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Natural_Learner

This project is very odd to me: http://solarflower.org/?content=faq

First, great tutorials. This work is of benefit to all of us trying to do something similar.

But...

He (pretty sure it is a guy) has put a lot of work into producing a replicate-able design but he doesn't specify any performance measurements. How does one know if they have repeated the creator's work if there is no documentation of what a properly functioning model yields? How would someone compare this design to another they are thinking of using?

His discussion of total intercepted energy is total speculation; estimates with no experiential reference. And he ignores the question of application based efficiency. For instance, if the focal point stagnates at 110C, and actually does intercept 500 watts, less than 50 watts are available for boiling water. This design (hopefully) achieves a higher stagnation temperature than that, but I haven't seen numbers on that and I haven't seen any numbers that suggest his optical efficiency is near what he predicts. Stagnation temperature and energy collected at not-much-above-room-temperature are two vital numbers in describing what he has achieved.

I don't know how he got this far in the design process without having benchmarks or reality checks.

I bitch in hopes that this guy and others will start documenting and communicating these important details of their projects. Otherwise we do not have a network of information, but a bunch of dreams and truths all mixed together. Nothing would be reliably replicate-able. There would be no communication because there is no reference or common understanding.

None of us would accept a chemist saying "I've synthesized this important compound which has only been done rarely and with expensive equipment. See the solution is about the color I'd expect. I (probably) achieved a conversion of 40% to the desired product, because someone else in another paper did something related and got about that."

That is all.

-Elliot

solarflower

Hi, this is Daniel, I designed and documented the device.

Basically, all of your concerns are legitimate. I don't have any data from any instances of field use of this technology, I had attempted to do so with both of the two working prototypes, but due to changes of continent wasn't able, and neither as it turned out were the people I left them with.

I know that the only thing that's real in a project like this are the numbers, and currently, after completing the tutorials, they're my main focus of interest in the project.

I need to be more clear on the website that with the release of the documentation the project has entered into the beta testing phase, which is to say the thing needs to be built and used, and the performance data gathered, as the essential next step before it can be said to be fully launched. I'll look at how to best state that on the site.

I'll be starting in on how to use and integrate it early next year when I'm back in Australia, but as I'm currently in Scotland heading into Autumn, there's probably not going to be a lot of opportunity til then.

What the project really needs are beta testers.

Regarding concerns over the efficacy of the device itself, I have observed that the trough collector's focus is finer than the diameter of the collector pipe, and that the tracking system is sufficiently accurate to keep it there throughout the day. The device takes about 30-40 minutes to catch up to the sun if it's ahead by the full 2.4 hour range.

This is in direct sunlight in south Western Australia on days in the mid thirties Celsius.

As to maximum temperature and overall thermal efficiency I've not had a chance to accurately measure that yet, but ultimately it will almost entirely come down to what materials are used in any given build of the device, and the application.

I'm looking forward to getting all these results in about six months or less, unless someone beats me to it.

It's like any open source project; starts out patchy and hopefully gets a better, quickly. And comes down to the level of involvement of whatever community comes up around it.

Natural_Learner

I do want to say that your videos are excellent and you've made a great contribution to the techniques available to people who want to use them. Very admirable. It is also a shame when people do the reverse of not giving data, and they give only their results but no real clue as to how reproduce them. You only have so much time and energy and I think you chose the better path. Though I might try a different design, I would still look to your videos as a rough guide.

>What the project really needs are beta testers.

But really, without even establishing a metric by which people could meaningfully report their results and compare them, you are still alpha. My limited experience has been that establishing this metric is not trivial, or at least requires some amount of failure. I look forward to hearing more about this project.

Thanks for your contributions so far,

Elliot

Natural_Learner

One reason why quantifiable metrics are needed before any claims are made about this system:

One could easily and grossly mis-estimate the the specularity of the aluminum reflectors. Especially in a conventional, imaging concentrator (simple parabola), the fact that aluminum is 90% or so reflective does not matter, only the specular component. So, these 90% reflective plates may only be 10% specular. In this case, one would still see a sharp line at the focus, but there wouldn't be very much energy there. It is amazing how non-linear/adaptable our eyes are. The difference between 2x and 20x concentration is discernible to the human eye in a side by side comparison, but I would not trust untrained intuition to judge the difference by sight without reference (even with a reference).

An issue like using 10% specular reflectors would be a crippling flaw. Addressing this could impose requirements for significantly greater up-front costs, necessary skills and infrastructure.

I suggest this test of specularity:

Open up a book and stand it up on top of the material in question. How far up can you read? If font size and positioning are standardized, and unfamiliar texts used, this could be a quantitative and repeatable method of measuring specularity that we can use in discussing solar concentrator designs.

This test illustrates the heart of the question, the loss of information (increase in entropy) due to imperfect reflection. An efficient design would not unnecessarily increase the entropy of the energy source it is using, since increase in entropy is defined as a decrease in usable energy.

solarflower

Think someone sent me a link of someone testing this with a laser pointer and getting promising preliminary results. I'll see if I can dig it up.

I might see about sourcing one here and having a play with it, but it'll have to wait til November.

I agree that this is important info to have.

The reflective surface can be anything which is flexible and low cost, if the printing plates don't turn out to be a workable option there are others. They can also be polished.

solarflower

I got some aluminium printing plates.
I shone a red laser pointer at a piece of paper, took a photo (locked shutter speed and aperture), bounced the laser of the plate onto the paper, took a photo. Took the images into photoshop and calculated the colour info via histogram.
Long story short, haven't yet been able to get a reliable number. For some reason it was mostly telling me the bounced light was more intense than the other, which seems unlikely to be the case. Finally got a figure of 92% specular, but wouldn't necessarily trust it based on the previous results.
What I can say is that the reflection is very anisotropic, at a distance of 3 meters it described a very tight (2cm) line on one axis which blew out by about 120 degrees on the other. Which is basically what I found in NZ; in a parabolic trough, providing you bend the metal across the grain rather than with it, it gives a very tight focus. Wouldn't be any good for making dishes tho.
And to my naked eye, for whatever that's worth, it looks very specular. The focus line is several order of magnitudes brighter than the small amount of diffuse wash.

This is what it looked like (once exposed down so as to avoid clipping):

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