What a remarkable project! We were so amazed by the response and the ingenuity of every participant! By the way "WE" are Anna and David. We're living in germany and studying mechanical engineering. Thanks to everyone at Jovoto and Greenpeace and anyone who cared enough to give us feedback.
The heart of our design consists of the stirling engine. Dimensioning it turned out be more difficult then we initially anticipated. Since it is analytically next to impossible to make accurate statements about the performance of a stirling engine, we went on from where others left and chose a design that had proven its worth. We chose to go with an α-Typ in V-Form, which promises great performance and stability for the size we aimed at. With a diameter of 80mm for each cylinder we expect the engine to generate about 500 W which would be more than sufficient to lift water from a depth of 8 meters at a decent Speed. Considering the depth with took cavitational effects into account and came up with a volumetric flow of 2L/s.
The summoned heat is conducted down to the expansion cylinder thus heating the working fluid. We'd use the waterflow to cool the working fluid forcably, which would lead to a significant increase in efficiency, compared to conventional solutions which tipically use a simple free-convectional radiator to cool the fluid. The compression "cold" cylinder is equiped with a magnetic inductor transforming the translational motion of the piston, itself being a magnet, into electric energy and thus charging a battery.