Video shows two buckets of water — one hot, the other cold. As the two heat exchangers from the Ergenics apparatus are immersed into the two buckets, the temperature differential drives a turbine, powering a generator that powers the light.
Ergenics is developing a metal hydride heat engine that converts the energy from hot liquid (e.g. solar hot water) into electricity for an estimated cost of about 1¢ per kilowatt hour. For example, solar panels produce hot water which is pumped to a hydrogen compressor that compresses a gas that is then expanded in a hydraulic motor-generator set that produces electricity.
The technology has a multitude of other applications and iterations. Please see www.ergenics.com