Kaplan turbine

The Kaplan turbine emerged because rivers refused to cooperate with existing technology. By 1910, the Francis turbine dominated hydropower, but it demanded heads of 100 meters or more to operate efficiently. Most rivers offered far less—gentle drops of 10 or 20 meters that dissipated energy through friction in oversized Francis runners. Viktor Kaplan, a professor at the German Technical University in Brno, saw the waste and wondered if a ship's propeller, run in reverse, might capture what the Francis turbine could not.

The adjacent possible was specific to Brno. Kaplan partnered with Heinrich Storek, whose ironworks had been casting steel since 1861 and had recently acquired a Siemens-Martin furnace—one of the first in Austria-Hungary. In 1910, they built a turbine laboratory in Storek's factory. Kaplan became the first engineer to account for water viscosity in turbine calculations, obsessively testing blade angles and counts to minimize friction losses.

His 1913 patent introduced the key innovation: adjustable runner blades that could change pitch to match varying water flows. Where the Francis turbine achieved peak efficiency only at specific discharge rates, Kaplan's design maintained 75-90% efficiency whether running at full capacity or barely loaded. The propeller-like runner spun faster than Francis turbines, eliminating the need for gearboxes between turbine and generator.

Then came crisis. By 1922, installations on large rivers were failing—blades breaking, concrete cracking, output falling short of promises. The culprit was cavitation, a phenomenon "unknown to water turbines until then." Air bubbles formed in the low-pressure zones behind spinning blades, then collapsed with destructive force. Kaplan, physically and mentally exhausted from years of development and patent litigation, abandoned research. His co-workers solved the problem while he recovered, building the world's first dedicated cavitation test stand.

In 1924, the 8-megawatt Lilla Edet installation in Sweden exceeded its guaranteed 87% efficiency, achieving 89%. By 1928, Voith was building seven-meter-diameter runners for the Rhine. Today, Kaplan turbines power run-of-river plants worldwide, from micro-hydro installations of 30 kilowatts to giants producing 230 megawatts. The world's first tidal power station at La Rance uses 24 Kaplan bulb turbines, their adjustable blades reversing to generate power on both ebb and flood tides.