The technology is able to harness a temperature gradient regardless of its direction, but you're right that the larger the gradient the better it works.
*Our 8-person team has 5 Ph.D.'s, including our founder who did his graduate work in thermoelectrics. Feel free to Google the rest of the team: http://matrixindustries.com/#team
*We have funding from Khosla Ventures and 3M, among others
*We have real prototypes in the lab right now that generate power when you put them on