Aquifer Thermal Energy Storage (ATES) accesses the stable temperature of groundwater to warm buildings in winter and cool them in summer. The solution uses much less power than conventional heating and cooling systems. As Daisy Chi at ECECP explains, ATES first took off in China in the 1960s but ran into problems with the required circulation of the groundwater. However, the technology has been developed and optimised in the Netherlands: of the roughly 3,500 currently operational ATES systems worldwide, 3,000 are based there. The Dutch systems are now being installed in China and can be seen as an excellent example of co-operation between the two nations. Chi takes a deep dive into the technology, its advantages, the challenges, and the policy initiatives that could make ATES a part of China’s – and possibly the world’s – strategy to reduce the costs and emissions of heating and cooling, responsible for 40% of energy related greenhouse gas emissions globally.

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The ground beneath our feet is repository of hidden treasures. It provides 95% of our food and all our minerals and precious metals alongside many other resources. It also has huge potential for the storage and recovery of thermal energy. In this article we look at the development of aquifer thermal energy storage (ATES) technology, a thermal storage solution that originated in China and is now flourishing in Europe, most notably in the Netherlands. It is a great example of successful EU-China energy cooperation. Is ATES set to play a bigger role in China’s energy system?

The latest IPCC report signals a ‘now or never’ tipping point for implementing low-carbon strategies to limit average global temperature rises to 1.5°C above pre-industrial levels. While the deployment of renewables in the power sector is in full swing across the world, the decarbonisation of the heating and cooling sector is trailing other sectors.

Heating and cooling: half the world’s total energy consumption

According to IRENA^[1], heating and cooling (H&C) accounts for half of the world’s total energy consumption. Given that more than 77% of that demand is met with fossil fuels and non-renewable electricity, the H&C sector is responsible for 40% of energy related greenhouse gas emissions. Recent spikes in gas and power prices have exposed billions of people to heat supply risks, especially in Europe, in a sharp reminder of how vulnerable our fossil fuel-dominant economies can be.

Various renewable heating and cooling solutions are now being proactively explored, including a ramping up of solar heating and heat pumps powered by green electricity. Most of these alternative sources, however, are intermittent in nature, relying on wind or sun for power. With the rising penetration of variable renewables in decarbonisation of the H&C sector, energy storage technologies are now taking centre stage, providing a variety of flexibility solutions.

Thermal Energy Storage: a neglected piece in the H&C decarbonisation puzzle

While electricity storage technologies such as lithium batteries have emerged as one of the hottest markets in the modern energy landscape, thermal energy storage (TES) technologies have not yet been able to make many waves. However, TES technologies offer unique benefits to the energy system: a sizeable quantity of energy can be stored on a seasonal basis, either in the form of heat or cold, and that is hard to replicate using electrical energy storage.

This particular characteristic of TES is particularly relevant to the H&C sector, as demand is led by the seasons. According to IRENA, of 234 GWh of TES systems installed globally at the end of 2019, almost 99% are used for heating and space cooling.^[2]

ATES: sustainable heating and cooling under your feet

It is a little known fact that at depths of around 200 metres, the temperature remains constant throughout the year and roughly equal to the average annual air temperature at the earth’s surface. In fact, connecting a building’s climate to a constant and mild temperature in the subsurface makes more sense than connecting it to above-surface temperatures, which can vary widely during winter and summer. The subsurface aquifer is characterised by the high specific heat capacity of water, while the natural subterranean water flow makes it an excellent medium to store and recover heat. This brings enormous potential for delivering sustainable heating and cooling.

This is where the Aquifer Thermal Energy Storage (ATES) comes in to its own. By means of injection and withdrawal of water from the aquifer using groundwater wells, ATES is a proven underground TES solution that maximises the use of the earth’s natural capacity to store heat and cold, thus minimising the use of external energy sources for climate control. With a fairly large storage capacity, ATES is particularly suited to provide a seasonal heating and cooling solution for large scale ventures such as public and commercial buildings, district heating or for industrial purposes.

Circulating the groundwater through the building

‘To put it simply, ATES has made it possible to store winter cold to cool the summer and to store summer heat to warm the winter, simply by circulating the groundwater through the building that carries natural thermal energy,’ explains Wu Xiaobo, chief technology officer of the Geothermal Company of China Energy Engineering Cooperation (CEEC). Wu Xiaobo has worked in the ATES field for more than two decades, and believes firmly in the technology’s potential. ‘It is much more efficient and eco-friendly to move thermal energy around, rather than burning fuels or using fossil-based electricity to generate heat or cold when it is needed.’

How does the ATES system work?

