I love it! This is exactly the type of things I dreamed Maslow would be used for.
Sketchup can be a great tool to make something quickly.
Can I ask what is probably a silly question? I understand that the goal is to heat water, but how exactly does it work? Does the clear front panel create a greenhouse effect which warms the air inside or does it shine on a black tube or something similar? I know this is the basics and everyone else probably understands.
Thanks for the kind world Bar. I am getting excited about this project too.
I wish I had the know how to design in a good quality cad software but I’m
stufgling to wrap my head around Fusion 360. It’s going to take a lot of
practice.
As to your question. The model is actually incomplete. Inside of this box
will be a series of pipes (pex or copper) with aluminum fins attached (made
from stock aluminum you can get at a hardware store) that will shuttle
water through the box. The box acts as a tiny greenhouse and the pipes+fins
capture the heat and shuttle it back to a storage tank.
If I can get a good design for the box together I will then set to
ctreating a method of using Maslow to build templates or jigs, or tools
that will help in assembling the pipe/fin portion. But I haven’t quite
sorted that part out yet.
Thanks again for the comments. I welcome any suggestions. I’m also going to
need help in converting this stuff from Sketchup to g-code (I’m especially
clueless on how to do the multi-depth parts with Maslow).
P.S. Bar, the link further up on this thread shows a set of plans that we
are basing this idea off of. That’ll give you and idea of what the end goal
is.
Thanks for the clarification! I understand now.
We have a video that might help you with the process of going from sketchup to cutting something out. It’s a little dated because we’ve made so many changes to both Ground Control and the machine itself, but I think the general information is still good 
Instead of attaching fins to tubing you could do something like soldering (or other ways of mechanically fastening) tubing (I’ve seen steel brake line suggested) to metal roofing. I’d want to consider how you’d drain it to prevent freezing, but it gets pretty cold here. Paint the whole thing BBQ black and you’d have a cheap collector.
One aspect of the design I immediately liked is that all of the tubing is aligned to allow it to drain into the heat reservoir (typically inside the house, where freezing is not an issue). There is a pump (a common sump pump IIRC) that pumps the water from the reservoir to the array. If the temperature “in the greenhouse” isn’t high enough (at night, for example) the pump shuts off and the water drains from the array back to the reservoir.
Submerged in the water in the reservoir is a long coil of tubing that connects the water supply to a conventional water heater. So the reservoir acts as a heat exchanger, transferring heat collected in the array to the water in the coil of tubing, preheating it before it enters the water heater. Very simple and clever!
Yes, @jwolter is correct. The original design identified above is what’s called a “drain back system”. If the reservoir doesn’t need more heat, or the solar panel can’t provide heat (that is, it’s cooler than the reservoir because it’s night time or too cold/cloudy to provide heat) the pump shuts off and all the water “drains back”. This protects the while system from freezing or boiling.
In thinking about how to get water pipes into the little collector without too many elbows or fittings (which tend to be the expensive parts) I think I might try to create a long piece of wood to the left, and to the right, those boards will have .625" holes (just big enough for pex pipe to fit through) every 6 inches. The pex will be fed back and forth through the holes, thus creating a continuous pipe of pex that turns back and forth as it heads from top to bottom.
Give me a bit and I’ll try to draw it out on Sketchup.
I don’t know what the minimum radius for pex is (I have some, but it’s almost bedtime, so testing will have to wait for another day). Depending on the desired spacing between the tubes, you could put a tee in the pex line and then have two (or more) lines zigzagging across the collector array. That would slow the water as it travels through the array, allowing it to collect more heat before it exits.
I did some looking online and it appears the minimum recommended radius is 6". For hydronic flooring they make a plastic turning bracket that will move the pex 90 degrees in 3", so 6" for a full 180 seems pretty doable.
Here’s what I’m thinking for creating a serpentine type “zig zag” across the panel. The pex pipe would go through a hole on the left board, then through a hole on the right board, make a 180 degree turn and feed through the next hole, etc…
The advantages of this are:
1.) the water will drain back easily. There’s no place for water to get stuck in a valley and freeze or boil.
2.) There are no internal connectors, t’s or elbows to worry about. That reduces risk of leaks and reduces cost.
The disadvantages:
1.) it may be less surface area than a few pipes going vertically down the length of the panel.
