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The greenhouses in The Netherlands are a major user of natural gas. The Trias Westland project is exploring the possibility to use geothermal heat as an alternative source for heating these greenhouses.
How does the harvesting of geothermal heat work?
Earth’s temperature rises with depth from the surface to the core. This gradual change in temperature is known as the geothermal gradient. In most parts of the world, the geothermal gradient is about 25° C per 1 kilometre of depth (1° F per 77 feet of depth).
Almost anywhere in the world, geothermal heat can be accessed and used immediately as a source of heat. The heat (energy) is stored in water which is present in the rock pores. When a well is drilled to this reservoir you can produce the brine. In some cases the water comes out of the ground automatically and in others you need a pump. In the Netherlands submersible pumps are required. After producing the warm water, the heat can be transferred to a heat network by heat exchangers.
Low-temperature geothermal energy can be used for heating greenhouses, homes, fisheries, and industrial processes. Low-temperature energy is most efficient when used for heating, although it can sometimes be used to generate electricity. High temperature flows can be used for electricity generation.
In the Westland area, how many MegaJoules of energy is currently used for heating greenhouses?
Currently, the Westland area uses 39 petajoules (PJ) per year of energy of which Greenhouses account for 31 PJ/year.
What are the main sources of this energy?
Total energy usage 31 petajoules per year. Of which 27 PJ comes from gas and 4 PJ from electricity.
How much of this can potentially be replaced with geothermal
The potential for sustainable use of geothermal energy is 38 PJ/jr.
Which layer do you want to research with the test boreholes?
The layer being researched here is referred to as the Trias layer. It was deposited between 252,2 till 201,3 million years ago. The name Trias refers to it being a three layered sequence; Buntsanstein, Muschelchalk and Keuper. In the Netherlands the Buntsantstein is the best reservoir for geothermal which consists of three sub-formations, the Hardegsen, Detfurth and Volpriehausen.
What are the characteristics that make a layer suitable for geothermal energy?
Good porosity and permeability as well as good layer thickness.
Before the drilling of the test borehole started, have you performed other tests of the geology and what were the results?
A lot of information about the Trias in the area is known from oil and gas drilling. Also seismic data is available.
Have there been similar drills in the area already?
Not till this depth. The deepest wells in the area are around 3500m. However, in the Netherlands there are multiple wells deeper than 5000 meter, so drilling technology is sufficient.
Once the borehole reaches a layer, how do you test the geothermal potential?
We hang in a submersible pump and produce the water to surface.
What is the timeline for the project?
Well tests will be performed in January for the first well. In case this is a success, we will drill another well. If not, we will open the well in a shallower layer.
Can the test borehole eventually be used for the production of geothermal energy?
Yes, if the Triaslayer is viable then a second borehole will be made. One from water production and the other for injection.
How long does a borehole stay productive?
The reservoir models predict a lifetime of at least 30 years, but probably more in the range of 50-70 years before the production well produces cold water. Another problem can be the wellbore integrity. Trias Westland has many corrosion and scaling mitigations in place, but there is always a risk that the well encounters problems during production.
How many MegaJoule does a borehole have to produce per year to be economically feasible at current energy prices?
The production capacity of Trias Westland will be approximately 25-45 MWth. Which saves about 25-40 million m3 of gas.
The energy systems of the future will probably require storage capabilities for medium and long term energy storage. One of the options is the conversion of (excess) electricity into a chemical energy carrier called an electrofuel. We interviewed Ning Yan, assistant Professor at Van ‘t Hoff Institute for Molecular Sciences (HIMS).
When we want to convert excess electricity to hydrogen for storage, what are the main technologies that can be used for this conversion?
The most straightforward approach is the electrolysis of water. By passing an electric current through the water, we can split it into oxygen and hydrogen.
What would be the advantages of hydrogen for energy storage?
Hydrogen has one of the highest energy density values per unit mass, higher than conventional fossil fuels. Besides, converting hydrogen back into electricity does not generate greenhouse gases or pollutants.
And what are the disadvantages?
Because the hydrogen molecular is so small, light and highly flammable, the efficient and safe storage of hydrogen is challenging. Besides, converting excess electricity to hydrogen via electrolysis is not very efficient either.
At some point the hydrogen will have to be converted back to electricity. Which technologies are available for this process?
Fuel cells are perhaps the best technology. They are electrochemical devices that enable direct conversion of hydrogen into electricity with high efficiency.
What would be the efficiency of the whole cycle from electricity to hydrogen to electricity?
This depends on the type of the applied electrolyzer and fuel cells. Typically, the practical efficiencies for both electricity-hydrogen and hydrogen-electricity conversions are around 50%, making the whole-cycle efficiency equal to 25%.
Do you expect that there is much room for improving this efficiency?
Considering that the theoretical efficiency for both processes is much higher, I would say that there is yet much room for improvement.
Has the principle of storing hydrogen for energy been applied on an industrial scale?
I would say Yes and No. A number of automobile manufacturers have launched their fuel cells powered cars. These vehicles are fuelled by hydrogen which is stored in the pressurized tank. Nonetheless, storing excess power from the grid in the form of hydrogen on an industrial scale has not been implemented yet.
How does hydrogen energy storage compare to battery storage in terms of energy density, efficiency and cost?
Compressed hydrogen has much higher weight energy density than typical Li-ion batteries (can be up to 100 times). The cost for storing of hydrogen is also significantly cheaper than most batteries counterparts. Therefore, it is usually believed that the battery is unsuitable for large scale energy storage though it is highly efficient.
If we want to create more complex electro fuels like transport fuels, which ones show the most promise?
In addition to hydrogen, hydrocarbons, such as methane, methanol and formic acid also show promise as transport fuels.
What are the technologies that can be used to create these fuels?
Conventionally, all these fuels are synthesized from syngas, a mixture of carbon monoxide and hydrogen. Electrochemical and photo electrochemical reductions of CO2 are also viable approaches for such synthesis.
Which carbon sources could be used for these processes? Is it for instance possible to use CO2 from point sources as a feedstock?
Natural gas, biogas and syngas are all possible feedstocks. Recently, CO2 has attracted much attention as a sustainable carbon source. In the laboratory, researchers have successfully converted CO2 into fuels with help tailored catalysts. However, the high energy cost associated with the CO2 capture and conversion prevents its practical use as the feedstock at the moment.
Can you mention one or more research projects at HIMS in the area of electro fuels?
In the Sustainable Chemistry Research Priority Area program at HIMS (www.suschem.uva.nl), we have a number of projects focusing on the sustainable synthesis of such fuels. For example, my team are now researching carbon and perovskite oxide materials, which are much more cost-effective and abundant than noble metal catalysts, for efficient water splitting. The research team led by Prof. Joost Reek are studying molecular catalyst for the generation of “solar fuels” using the sun light.
Are electro-fuels an economically viable option at this moment for energy storage and transportation fuels or do we need major technological breakthroughs to accomplish this?
Though such electro-fuels are not a good option for energy storage at the moment, I see a bright future for its real-life application if we can increase the efficiency of the conversion using the affordable catalysts.