Aquifer thermal energy storage

That is why Deltares is also researching combinations of ATES with other sources, such as aquathermal energy, in the earliest possible stage. We have been doing that work in, for example, the Dtuch WarmingUP programme, acquiring knowledge about sustainable, collective heating systems with forty organisations.

Deltares identifies opportunities for governments and developers of ATES systems with respect to combining ATES with heat extraction from surface water, waste water and mains water (aquathermal energy), fresh water storage, and remediating soil pollution.

How does aquifer thermal energy storage work?

The thermal conductivity of soil material is limited and the soil acts as a thermos flask. Groundwater naturally has the annual average temperature of the outside air (approximately 12° centigrade). Cooling, or extracting heat from, buildings with cold from groundwater in the summer supplies heat that is stored (using a heat exchanger) in the groundwater of an aquifer.

The heat in the heated groundwater (approximately 18° centigrade) can be used in the winter for heating buildings. As it releases its heat, the groundwater cools off to approximately 6° centigrade. The resulting cold that is released in winter is stored separately and can be used again effectively for cooling in the summer.

A cold and a warm ‘bubble’ is created in the groundwater by cooling to below the groundwater temperature and warming to above the groundwater temperature. This is highly energy-efficient because it maximises the heat storage potential of the subsurface.

Our studies indicate that large-scale aquathermal energy systems are an appropriate way of producing and storing energy because:

• Building ATES is easily applicable technology.
• The only power you need in this system is for pumping the water around. You can generate that energy with solar panels.
• This is low-grade energy, which you can extract from the soil relatively easily. That considerably reduces the need to burn fossil fuels.
• The soil has a constant temperature of 12°.
• Once installed, and unlike wind turbines and solar panels, these systems are invisible to the naked eye.

The Netherlands is leading the way in ATES

In the Netherlands, ATES is a tried and trusted method for sustainable energy production. It is also increasingly being combined with sustainable sources such as aquathermal energy. We are leading the way. In other countries, the introduction of ATES is more challenging because seasonal storage is not allowed in all countries, the soil structure is not always suitable due to the lack of shallow aquifers, and, outside temperate climate zones, the demand for cold and heat is not sufficiently balanced.

In the project 'Europe-wide Use of Sustainable Energy' (E-USE) from aquifers, Deltares worked with seven partners to study the availability of locations for ATES in Europe. Six pilot plants were designed and built to demonstrate the feasibility of combined applications of aquifer thermal energy storage in five different countries.

ATES is also possible for high temperatures of 70 to 80 degrees

On the basis of our expertise relating to water, the subsurface and mains systems, we advise our clients about how to store heat and cold in the subsurface effectively, cost-effectively and sustainably. It should be pointed out that we do not install those systems ourselves, and so the advice we give is independent.

We also provide developers of ATES systems with expertise that makes it possible to store heat at high temperatures such as 70° to 80°. Most demand for these systems is found in existing residential areas with relatively small houses. There is generally less space available for economical improvements in sustainability.

To recover and use this energy through a 70° heating grid, all that is needed is a small box that takes up less space than a central heating boiler. And a buffer tank – or a much smaller one – will no longer be needed for tap water. The situation is very different when temperatures in the water mains are low because activities such as showering, for example, demand a lot of heat capacity. We can extract that heat and cold from groundwater in the ground. In that way, the soil makes a sustainable contribution to our energy supply.

Tests are being conducted in the Deltares Water-Soil Flume with various measuring techniques to monitor the heat distribution of High Temperature Storage (HTS) in the subsurface. This will further the optimal use of heat production from sustainable heat sources. Heat suppliers and operators of heat distribution networks can use this knowledge to optimise heat production.

In addition, municipal and provincial authorities can draw on the results to develop monitoring requirements for HTS operators. The tests are part of the WarmingUP project, which is developing applied knowledge to make collective heating systems reliable, sustainable and affordable for the heating transition.

Research into the effects of subsurface energy

Aquifer thermal energy storage systems can affect the subsurface. The number of systems is now increasing rapidly. However, the hydrological conditions and properties of the systems determine the extent of any possible impact. Particularly in the research programme ‘More with Subsurface Energy’, Deltares worked with partners IF Technology, Bioclear and Wageningen University to measure and assess the effects.

This knowledge is now being used by designers, policymakers and permit authorities to manage the negative impact of ATES. The effects of temperature variation and groundwater displacement that were studied are hydraulic head changes, interference, groundwater quality and groundwater ecology. The study has demonstrated, among other things, that the injection temperature can be raised from 25°C to 30°C in many situations.

ATES and soil remediation

ATES is being used increasingly in urban areas, which is where most soil pollution and/or remediation operations are located. ATES can have a positive or negative effect on the contaminants. The systems can contribute to the more efficient cleanup of locations by establishing a smart link between the two technologies. However, the higher intensity of the dynamics in the groundwater can complicate the cleanup, or the spread, of pollutants.

Troubleshooting and improved energy performance in ATES systems

Drilling for ATES is relatively expensive, which is why it is important to obtain the maximum amount of information from boreholes. Deltares borehole measurements provide detailed information about the lithology of the subsurface and groundwater. This makes it possible, for example, to optimise the filter systems, monitor clay seals and regulate fresh-salt transitions. The temperature distribution in the subsurface can be measured using fibre optic cables in monitoring wells (or probes). These are continuous measurements that create a dynamic picture of the development of the cold and hot zones. Modelling can be used with this monitoring technology to detect clogging in filters at an early stage and to optimise the efficiency of the source system.

Support for policy processes

We use our knowledge to help government authorities decide about granting permits for ATES. We conducted an evaluation for the provincial authority of Flevoland (NL) of the permit conditions for monitoring ATES in the light of the potential risks. In addition, we have also advised about complications and interference. Deltares has developed an approach to make an integrated assessment of the interests that play a role in the subsurface.

Optimal control of heating and cooling demand for clusters of buildings

If there is more demand for heating and cooling from several buildings in a given area, the management and coordination of the ATES plant become more complicated. The aim is to prevent disruptive interference, and to use the source systems as efficiently as possible in order to minimise the energy loss.

Deltares is working on several projects to optimise and simulate the real-time management of large air-conditioning systems with multiple sustainable and conventional sources. That involves predicting demand for heat/cold on the basis of the weather forecast, after which the use of the various sources is optimised while the current situation is continuously updated.