2.) it may be difficult to add aluminum fins to the pipes, thus reducing it’s surface area for absorbing heat.
3.) Unless the long pieces (with holes in them) are cut into smaller sections it’ll be hard to “print” them with Maslow. It would be better if one could cut multiple 2’ sections of holes, and then assemble those into a longer piece. This way Maslow can work from the center of the cutting area.
Here’s the updated Sketchup file: https://drive.google.com/open?id=0B-ZcXNFKzjU9Zjh1bDNMaWdmQmc
The inside board with the holes needs work… I need to think about how to make that in multiple pieces instead of a long board like that. It needs to be producible via Maslow.
Maybe instead of holes you could cut semi-keyhole shaped “slots” that would allow you to press the pex into the slots instead of having to feed lots of feet through every hole…?
Like this:
This could save some time with Maslow Z-travel too… (I don’t actually know how long it takes to move the z-axis).
The pex angle bender bracket things I’ve seen help hold the tubing so that it doesn’t kink, hopefully that wouldn’t be a problem.
Maybe this violates the spirit of this project but what about using a cheap plastic or rubber solar collector that is already commercially available? You could still mount it in the frame for added efficiency.
There are many different designs and some would allow for auto draining.
Or maybe use cheap irrigation tubing that is already black, inert, flexible, and can handle being in the sun… Way cheaper than pex and the black tubing with thin walls will likely do a better job at transferring heat to the water than a pex/aluminum sandwich.
I’m not sure if it would help anything, but for PEX based under-floor heating, there are shaped panels that transmit heat from the hot water in the tubing to the wood subfloor. It might work great to transfer the “heated air” to the PEX tubing. Just a thought.
Purchased heat spreaders, like those from pexsupply.com (who I recommend, but spend too much there on the overly complex manor heating system) can be spendy. Here’s a DIY version.
Just a thought, but the maslow with a suitable bit could cut grooves in the surface of a insulation panel for the pipes to ‘clip’ on, add a sheet of foil pressed into the slots for heat spreading then spray the whole thing black?
At first I considered something slotted but I worried that it maybe weaken the plywood piece too much since it needs to be relatively short to fit withing the solar collector box. Plus I thought the pipe might tend to pop out of place when being setup. But that’s all speculation - to really know the best design I’d probably need to test a few different ideas. Thanks for sharing!
I’ve seen those swimming pool heaters in various forms as home water heaters but I don’t know about their longevity. It might be that a simple insulated box with clear cover would be a fantastic system… again, probably something that needs to be tested.
The cut foil idea is really interesting. I’ve never heard of that before… I wonder how much heat would actually be transferred as opposed absorbed or reflected out. I suppose a black painted foil would capture a lot of energy. I think this needs to be tested! What a neat idea!!
Any ideas on what bit should be used? I imagine something like this: https://www.amazon.com/EnPointTM-Grooving-Carbide-Tipped-Woodwroking-Industrial/dp/B01MRUOPAK/ref=sr_1_7?ie=UTF8&qid=1507900153&sr=8-7&keywords=.5+half+round+router+bit
If you look at the original (non-cnc) design you will see the foil heat spreaders used, and their finding that silicone caulk acts as an effective heat transfer medium.
Heat transfer, like electric current flow is a function of cross sectional area (more area, less resistance). A few thousandths thickness foil won’t transfer a whole lot of heat.
Our radiant heard floors have the pipe, some rooms copper, some PEX, mostly in over an inch of sand mix concrete for heat transfer and thermal mass. That’s probably too heavy to use in a solar panel 
Looking at commercial equivalents is an excellent idea! One of those slap-my-head-and-wonder-why-I-didn’t-think-to-check-that kind of ideas.
I took a look on Amazon and the product you linked to only got three stars (on admittedly a very small number of ratings and mostly unhelpful reviews). One reviewer complained that theirs came apart at the seams which suggests that you would have to be very careful about the pressure you expose that product to. You would want to put it into an insulated greenhouse box to 1) protect it from damage, and 2) hold the heat in (reducing cooling by conduction, convection, and radiation)
Just a thought regarding the use of polycarbonate sheeting, does it lock in the heat or allow it to radiate back out of the box. The theory of the glass house works because the glass will allow the light in which will heat up everything it hits but than blocks the infrared(? I think) heat from escaping which allows the heat to build up.
