Hello Richard, I have waited until now to respond to this. I have long term experience with living in a Solar house. My Hotwater heating system is what is known as a bread box (2-40 Gallon tanks in an insulated box with about 2 sq m surface area with a glass top. I initially had an on demand backup heater (AC Powered) this was a nice idea, but cost more in maintenance than it saved. I replaced it with a conventional 40 gallon hot water heater, and changed the computers code to bring it on only when needed (it's been there 21 years) The solar hot water heater has been there 25 years. Since every thing except the blowers and shutters are passive every thing has worked well for 25 years. I had to replace a blower motor about 10 years ago ($50 USD) The original Solar hot water heater was $1800 with a tax rebate of $900 at the time. Wood heat is used as the backup source of heat (only needed when there is cloud cover for more than 2 days in the winter). Summer cooling is provided with Cool Tubes (large plastic pipes buried under ground) air is pulled through these by a blower. Powered louvers are used for controlling air flow for heating or cooling. Under the house is an insulated rock storage area with an area if 118 cubic meters. Cooling and/or heating air is circulated through this storage area. Controlling this system was a Z80 with Analog temperature inputs and Relay outputs for the fans, blowers and louvers. This all worked fine until a couple of months ago, ZEEK, my old trusty Z80 died this winter, so things haven't been working too well. I am in the process of building a new computer control system to take over the duties of house sitting. (25 years of service with a Z80 working 24x7) The e-proms were only supposed to be good for 10 years. Overall when comparing utility bills, this system has saved about $60 to $80 per month for the last 25 years. The only real failure was the On Demand hot water backup heater. I had 3 major falures requiring complete replacement of the unit, and 1 partial replacement. The unit was $400 USD in 1980. A conventional heater was about $100 and $40 for a contactor to control it and some added code for ZEEK. If I had it to do over, I would make very few changes. The major key to the success of this is low tech devices controlled with a fairly simple high tech device. Heat/Cool storage and lots of insulation. Vern ----- Original Message ----- From: To: Microcontroller discussion list - Public. Sent: Wednesday, February 09, 2005 4:22 PM Subject: [OT:] Solar water heating economics > > I'm looking into the possibility of getting some solar panel for hot water > heating and I've just got some rough costings that seem to point pretty > clearly toward it & would appreciate comments. > The basics are that I can get a system installed for $NZ4000 and get an > interest free loan over a 3 year term to cover it. > > The Figures are :- > > Monthly Power Bill (averaged over year) - $250 > % spent on water heating 66% Estimated (will have to look into this) = $165 > / month water heating costs > % Replaced by solar panel (according to the shop) - 66% > = $108.9/month saved. > > $4000 over 3 years, interest free = $111 / month. > > i.e. After 3 years at my current costs I will get 67% free hot water. If > the price of power increases I will start saving sooner. > > Any comments on the figures? - particularly the claim wrt 66% power > reduction in hot water heating using the solar panels. > > Incidentally, these are standard panels, no heat pipes or evacuated tubes, > just black panels with a glass cover. > > Richard P > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist