Step 7: Mana from Heaven aka: Money from Sunlight
Now go build one. It's not going to build itself! You can preheat water for any type of water heating system, gas or electric, tankless or with a tank, and it will translate into savings for you. Just be safe and get professional help if you have to in order to follow local codes and so forth. Yes, that was a disclaimer.
Remember, even if what you build is not enough to supply all your needs, that doesn't matter. If it just supplements what you have, then every bit of energy you harvest is money saved! It amounts to turning sunlight into money!
Oh, one other thing --- If the ambient outdoor temperature is higher than the temperature of the water coming out of your supply pipe, this thing will work even without sunlight. That's right... on a cloudy day or even at night! If your water comes out of the supply pipe at 55 degrees and it is a cloudy, but warm 80 degree day (or night), the water will still circulate until the holding tank is at 80 degrees. And feeding 80 degree water to your heater is better than feeding it 55 degree water!
Money saved - day AND night!
Q - "What if it gets cold at night? Won't that cool off the water in my holding tank?"
A- No. If the water in the collector is cooler than the water in your holding tank, then the cooler water will just sit there because it is heavier. Circulation will stop until the sun comes up and heats the water above the holding tank temperature. Perfect automatic control!
Just remember that hot water rises. If your regular heater has a tank, then it needs to be at the highest point in the system. The solar collector needs to be at the lowest point and the holding tank between the two.
If you use a tankless heater, then you only have to worry about having the collector lower than the holding tank and you don't have to worry about the height of the tankless. It could even be in your basement. Don't forget to insulate all your connecting pipes!
Well, I need automatic control of the mirrors.
I'm learning about heliostats. Heliostats are different from solar trackers. A solar tracker keeps something (like a pv panel) pointed at the sun. But we don't want to point a mirror at the sun.
A heliostat follows the sun and positions a mirror in such a way that it keeps the sun's reflection on one spot... your collection box. It is a bit more complicated than a solar tracking system because the mirror has to be pointed at an angle that exactly bisects the angle between the sun and the collection box and that angle is always changing. Also, PV panels are forgiving about the vertical tilt angle but a heliostat has to be accurate in the Z axis as well as the X in order to keep the reflection on one point.
I don't want a M$ Windows controlled system. I don't really want to have to learn to use a Pic controller if I don't have too. I want it to be powered by a small lead acid battery charged with a small pv panel.
I'm leaning towards a system that uses GaP (green) LED's as sensors which control a Full Bridge Motor Driver. But I'm still in the initial stages of that. One thing I have learned is that thinking about heliostats makes my brain hurt.
For those not familiar, LED's can convert light into electricity, similar to a photovoltaic cell. Gallium Phosphate (green) LED's do it best. Three green LED's wired in series and exposed to bright sunlight will produce a voltage high enough to switch TTL logic circuitry. Before you get any ideas, LED's are not a practical replacement for photovoltaic panels. They will produce a voltage but practically no current.
I just ordered a bag of 100 water clear green LED's and spent last night destroying/salvaging two defunct printers for motors, gears, etc.
I hope you liked my first Instructable. Visit my project site: http://davetech23.tripod.com to see other diy projects I have documented. Also documented is my Electric Tankless Water Heater with performance observations if you are interested. Hey, it's free.
UPDATE August 8, 2009 - I'm still working on the heliostat but have been slowed down by the need to make a relatively complex circuit board for the controller. I got sidetracked building a tabletop cnc machine (a la Tom's Easy Mill) to make the pc board with. I'm almost to the point of making the board, waiting for engraving bits to arrive from the other side of the world.
My build of the mill and pretty much day-to-day progress is being documented at:
If you don't mind, click a star up there and give us a rating. Thanks!