ESI was a commercial spin-off from the US wind R&D program. The ESI turbines were distinctive for their fairly large diameter (compa­rable to that of Danish turbines), the high speed of their rotors, and the tip brake at the end of each blade. The tip brakes, or flaps, were intended to protect the turbine during high wind emergen­cies. The design used two fixed-pitch, wood-epoxy blades downwind of its hinged, lattice tower. Two versions were introduced. Nearly 700 of the ESI-54 (16.4-meter) and 50 of the ESI-80 (24-meter) were eventually installed in Califor­nia.

I’ve described the photo of the ESI-80 drive train buried in the sand in the San Gorgonio Pass thus. “ESI-80. Another US-built series that followed Hütter’s design philosophy were the ESI-54 and the later ESI-80 shown here. The ESI turbines also used a downwind, two-blade, teetered rotor driving an induction generator through an integrated gearbox. The brake is mounted on the back-end of the generator (far left). ESI used tip brakes not pitchable-blade tips. The high rotor speed in combination with the downwind design and tip brakes was notoriously noisy. The ESI-80 used an 80-foot (24-meter) rotor made up of laminated wood blades coupled to a 250-kW generator.”

The turbines didn’t fare well in California and were considerably less reliable than their Danish competition. The principals behind ESI eventually folded up shop and went back to work for the DOE-NREL wind program.