The entrepreneurs of tomorrow were on display this weekend, as 250 students competed Saturday in the Chicago Student Invention Convention, with the 30 top students winning spots at the national finals in Dearborn, Mich., next month.

Some were veterans of such competitions, but not all.  Elvin Rodriguez's second-place overall finish was driven by the continuing crisis in Puerto Rico -- a purifier that could turn bad water to good with minimal waste.  But not everyone would pay. He said he would price it so that four free units, fully powered, would be sent to areas in need for every one sold.

Noble idea, but Elvin had never competed in a similar contest or science fair and didn't give himself much of a chance.  His family knew better.

The idea of marketing these inventions scare most of the students and some of the parents, although one eight-year-old who admitted to watching "Shark Tank" with her mother offered the judges a stake in her invention -- if they'd put up $1 million.  National exposure is not out of the question.  Comedian Jimmy Fallon hosted one of last year's winners and his invention -- a dog food bowl that funnels spilled kibble back into a bowl.

This is the sixth year for the Chicago Student Invention convention, the culmination of a 10-week curriculum on innovation that is taught in more than 30 city public and private schools.