One problem, the concave surface of the balloon (which is not natural) will deform with changes in pressure or temperature.

If you however find something pass me the name - I am looking for an inflatable dart board. (Del may need an inflatable target to save his monitors)

Alternatives

A reflector like one on older flash lights however does work.

(Triangle aluminium sectors fanned open and interlocked.) The one I made only had a diam of 5ft and even without tracking boiled water in a jiffy.

An umbrella type of design should also work.

Patents? I don't know we only care about solutions.

I'm guessing you start with two parallel sheets of plastic sealed to a framework: a clear sheet at one side and the reflecting surface of the other sheet on the inside. When you pump up the assembly the sheet naturally forms a parabolic mirror.

Why not go the other way. Use an expanding foam filler which solidifies:-

Mix slightly more filler than you need.

Pour the mixed liquid into the hole at the top.

Fit the expansion tank and vacuum pump (a vacuum cleaner will probably do).

Suck the mirror into shape.

Maintain correct vacuum until filler sets. This could be tricky to begin with (the foam is expanding).

Remove the expansion tank, and clean out the waste foam.

You might want to consider a long rectangular (only curved about one axis) mirror focused on a pipe instead of a standard circular or square mirror focused on a point. That way you only have to track the sun up and down. The same technique for forming the mirror will still work.

You can easily buy mirrored mylar sheet.

The back of the mirror assembly does not necessarily have to be flexible like the front, but, if you made it that way you could easily strengthen the back with more expanding foam. And of course the back could have strengthening struts (so could the front thinking about it you wouldn't be wasting that much sun: if you go for the long mirror better to make the front struts diagonal so that you don't get cool "spots" on the collector pipe).

If you are building this for your own use, then the patent doesn't matter - or more accurately you can't be prosecuted under patent law.

If you plan to sell the device that is covered by an live patent (one that is less than 20 years old and for which the owner has kept paying renewal fees), then you must contact the patent holder and talk licence terms. Failure to do this can result in enormous court fees and fines when you're caught. The Patent Office will have contact details, since they have to collect the fees each year!

Looking at the date you quote, whether or not the holder kept paying his fees, this patent is out of date. This means you can copy his invention directly and sell it with no penalty. It also means you can't patent it, as, yes, he got there first! If you make any novel and non-obvious improvements to his design, then you can look at patenting those. It's worth talking to a patent lawyer (expensive) if you're not familiar with the way this is done.

Generally, the cost from filinig to grant and validation is half a dozen states is of the order of £20 -30,000 (GBP).

Hope this helps. good luck !!!

Sometime in the mid seventies HP at Pasedena, USA, experimented with an array ordinary falt mirrors each slightly smaller than the receiver interception area. All the mirrors were adjusted to make the reflected beam fall on the receiver. A computer made all the mirrors track the sun.

The usual problems of large area exposed to wind forces, imbalanced tracking load and need for focussing were avoided. If a few of the mirrors failed nothing much was lost.

Bioramani

There is published work on this idea. A site with lots of different geometries can be found here;

http://www.builditsolar.com/Projects/Concentrating/concentrating.htm

There have been several groups that tried a giant inflatable sphere with the front being clear, and an internal reflective surface dividing the sphere into two parts. A pressure difference in the sphere causes a curvature.

http://www.coolearthsolar.com/

http://www.seao2.com/solarsphere/technology.htm

I also remember a lady who suspended mylar across a DirectTV dish, and by drawing a vacuum would cause a deformation. On youtube you'll also find a few videos (Green Power science) of something similar.

Other ideas; there are telescopes that use spinning pool of mercury. That one does make a prefect parabola, but is very sensitive to vibration and only points up.

The good think about inflatable collectors is that they are light, and have an adjustable focus. That bad things are that they are big and light, so that a breeze can misalign them, and that the focus (as noted earlier on) can be changed by changing atmospheric pressure. The big ball mentioned above solves this since it is the difference in internal pressure not external that controls the focus.