This combination Thermoelectric Generator and Thermoelectric Cooler set is designed for teachers, and includes a Thermoelectric Generator Set with Cups and a TEC-12709 Cooler. This set contains the regular Thermoelectric Generator kit (fan assembly and 2 cups) and also a TEC-12709 Thermoelectric Cooler Module with wire leads. Complete instructions are included. Thermoelectric generators are devices that convert heat energy into electricity. This device utilizes a thermocouple (thermoelectric cooler) sandwiched between 2 aluminum conductors (the aluminum "legs" you see in the product photo). A thermocouple is formed when two electrical conductors composed of dissimilar materials, come in contact with each other. Thermocouples are able to generate voltages through a process called the thermoelectric effect. The underlying principle behind thermocouples, the thermoelectric effect, was discovered by Thomas Johann Seebec. The thermoelectric effect, sometimes called the Seebec effect, occurs when a thermal gradient is applied to a conductor and produces an Electromotive Force generated across the gradient. The magnitude of the Electromotive Force is a function of the temperature differential applied. This smart little demo is designed to be immersed in 2-3" of water, each "leg" being immersed in a separate cup (2 clear plastic cups included). Immerse the generator in cups of water of equal temperature, and nothing happens. Immerse the generator in cups of water with a substantial temperature gradient (hot or cold), and the fan will begin to spin. Has 4mm input/output terminals and switch to redirect electricity to a meter for measurement, allowing the user to monitor temperature gradent and output data. A truly wonderful and facinating device. A must have for those interested in exploring alternative / renewable energy sources. Comes with complete instructions and sample questions for students.