The double-flash steam plant is an improvement on the single-flash design that can produce 15–20% more power output for the same geothermal fluid conditions. The plant is more complex, more costly, and requires more maintenance, but the extra power output often justifies the installation of such plants. Double-flash plants are fairly numerous and are in operation in 10 countries. As of December 2014, there are 54 units of this kind in operation, about 9.4% of all geothermal plants, and the average unit power is 35 MW per unit.