42 million megajoules, that is the amount of energy the inside of our planet is conducting to the earth surface every second. If we could only capture a fourth of that energy it will be enough to cover the energy expenses of the entire world population. Despite this enormous potential, people are still unfamiliar with the concept of geothermal energy.
It is clear that we have to make the transition from a world that is based on fossil fuel to one that is based on renewables. In this new world geothermal energy could play a key role because it has some advantages compared to others sources of renewable energy. One of the biggest disadvantages of renewables is that they use a lot of surface area to produce the amount of energy that is needed. Geothermal energy also needs a lot of space but the area it occupies is in the subsurface. Another advantage of geothermal energy is that it’s not dependent on the weather. It will keep producing energy despite there is no sun and no wind. This makes it a baseload power source, which can be the backbone of the new energy mix.
Of course geothermal energy is not as favorable in in the Netherlands as it is in countries like Iceland where the steam is blowing out of the geysers. But our country still got a lot of potential. The geothermal gradient in the Netherlands is above average. For every kilometer that is drilled the temperature of the subsurface will rise with more than 30° Celsius. We also know a great deal of the subsurface because most of our geology is mapped in the search for oil and gas. We know like no other which layers have a high porosity and permeability and what the optimal spots are for geothermal wells.
We know for example that in Leiden on a substantial depth (1,5-4km). There are highly permeable sandstone layer dating back to the Triassic period (250 million – 200 million years ago). Those aquifers have such a large flow rate that lots of energy can be brought to the surface in the form of hot water. In the nearby city of Delft they already drilled four wells to a depth of 2,5 kilometer where the results are very promising (Delfts Aardwarmte Project).
The city of Leiden will also benefit greatly from the use of geothermal heat. The municipality is already making the transition to district heating. In the beginning this system will be heated by surplus heat from oil refineries and power plants of the Rotterdam harbor. But eventually this can be replaced by 100% renewable geothermal heat and Leiden will be no longer dependent on fossil fuels. Right now the city of Leiden uses 1.7 PJ (1015 joules) for domestic heating. This can already be replaced by 12 relatively shallow wells (2 km depth) of 5 MW or even less wells with a larger depth and a higher capacity.
With a fully functional district heating system powered by geothermal energy, Leiden could be the first city in the Netherlands, which is completely independent from fossil fuels for heating. Then we can proudly say: ‘Leiden gaat goed!’