Can we power electric cars?

There were 240.0 billion car miles driven in the UK in 2013. That’s 386.2 billion car kilometres. [source]

If electric motoring costs 0.34 kWh per kilometre (from your 4 year old link), then that requires (386.2 × 0.34 =) 131.3 TWh of extra electrical energy.

Total electricity generation was 359 TWh in 2013. [source]

So switching to all electric cars would required the UK to increase electricity generation by 37%, according to the article you linked. If we all drove Teslas, which achieve 0.24 kWh/km, then generation would only need to increase by 26%.

EPS, XPS or PIR for EWI?

I’m having second thoughts about using Polyisocyanurate (PIR) boards for our external wall insulation (EWI). PIR is the best commonly available insulator, so it will enable us to get the most insulation into the limited thickness that we have available. Unfortunately, I’ve just learned that PIR has some problems that may cause it to deteriorate with age. Firstly, it is liable to shrinkage, which means that gaps might open up between the boards. Not only would that compromise thre insulation, but it might show through the render, and spoil the external appearance of our house. Worse, PIR can deteriorate if it gets damp, which is something that is hard to rule out. Finally, the gasses trapped in the foam could leak out over time, further degrading the material’s performance. Is that bound to happen? No. But it’s certainly got me considering alternatives…

Here’s a useful table of common insulators from the Energy Saving Trust.

The most common alternative to PIR is Extruded Polystyrene (EPS). It’s about 30% less efficient, which means our EWI would need to be 150mm thick, rather than the 100mm of PIR that we were planning. It’s generally very stable, so there should be no shrinkage or damp problems, and it’s a bit cheaper too. Also it’s much more environmentally friendly to manufacture EPS, which is a bonus. However, this post on contains a report of someone who’s EPS did suffer from shrinkage, so I’m still not 100% confident that’s safe.

The same post reports that expanded polystyrene (XPS) boards were totally stable over the same period. XPS is the “normal” white poystyrene that everyone is familiar with as a packaging material. It’s an even worse insulator than EPS, but it it saves me from having to tear down & replace the who EWI in 10-20 years time, perhaps it’s worth it?

Finally, there are ways to reduce some of the risks with PIR. For example, if you use two layers of boards, with the joints staggered, then any shrinkage does not compromise the insulating layer. Also, most of the shrinkage happens shortly after manufacture, so the boards can be “aged” before use, so that most of the shrinkage has already happened before it’s fixed to the wall. Of course, those strategies would both make the project more expensive and more labour intensive.

Right now, I’m leaning towards EPS. But I need to do more reading around.

fostertom on EWI

Excellent advice from fostertom on external wall insulation (EWI):

The ideal is EWI to walls, continuous with similar EPS [expanded polystyrene] on OSB [a kind of plywood] boarded over the top of the rafters, tiles/slates replaced but a bit higher up. The roof OSB is adequately airtight, without any problems with interruption by internal trusses etc. Unfortunately EWI can’t be relied on to be airtight, so either an external rough-render (breatheable) on the brickwork before EWI-ing, or the internal plaster wd be your wall airtight barrier.That (like IWI [internal wall insulation]) is problematic because of joist penetrations and joists so close parallel to wall that you can’t make the internal plaster continuous through the floor thickness. Also needs connecting up with roof OSB (or with over-joist membrane if trying to air-tight at loft floor level).


Electric kettle vs. induction hob

I have a 3kW electric kettle, and a 2kW induction hob, and I find the induction hob faster and more convenient. (My wall sockets are all 240V.)

However, I’ve just actually measured it, and the situation is more complex… I timed how long it took each of them to boil a single cupful of water. Unsurprisingly the 3kW electric kettle boils the water much more quickly, but it takes ages for its temperature sensor to notice. The electric kettle turned off at almost exactly the same time as the stove-top kettle started to whistle.

So for small volumes of water, it’s a draw. For larger volumes of water, the electric kettle is noticeably quicker.

Why then, do I find the stove-top kettle much more convenient? I think it’s because it has a better “user interface”. When the electric kettle has boiled, it clicks off and I often finish whatever else I’m doing before going to use the hot water. By then, it’s usually cooled down a bit, and I have to turn it back on and wait to bring the water back to the boil. (Actual boiling water is very important for making tea.) OTOH, the stove-top kettle whistles and stays boiling, so I am forced to go and deal with it immediately. The result is that I get my tea made a little bit quicker, with less waiting around.

Interesting. Perhaps electric kettles should replicate that UI, by having a continuous alarm, instead of automatically turning off.

Soldering Pipes

Things I have learned today about soldering pipes…

  1. It’s not a one handed job.
    As a beginner, I wanted to hold both the blowtorch and the solder in my right hand. So I heated the pipe with the torch, then put it down and applied the solder. Bad idea. I guess the solder cools the metal as it melts, so you need to keep on applying heat. I’ll just have to learn to use my left hand.
  2. Solder flows downhill.
    So arranging the workpiece accordingly makes it all go a bit more easily.
  3. Americans pronounce it “sodder”.
    …For some reason best known to them.

Here’s the best “how to” video I found…


We want to maximise the production of firewood on our little patch of land, so coppicing seems very attractive. We will plant some ash in the front garden, which is not otherwise very productive, and there are already a number of young informally coppiced hazel stools around the back. Hazel is attractive because it grows even faster than ash, and we can harvest nuts from it while it’s growing.

Some of our best resources are in the hedgerows. We have a number of fairly mature ash trees, and lots of already-coppiced hazels which look like they are ready for cropping.

Windows #1

Here’s a first idea of what windows we’ll have, and how they will open.

The opening lights are shown with a red chevron. I’m planning to ask for quotes for “Euro” style tilt-and-turn windows, and regular casements. Even if we just get casements, Hilde is very keen that they should open inwards, since it makes cleaning them so much easier. I’ve tried to keen the number of opening lights to a minimum, in order to keep the cost down.

Windows B and E are show with top-hinged upper casements. If we get tilt-and-turn windows, then these lights can just be fixed.

Window I is a sliding/folding door with a level threshold.

(The side-elevation isn’t very accurate, but it’s good enough to show the window design.)

(Same thing as a PDF.)

Energy efficient windows

I’m going to have to choose some windows, and a window fitter soon.

Most of the windows that we want to reduce are in solid brickwork, so at least I can do the new brickwork myself. I like that idea, because it will allow me to add chamfered jambs, which will let in more light, and be an interesting feature.

Fitting windows to cavity walls is complicated, so I don’t fancy doing it myself. But do I go to a local window company and get UPVC (U-value about 1.4) or to someone like Green Steps or Green Building Store who make wood-framed windows with a U-value of 0.8-0.9? I calculate the better insulation will save about 400W, which is about 5% of my current heating estimate. That’s not a lot really, but they will also look better – and that is important.

Furthermore, who will fit the windows for me? Green Building Store offer a supply & fit service, but Green Steps seem to be supply only. I suspect that it’ll be way cheaper to find a local fitter.

Cove Lighting

I calculate that we’d need over 100 LED spot lights (at about 200 lumens each) to get 500 lux in the big room. That’s £1000 of light bulbs! So now I’m considering fluorescent bulbs (T5) concealed behind an architrave or coving.

Altima have an all in one solution, but frustratingly, they don’t say how bright it is. PJ Engineering have much simpler luminaires, but then I’d have to construct my own coving – and I’d have to make my own reflectors too.

In any case, we’ll also need some spots for detail lighting. Dimmable fluorescent tubes would be good too.