Work Plan 2008

Here in southern Canada, near Toronto, the last winter ice has melted and we have been enjoying some very nice sunny days. I have been thinking a great deal about my parabolic solar pool heater project. There are several main items that I want to accomplish this season:

1) Dis-assemble, rebuild and enlarge the solar array with completely new components.
2) Move the motor drive to the other end of the array and install it on a permanent cement post.
3) Stiffen the pendulum drive rod assembly by replacing it with stronger components to accommodate 12 panels.
2) Install new re-designed sensor head mount at the other end (more sunny earlier) of the array.
3) Install a 3 way by-pass valve so that the pool pump can operate while work is done on the array.
4) Install a DC pump and solar panels to enable the system to run without the main pump on.
5) Install a UV-C water sterilizer unit powered from the solar panels.

Last year I spent about a month making new ribs and hangers carefully finished with epoxy primer and urethane topcoat. The new set of about 100 ribs and hangers (enough for 12 reflectors) is ready for assembly.

I would like to try Lexan flexible mirror and I did find a supplier. Lexan should be more durable than Acrylic. Likely I will end up with an assortment of reflective materials on this year's array, allowing comparison between them. I'd also like to check current pricing of the main materials.

I am going to tip the array up a bit more to better match the sun's orientation in this climate. Although the array can even be flat to the horizon with some loss of efficiency, the performance with improve the closer that the plane of the array is matched to the sun's azumuth at your location. Here is about 42N. I won't go that far, but currently they are only at about 20 degrees or so. I may push them up to 30.

Thank you for your interest in this project. I am logging your emails received and I hope to announce the availability of a set of plans by the fall. Please check in here to see how I am doing.

Update

Dear Joe (and everyone else who has written!)

Thanks for your kind note.

I AM still working on this project and I did make some progress last year which I have yet to write about.

I manufactured about a hundred ribs in preparation to replace and double the number of the collectors in my array to a dozen (each is about a sq metre). I shot video to clarify some of the steps in the process. I sourced new components and especially new thin lexan mirror which should be more durable. I refined the sensor housing. I obtained instruments to help me verify temperature and flow to better assess performance. I rejected and then re-thought an approach to UV sterilization of the pool water.

As you can see from earlier write-ups I use these DIY collectors in a high flow, low temperature rise mode to heat lots of pool water by only a small amount. Most people don't use concentrating collectors this way yet they have some advantages over flat plate type collectors, like lower cost, although they have higher complexity.

It could be very useful to heat fluid at a lower flow to a much higher temperature, which you can do with a concentrator. If the water doesn't flow in my system, that is if the pump is off, the water in the collectors will boil in about 20 minutes. I have no doubt that if you paid attention to the fittings, you could safely make steam and lots of it.

My mom died last summer and that put a damper on things.

I will let you know when there is something new to see here.

Many thanks for your interest, I do welcome your correspondence.

George Plhak

motor drive mechanical 2

Here is the motor drive for the parabolic solar heater on the bench while I was running the yoke from one end to the other using the small DC lab power supply in the background.

You can click on any picture here to enlarge it.

The DC gearmotor is in the green box to the right. The output shaft of the gearmotor is coupled to the galvanized steel drive screw shaft inside the box. Both ends of the drive screw are supported with pillow block bearings, a flange mounted ball bearing unit (Dayton 4X727) at the motor box and a bronze bearing pillow block (Dayton 2X567) at the far end. That is an ordinary pressure treated 2x6 that forms the support. You can see the yoke assembly in about the middle of the screw. The limit switches haven't been added yet.

I don't have an up-to-date picture of the inside of the motor box, but here is a picture of an early version to show how simple it is. I used a Dayton 2L008 Permanent Magnet DC gearmotor with a 560:1 reduction ratio. Dayton products are available nationwide in Canada and the USA through Grainger Industrial Supply (www.grainger.com). This motor only costs about $50 and is available from stock. It is rated for 12 VDC, and draws 1.2 amps at full load while turning 12 rpm. Only 15 watts to move the entire solar array! This little motor with the drive screw is plenty powerful enough for the job.

The 1/4" motor shaft is coupled to the 1/2" drive screw with a pair of spider couplers, like Woods L050 series which match the size of the two shafts and provide for a bit of mechanical misalignment if there is any.

I'm not that proud of the motor mounting which is just a pair of galvanized steel perforated strips, shaped to suit the motor distance back from the panel, but I was in a hurry to see it work and this seemed to do the trick. It's stayed that way for the last two years and works to hold the motor securely in place.

The yoke contains a captive 1/2 inch hex nut with the same thread pitch as the rod. The two outboard steel wheels just graze the 2x6 and keep the yoke from spinning around the drive rod.

The white goop on the thread and at the nut is white lithium grease. I connected the gearmotor to a DC supply and allowed the motor to turn steadily while I dabbed the white grease in it's path. To the left, you can see the grease spread out on the screw. I ran it back and forth over the whole distance I expected it to travel and kept dabbing grease on it until it was liberally coated smoothly and evenly. After two seasons, there is no rust and no apparent wear to the thread or the nut. I haven't re-applied the grease but probably will this spring.

Here are the two main components of the yoke prior to threading and gluing. You can see that I have brazed a short section of 3/16" steel rod into a drilled recess in the hex nut. This was actually my second attempt, since I am not a welder. Prior to drilling the recess for the rod, I centerpunched a guide dimple for the drill on one of the hex edges. I found that it was important not to drill the pilot hole completely through the side of the nut so that the brazing alloy didn't flow through and clog the thread. I suppose that if I had had a tap of the appropriate size, I could have run it through the nut to clean up the thread afterwards, but I didn't have one at the time.

Here is the yoke with the steel rod threaded 10-32 and the nut glued into the 1/2 inch band iron frame with industrial epoxy. The two holes in the legs of the frame are for the steel wheels. The threaded rod couples to the actuator rod.

If I was a better welder, I might have brazed this whole assembly. Because of the large area beween the nut and the frame for the glue to grab, I had much better confidence in this approach. I am using an epoxy by Locktite called Hysol 907. It is amazing stuff, but does require suitable curing time (24 hours is recommended for full strength), or a heat cure (150 degrees F for about 2 hours). The surfaces to be glued should be roughed with silicon carbide sandpaper and cleaned with de-greaser prior to gluing.

This is the pillow block which supports the far end of the drive screw. It is a bronze bushing which can pivot slightly in its housing to provide for some degree of mis-alignment. I used a bronze bushing pillow block out of concern for exposure to the elements. A sealed ball bearing unit was quite a bit more expensive and probably not necessary.

The oil cap is a nice touch and I even put a few drops of oil in it. The protruding oil cap did end up being a bit of a nuisance later as it interfered somewhat with the actuator rod which swings near it on it's way to the drive rod.