Notes: Time - 15 Minutes Solar Water Heating and Open Source IT Solar hot water Why Solar Thermal? CO2 savings: Residential water heating accounts for approx 6% of UK CO2 emissions (Cambridge City Council). =~ 30 million tonnes CO2 per year. After 2 years, a typical solar hot water system has saved as much CO2 as was released as a result of its manufacture (University College London). Solar thermal systems are among "low hanging fruit" in terms of residential CO2 saving. Financial: Really depends on what fuel you currently use for heating. Gas is the cheapest. As of last week, if you wanted to buy gas at wholesale prices, for delivery during Jan 2009, you would have to pay £1.13 per therm, compared to 25p per therm, in Jan 2003. Compared to gas water heating, for domestic installations a good site and a good, low cost installation, something like 7 years is probably reasonable time for the system to pay for itself financially. Varies wildly depending on source of figures e.g. 3 years (housing charity vs. previous oil boiler Independant assessment from Solar Sense web site Jan 2008) 208 years (Royal Institute of Chartered Surveyors Oct 2007 - who didn't state their calculations). Part of the point of this talk cost savings, The tech: Water tank with loop of pipe, pump and collector on a south-facing roof. (pic) Sun heats collector (a thing with water in, which is a special shade of black), when water in collector is hotter than the water in the pump, something turns the pump on, and then back off again. When the collector isn't hotter than the tank, it turns it off again. Economics now favour the "evacuated tube" type solar collectors, this is basically a Thermos flask, with a window in one side, and the black thing in the middle. This has basically happened since Chinese companies started producing this type of tube - UK prices have fallen by approx a factor of 3 in the past 10 years as a result. What the Hell has this got to do with Open Source? 1. Basic IT cost-cutting methodology is a good example Use the Google methodology - spend time developing clever software which you only have to make one of, and use commodity hardware where-ever possible. e.g. One possible "disruptive" tech which is being tried out at the moment is the use of cheap+effective heat exchangers which are commonly used in gas combi boilers - these allow you to use cheap off-the-shelf hot water tanks, and retrofit solar to existing tank-based systems at minimal cost. The also allow for cheap mains-pressure hot water systems. 2. System design software Compared to installing an electric, or even a gas hot water system, you have to be quite clever to design an efficient and cost-effective solar hot water system. Fortunately, some clever software could make it considerably easier for Bob the Plumber to install a system. It could also make the householder more comfortable (solar industry currently has its share of double-glazing grade salesmen). Plumber says to householder, "Don't just take my word for it, go to this independant website, stick in this design number, and see if you agree with the figures". 3. Controller design and development (hardware and software) Existing commercial controllers are stupidly expensive, and don't seem to do much, plus those interested in doing so have no opportunity to alter the control algorithms, or add extra sensors. This is actually quite a useful thing to be able to do if you have an out-of-the-ordinary system. Arduino is an open hardware general purpose microcontroller board, with lots of off-the-shelf peripherals and features (USB, bluetooth, LCD modules etc.), and I know of at least one person using one as a solar controller. Wookey uses a Baloon, which is a very over-speced ARM for this purpose, he runs Debian/ARM on it... A good + cheap Linux based commercial solution would be the "slug" Linksys NSLU2 product - which can be purchased, and turned into a viable controller for £80 or so, using off the shelf components.. Cheaper than most commercial controllers.