Aquifer storage uses a natural underground water-permeable layer as a storage medium. The transfer of thermal energy is achieved by mass transfer of groundwater by extracting/re-injecting water from/into the underground layer. While conventional geothermal systems only store warm/cold water in the drilled wells, ATES systems store heat/cold in the entire aquifer (water and soil). A major prerequisite for this technology is the availability of suitable geological formations such as the existence of the aquifer.

The ATES system typically consists of a hot well and a cold well. During cold winter weather, ground water can be pumped through a simple heat exchanger where it is chilled and stored in a designated ‘cold store’ portion of an aquifer. Cold groundwater is recovered from the cold store during summer months and used for cooling. The water that has been used for cooling becomes warmer, and is injected into the designated ‘warm store’ portion of the aquifer. The cycle is repeated seasonally. Some ATES systems use heat pumps to boost the temperature depending on the outlet temperature from the aquifer storage.

The rise and fall of ATES in China

It is perhaps not widely known that the idea of storing heat and cold in aquifers originated in China, and can be traced back to the mid-1960s. ‘ATES is truly a Chinese born concept that has inspired the world!’ says Dr Wu. The technology emerged in Shanghai when Chinese engineers were working to reduce subsidence as a consequence of long-term groundwater over-pumping. They decided to recharge the aquifer artificially and soon discovered that the injected surface water could maintain its temperature over several months. Subsequently, Shanghai’s textile industry became aware of the potential of artificial water recharging for industrial cooling purposes that can be applied to store winter cold for summer cooling^[4]. Given the high demand for industrial cooling, construction of these early generation of ATES systems was rolled out rapidly across 20 cities in China.

However, by the 1980s such systems were gradually being phased out of the market: many of the wells clogged up due to the hydrochemical properties of the aquifer fluid and inappropriate well construction methods. Additionally, groundwater could not be effectively recharged back into the clogged up wells, resulting in a severe reduction in system efficiency and operation. In some instances, it even led to groundwater pollution by surface water, fluctuations in the seasonal groundwater level, and waste of water resources.^[5] These unresolved technical barriers and related environmental concerns, among other reasons, meant that ATES deployment ground to a standstill. ‘The premise to ensure an ATES solution can fully deliver its value is effective groundwater re-injection that helps keep the balance of the natural aquifer while minimising the man-made influence on the underground environment,’ notes Dr Wu. ‘Without further improvement to well quality and a better solution to the clogging issue, ATES is not sustainable’.

The Netherlands: a frontrunner in the commercialisation of ATES

European technology has helped to remove some of the blocks on the use of ATES technology. While China has put a hold on ATES projects for years, in Europe ATES has attracted more and more attention and is now showing its unique qualities to a wider audience. The best example of ATES commercialisation is in the Netherlands. According to the latest country report by IEA Technology Collaboration Program on Energy Storage^[6], of roughly 3,500 currently operational ATES systems across the world, 3,000 are based in the Netherlands.

What makes the Netherlands a frontrunner in ATES commercialisation? According to Dr Wu, the Netherlands has a superior aquifer resource and a high density of buildings which are suitable for large scale ATES deployment. However, the core factors that contribute to the Dutch success are their advanced drilling technology know-how, and the solid expertise and rich knowledge of hydrogeology and geological science gleaned from the country’s long track record of traditional oil and gas extraction. This wealth of experience has successfully resolved the re-injection clogging issue, one of the key blocks to ATES technology in China.

The Dutch government has also played its part, introducing various facilitating policies and measures to help realise the great potential of ATES. At a national level, a minimum energy performance coefficient value requirement in the Dutch Building Decree was introduced to create a market for energy efficiency technologies including ATES. The Geo Energy Systems Amendment was adopted in order to improve the planning and the reliability of ATES systems by unified and simplified application procedures.

All these factors have helped to deliver a fully-functioning ATES industry in the Netherlands, and have facilitated the construction of more demonstration and commercial projects. ‘It is in fact the close cooperation between industry, government, and knowledge institutions that has facilitated this expansion,’ noted Dr Wu. ATES is now a standard H&C design option for large public commercial buildings and residential blocks in the Netherlands, although awareness of the technology is still absent in many other countries.

Dr Wu is convinced that this clean technology is set to attract the interest of more countries. ‘For one thing, ATES is an architecture-friendly technology; it has a very small footprint on the building because it doesn’t require chillers/condensers on the roof. It is so unobtrusive that when you walk into climate-controlled buildings equipped with ATES systems, you can hardly feel their existence as they mainly operate quietly underground all the year round. For another thing, ATES is environmentally friendly, as the system simply borrows the groundwater for its energy capacity without disrupting the balance of the aquifer or introducing chemical alterations.’

