An Eccentric Anomaly: Page 5

Ed Davies's Blog

Trip to Castle Sinclair Girnigoe

This morning Karen Munro tweeted:

2 large whales spotted blowing in Sinclairs Bay, near Wick today, I am stuck at work car-less. Really hoping someone gets an ID on them

By the time I read that, about an hour later, it was a bit of a long shot but, still, I needed to get out for a while so I went up to Castle Sinclair Girnigoe which is on the north coast of the little peninsular sticking out from Wick past its airport forming the southern boundary of Sinclairs Bay, at the end of the footpath shown here on OpenStreetMap. (Memo to self, go back and map the car park and castle.)


Stefan's Law and AGW

A while ago on the Green Building Forum, in the context of asserting that current theories of anthropogenic global warming are wrong, Tony wrote:

Finally any model that shows consistently rising temperatures or exponentionally rising temperatures must be ignoring Stefan’s Law which says that heat is lost in proportion to the fourth power of the absolute temperature, setting up a very strong force to stop or at least reduce any increases.

I think that's not right and I gave a quick response in the next post on that thread giving a “meta” reason why I thought so: that it's ridiculous to think that climate scientists aren't perfectly well aware of this law. Another quick near-meta argument I could have given is that feedback resulting from the supposed steep effects of Stefan's Law were not enough to prevent global temperatures dropping by around 6 °C during the last glacial maximum.

However, there's a physical reason, too, and the details are interesting enough that it seemed worth writing up my understanding of the situation.



My previous Decrofting post summarises the situation with the purchase of the plot as it was at the beginning of November. Since then not a lot has happened but just about enough to be worth reporting.


Which is more scary: volts or amps?

It both amuses and scares me how people are frightened of high voltages but often seem amazingly relaxed about low-voltage high-current situations.

High voltages are relatively easy to deal with. Wrap them up so people can't contact them with bodily parts and put an over-current protection device (fuse or circuit breaker) in the way so they're not likely to start a fire. For extra points, put an RCD in the circuit to defeat those more intent than normal on a Darwin award and even an AFCI to stop relatively small sparks causing fires.

High current circuits, particularly DC ones, are intrinsically harder to make safe even at low voltages as any poor connection, with higher than nominal resistance, can dissipate significant amounts of power as heat and so, maybe, cause a fire. Over-current protection doesn't help as normal operating currents can cause such problems.


Components and Layers in Google SketchUp

I've been doing some redrawing of my house designs in Google SketchUp. SketchUp is generally pretty well thought out and impressively clever at working out what you want it to do except the odd occasions it isn't at which point it can become seriously frustrating. Here's something which has a simple explanation which took me a while to figure out.


UK Email Surveillance

Apparently, and sadly, this Daily Mail article (FreezePage) about the Home Secretary's wish for the security services to have access to records of a lot UK internet accesses is not a spoof. Expressions like “non sequitur” and “foaming at the mouth” float into my mind for some reason. They're followed, not far behind, by “mission creep”.

The BBC manages not to get quite so embroiled in the nuttier aspects of the home secretary's rant. I'm not sure this is entirely good; maybe people need to see the whole thing to make their own (non-clinical) judgement.

Still, from a practical point of view it's interesting to consider what the implications of email logging would be.


PV to Immersion Heater Problems

In my previous Photovoltaics for Domestic Hot Water post I said I'd write more on the use, caveats and interpretation of that calculator later. A recent thread on the Navitron forum triggers me to write about some of this.


Photovoltaics for Domestic Hot Water

I've previously written about the possibility of using the output of photovoltaic panels for heating applications in circumstances where traditionally solar thermal (evacuated tube or flat plate) panels would be used: PV For Space Heating, PV, ETs and Flatties and, slightly less interestingly, Solar By Area.

Since then the price of PV has continued to drop. At the moment Navitron, for example, are doing Kinve 235 W panels at a fraction over £0.57/W (incl. VAT) compared with another supplier's £0.74/W + VAT at the beginning of the year. In the mean time I've been fiddling around doing a calculator web page to try to explore the trade offs in systems which combine solar thermal with a heat pump driven by photovoltaic panels. I'm not happy with the design of this yet (it works as intended but it's difficult to get anything very insightful out of it) but playing with it a bit did show over how wide a range of operating conditions the costs of output power of PV and solar thermal are similar.

This page is, therefore, a simplified version of that calculator designed specifically for comparing the cost of power from PV and solar thermal.


Crossover Cables and Red Tape

The other day Akkana Peck wrote about using a crossover cable to her Raspberry Pi. All good stuff but there are a couple of points worth adding.



At the end of my So Far... post I was wondering what to do about the pair of plots I had my eye on. After a bit of contemplation I put in an offer on it but there's a bit of a problem.