These fuel cells come in many forms. One type of solid oxide fuel cell uses an array of meter-long tubes. Other types include a compressed disc that resembles a CD. The solid oxide fuel cell promises to be extremely useful in large, high-power applications such as full-scale industrial stations and large-scale electricity-generating stations. Some fuel cell developers see solid oxide fuel cells being used in motor vehicles. Currently, two small 25-kilowatt units have been produced in Japan and a 100-kilowatt test is being readied in Europe. A solid oxide fuel cell system usually utilizes a hard ceramic material instead of a liquid electrolyte. Efficiencies for this type of fuel cell can reach up to 60%.