Windbelts were the ultimate in wind power. It was just like the Tacoma Narrows Bridge of 1940.
(Note: The background section of this page uses most of the same words as Terra Futura's page on drum turbines to save time.)
Windmills had been around since Roman times, but the first practical windmill was was built in AD 500 in Persia. The axis was vertical and the sails were horizontal. The windmill was set inside stone walls that funneled wind through a gap. Around the year 1400, as many peasants were moving into the towns, millers started using windmills to grind wheat into flour. The Europeans improved the design by mounting the sails vertically on a tower. This allowed the wind to strike every sail at once. Windmills became more common as a result. In 1850, the agricultural windpump was invented. A tail fan was used to keep the main fan facing the wind. They would continue to be used into the 21st century along with wind turbines.
Conventional horizontal axis wind turbines were invented in the 1890s. They consisted of a shaft that turned an electric generator. The shaft normally contained three blades. In the late 20th century, these blades were pointed into the wind by motors that were controlled by a computer. The blades were stiff to prevent them from braking. A wind sensor was used to measure wind speed. A servo motor turned the turbine. All turbines had to be protected at high wind speeds. For this, the blades were feathered, and the brakes came on. Wind power became common in the early 21st century. By then, other turbines were being considered like a vertical axis turbine.
Vertical axis turbines were just as old as horizontal axis turbines. They were faster than horizontal axis turbines. They did not make noise. The support structure was not over-stressed. The sails were omnidirectional. Despite these advantages, there were too many disadvantages. They stalled in gusty winds. Vertical axis turbines were also unstable and prone to fatigue. The sails even often ripped apart. Thus, vertical axis turbines never became popular. Horizontal axis turbines were the way to go. New turbines called super wind turbines were coming into the market.
The main problem with conventional turbines was that the blades were large and cumbersome. Any negligence leading to breakage of blades and the large gearbox that turned them could cause a technician to wind up in hoosegow. A solution developed at Selsam was the Super Wind Turbine. This new turbine had a long and flexible drive shaft like a human spine. On it were six to eight small turbines. Early prototypes produced 6,000 watts. The amount of energy was increased by adding a dirigible. This allowed the shaft in wind direction. Super Wind Turbines were used in offshore windfarms. There was a problem not easily solved. Breakage could cause a boat to be damaged. Negligence leading to this could still cause a technician to go to hoosegow. On land, there was a better alternative. It was the inflatable wind turbine.
The main problem with ground-based wind turbines was that they were using surface winds which were notoriously unreliable. 300 meters up winds blew much more steadily and with more overall energy. The Magenn Air Rotor System was an inflatable wind turbine tethered to the ground. It spun around a horizontal axis like conventional turbines. The spin generated power which went to the ground through the tethers which were in fact power cables. The turbine used the Magnus effect which created a vortex of air around itself. This created additional lift and stabilized it in place. Efficiency was 60 % compared to ground-based systems. An inflatable wind turbine could be used anywhere. If the tethers snapped, an automated deflation system would bring it to the ground. An inflatable wind turbine could go up to 300 meters, but a flying wind turbine could go higher.
Sky Windpower, a start-up company from San Diego, California, came up with the idea of putting wind turbines 15,000 to 45,000 feet in the air. There, the jetstream was strong and constant no matter what the weather. To use the jetstream, Sky Windpower deployed a array of large rotorcraft with four rotors 130 ft long tethered to the ground like kites. The cables sent electricity to power lines. Each rotorcraft was brought into the air by motors which were also used as maneuvering thrusters. Computers were used to control a windfarm of flying wind turbines. Air traffic had to be rerouted to avoid collisions. If the cable snapped, there was likely chance it could crash into a house far away. Then, the technician would really go to hoosegow. (Note: By the way, hoosegow is slang for jail.) Not all wind turbines used shafts. Some used drums.
A drum turbine used a drum instead of a shaft. Essentially, the entire top of the wind turbine spun in the wind. This never became common because they often got scratched. In some cases, the drum which held the blades would wear down and fall off if a technician waited too long. That was a one-way ticket to hoosegow. Thus, drum turbines were never popular. Wind turbines would be replaced by windbelts.
Tech Level: 10-11
A windbelt was very similar to an aeolian harp. The main difference was that the motion of the string was used to move a magnet between two magnetic coils using the aeroelastic flutter effect, the same effect that destroyed the Tacoma Narrows Bridge in 1940. This induced electricity. Windbelts were more efficient than wind turbines at harnessing the power of the wind. In the mid-2020s, the windbelt replaced the wind turbine as the dominant source of wind power.