I have acquired a number of parabolic "satellite dishes" dishes (6 or so
all up) which I wish to 'play' with as solar concentrators.
I'm interested in suggestions for reflective coating methods not on the
list below and for comments by people familiar with these methods.
"Spray chrome" seems attractive if it works "half well".

Aim is investigation of cooking, water heating and water sterilisation.
Purpose is evaluation of practicality for developing country use. IOF the
3.3m dish proves useful it could grow a solar tracker (fairly easy) and may
even be useful in personal applications.
When used with a counterflow heat exchanger the water sterilisation
capacity should be 5 to 10 times as much as water heating throughput at a
given temperature.

Intention is to gain practical knowledge - if anything practical results
from this construction methods may well be quite different.

Dish sizes are from about 300mm through about 1m dia in steel, 1.5m dia in
Al and a 3.3m dia Al mesh dish.
[Mesh dish proper is very light. Dish dismantles to 8 panels which can be
carried easily by one person wrt weight. Shape a bit annoying :-)].

I wish to coat the surfaces with an optically reflective layer so as to
provide concentrated solar energy at the focus.
Ease of coatings and not much cost are rated ahead of efficiency - but high
efficiency is a welcome bonus.

Flatness of surface and lack of 'bumps' not too too critical - these spread
the focus point but this need not be as tight as in RF applications.

The 3.3m dish is about 8 m^2 in area. In full sun at 50% efficiency would
give about 4 kW. Useful :-).

The mesh dish will need to be filled with a filler of some  sort and sanded
to a smooth surface - not too hard (ha!)
The largest solid dish is Al and MAY sand to an adequate surface as is with
eg a clear spray on coat to reduce ongoing oxidation.

Possible options are:

- 1. Adhesive backed aluminised mylar foil./ Less available here than in US=
..

- 2. Non adhesive backed aluminised mylar foil - more available here.

- 3. Space blanket - similar to 2. but usually more wrinkled from folding
than desired.

- 4. Al cooking foil (non adhesive backed). Cheap, available, lower
reflectivity

- 5. Spray on "fake Chrome. Goodness tbd

- 6. "Real" chrome plate - commercial - even done with minimum effort cost
is highish.s

- 7. Real chrome plate DIY - doable but high effort.

-8. Other chrome imitators applied by eg tumbling. Dearish but cheaper than
chrome.

- 9. Al surface sanded and clear coated.

- 10. Front surface silver mirror using silver nitrate + clear coating.
(Cost may not be TOO high. Result superb if doable).

- 11. Small mirrors or broken mirror material stuck on surface. (Smallest
focus size is about the same as mirror size and mirrors not sitting exactly
at dish angle beneath them will further degrade focus area minimisation. )


Comments / ideas ???



               Russell

* "quick, easy & cheap" - choose any three.
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.