The history of geothermal energy is a journey from simple natural use to complex engineering, meaning there is no single date for its “invention.” Geothermal energy, which is heat derived from the Earth’s interior, has been utilized by humans for millennia, long before it became a power source. Harnessing this natural thermal energy evolved through distinct technological phases, moving from passive enjoyment of natural phenomena to active engineering and, finally, to the generation of electricity. This progression involved multiple innovations across centuries, making the development gradual and multi-stage.
Early Utilization of Natural Heat Sources
The earliest human use of geothermal resources was opportunistic, requiring only simple infrastructure to access a natural hot spring. Archaeological evidence suggests humans have utilized thermal waters for at least 10,000 years for cooking, bathing, and cleaning. The ancient Greeks and Romans were particularly adept at incorporating naturally heated water into their daily lives. The Romans developed elaborate bathhouses, or thermae, around natural hot springs across Europe and North Africa.
These thermal baths served as important social and political hubs, not just centers for hygiene. The city of Bath in England, originally named Aquae Sulis by the Romans, is a prominent example of a settlement built around this natural heat source. Indigenous peoples in North America, Iceland, and Japan also used hot springs for medicinal, spiritual, and domestic purposes for centuries. This early phase was characterized by utilization, where people built near the resource rather than actively engineering systems to access heat from depth.
The Birth of Engineered District Heating
The first major shift toward actively engineering geothermal resources occurred in the late Middle Ages with the advent of district heating. The world’s oldest continuously operating geothermal district heating system was established in Chaudes-Aigues, France, beginning in the 14th century. This system channeled natural hot spring water through wooden pipes to heat local homes and buildings.
A more modern, drilled-and-piped system began operating in Boise, Idaho, in 1892, marking the first geothermal district heating system in the United States. This system required drilling wells to access the hot water reservoir and distributing the heat through a network of pipes to residences. The success of the Boise system was copied in Klamath Falls, Oregon, by 1900, demonstrating the viability of this engineered approach. This established that geothermal heat could be distributed over a distance, transforming it into a practical utility.
Commercialization of Geothermal Electric Power
The most significant historical step was the use of geothermal energy for generating electricity, which began in the early 20th century. This pivotal development occurred in Larderello, Italy, a region known as the “Devil’s Valley” due to its intense geothermal activity. In 1904, Prince Piero Ginori Conti successfully used steam from a geothermal well to power a small dynamo, illuminating four light bulbs in an experimental demonstration.
This success led to the construction of the world’s first commercial geothermal power plant at Larderello. The plant began commercial operation in 1913 with a capacity of 250 kilowatts (kW), supplying electricity to the Italian railway system and nearby villages. The engineering challenge involved harnessing the highly corrosive geothermal steam and converting its thermal energy into mechanical power to drive a turbine. Larderello remained the world’s only industrial producer of geothermal electricity until 1958, setting the foundation for subsequent large-scale power generation, such as The Geysers in California, which began large-scale operation in 1960.
Development of Geothermal Heat Pump Technology
A final, distinct evolution in geothermal technology emerged in the mid-20th century with the development of the ground-source heat pump (GSHP). Unlike deep-earth power plants, this technology utilizes the relatively constant, shallow temperature of the earth—typically 10 to 20 meters deep—to provide efficient heating and cooling for individual buildings. The earth acts as a heat sink in summer and a heat source in winter, exchanging thermal energy through a closed loop of buried piping.
The first successful commercial application was installed in the Commonwealth Building in Portland, Oregon, in 1946. This system, designed by J. Donald Kroeker, proved that the ground’s thermal stability could be used for year-round temperature control. The first residential systems followed in the late 1940s, with Carl Nielsen creating an open-loop version for his home in 1948. The technology gained popularity in the 1970s following the oil crises, as improvements like polybutylene pipe made closed-loop systems viable for widespread residential use.