Wednesday, 16 January 2013

Loads of snow and no generation

For the first time we had zero electricity from our panels for a whole
day. Until then the least we'd generated in a day was 3 kWh. There's
no particular mystery as to why we had no electricity. It was snowing
all day, starting at around midnight and not finishing until after 4
pm. reckons it snowed 22cm. This was a very
snowy day.

Also, the timing was not very good. It had been clear before it
started snowing, so the roof had been chilled below ambient
temperature, radiating its heat beyond the stratosphere. The first wet
snow falling onto it would have frozen on impact, making a perfect
foundation for the later snow to stick onto. So as well as opaque snow
falling while the sun was coming up, there was a layer on the roof
making the panels impenetrable to the sun's radiation.

The following day the sun was out, and I was hoping it would clear
some of the snow off the roof. When I got home most of the snow was
still there, and we'd only clocked up 3kWh for the day. A bit of the
snow had fallen off the bottom, south edge, and the first two or three
columns of panels from the west side of the roof were all clear. One
reason I can imagine for this is that the west side of the roof sticks
out from the side, so it will have been warmed by the air underneath
it. The rest of the roof, on the other hand, is a victim of the
insulated roof, and its bottom layer will have been kept nice and
cool, stopping the layer of ice from melting and helping the snow
sticking firmly to the panels.

Two days later, the sun is beating down from a beautiful blue sky, and
under normal circumstances we'd be generating seven kW. But only
around two were coming out.

Now I'm as concerned about de-glaciation as the next person but I
don't particularly want one forming over my solar panels. So I went up
to the balcony to try to help some of the snow down. I have a plastic
snow shovel, good for snow, and a metal spade, good for ice. The spade
helped some of the snow above the bottom row coming down.

When the first row of panels was clear, I went back to check and the
generation had gone up from 2.5 to 2.9. Of course this difference may
have been due to the higher angle of the sun, as this had taken about
half an hour, clearing the ice and snow off the balcony too, and may
have had nothing to do with my work. I went back up again with the
snow shovel, which has a longer handle and is less likely to smash the
panels, and this got some of the snow off the second row of panels.

I went back to check the generation and it had gone up from 2.9 to
3.2. At first sight this seemed a pretty poor return for my work.
Financially speaking I would have been better off spending the time
giving out tissues in front of the station. Also, this seemed a poor reward
for the risk of falling off the balcony and breaking my neck, or
accidentally putting the spade through the panels and causing them
permanent damage. But then, a few minutes later, there was a rumble
and a crash as half the snow slid off the roof. The generation shot up to 6
kW, and then over 7 when a second load of snow crashed down from the
middle of the roof. The panels at the bottom had heated up, in turn
heating up the air passing under the panels. After clearing the bottom
of the roof, I noticed it was over 25 degrees in the air channel. This
must have helped melt the snow further up the roof. Or perhaps this
was going to happen anyway, whether I'd been clearing snow or not. I
like to think that this bit of snow clearing was not entirely
pointless. Ironically, if we had less roof insulation, the snow would
have melted much quicker.

But this kind of snowfall is pretty rare so it's hardly
worth worrying about anyway, unless the climate shifts significantly
and snow starts getting over the protective ring of mountains and
falling more heavily and more regularly, or unless we get to a
situation where there's no grid and we have to rely on our own
electricity. There's a lot to be said for connecting to solar panels
and going off the grid if you're in a sparsely populated area or have
unreliable generation, but where we are, we stand to gain a lot more from
being connected.