Who patented the first commercial solar water heater, the Climax, in 1891?

Clarence Kemp patented the first commercial solar water heater, the Climax, in 1891.

Kemp’s system combined a black-painted water tank with insulation and a glass enclosure. Sunlight heated water directly inside the tank, making the device a simple early example of passive solar heating.

The Climax was marketed in the United States, especially in sunny regions. It was not a photovoltaic device: it produced hot water rather than electricity. This distinction matters because solar energy can be used for heat as well as power.

Later solar water heaters used separate collectors and insulated storage tanks, improving efficiency and making freezing conditions easier to manage. Clarence Kemp is therefore associated with commercialization, not with discovering solar radiation or inventing modern solar cells.