Snow gone, for now

Since winter set in and the returns from the solar panels hit the floor, I have noticed a tendency by folk to dismiss the concept of panels as being pointless if they cannot generate significant energy for weeks on end. I sigh a little before explaining to them that the way to approach this is to look at what is generated over a year. If that figure meets expectations then the investment should come up to scratch. So to the monthly update. Not a lot!

The snow has gone so the panels have returned to making the most of their incident light. But a persistent high pressure system over the UK laid a blanket of cloud that darkened the skies and I haven't gained a full daily unit since mid December. When the blanket shifted, in came a huge front that threatened to dump more snow on the panels. I will admit, I am surprised how low output has been over the solstice but since there so little light anyway, the loss isn't too great.

So to figures. Total generated is 1,771 units. I hope to make 2,480 by 18 May. The overall daily average is 7.63 units, edging close to the 6.85 figure that I want to beat by the system's anniversary. The 30-day average, once up at 15 is almost not worth bothering about - 0.63 units.