a parabolic workshop light

I had made up a number of four foot parabolic solar reflectors for prototyping the solar heater project.

By supporting a single four foot florescent tube at the focus of one of these reflectors, I made a very effective workshop light, shown here illuminating my garage workbench.

The same ribs are used as in the longer, eight foot reflectors but with shorter side rails.

I haven't done a scientific test against a two tube fixture without a reflector, but I'm very pleased with the even and bright lighting of the bench surface and delighted to be using half of the electricity of a two tube fixture which I might have otherwise used without the reflector.

shop lighting reading list
a parabolic workshop light (this article)
led household bulbs
exploring efficient workshop lighting alternatives
work light led retrofit
testing fluorescent light fixtures - the test jig
testing fluorescent light fixtures - the test method (video)
testing fluorescent fixtures - 40 watt
efficient workshop lighting 2
updated bench lighting

the end of another season

It's the end of another wonderful summer here in southern Ontario. For the first time, we've managed to heat the pool without burning any propane. (The solar tracking parabolic heater is behind the fence in the picture, click to enlarge). In fact, last month the propane storage tank was removed since we were being charged rental by the propane supplier. I would have liked to have kept it here as another potential energency fuel source, but realistically have no use for it. Our propane pool heater sits idle and disconnected.

This is fine while the sun shines.

Unfortunately, the weather here has been overcast, cloudy, rainy and cool throughout the end of August and most of September.

The sun comes out only infrequently and it is seldom for long enough to even bother turning on the pump and the heater tracking. Most of the time, the weather forecast has looked like this:

So the idea of a solar heater as a "season extender" depends on the weather (and your location).

Without sun, the pool tends to follow the ambient temperature and it is now cool enough that no-one wants to swim in it anymore. It really is time to start thinking about putting it away for the winter.

I consider that the project is a success and that our home made solar parabolic heater contributes meaningfully to pool heat and helps in a small way to prevent some global warming. However if we lived in a sunnier climate, the results would be even more meaningful.

For much of July, the pool temperature was in the 82-85 degree range hitting a peak of about 86 in the middle of July. For next year, I plan to contue the building effort to fill the frame with collectors. I currently have six operating. The existing frame will hold 12 reflectors. This will double the potential heat output.

I am working on the plans. Progress has been slower than I had hoped because it has been a busy summer with other work.

Thanks for your interest.

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.

the start of a new season

Spring seems early this year and I'm back to work on the tracking solar pool heater project. Yesterday I progressed a bit further than this picture and had the water flowing through six collector panels.

Here you can see the zig-zag path of the water pipes (click on the image to enlarge). The two left collector panels have not yet been mounted nor the flex hoses to attach the collectors to the inlet and outlet pipes.

The motor drive and tracking electronics have not yet been added either, but since I was working in the garden it was really no trouble to check the aiming of the panels every hour or so to keep them pointed at the sun. Because the collector pipes are fairly large (1.5 inch diameter copper), the focussed sunlight travels across the width of the tube over about an hour so the movement of the reflectors is not at all critical.

It was cloudy for the first part of the day and a steady breeze blew for most of the day. It seemed warm, but the air temperature didn't rise much above 60F in the shade. From about 1pm on, the clouds broke up and it was fairly steady sun for most of the afternoon.

I had been running the pump daily for a few hours over the last two weeks as we opened the pool and got the algae and winter debris cleaned up so the water was already pretty well mixed.

At about noon, when I had the water path through the collectors hooked up and the pool pump running for about an hour, the water temperature was about 55 degrees F. At 6pm, when I turned off the pump, the water temperature in the pool was about 60 degrees F, a heat rise of about 5 degrees F for the afternoon.

I was measuring the inlet and outlet temperature with some difficulty because of my primitive equipment. Because the full flow of the pump goes through the system, the water flows through the collector panels at a great speed. My temperature meter allows me to measure two temperatures and to take the difference between them, but with no decimal places on the measurement. Nevertheless, I was getting in excess of a one degree F rise in the water temperature through the system. I am using F because the degrees are smaller and if I use C, the meter only gives me zero, since the temperature rise is more than an F degree, but less than a C degree.

With the fast flow of water, even a one degree rise is fairly significant and within my expectations. The collectors feel cold to the touch although if you hold your hand in the focus you see very bright light on your hand and your fingers feel funny. I don't do that for more than a second or so, just to convince myself that heat is really flowing into the tubes!

I hope to improve my temperature measurement resolution and also to determine the flow rate accurately so that I can confirm the amount of heating. My estimate is that each panel should add the equivalent of about 500 watts of heat, making the six panels equivalent to a typical electrical clothes dryer (about 3KW). The frame I have built will hold seven more such panels.

This morning there is frost on the ground and the air temperature is about 32 degrees F. I can see that the water in the flex hoses is frozen, so I may be pushing it a bit, since the water does not drain from the system when the pump is off. The temperature last night didn't go much below freezing, so I hope that expansion of the ice didn't cause any damage. We'll see later today when I start it up again.

snow load

I had been concerned about getting the parabolic solar pool heater ready for winter.

Those of you in a warmer climate probably won't need to worry about what happens when the snow falls. Here in southern Ontario, Canada, there is a good six months when the collectors, if left in their operational position, will fill with snow like they are here. If it doesn't look that bad, consider that its a fairly warm day, just above freezing, and it has been raining too, so the snow you see is saturated with water and fills the whole length of the collector, eight feet.

I'd estimate that there is about two to three hundred pounds of extra weight in each collector when the picture was taken. They don't move very well, in fact, the motor drive is removed for the winter.

I'd considered turning them upside down for the winter, or removing them from the frame altogether and storing them inside for the winter. But I've left these four to their fate, to see what happens.

So far, they are doing quite well. I can look down the collector tube to check if the tube is sagging and it doesn't seem to be. If there is damage, or distortion of the reflector, I won't see that until the snow melts.

Incidently, water from the melting snow runs out the holes in the white hanger plate quite nicely.

Warm and dry inside, I am working on the motor drive and solar tracker for the Spring.

Happy New Year and Best wishes for a peaceful 2006!