Archive for September, 2009

Natural History Museum: Butterflies


On Friday popped into the Natural History Museum and went to the Butterfly Jungle. I’m a member, and entry to the for-money exhibitions is free (already paid for). It makes me feel terribly middle class.

Before entering into the “jungle” (it’s a temporary hut made of out polytunnel) I thought we could go see the insect gallery so we could learn something about butterflies before seeing them. Well, there is no insect gallery, there is the creepy crawlies room. Where’s the long room full of display cabinets crammed with dead insects pinned to neatly labelled pieces of cardboard? Needless to say the creepy crawly room sucks.

So we sort of wandered about at random. Hey, did you know the toilets have bacteria zapping UV on the hand dryers. Cool. But no interpretation. Not Cool.

Tania Kovat’s TREE is very good. It’s a slice of a 200 year old oak set into plaster panels in the ceiling; the pieces are arranged more or less how they would have been on the tree, in other words: in the shape of a tree. I find the connexion to Darwin a bit lame. The inspiration is Darwin’s now famous “I think” cladogram from his Transmutation Notebook B (ain’t the Darwin online project great?). The cladogram, you know, looks like a tree. And so does Tania’s TREE. Cunning. TREE is displayed in a rather nice gallery at the top of the splendid staircase in the Central Hall. Behind the statue of Darwin, and between the statues of Hooker and Owen. A holy place.

In the same gallery is Ida, apparently the world’s most complete fossil primate specimen. She’s a beautiful little bush-baby-like creature, Darwinius masillae. She lived 47 million years ago. Of course, I know the vast majority of species (well over 99%) become extinct, so it is, statistically speaking, unlikely that Ida is our ancestor. Nonetheless it is difficult to dispel the romantic notion that Ida could be our ancestor. Certainly she will have shared a lot in common, looks, behaviour, social grouping, with our actual ancestors. Ida’s cabinet featured something that I think the NHM should have a lot lot more of. A cladogram.

After wandering past the primate gallery (now quite aging) and the Sequoiadendron giganteum we found the entrance to the Minerals collection. I didn’t actually know the NHM did rocks. And this is awesome. A big gallery full of oak cabinets (original 1881!), stuffed full of… rocks! We didn’t want to spend much time here (we were getting hungry), but I thought it would be interesting to see what the NHM had to say about the alexandrite effect and birefringence. It was a simple pleasure to use the alphabetic mineral index to find the cabinet displaying alexandrite.

Alexandrite appears to be different colours under different lighting conditions. One colour under natural sunlight, and a different colour under incandescent light. I was slightly disappointed to find that cabinet didn’t have a button to press to illuminate the alexandrite with different lights. Oh well. I suppose every mineral is special in its own way, so I can’t expect every one to have a cute interpretation. Of some local interest to me was spotting the enormous Blue John specimen, about as big as my chest. Blue John is a fluorite variety local to Castleton. Of course, I’ve seen far better examples in the shops in Castleton.

I knew quartz was a birefringent material, so I popped over to the quartz cabinet. No birefringence here. As we were ambling out of the room, I luckily found a fine quartz crystal ball on display in the jewellery cabinet next to a rather fine jade box on loan from the Queen. Gazing into the crystal ball gives the birefringent double image effect (this is deliberate, there is an interpretation sign to explain the effect). Nice, but I think Wikipedia’s image is more impressive.

After lunch and a quick trip round the wildlife garden (impressive use of a small urban space, and I expect it to keep improving; didn’t see the foxes though) we did eventually make it to the Butterfly Jungle.

Which I thought was a bit disappointing. However, there’s something intrinsically delightful about having lots of butterflies flapping about, and it hard not to enjoy that rather pleasant experience. And they are pretty to look at. As for science though, there was precious little to be found (not none, but not a great deal). It wasn’t all butterflies, there was an amusing collection of slightly exotic creaturees in glass cages. Giant african millipede, death’s head cockroach, Charlie the Iguana iguana (who I last saw in the Darwin exhibition!); that sort of thing. And a kiddies playground. Which looked quite good, but no use to me.

The Natural History Museum is such a large museum and with so much on display, I find that it’s impossible to do anything but see a small sample of it in any of visit. I’ve been three times recently and I’ve still only seen a small fraction of what it has to offer. There are still things to discover in the Central Hall: I was pleased to see a Glyptodon that I had missed on my previous visits.

I did learn one thing in the Butterfly Jungle. Butterflies taste with their feet.

Windy isn’t it?


Damn hippies think we can just sprinkle a few wind mills around, and because Europe has “huge wind resources” we’ll be okay.

