KESS is designed to be configured to provide voltage regulation and support, reduction of peak power demands, recapture of braking energy, and short-term energy sink. Current and planned installations range from single UPT Kess 50kW units to multiple systems with a capacity of 2.4MW. The technology has been selected by a number of operators including New York City Transit (NYCT), Sytral in Lyon, France, Paris Transport Authority (RATP), and NDK, Japan, on behalf of JR East.

At the heart of the UPT Kess is a patented, high-speed composite flywheel. The modular unit stores 14MJ of energy, of which up to 11MJ can be used usefully, depending on the application. The design life of the rotor and beatings is 20 years or 10 million discharges. The flywheel and bearings are maintenance free, with annual maintenance checks required of the vacuum pump oil and cooling systems.

Kess is differentiated from many other forms of energy storage such as large battery banks, by being able to respond rapidly and regularly to cyclic loads and hence provide a power management capability. In such applications, a control algorithm calculates the required energy flow (in both direction and magnitude) based on the dc bus voltage.