Even though the market share of ATES remains limited in the Netherlands – only around 2% of the country’s H&C demand (127 TWh) was supplied by ATES systems by 2020^[7] – the country envisages a bright future for the technology in its energy landscape. ‘Think of it, this gas-rich country is now firmly dashing away from gas^[8]. The successful commercialisation of ATES has already proved its value in decarbonising the country’s cooling and heating sector, and will see a rapid takeoff in the next decade’, said Dr Wu.

The proven gains

Will the showcasing of ATES in the Netherlands encourage uptake of the technology elsewhere? Thirty years of proven Dutch ATES experience have already revealed some valuable energy saving and economic benefits that ATES offers compared to traditional heating and cooling solutions such as central heating with chillers or ground-source heat pumps (GSHP). These benefits include 40% lower heating energy consumption, and 65% lower cooling energy consumption^[9].

As for system efficiency, the coefficient of performance (COP) of an ATES system in cooling mode can reach as high as 10-20, compared to only 4 for a GSHP (ground source heat pump) system, while in heating mode the COP is 5, also much higher than that of GSHP. In particular, using ATES for cooling can achieve storage efficiencies of up to 90%: the stored cold can be used for passive cooling, without using a heat pump, thus significantly reducing peak power demand.

In addition, ATES can deliver up to 60% carbon emissions reduction compared to traditional solutions^[10]. Case studies of more than 74 Dutch ATES projects show an average CO₂ saving of 0.46 kg per m³ of pumped groundwater. This corresponds to an estimated annual reduction in CO₂ emissions of 150 t/yr for a small-scale system (100-300 KW) and of up to 1,500 t/yr for a large-scale system (5-30 MW). By comparison, the average CO₂ savings for a GSHP unit ranges between 1.8 and 4 t/yr, depending on the heating system it replaces and the electricity mix.^[11]

Due to the hydrogeological and engineering knowledge required to design an ATES system, the upfront design and construction costs are relatively high compared to a conventional Heating, Ventilation and Air Conditioning (HVAC) system. Nevertheless, the lifetime cost remains competitive due to the reasonably low operating and maintenance cost. Typically, the initial costs of an ATES project can be recouped within 2-10 years^[12].

EU-China cooperation revives ATES in China

Can the upgraded technology revive ATES in China, giving it a greater role in the country’s journey towards its dual-carbon targets?

According to Dr Wu, the Chinese market for ATES systems is already beginning to take shape. Shanghai Chongming Island National Facility Agriculture Center, which began operations in 2013, is the first new-generation ATES system in China, consisting of two cold wells and two hot wells serving a 20,000 m² greenhouse.

The system was almost fully imported under a Sino-Dutch cooperation framework (financed by the Dutch government’s Package for Growth (P4G) program and China’s Ministry of Science and Technology). The introduction of the Dutch advanced well design and drilling technique has overcome the well clogging barrier that had kept China from deploying ATES for years, and the extracted groundwater is fully re-injected.^[13] Monitoring data shows that the annual heating cost of this pilot project is 62% less than traditional gas heating, and nearly 75% less than electric heating, which remains highly coal-dependent. Overall, the pilot achieves roughly 75% CO₂ reductions compared to traditional heating systems.^[14]

Following this successful pilot and China-Dutch cooperation, ATES are now seeing increasing penetration into the Chinese market. According to Dr Wu, four large scale ATES projects have been built in Hubei, Shanxi and Jiangsu provinces in China, with several more in the pipeline.

‘By continuing close cooperation with the Dutch, we have further developed this technology to cater for the diverse geological and climate conditions of China, and even successfully applied our collaborative outcome into a third-party demonstration project in Japan. The success of these projects indicates that sustainability of ATES could be reached through technology innovation. EU-China cooperation could further facilitate technology development, which is beneficial to both sides and contributes to the battle against world climate change.’

Looking forward, Dr Wu anticipates particular relevance for ATES in eastern China. ‘ATES has promising prospects in shallow groundwater-rich areas, especially in the middle and lower reaches of the Yangtze River. These areas are heavily populated regions which enjoy high economic activity, and therefore higher energy consumption needs. Most importantly, these regions share seasonal temperature differences, with typical cold and heat demand peaks. However, they are normally out of reach to existing district heating networks, while H&C often relies on gas and electricity. This is just where ATES could better realise its potential as an optimal energy conservation and flexibility solution.’

Policies needed to unlock the potential of ATES in China

Perhaps a key lesson learned from the successful energy market penetration of ATES witnessed in the Netherlands is how effective incentive policies and light-touch legislative barriers could help to increase the attractiveness of the technology.