This silly web article claims that europe’s wind energy potential is “huge”, and “equivalent to almost 20 times energy demand in 2020”.


YA RLY, according to the European Environment Agency’s report, Europe’s onshore and offshore wind energy potential.


YA RLY: It’s hard to miss this sentence from the executive summary: “Europe’s raw wind energy potential is huge. … it may be equivalent to almost 20 times energy demand in 2020”.

“energy demand”, that’s the problem. Their assumed energy demand is between 3537 TWh and 4078 TWh. (By the way, notice that the EEA cover their backs with a “may” when they use the lower demand figure to get the “20 times” headline-grabbing numbers, but the web article referencing somehow manages to drop the “may”). So, Europe has 271e6 people (according to Google); that’s 15.3 kWh per person per day. Oops. They must have meant…

Electricity demand.


The electricity demand, in Europe, in nothing like our energy demand. In the UK we travel around by burning oil, and we heat our houses and food by burning gas. That hugely swamps our electricity usage.

Energy and Electricity are not the same thing.

Double twats for the people who ignorantly repeated them. Of course the European Environment Agency know the difference. There are two occurrences of the phrase “energy demand” in the document; 7 occurrences of “electricity demand”. Both the “energy demand” phrases related to the “20 times” sentence. One is in it, the other is in the footnote of the table of data on the same page as the “20 times” sentence. Before I did the textual analysis (by which I mean I used the PDF search feature; it’s abysmal, but it’s what I have available) I put the use of “energy demand” down to sloppy practice. Now I think it’s mischievously deliberate. I think they used “energy demand” in that “20 times” sentence in the executive summary because they knew people would make a headline of it.

I have to say that apart from this headline grabbing glitch, the report is well worth reading. Map 6.1 is particularly interesting (apologies for the pixelly rendering, partly their fault, partly mine, but mostly the fault of STOOPID PDFs):
Cost of wind in europe

Basically the British Isles is the only place in Europe (not quite, but nearly so) with cheap on-shore wind. And we’re full of NIMBYs.

Screw Hydro!


The Archimedean screw. A venerable machine for lifting water. You can run it in reverse to generate power. How much?

New Mills, where the Sett meets the Goyt, has a community owned Archimedean screw. From their blog the energy generated for each month is:

September: 11108 kWh
October: 25356 kWh
November: 24232 kWh
December: 29513 kWh
January: 19512 kWh
February: 9185 kWh
March: 20330 kWh
April: 3091 kWh
May: 4436 kWh
June: 1389 kWh

Somewhat arbitrarily, but giving them some benefit of the doubt, I’ll replace September’s figure with October’s (perhaps the low September output was mostly teething troubles), and for the missing July and August figures I’ll use May’s.

So the total is: 25356 + 25356 + 24232 + 29513 + 19512 + 9185 + 20330 + 3091 + 4436 + 1389 + 4436 + 4436 = 171272 kWh per year.

or 19.6 kW. This is considerably lower than the 31 kW quoted by one of their investors.

Nice rule of thumb I discovered whilst writing the post: 1 kWh per year is 0.1 W.

The people who built it give it a plate rating of 63 kW (it’s capacity, or maximum power output). So it’s load factor is a little less than 1/3 at 0.31. They also quote a flow rate of 2860 l/s with a drop of 3m. Neglecting the water’s kinetic contribution (which I’m not sure is reasonable), the water has a power of about 86 kW (2860 litres of water is about 28600 Newtons, dropping 3m every second). So the extractive efficiency is about 73%. Quite impressive. I wonder if it can really be that high? Perhaps at high flow rates the kinetic energy is a more useful contribution.

The seasonal nature of the power is clear from the graph:

(the empty bars are missing data, not zero generation)

Basically, you only get power in winter, when it rains. The rest of the load factor gets eaten away by maintenance (oiling, fishing, that sort of thing), high water flow (!) and HSE requests (which I take to mean noise complaints).

David MacKay, in his book “Sustainable Energy – without the hot air” has a cute chapter about hydro. He analyses the total energy of the rain falling on our land and concludes that we can only ever produce about 1.5 kWh per person per day from hydro. After that there’s not much to say, and the chapter is correspondingly short. His figures for actual UK production (page 56) suggest a load factor of 0.29 for large scale hydro, and 0.16 for small scale hydro. So Torrs Hydro is doing atypically well (or I’ve been overly generous in filling the data).

The thing that surprises me is that the Archimedean screw produces a solution that is comparable, in load factor and efficiency, to large scale hydro.

[edited in 2014-07 to remove/change broken links]