They are recorded from 1-wire temperature sensors - I bought just the sensor (relatively cheap) and wired them up myself using a straw and some heat shrink tube to make a temperature probe; and telephone cable for the network. The sensors draw power from the 5v USB line from the computer.
Connects via USB (see above link) to a small cheap second-hand laptop running linux, digitemp and rrd database to record the data over 24 hrs.
The graphs I posted were from the windows os version of digitemp. Unfortunately my cheap second hand laptop gave up the fight after 3 years in the warm airing cupboard! I've switched to a small cheap eeepc running a version of ubuntu (linux), using linux version of digitemp. Graphs aren't quite as nice, but do the job (see below).
Absolutely. I cheated and bought the EV tubes - although I did install it all myself and kept cost down by plumbing straight into an existing HW cylinder (i.e. no pressure stuff often required for closed loop systems).
In that case, judging by threads on other forums, there's quite alot of 'sad' people around the country doing the same! - that or watching their solar PV inverter
Can't beat a bath or shower in hot water that's been entirely heated by the sun!
This post has been edited by grahamread: 10 March 2012 - 00:30