Sunday, July 31, 2005

DIY tracking solar concentrator project

This is my "Do It Yourself" project for a high-performance but low-cost modular home-built solar water heater that is largely made with common tools and building supplies.

It is also way cooler to have one of these than the traditional flat plate design that most people think about when they consider making a solar heater.

Here is another prototype (my third) of the solar tracking heater just before I take it apart somewhat to make some modifications.

This one has run well throughout the month of July here just outside of Toronto, Canada and certainly has warmed our swimming pool several degrees each day. Without water in the system, the central copper collector tubes can reach 270 degrees F although when it is operating with pool water flowing through it (about 60 gallons per minute), the heat rise is hard to measure, less than a degree F. The pipes are cold to the touch although the wood frame heats up a bit where the concentrated sunlight spills off the ends.

The motor drive has performed well and moves the collectors smoothly. The new plastic reflector material is beautiful. I have learned much and am very encouraged, but have some refinements to make before offering the plans to others.

I want to go ahead and build more reflectors, since more capture area is certainly needed, two two foot by eight foot reflectors is just too small for the size of our pool (32x18 feet, volume 106,000 liters) and eight reflectors are planned for the next stage.

A new method of coupling the reflectors together mechanically is in the works, together with a new frame and pipe couplings. We had several leaks because of the slip joints at the ends of the copper pipes slipped off a couple of times.

I've managed to gather some temperature data and simulate several "failure" conditions to check some safety concerns. The design appears to be quite safe, it won't burn itself up even though it concentrates the sunlight about 20 times, although you might want to wear strong sunglasses while around it on a sunny day. Construction work is probably best accomplished on a cloudy day or with a tarp thrown over the reflectors.

I have tried several automatic control strategies for the collectors movement to track the sun and have tracked the sun automatically with varying degrees of success so far. My main tracking control for the month of July was manual however. The good news is that the focus is not very critical and throughout the hottest part of the day, a trip to the control switch was only required about once an hour to keep the strip of hot light focused on the target copper tube.

I also have concerns about the dissolving copper that seems to be plating out as a brown stain on the bottom of the pool. It's pretty slight so far and I've stopped the flow of water through the heater in preparation for the rebuild. While a bit of copper in the pool water is actually beneficial (less than 0.2ppm) in terms of controlling algae, too much can lead to staining. Adding more copper pipes to the system is no doubt going to lead to more dissolved copper.

The blue barrels in the picture are for rainwater collection and not a part of the heater.

Thank you for your interest.

George Plhak