In the 20th century, demand for electricity led to the consideration of geothermal power as a generating source. On July 4, 1904, Prince Piero Ginori Conti tested the first geothermal power generator at the same Larderello dry steam field where geothermal acid extraction began. It successfully lit four light bulbs. Later, in 1911, the world's first commercial geothermal power plant was built there. It was the world's only industrial producer of geothermal electricity until New Zealand built a plant in 1958. In 2012, it produced 594 megawatts.
Lord Kelvin invented the heat pump in 1852and Heinrich patented the idea of using it to draw heat from the ground in 1912, but it was not until the late 1940s that the geothermal heat pump was successfully implemented. It’s thought that the first was Robert C. Webber's homemade 2.2 kW direct-exchange system, but sources disagree as to the exact timeline of his invention. J. Donald Kroeker designed the first commercial geothermal heat pump to heat the Commonwealth Building in Portland, Oregon, and demonstrated it in 1946. Professor Carl Nielsen of Ohio State University built the first residential open loop version in his home in 1948. The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The 1979 development of polybutylene pipe improved the heat pump’s economic viability .