sentences:  The reason Hydro wanted to establish itself in the Grenland region was the proximity to limestone, one of the necessary components in the fertilizer, Calcium nitrate.Norsk Hydro had previously had to build its fertilizer plants in Notodden (in 1907) and Rjukan (in 1909) because technology at that time didn't allow for efficient transport of electricity long distances from the power plants to the place of use.But in the 1920s technology had developed and it was possible to locate the plants close to the natural resources instead of close to the hydro electric power plants, that were located in the mountains in Northern Telemark.