tracking the sun automatically

Click on any of my pictures for an enlargement or click here to see an animation of the array tracking the sun over a full day in less than a second.

My solar parabolic collector array now tracks the sun automatically. It's been working reliably for about the last couple of weeks. The improvement in heat gain is pretty remarkable as I don't have to be around to point the collectors at the sun as it moves across the sky.

I'm working on several tracking control strategies. Currently, I am using a small device available from Duane C. Johnson, Red Rock Energy (www.redrok.com) and I like it. Duane has a large and very interesting website with tons of suggestions and technical ramblings. I'm using his LED3X to control a similar Grainger gearmotor to the one he recommends. My gearmoter runs a screw shaft which moves the reflectors. On last year's prototype, I'd missed his suggestion about the extremely low gear ratio required and consequently my prototype was missing the sun and hunting constantly. Lower gear ratio, mine is about 6000:1 overall solves the problem.

The advantage of the LED3X is that it is small, ready made and inexpensive, about US$35 plus shipping. I bought three to have a couple spares for experimentation and in case of failure. Red Roks's delivery by post was prompt.

The hookup is simple. LED3X requires connections to the motor, a couple of limit switches and the battery. LED3x is mounted in the plastic peanut butter jar on the stick.

The Jiffy peanut butter jar radome is actually one of the Red Rock suggestions, although my jar isn't large enough to accomodate the LED3X sideways, so that it "sees" the sun through the side of the jar. The bottom of the jar distorts it's view of the sun and causes positioning errors. My arrangement is also hardly weatherproof and only a temporary solution for me. On clear days, I remove the jar and just leave the LED3X to operate in the open.

It works great. The two fat LEDs at the top sense the position of the sun and drive a MOSFET H-bridge to send DC current through the motor in one direction to go east, or in the other direction to go west. See Duane's website for a complete explanation of how it works.

The LED3X works in short "bursts". The motor will run for a while in one direction or the other or sometimes in both directions in the same burst if it is close and senses that it has overshot. Each burst is a few seconds long.

Because of the high gear ratio, you don't really see the reflectors move during each burst but after a series of these bursts, slowly but surely the reflectors move into position. When either of the limit switches is reached (west or east) it stops trying to move in that direction, but can move in the other direction. The limit switches stop motion at the extreme ends without damaging the motor or reflector linkage since the geared down motor while very small is extremely powerful.

The timing between the bursts is adjustable using the tiny blue control at the top left of the LED3X. You can have it constantly in motion where the bursts occur almost continuously or up to several minutes or so between the bursts. I have it set to about 30 seconds between the bursts to conserve battery life.

In the bottom right corner of the LED3X, you can see a tiny bi-mode green-red LED. This is GREEN when the motor is turning the array EAST (picture above) and RED (this picture) when the array is turning WEST. Otherwise the LED is OFF between bursts. This provides a useful diagnostic to let you know what is happening.

One of the things that I don't like about the LED3X is that it runs the motor during every burst, even if the array doesn't need to go anywhere. It will start to run in one direction and then reverse and go back. In my mind this wastes battery power, but it's minor. The motor draws only about 100mA from 12 VDC. The burst length is not adjustable but the timing between them is. You can set the bursts further apart to save power.

Another behaviour that is a bit annoying is that when the weather is cloudy, the LED3X runs the motor and sometimes moves the array quite a bit off target. Of course, when it is hazy or cloudy, it can't know where the sun is. But again, to save a bit of battery power, wear on the motor and to avoid guessing incorrectly and moving off target, in my mind it should just stop commanding the motor.

One last quibble with Duane's device, which otherwise I am very pleased with, is that because of the bursting behavior, it takes quite a while in the morning (about half an hour in my case) to move from it's resting position in the west back to the east to catch the morning sun. Of course, if I didn't have the bursts set quite so far apart, it would swing over much more quickly. But the sun is not very hot in the morning anyway, so this is not a big deal.

Yesterday was a particularly hot day here in Southern Ontario with the temperature in the shade over 95 degrees F. At the solar peak in the day, about 3:30pm, the water returning to the pool reached 85 degrees. The pool temperature has reached 80 degrees. It is a big inground pool, about 32 by 18 feet and about 10 feet deep. Quite a lot of water to heat.

