Snow architecture

The Winter Olympics were held in Nagano sixteen years ago. With less than a month to go, there wasn't enough snow, and there were worries about events needing to be cancelled. Some of the organising committee went to a local shrine and prayed for snow. The gods answered their prayers and on 15th January it snowed. And snowed and snowed. Although Matsumoto wasn't holding any of the events, it was affected by this divine intervention, with a snowfall of 69 cm, the biggest since records began. This was hailed as one of those once-a-century snow falls, although 1946 seems to have been a bit snowy too. 

Last week it snowed 49 cm. Another one of those once-a-century snowfalls, then on Valentines day and into the next day it snowed 75 cm, so these once-a-century events seem to be getting a bit more frequent. Climatologist James Hansen, formerly of NASA claims that global warming means once-a-millennium weather events will happen once a century, and once-a-century events every decade, and decadal events every year. Read how warm was this summer here.

Anyway, one big impact locally is that there is a metre of snow on the ground. My obvious reaction is one of joy. People pay money to go on holiday for this kind of stuff, and there it is, right outside my window! Everyone else is muttering and grumbling about having to clear it, which is a civic duty here, since there are no municipal snow-clearing facilities. It's the height of shame in the neighbourhood if you're not out there shovelling snow the moment there's more than a few centimetres. 

As well as the mechanical implications of this, and the dangers of injury from shovelling too much or too quickly, I realised the worst thing for your health could be to not enjoy shovelling snow. So rather than digging from the road and the drive into a big pile against the neighbour's wall, and increasingly falling over the neighbour's wall, I decided to roll some of the snow up into giant snowballs and start making an igloo. At the beginning I was making an igloo while  clearing snow, but pretty soon I was clearing snow as a consequence of my igloo building project.

I've tried making igloos before, but never been successful. I've managed to dig a hole into a large pile of snow, but that doesn't really count, and usually doesn't get very big. I've managed to make a ring of big snowballs before and started contemplating the roof, but usually the snow needing clearing has run out, and the problem of making the roof has been too great. 

An igloo is a dome. An arch rotated into three dimensions. As such, it's a very strong structure. The weight of each part is transferred laterally, and I've heard that the bigger arches get, the stronger they get. The problem is that they only have this great strength when they are complete. Until the top-stone is in place, an arch is just two bent walls that are likely to fall over. 

So it was easy enough to make the bottom of the wall, and another layer of snow balls on top of that slightly further in. Then I started to worry. The form was fine but the process perplexing. My respect for those ancient arctic architects grew.

After a while I realised that I could keep building the structure upwards with smaller arches, not going through the middle of the dome, but from adjacent snowballs, then further apart. 

I also got better at making snowballs. In fact they were more like snow-bricks, from forcing my snow-shovel in, and packing the snow onto it. Better still were those cut out of trampled snow with a spade.

A big snowball made the lintel over the doorway, and then it was easy to fill the hole at the top. Next I used the same principle to build an arched entrance, just like they have on real igloos.

So this first igloo has taken me 46 years to build, but the next one should be a bit quicker!

See how the experts do it

Shovelling snow and suffering pain

Winter is here, and that means sooner or late it's going to snow. And that means sooner or later having to shovel some of it. Not only does this seem a largely futile activity since you can walk over snow while it's there, and if you leave it, it's all going to melt before too long. Also, it tends to result in back pain, either chronic, acute or both. 

I've always assumed this is because snow appears to be light and fluffy, but is in fact much heavier, so the body is unprepared for the amount of work and the strain each lifting will take. 

I think there may be more to it than that. Snow also has air in it. This does not make it any heavier, but does make it more massive. The extra air is not going to make a difference to the weight, since the snow is already floating in air, but it is going to affect the mass since you have to move all that air as well as the snow. 

Japanese science-hero Denjiro-sensei performed a really good experiment to show the difference between weight and mass. He took a large balloon, something over a metre in diameter. First, he threw it uninflated across the stage at a foldable chair, which had little impact. Next he threw an inflated balloon at the same chair, causing it to fly across the stage. You could probably repeat this experiment in your own living room using a regular balloon and something like a pet bottle. 

So back to shovelling snow, not only does snow look much lighter and fluffier than it actually weighs, so we are not fully prepared for the strain of the lift. It is also more massive than it is heavy, so we need more strength to move it around, changing its inertia, than we would guess just from holding up a shovelful.

Snow in April

It snowed in the night and the there was a couple of centimetres left on the roof on the morning of April 11th. I had to go to work and didn't have time to clear it, so there's an opportunity to see how much less electricity we generated and the value of clearing snow. 

Here's a comparison between the generation on the snow-covered day with the day before, which was otherwise similarly sunny.

In these graphs, the pink is the electricity consumption, highest in the wee hours when the eco cute is making us hot water. The blue is the generation, peaking with the rising sun. Notice the difference bewteen 6 and 9am.

