Monday, October 01, 2012

reader project

Bruce from Florida about his solar concentrating hot tub heater which he built after reading my book:

Hi George,

Thanks for the compliment. I stand on the shoulders of giants (like YOU). {blush}

It has worked out very nicely. It actually produces WAY TOO MUCH heat in the spring and summer. It goes past 108°F and trips the hot tub's overheat safety circuit. (I'm adding a thermal sensor that plugs into the Arduino) As you can see I have it in series with a passive unit my friend built. I may bypass that in the summer and use just the array. Now that I have it working, I'm of course working to refine it, simplify and miniaturize it even more.

I'm planning on building a Tiki hut near the hot tub and putting the array on the roof of the hut facing south. That would give it at least 2 more hours of exposure per day. It will also give me my back yard view back. Right now the whole contraption dominates 1/2 of my little back yard. But what a conversation piece.

I will make the Arduino kit available eventually. I still have some tweaks to do. Right now I'm fine-tuning the routine that dynamically switches in and out of "timed mode" when it gets cloudy on a sunny day.

You probably noticed some things about the operation of the tracker movement. It never goes backwards to search the sun. That was a concept I decided to tackle when I read one comment on the internet "You can count on the sun to never move backwards". I thought that was funny and true… most of the solar trackers actually hunt for the sun moving west AND east. You are surely right— that little amount of movement east doesn't matter much energy-wise, but it still irritated me. It wasn't "elegant".

The other thing you may have noticed is the speed. My array moves way faster than others. That's thanks to the combination of the speed of the processor and the sensitivity of the garden light's PV "sensor" and the fact that I'm only moving 4 little 4-foot troughs. I'm sure the little screwdriver could not move your big array without being geared down. It takes less than 30 seconds to return east. Seeking the sun happens in less than 1 second. There's no wasted energy and a minimum of irritating motor noise and wear on the motor.

The drive setup is cheaper and more compact than yours, that was one of my goals there. The one thing I don't have that yours has is spring isolation from the motor to the array, but so far it hasn't been necessary. I think the advantage of its positioning under the array, not extending out the side makes up for that flaw.

I also the idea of putting the 'brains' in a fishbowl in the heat of the sun worried me. Here in Florida, I could imagine a china-syndrome happening. That's what steered me towards putting the controller down below, with just the "eye" up on top. Plus, I was itching to do something cool with the Arduino. What a fun and powerful development platform that is!

I will be able to eventually have the whole control system manufactured at a fraction of the size and cost. Everything is based on easily available and inexpensive components.

$20 for the screwdriver, $14 for the shower door wheels, I got a shop to cut and thread a piece of Delrin with standard 13 threads/inch for $25. The "housing" for the motor is a 2" conduit body $8. The Arduino, sensors and relays altogether cost less than $40.

I tried using my own voice on the video, but I alas, am the world's most sleep-inducing narrator. I ended up using one of the speech voices on my Macintosh and I think it adds just the right touch. I slowed it down quite bit to sound more like the real me. Also I worked on the video to add interest and humor. Version 1 without those elements was un-watchable.


You can write to Bruce via Youtube.

Some more pics and description of Bruce's project

Projects from Andrew Gray (US) and Sulaiman (Jordan) shown in videos.


george plhak said...

It occurs to me that having a concentrating heater nicely solves the overheating in summer problem - by simply turning off the tracker. There will be no overheating while the collector is not focused. The flat plate collector cannot easily be "turned off".

Anonymous said...

You could also set the tracker to point the trough slightly off target a bit to reduce how much heat is being produced when it gets too hot - in effect "de-tuning" the efficiency to lower the heat output.

George Plhak said...

Yes, this is truly one of the advantages of a concentrator, that it does not have to stay blindly focused on the sun but can be moved off axis to prevent stagnation, unlike a fixed, flat plate collector. Thanks for your interest. George