Thermal energy from surface water

Thermal energy from surface water can be a sustainable alternative to natural gas. Deltares develops knowledge, techniques and management measures to make good use of this energy source.

Approximately 25% of our current energy consumption goes to heating and cooling the built environment. The use of surface water as a new energy source has the potential to make a serious contribution to creating gas-free residential areas. Thermal energy from surface water – or surface water heat pump systems – can be used to heat and cool more than 40% of the built environment.

How does the system work?

Surface-water thermal energy (SWTE) systems use temperature differences in surface water between the seasons. They bring together a number of existing technologies. Heat is extracted from the surface water using a heat exchanger in summer. This heat is transported in a network and then either delivered directly or stored in an aquifer thermal energy system (where heat and cold are stored) in the subsurface. This heat can be used at colder times for heating using a heat pump, which operates a lot more economically in this situation because the temperature of a hot ATES well is about 18°C. That is much higher than the temperature of the surface water or the air outdoors in the winter.

Less heat stress and better water quality

A major advantage of SWTE is that, unlike solar parks or wind turbines, the technology has very little impact on spatial planning. It can even have a beneficial environmental effect. By extracting heat and returning cold to the surface water, SWTE can cool down a locality and reduce heat stress.

Furthermore, energy production from surface water can improve water quality. Heat is removed from the water in the summer, reducing the risk of, for example, algal blooms and botulism (bacteria that are toxic for water birds and fish). Because the system removes cold in the winter, it can help to keep waterways navigable. And finally, the technology reduces the burden on the electricity grid, unlike many other alternatives, which involve the investment of billions of euros in that network.

From local to regional use

A national study by CE Delft and Deltares has shown that SWTE can meet more than 40 percent of heating demand. The successful specimen projects are being conducted at the local scale, in buildings or blocks of houses. But the challenge for now and the future is to make wider application possible. It will be necessary to scale up from these small-scale initiatives to a structural transition to SWTE at the urban, regional and national levels, making it possible to exploit the potential of suitable locations and to develop infrastructure for the large-scale exchange of heating/cooling demand and supply.

The technology is still in the development phase. Together with the Dutch Association of Regional Water Authorities, STOWA, Rijkswaterstaat and a number of municipalities, the aim is to raise awareness of SWTE in the time to come, to establish a higher profile for the opportunities it affords and to establish more confidence in this source of energy. Deltares is collaborating with these parties on a range of issues involved in the implementation of SWTE.

Impression of pumps, piping and heat exchangers in an SWTE system.

 

The role of Deltares in the development of SWTE

By mapping out the opportunities for SWTE in urban areas, Deltares will help municipal authorities to select the appropriate locations and to start on design. How will the large-scale application of this technology – in combination with heat networks and underground storage – be designed in technical and spatial terms, and how can it help to reduce carbon emissions? Once promising locations have been identified, the next step is to work out the technological details in a concrete design and to study the financial feasibility. Establishing an indication of the costs implies producing not only a model of the urban water system but also a detailed model for optimising the inlet and discharge structures so that maintenance costs are kept to a minimum. In addition, we look at the possible effects on water quality and the subsurface of heat/cold releases.

Strategy for the future

Almost 100 municipal and provincial authorities have signed a Green Deal with the government for gas-free residential areas. This will require vision documents for heating that explore and assess alternatives to natural gas. Deltares provides strategic advice about the sustainability of the energy mix that will include surface-water thermal energy and aquifer thermal energy systems. And we look at how the transition to SWTE can be rolled out. What are the options and which considerations play an important role?