As China steadily moves towards meeting its carbon neutrality targets, a series of favourable policies have been introduced recently that place an increased emphasis on improving building energy efficiency. These include the 14th Five-Year Plan on Building Energy Efficiency and Green Buildings and the national General Code for Building Energy Efficiency and Renewable Energy Utilization (GB 55015-2021), which came into effect on 1 April 2022. The latter introduces mandatory renewable utilisation and carbon emissions assessments at the feasibility study stage for building projects. As in the Netherlands, these measures are set to create market space for energy conservation solutions such as ATES.

At the same time, energy storage is now top of the agenda in China’s push to shift towards a greener energy system. On 21 March 2022, China NDRC and NEA jointly issued a road map for the country’s energy storage sector in the 14th Five-Year Plan period, which advocates a boost to commercialisation of new energy storage systems and to large scale developments by 2025. Durable thermal storage solutions, including ATES, are described as key breakthrough technologies for ensuring system flexibility.

Research and development on energy storage technologies is also set to get more support. On 2 April 2022, in China’s newly released 14th Five-Year Plan on Energy Technology Innovation, ATES technology was singled out for mention when emphasising the crucial need to promote the utilisation of seasonal energy storage in the next five years. Moreover, the plan calls for efforts to achieve major technological breakthroughs on higher temperature ATES which have the potential for storing waste heat from the industrial sector. More detailed plans and ATES demonstration projects are likely to be unveiled in the near future.

In addition to encouraging policies, Dr Wu believes that better communication and more demonstration projects will be vital in raising the visibility of the technology, and so boosting uptake of ATES. ‘Various demonstration projects on different ATES application scenarios in the energy system will be crucial to improve stakeholders’ awareness of the benefits that it can deliver to different parts of the energy system.’

As sector coupling increases in the transition towards a zero carbon economy, a technology neutral, whole-system approach in national and local policy making will be crucial to overcome the conflicting rules and regulations that arise from siloed thinking across heat, power and end-use sectors. That approach will help unlock the potential of ATES in China’s energy system.

About CEEC Geothermal: CEEC Geothermal is a subsidiary company of China Energy Engineering Corporation, one of the major construction groups in China and the first state-owned enterprise to develop geothermal energy. The company is now leading on the country’s shallow geothermal development featured in renewable centred geothermal + smart energy regional integrated solutions with specialties in ATES and BTES.

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Daisy Chi is the Editor-in-Chief, EU-China Energy Magazine, at the EU-China Energy Cooperation Platform

This article was first published in the EU-China Energy Magazine – April Issue, available in English and Chinese, and is published here with permission

 

REFERENCES

1. IRENA, IEA, REN21: Renewable Energy Policies in a Time of Transition: Heating and Cooling (2020) ↑
2. IRENA (2020), Innovation Outlook: Thermal Energy Storage ↑
3. IF Technology, 2012: An Introduction to Aquifer Thermal Energy Storage (ATES), https://icax.co.uk/pdf/ATES_Presentation_Rehau_31May2012.pdf ↑
4. Paul Fleuchaus, et al. Worldwide application of aquifer thermal energy storage – A review. Renewable and Sustainable Energy Reviews, 2018. ↑
5. Xiaobo Wu and Xinnan Ouyang, 2019 IOP Conf. Ser.: Earth Environ. Sci. 249 012023. Successful Application of ATES/Groundwater Source Heat Pump in China. ↑
6. IEA ES, https://iea-es.org/wp-content/uploads/public/Netherlands_Country_Report_2021.pdf ↑
7. Aquifer Thermal Energy Storage (ATES) systems – current global practical experience. ↑
8. The Netherlands used to be the biggest gas producer in EU, with gas meeting 90% of building and 40%-50% of heating energy needs. In 2016, the government revealed an ambitious plan to stop major domestic gas production activities by 2022, and to phase out gas in heating and cooking in all residential buildings to reduce the sector’s CO₂ emissions by 80% before 2050. Seven million existing homes will gradually be disconnected from the gas grid. Source: https://energypost.eu/netherlands-gas-phase-out-transition-must-tackle-the-geopolitical-implications-of-importing-from-russia/http://energypost.eu/a-revolution-the-netherlands-kisses-gas-goodbye-but-will-it-help-the-climate/ ↑
9. Dutch ATES, Dutch Policy on ATES systems. https://dutch-ates.com/wp-content/uploads/2016/09/DutchPolicyOnATESSystems092016.pdf ↑
10. See footnote 3. ↑
11. See footnote 4. ↑
12. ibid. ↑
13. See footnote 5. ↑
14. Monitoring data provided by Dr Wu in a project report. ↑