What is geothermal energy?

From the earth's core, cooling has been occurring since the earth was created. This cooling takes shape through the formation of huge plumes that move from the core through the earth to the outer edges of the globe over which it spreads. A never-ending process that will continue for billions of years. To illustrate, in some areas these plumes rise to the surface of the earth, as for example in Hawaii, Iceland and Yellowstone Park.

The heat flow which this process results in is perceptible at any place on earth and moves by convective and conductive processes which make use of the fact that the earth's crust is saturated with water which takes care of the transport of the heat. Conduction is the heat coming from the earth's core and flowing out to the earth's crust (so vertically directed) so as it were the cooling of the core. Convection is the spreading of this heat over the earth's crust (mostly horizontally oriented).

Depending on the geological makeup of the Earth's crust, the degree of heat flow varies but is "harvestable" at almost any location in the world. Below is a geographical representation of how heat flow spreads through Europe.

This heat flow is also measurable, predictable and behaves through physical laws: the thermodynamic laws. By recording a number of measurable parameters at a location, it is therefore possible to determine the geothermal potential at that same location. These are mainly the permeability of the geological layers (the permeability) and the density (porosity) of the rock, but also the conductivity of this same rock, the heat flow (flux) and finally the thermal gradient. This is the degree of increase in temperature per every 100 metres of depth. In Western Europe, the thermal gradient is on average 3. So with every 100 meters of depth, the temperature increases by 3 degrees.

The NotusPid system

Geothermal systems can be distinguished by their mode of operation. The oldest systems used (and still use) heated fluid pushed up by underground pressure, geyser, hot water springs. Unfortunately, the situation where the fluid reaches the earth's surface can only be found in a limited number of places in the world. Nevertheless, it is known that water travels all over the earth's crust in underground geological layers, usually through sandstone. Most systems used to date take advantage of that presence of underground fluid reservoirs. By this is meant that there is rock present in the geologic structure at a location through which fluid flows. Groundwater but at a greater depth. Because these permeable layers (also called aquifers) are at different depths, the fluid takes on the temperature of the immediate environment at that depth. The deeper, the hotter. The fluid can then be forced to the surface by pumping it up. At the surface, the heat can then be extracted and the then cooled water is then usually returned to the same earth layer. This form of geothermal energy is also known as hydrothermal geothermal energy.

A second possibility is not so much to extract the hot fluid from the geological layer but to ensure that the heat is brought up through a medium circulating in the borehole. No fluid is then extracted from the geological layer but the heat is transferred to the medium by thermodynamic processes. This medium can be circulated in a closed pipe system but can also be an open system where the medium is the original fluid present in the earth's crust. The earth's crust is generally so saturated with liquid that if a hole is made in it, this hole will automatically fill with this liquid. This can also be circulated without extracting more fluid from the environment. This form of geothermal energy is called petrothermal geothermal energy.

The single-hole system developed by NotusPid concerns a system that can be used both for hydrothermal geothermal energy (such as doublets) but also for petrothermal geothermal energy. So in non-aquiferous conditions. In plain English this means that the system is not dependent on deep water reservoirs in the ground.

The technology makes use of the fact that heat conduction and convection take place throughout the earth's crust as a result of a continuous flow of liquid rock from the earth's core, called plumes. Second, the water saturation of the rock in the earth's crust is used. Based on physical thermodynamic processes, the heat is distributed over the earth's crust via conductive and convective processes in which porosity, permeability and conductivity of the rock play a far-reaching role.

The returned fluid (with a lower temperature than the extracted fluid) is brought back into the formation until the point that the ambient temperature is between 5 - 10 % higher than the temperature of the returned fluid. Due to the temperature difference with the environment, a temperature difference ("temperature sink") is created at the "release" point that will generate induction of heat flow in the formation. 

The fact that the returned fluid increasingly enters a higher ambient temperature results in heat exchange with the fluid present in the formation pores. This exchange increases with the increase of depth in a pear shape which is therefore also called the convection pear. The temperature difference created between the drill shaft on the one hand and the formation rock on the other initiates a heat flow which, through the permeability and interaction with the pore fluid, leads to exchange and heating of the returned fluid. It has been scientifically proven that within this process, an energy compaction is created which is higher by a factor of 4 to 5 at the drill shaft compared to the convection boundary area. The returned water also experiences heating by means of conduction.

Since convection takes place over a long vertical distance, geothermal energy is also generated over this same length. This is in contrast to doublet technology, in which energy is recovered over a relatively short horizontal section.

How many times have we bumped at the same stone....

The single-hole system is therefore universal, multi-applicable, low maintenance, no "down-time" for replacing parts or re-power the well.

It is also predictable in terms of yield in both the short and long term, 

The lifespan is virtually unlimited.

It does not have all kinds of unpleasant side effects such as earthquakes, clogging of filters, changes in the subsoil, pollution by heavy metals.

It can be used for both very large and very small projects, tailor-made energy.

No complicated constructions to get rid of possible overcapacity. If there is no need for heat, simply switch it off. Just as simple as a light switch!

So why is it not widely applied? That is indeed the big question and the answer is both staggering and simple. In today's investment climate, people are totally focused on what the return is per euro invested. On paper, the big returns from doublets beckon. By applying even greater pumping power in the wells, the returns are great, this seems too good to be true,...and it is. 

Does the revenue model take into account that there are continuous problems with filters, that the permeability of the earth's strata changes due to the forced flow,...that millions are spent regenerating wells,...replacing equipment? 

It is time to replace the illusion with a workable alternative.

The solution lies in simplicity. Heating by a simple uncomplicated bore and ditto installation, apartment building by apartment building, factory hall by factory hall, gymnasium by gymnasium, the applications are endless, simple and cost effective