In the twentieth century the Dutch government dug a vast system of mine passages in and around Heerlen for the extraction of coal. Coal mining was the most important economic base for the Oostelijke Mijnstreek (eastern mining region) and Heerlen in particular.

Underground water reservoir
Tens of thousands of miners and their families and those in related sectors lived from the mining industry. In the heyday there were three active mines in Heerlen: Oranje Nassau I, III, and IV. After the closure of the mines in the period 1965-1974 the tunnels filled with groundwater, which was heated by the earth naturally. The deeper in the earth, the higher the temperature of the water. Yet decades passed before research was conducted into the development of low temperature sources in the coalfields, now a mine water reservoir.

Renewable energy production
In 2003 the municipality of Heerlen conceived the plan to do some exploratory drilling for the appraisal of potential renewable energy production. It soon turned out that the geothermal source – the mine water – could be used to meet future energy needs. Not only did the deep groundwater prove suitable for heating buildings, but the cooler water closer to the surface could also be used to cool buildings and homes, effectively recovering heat energy. That was the start of a successful initiative of the municipality of Heerlen – the Mijnwater project – with which Heerlen gained a position of leadership in the field of new energy in Limburg and Zuidoost-Nederland.

First mine water geothermal plant
In 2005, with support from the EU and Agentschap NL, five wells were drilled and an underground piping system stretching approximately 8 kilometres was built to circulate water. In 2008 the first mine water geothermal plant in the world, Gen Coel in Heerlerheide, was put into operation and the first connection serving approximately 30,000 m² of indoor space was established. Not long after followed the connection to Statistics Netherlands (CBS), with 22,000 m² of indoor space.

With thanks to former miners
During the planning stage (2003) the project gained valuable knowledge from former miners who knew exactly where to drill straight into the ground to depths of up to 700 metres to bring the water to the surface. Following the closure of the mines the entrances – the mine shafts – were completely blocked off with concrete and debris, referred to as a ‘plug’. This precluded any possibility of pumping up the mine water directly through the mine shafts.