It looks like the snow was still there until around 9 o'clock, stopping the rays of the sun reaching the panels, and stopping any chance of the heat melting it from beneath.

time	Generation / kWh
	11th	10th	Loss
6:00	0.0	0.6	0.6
7:00	0.1	2.0	1.9
8:00	0.4	3.1	2.7
9:00	4.0	4.9	0.9
10:00	5.9	6.0	-
total loss			4.1

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The total loss was 4.1 kilowatt hours and we're getting 48 yen per kWh, so that's a couple of hundred yen. Is it worth spending five minutes clearing snow off the bottom of the roof for that?

More revelations from a snowy roof

Another snowy night, and around 20 cm on the roof this morning. This made my trip to the balcony rather exciting, although I was reassured as there was also 20 cm of snow on the terrace below to break my fall.

The sun was trying to poke its head through the clouds soon after it climbed over the mountains, so I cleared the bottom row of panels on the roof before breakfast, then waited for something to happen. There was no generation for quite some time, even when the sky was the blue, and as the sun was out and climbing. By 9:30 large drifts of snow had started sliding off the roof and crashing into the garden. There was still no electrical action, so I went out to look at the roof and around a third of it was clear of snow. Then I went up to the loft to see what the two power conditioners were doing. They weren't doing a lot. I tried switching them off and on again. I think this may have done something but perhaps it was just a coincidence.

I went back up there a little later and the one on the left was generating 0.22 kW while the one on the right was generating over 2. I had assumed that these power conditioners each dealt with half the panels on the roof, the one of the left dealing with the panels on the left, and the one on the right the panels on the right. The roof has 48 panels, Eight high and six wide. The connectors are at the top and bottom, so it makes most sense to connect them in series vertically. I remember they were talking about connecting the panels up in sixes, although I can't find any written evidence of this now. From what I remember, the bottom six panels of each row were connected vertically, then the top two rows of panels were connected in two arrays three wide and two high. A total of eight sets of six panels.

My only explanation for the difference in the two power conditioners is that the top two panels were both connected to the left power conditioner, leading to a lower generation for the panels at the top that were still covered in snow since the snow was falling from the bottom of the roof. Once all the snow melted from the roof, and the generation was higher, the power conditioners were generating around the same amount.

I have noticed that the two power conditioners generated different amounts. This can be explained by three things: differences in the performance of each panel, different lengths of wire and different temperatures.

Each panel produces a slightly different amount of electricity. Although they are rated at 190 watts, they vary in power between 190 and 200. In theory, if all the low generators are in one circuit and the high generators are in the other, there could be 5 Watts difference between the power going into the left power conditioner and the right one, but it's much more likely that the difference will be small and no more than 1 or 2 watts. Even if it is 5 Watts difference, that's only 0.05% out of the 9.12 kW.

The wires to the bottom of the panel are longer. Also, and conversely, there will be more wire in a straight vertical array of six, than an array two high and three wide. More wire means more resistance. Power loss is the resistance times the square of the current. The maximum current of the panels is rated at 5.62 Amps. I'm not sure what gauge they used, but if they used the sums in this EcoWho solar wire sizing calculator , they will have come up with a AWG 12, 2 millimetres gauge, 3 square mm, which according to the Engineering toolbox has a resistance of about 5 milliohms per metre. This would lose 0.17 Watts per metre. Altogether, the panels lower on the roof may have 10 metres more cable, then that's a 1.7 watt difference. This is going to be around 0.05% too.

Since air is flowing under the panels, taking heat off each one, the temperature of the panels at the top of the roof is going to be higher than those at the bottom. The air temperature in the channel gets over 60 degrees in the summer, and there could be a 5 or even 10 degree difference in the panel temperature. Since electrical efficiency drops by around 1% every degree or two, this could drop the output by a 1 or 2% for the circuit with the top arrays compared to the bottom.

Now I don't have any live data for the different generation going through each of each power conditioner, but if you press the right button, rather than the on/off switch, they display the cumulated generation, which is 7,198 kWh for the one on the left, and 7,262 for the one on the right. This is a difference of around 0.8%, so it looks like they connected the two top arrays into the same power conditioner. I suppose the odds of this were even if they had stuck the wires in at random.

When we were talking about the connection of panels I had tried to encourage some kind of optimisation in shortening the wires as much as possible, but the eyes of the contractor started to glaze over and they brushed away my suggestions of optimisation over the next half century of generation in favour of being able to make things easy for the afternoon they were clambering around on my roof.

Knowing what I now know about the rating of the power conditioners being an absolute limit rather than a rough level, so we lose power when the panels get any where near their maximum output, I would have probably pushed more strongly for six vertical arrays of eight panels.

The Power Conditioners will take up to 370 Volts and 24.5 Amps, although it's rated at 250 V, at which it is most efficient. Its maximum power is 4kW at 30 degrees C, and 3.2 kW at 40 degrees C.

