As wind powers an increasing amount of electricity generation, entrepreneurs are hoping to replace modern windmills with a high-tech version of an even older technology: kites.

Winds are stronger and more consistent at higher altitudes, but building a 100-story-tall turbine isn't cost effective. So engineers are working on using kites to send aloft power generators that create energy when mounted rotors are spun by the wind; they transmit electricity through the cables that tie them to the earth as a string tethers a child's kite.

Among the companies building prototypes are KiteFarms LLC in Kilauea, Hawaii; Joby Energy in Santa Cruz, Calif.; and Kite Gen in Torino, Italy, as well as a couple university-based consortia in Europe. Further along in commercializing the technology appears to be Makani Power Inc., in Alameda, Calif., which says it has built one model capable of generating 30 kilowatts of electricity, enough for about 20 average U.S. homes. Makani, which is partly backed by Google Inc., is also working on a portable kite-in-a-box for the Army to deploy during disaster-relief operations.

Some kite-power developers say that they were inspired by kite-boarding, a sport where people on modified surfboards holds large kites to propel them over the waves. "You are cruising along with your kite and realize you replaced a 100-horsepower motor boat," said Robert Lumley, the founder of KiteFarms, which recently got financing to develop a prototype kite.

Land-mounted wind turbines are a small, but rapidly growing, segment of global power generation. Conventional wind-power operators had 238 gigawatts of power-generation capacity in 2011, up from 24 gigawatts globally a decade earlier, according to REN21, an international, government-supported institute that supports renewable-energy development. Global power-generation capacity of all types is around 5,000 gigawatts, according to the U.S. Energy Information Administration.