Great quantity of free solar energy constantly

sigh............

So much education to do, so little time.......

Tom H.

I look at it and all I see is a big'ol pot of steaming hot beefstew with taters and onions and carrots and barley and all on a cold winters day. Maybe some buttered sourdough bread.

Kidding aside, what you are proposing may or way not be cost effective. I will be interested to see your economic figures on future updates of your site.

Are you stating that the portable solar oven that is pictured on the link can reach temperatures of 300 C? Thats 572 F.
Now correct me if I am wrong but increasing the size of the portable solar oven by say... a factor of ten, would not increase the temperature by a factor of ten, it would only increase the volume of solar heated space by a factor of ten.
 As well the best way to increase the temperature would be to multiply the number of Sun's by a factor.
 Such things have been done with parabolic mirrors aimed at the Sun but the Sun's reflections all set to a central point which can reach temperatures in excess of 1,000 F.

 Here is a web site that you may find interesting while completing your research.
http://www.redrok.com/main.htm

Platini, looks like you have some chemistry working for you but you forgot the thermodynamics and physics. Since chemical reactions depend on contact, or surface area interaction, salt may work well on a small scale but a large volume of salt will have a small surface area in comparison, especially if dropped in a large bowl. (eg. A finer grind of sugar will dissolve or react in water faster than a sugar cube due to it's greater surface area.) In both cases, salt and sugar, vigorous mixing is needed to get the larger mass to react.Then, once the surface of the salt gets hot, it will begin lose heat out to it's surroundings and it's heat will begin to move in that direction easier than into the remaining salt, which is also insulatd and cooled by it's earthen surroundings.....
  I could go on and on but you should get the idea. Maybe you should just think about using multiple smaller units together for other types of heating applications.