Kent,
I believe, IMHO, that temperature control would need constant monitoring or you would cook the sap overly much. I have a passive solar air to air panel (a perpetual experiment) and the temperatures achieved vary wildly. I love the idea, makes a lot of sense, you would just need a way to maximise heat sometimes and reduce it when the Sun is out and the sky is clear. 
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Mike, I have often wanted to try an air heating panel in the winter time, but have never gotten it done. It makes sense that an air flow system would vary more rapidly than something with water, but it didn’t occur to me. The simplest thing I can think of is a speed controller for the pump, so you could set an average working flow rate, and a thermostat that would run the pump at full flow if the temperature gets too high. You could add a cross flow air fan that turned on at a little higher temperature, to drop the temp and increase evaporation.
The best way would be a microcontroller to vary the pump and fan speed as the solar input changed. Seems like over-kill though.
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I love open source projects like this one where people combine efforts…
If he insulates those lines and deals with the wind he will have a large amount of energy.
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The irony to all this is they are taking down SEGS and Ivanpoh thermal electric generation. Ivanpoh never generated as much as they claimed they could. I don’t know about SEGS. Thermal electric was supposed to be the ‘cheap’ way to generate gigawatts of electric when panels were 3 dollars a watt, and there was ‘no way’ PV could be cheaper. We tried it, it didn’t work. PV is actually cheaper now.
I am not trying to discourage you. I always find it a neat project. I had kind of forgotten about Ivanpoh and saw a blip about them decommissioning it. claiming government waste. It really wasn’t, sometimes you have to try knowing sometimes you fail. It shuts up people spewing whataboutism and offering alternative theories.
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Ah, yes, Ivanpah. It’s been almost 20 years since we took a bunch of students on a serious field trip out there. It worked okay. Lots of folks involved in keeping it working. To be honest, what I remember most about the trip and the talks is desert tortoises. The State of California was concerned about damage to the tortoise population. The courts determined that ten tortoises would be a reasonable number to kill. Eleven, and the facility would be closed by court order. There were 8 or so paid professional naturalists, required by the state, keeping track of tortoises and other environmental concerns. When we visited, about 7 years into, I think, a 10 or 15 year design life, one tortoise had died. Amazingly, it was backed over by a pickup truck driven by one of the naturalists. I’m no expert, but I think the major design flaw was building it on the California side of the state line with Nevada.
Solar thermal is a nice local product. I can work with paper mache and foil. I’ve worked with silicon, dopants, and aluminum too, but it’s a lot more work, and there’s a lot more to go wrong.
Pardon the topic drift, now back you your regularly scheduled programming.
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If it were not for rabbit trails, I would not be here, so feel free to go off topic 
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Charcoal + solar cooking… interesting…
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This was a flop, but painful lessons learned.
Well… First round on making a parabolic solar cooker was a flop.
What I learned in using paper crete:
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The mixtures to be mixed well, some of the mixture did not mix well and the cardboard did not setup with the rest making weak areas.
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This would of been much stronger if there was a mesh added to this. Being so large when I lifted it broke the bottom sections. Either this needs mesh, or to be made up of multiple sections for this size that can be joined together.
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The method I used is a ton of work breaking up the cardboard about 6 hours of breaking the cardboard down, mixing and smoothing out…
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I first just used sand for the mold shape, which lost form after I applied the paper crete on top… This was a mistake as it did not keep form, Better would be to make the mold out of plaster or cement then use the template I created to make the form, then let harden, then make my forms off of that…
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Buying a 120$ 5 foot metal parabolic cooker off ebay is very cheap compared to the work I put into this :-)
After thoughts:
In doing this I believe that I want a different shape for the parabolic design, one that is much flatter and will throw the focus point further out.
Paper crete to be done right demands to have the right tools to make it work. The thicker parts of this design do seem to be durable. I do see potential here for other projects.
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I was trying to figure out how to make a square parabola then after watching this video came to realize a square one is a circle one with the sides cut off…
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You are better off using either mylar like this guy.
Or using the flat honeycomb shaped mirrors which they use for telescopes. He used a 3d printer and some stuff from pcbway but some of that stuff can be subbed out with more common materials. I think his design is free, and has a whole series of videos on it. And you could probably use mylar over the plates instead of the flat mirrors. And it might actually handle being in the wind better, and if you want to screw around with focal points, it is more frame adjustments, not making a whole new one.
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