Our pool has never been this warm, even when we did allow ourselves to use the propane gas heater.

I have more improvements in mind as I watch it work and will be adding more collectors in the coming weeks to increase the heat output. The sterilizer is yet to be installed.

heating with the sun

We are swimming regularly now and the pool temperature is holding about 76 degrees F, thanks to the home built parabolic tracking solar collectors and the pool blanket.

Here you can see the six collectors currently installed (click any picture to enlarge it). The mirrors are linked together mechanically and pivot around the collector tubes to focus the sun onto the tubes. Pushing or pulling on a single steel rod underneath moves them easily into position toward the sun. The reflectors are balanced, so it doesn't take a lot of force to move them.

Tracking the sun is still done manually. I go out to the collectors and move them every hour or so to get them back on the sun.

I am working on the automatic tracker, but the motor drive attached to a battery and a switch works well. No doubt there will be more heat collected when the automatic tracker is installed, probably this week.

Dust and leaves gather on the collector surfaces. No doubt the dust scatters the sunlight somewhat and cuts down on the heat reaching the collector tubes. The tilt of the collectors helps to wash them when it rains, but there hasn't been a lot of rain recently. I've tried washing them down with a sponge mop and a pail of water, but I will need to make a curved sponge to better fit the reflector surface and a longer handle, to reach the top of the collectors. If I'm not careful, I scratch the surface of the plastic mirrors.

We turn the pool pump off at night and on cloudy days to save energy. The pool pump uses a fair bit of electrical power since it is rated at 1 HP.

With the pump on and the collectors focused at the sun, everything is cool to the touch. The water flows so quickly that it only heats about a degree by the time it's gone through all six collectors.

If the pump isn't running and the collectors are focused at the sun things are a different matter, the water in the collector tibes will reach boiling within about half an hour. This will happen at least once a day as the sun passes overhead to wherever the collectors happen to have been left the previous day.

I'd done some tests on this previously and found that the boiling water expands down the pipe and back into the pool. Previously I'd had some problems with the compression fittings popping off the ends of the collector tubes so I added metal straps to hold them in place. No damage was caused to the plumbing I thought.

I've included this picture to show the damage that occurred to one of the flex hoses due to the hot water. It has almost completely collapsed due to the heat. It was also leaking quite badly at the end nearest the collector tube that was the source of the heat.

I've since replaced the tube with another type of flex hose. This is a fault condition only and shouldn't occur in normal use.



I've also received my first two stainless steel collector tubes which I plan to build into the next two collectors over the next few weeks. The stainless, while not quite as good at heat conduction as the copper will have the advantage of not being attacked by the chlorine we must currently add to the pool water.

The glass sterilizer tube may allow us to do away with, or reduce the chlorine.

Also, with the recent rise in base metal prices, the stainless is now about the same price as copper.

It's time for a swim!

You might also be interested in https://georgesworkshop.blogspot.com/2015/08/pool-heating-2.html

waiting for the sun to shine again

By May 9th, we'd had three fabulous sunny days in a row and the pool temperature was up to almost 70 degrees F (starting from about 55).

Since then, the weather has turned cold and rainy and there is no sun until next Tuesday according to the current forecast. Almost two weeks without sun.

I've diverted to other projects temporarily.

Here is the current setup of six collectors waiting for the sun to shine again.

The current drive system (click on any image to enlarge it) consists of a motor driven screw which carries a traveller connected by push rod to the end of the metal shaft connecting the reflector arms.

The tracking sensors and drive electronics are not yet installed. The reflectors are moved manually by connecting a battery to the motor wires as long as it takes to move the reflectors toward the sun.

Here is another view of the drive mechanism. The springs at each collector arm help to absorb buffeting from the wind.

While the heat collector tubes are metal and opaque to light, I will add a glass tube at the focus of one or more of the collectors to allow the intensely focussed sunlight to travel through the water. While the heat absorption may not be as good as the black coated metal collector tubes, since the sunlight is concentrated about 20 times, I expect that the concentrated UV rays will sterilize microorganisms in the water.

I've pressure tested the seals of the one glass collector tube which I've assembled, shown here waiting for installation.