Multifacet parabolic solar concentrator

Step 6: Focal Assembly

The focal assembly is simply four angle stock pieces set up so that they are screwed to the corners of the concentrator and meet at the center. If you use 8 foot pieces, they will meet at a point about 7 feet from the center of the mirror assembly. This gives you about 1 foot between where they meet and the focal point so you can mount things easily at just about the exact focal point.

NOTE! When you're not around the concentrator make VERY SURE that it is pointed in a direction that the sun will NEVER be. It WILL catch things on fire. Think very carefully about how the sun moves and remember that it traces out an arc in the southern hemisphere (northern if you're an Aussie).

The broom below took only 30 seconds to burst into flame. I cannot stress enough that concentrated sunlight is VERY dangerous. Also much fun if you're careful.

Comments

[burnerjack01]

Another focus method :Cover all facets with pieces of paper. Suspend a fixed target at the intended focus point. Uncover one facet at a time and adjust until reflected light is cast onto target. when finished, turn assembly away from sun and remove all the paper sheets. No math, no spreadsheet and very accurate. Not my idea (found it on the web) , but simple and effective.

[Johhny]

I think that you would have to be very quick to set each panel and maybe reference to the first panels focus (by moving your hole frame) every five or so minutes to allow for the suns movement in the sky @ 15 degrees per hour. If you were taking 3 hours to set up, the last panel would have a very different focal point.

[STBro]

1 Select one panel as a reference panel (ideally one centered on the desired focus point with the selected light source.) Use a large flat target to see the beam cast by the reference panel.
2. Cover up all the reflectors EXCEPT the reference panel and the adjustment panel.
3. Adjust the screws on the adjustment panel so that the light of its beam center coincides with the beam center cast by the reference panel.
4. Once both beams are aligned, cover the panel adjusted and move on to the next panel, removing its cover.
5. Repeat steps 2 to 4 until all panels are aligned.
Reasoning: since the light of the reference panel moves as the sun tracks across the sky, adjusting all the other panels to it create a focus that is referenced to both reference panel focus and sun angle. Since the reference panel points to target, the entire frame can be moved to track sun. All other panels will always point to reference panel beam focus. Use of reference panel allows alignment procedure to no longer require an adjustment for sun movement.

[sh_joe]

You could place the concentrator on a flat surface (like a garage floor) and hang a laser pointer on a plumb-line from the ceiling. Then you could adjust the mirrors by sliding the concentrator around. The direction of the incoming laser beam would remain constant so the focus would be accurate, no matter how long it took to set it up. This way you could also do it when it's cloudy or dark.

[Mechanic2011]

Ha ,
I had the same idea using the garage floor to level the mirrored reflector so it is pointing exactly strait up.
I wanted to use pulleys , small steel cables and electrical metallic conduit for the frame.
Think etcha-sketch toy for kids.
I could then move the laser pointer around via 2 knobs in an Y and X coordinate type of arrangement.
You could then aim each of the small mirrors individually on the face of the dish at the exact focus point.
I even bought one of those party fog machine kits which will help find the laser light beam when I can't see it.
I have a project in the works that uses 7 of the old C-band satellite TVRO dishes.
I want to recycle the dishes and heat my house with the collected heat .
4 of them are 8 feet in diameter and 3 of them are 10 feet in diameter.
That is why I need a more rigid system to aim them with before I install them.
The nice thing is that I can do this inside the garage where the weather or sun is not a factor.

[burnerjack01]

With dishes that big, wind loading should be figured into your structure.
That's a lot of power at your command. Remember to use you power for good.
Hey Mech, let me(us) know how it woks out, OK?

[jarney1]

The focal point is set by the parabola formula. It does not have to be pointed at the sun for an accurate focus to be achieved. The system was designed to be mounted on a tracking device that moves the entire assembly to track the sun. I agree that if I was aligning the focus by moving the mirrors and aligning them to the sun, that would be highly impractical. This is why I decided to calculate the height of each corner based on a parabola and aligned it in my workshop in the shade. Only when it was complete, did I take it into the sunlight to test the quality of the focus and make minor adjustments.

[eston macharia]

hey guys am eston,currently a final year engineering student in jomo kenyatta university in kenya.I wish to develop a project on a solar powered steam soil sterilizer to assist in control of micro-organisms in seedbeds.However am not sure whether to use parabolic dish concentrators or trough concentrators.i wanted to try the latter but am not sure how to go about it and what materials 4 the troughs would be best suitable.any ideas pls? your assistance will be greatly appreciated.u can reach me on [e-mail]

[Mechanic2011]

I did something by accident one time that you could probably use .
I laid a sheet of black rubber roofing membrane that was about 1.15mm or .045inches thick on a bright sunny day .
It got soooo hot beneath the rubber sheet that it literally killed everything that was growing in the soil at that time even the weeds and thistles.
I had to reseed my grass lawn to get it green again .
Depending on how long it is left on the soil and how hot it got ,it might make a very worthwhile weed control system.
I should do another experiment like this again and this time install some temperature probes at different depths in the soil beneath the black rubber sheet like right on the surface and then every 1mm or so and record the results.
I believe to be effective ,the heat needs to get down to about 3 inches or 7-8mm in depth to kill all spores ,roots ,nodes etc.
Again you would have to rely on the sun for the heat but it would be very clean as there would not be any chemicals involved .
The rubber sheet could be moved in the mornings or evenings to a new location once it cools enough to hold onto .

[burnerjack01]

That is a pretty good idea. I have weeds etc. but I'm just not into poisoning my property. Just seems wrong. This sounds like a good alternative.

[dwrenne]

Nice idea to use solar concentrators for soil sterilization. Did you proceed with the project. That said, with the solar potential in Kenya, Just using plastic for a month or two on a seed bed would probably be better. Building a solar system to create steam to use on a seed bed only every so often would be expensive.

[Johhny]

Sorry Jarney1 I was directing my thoughts to Burnerjack01 and his method, I forgot to address it properly. I fully agree with the 'measure first' then if thats not quite good enough correct it practically way.