The panel maximum voltage is 36.6 Volts. So you could put 10 in series and the voltage would still be under 370 volts. Six panels is only going to be 220 V; less than the rating. Eight panels would be 290 V if they are all producing their maximum voltage. Of course, they're not always going to be producing their maximum voltage, so that's likely to come out around 250 Volts. So I'm not sure why they were putting them together in sixes.

Six circuits of eight rather than eight circuits of six would have reduced the amount of wire on the roof by about 20 metres, which would account for about 0.1% of the power. This doesn't sound a lot, but when you multiply by 50,000 yen, it's one lunch per month. It would also have made the fitting substantially easier, but perhaps they had a good reason for doing it in that way. I can't see any charge per metre of wire used on the invoice, so that's not it.

Maybe when the ten year contract with the electricity company runs out and we look at alternative heat generation, we can fix the wiring on the panels at the same time.

Another possibly meaningless experiment in solar snow clearing

There was about a centimetre of snow outside this morning, making the ground crisp and clear beneath the blue sky. I postulated that there would be a coating on the roof too. This postulation, at least, was correct.

I also postulated that clearing this snow off the roof would increase the generation, and sure enough it did. Before I cleared the snow, it was generating 1.5 kW, which is not bad for 8 o'clock on a winter morning. I cleared the bottom  row of panels of its thin covering of snow, and it went up to 1.8 kW, an increase of 300 watts. The array is 8 x 6, so I'd cleared 1/6, which presumably had been generating 250 watts before, more than doubling when I removed the snow. Another way of looking at it is that the panels generate a little less than half as much electricity when covered with a thin layer of snow.

They will also be absorbing half as much heat, so, as before, clearing these bottom panels speeds up the clearing of the whole roof. Ten minutes later, we were generating over 5 kW.

One interesting thing was that the cosmetic panels, which run up and down each side of the roof to make up the difference between the width of the roof and the dimensions of the panels, were already completely clear of snow from the melting effect of the sun. 

I should probably warn you not to try clearing snow off your solar panels yourself. The only reason it's easy and relatively safe in our house is that we have a balcony running along the south side of the house, so I can step onto it from upstairs and easily reach the roof from there with a brush. The biggest danger is bits of snow falling down my neck.

Let it snow!

I love snow.

In England when it snows everything stops. People miss school and don't go to work. Traffic systems close down and people can't get to the airport to go on their skiing holidays. Sometimes power cables are brought down and the food in people's freezers is spoiled.

Here in Japan people are used to snow. Matsumoto is not in Snow Country, but is surrounded by it. The snowiest city in the world is apparently Aomori, where it comes in from the sea like waves over the winter. In Hokkaido they have a different front door upstairs, and neighbourhood battles go on as people clear snow into each other's parking spaces as soon as they vacate them.

Clearing snow here, for the most part seems to me a waste of time, although everyone gets very busy doing it. Sooner or later it's going to melt, so why bother? While it's snowing, you can walk on it or drive in it as everyone changes into snow tires from some time in early November when the first hint of white hits the highest mountain peaks. I don't really like driving in snow, so I don't unless I really have to. Like if I'm going skiing. Usually I don't really have to drive. I cycle to work, but can walk or get a bus if necessary.

As a house owner, my view of snow should have changed a little from this childish enthusiasm, but it hasn't yet. My house is effectively at the end of a cul-de-sac, so I don't have any responsibility to clear the thoroughfare in front of it. The biggest worry is the roof and the balcony on the south. Snow is rather heavy. It may be much lighter than water, but you don't get fifty centimetres of water building up all across the top of a house. Actually we don't get snow building up over our roof either, so far. It slides off the southern solar roof well. Some of it does hit the balcony on the way down making a ridge there that seems to sit happily, although most of if falls straight onto the terrace below. Probably a good idea to clear that off in the interest of balcony longevity, but it is not doing too much harm, and we wouldn't need to worry if it snowed while we were out of the country. 

Snow is more likely to stay on the north roof as it's shallower, and part of it is in the shade. Snow goes through a melting freezing cycle, and bits of ice come crashing down to where we keep the bicycles. 

Obviously snow impedes the performance of the solar panels. When the roof panels are covered, not much sunlight gets through, although of course the radiation that does get through heats the panels, melts the snow on top of it, and helps the snow slide off. Also, when it's actually snowing, few rays get through the clouds and snow. Even so, it was producing something while it was snowing. Admittedly only a hundred watts or so--in the battery charger ball park--and half the 200 watts that the house seems to consume even when everything is switched off. Over a day when it snowed pretty much all the time, we still made 2.3 kWh, which is about 10% of what we used. 

I was hoping we'd hit 1000 kWh within the first month of living in the house, but it's snowing again today, so it's looking unlikely.