Developing geothermal energy from nothing: Scientists on unearthing a potential energy source in Singapore

Drill beneath the surface of grass and soil and you'll find rocks – known as Simpang granite – with temperatures high enough to cook an egg. 

Go deeper and it gets even hotter, raising more possibilities of what the heat resource could be used for. 

These findings were detailed in a groundbreaking study by researchers from the Nanyang Technological University (NTU) and the Technical University of Munich's multidisciplinary research platform TUMCREATE, located here, in collaboration with Surbana Jurong, an infrastructure consultancy.  

In a project which took more than two years to complete, the team in 2020 set out to find Singapore's potential for geothermal energy as a source of clean energy to power everyday needs. 

Geothermal energy refers to heat from the earth that could be harnessed as a renewable energy source. It was previously thought not to be commercially viable in Singapore due to the lack of conventional geothermal resources and its small land size. 

The use of geothermal energy will produce less emissions than burning fossil fuels, which Singapore is largely dependent on for its energy needs currently. 

About 95 per cent of Singapore’s electricity is generated by burning natural gas, the cleanest form of fossil fuel. 

And unlike fossil fuels, the geothermal resource underground could last decades and could reduce Singapore's reliance on other countries for natural gas. 

A handful of members from the team – which included 10 to 15 researchers – sat down with CNA earlier this month to detail the process of the study, their biggest takeaway and the challenges they faced. 

The team, comprising scientists from NTU's Energy Research Institute and TUMCREATE, also gave CNA a crash course on geothermal energy – research into which is still nascent in Singapore. 

In the quest for subterranean heat, researchers first found geothermal potential in Sembawang Hot Springs and Pulau Tekong, which is currently used by the military.

Singapore's only natural hot spring in Sembawang is located within the Simpang granite pluton, which has a high concentration of naturally occurring heat-generating elements, according to an earlier study. The granite covers a quarter to a third of Singapore.

After collecting temperature data from various boreholes drilled into Singapore, the team of scientists created a shallow temperature map and eventually settled on the Admiralty Lane site, about 2.5km away from Sembawang Hot Springs. 

"In the northern part of Singapore, where the hot springs are, the shallow ground temperatures are hotter than other parts of Singapore. Largely based on this data set, we decided to focus our efforts on that region," said NTU senior research fellow Hendrik Tjiawi. 

There, the team achieved a milestone, drilling to a previously unplumbed depth of 1.1km to pull up rock core samples of Simpang granite through a slim hole. 

This runs deeper than civil infrastructure, such as sewer pipes which are around 60m underground, MRT tunnels which go down to 43m and the Jurong Rock Caverns, which are 150m below the ground. 

"In the northern part of Singapore, where the hot springs are, the shallow ground temperatures are hotter than other parts of Singapore. Largely based on this data set, we decided to focus our efforts on that region," said NTU senior research fellow Hendrik Tjiawi. 

There, the team achieved a milestone, drilling to a previously unplumbed depth of 1.1km to pull up rock core samples of Simpang granite through a slim hole. 

This runs deeper than civil infrastructure, such as sewer pipes which are around 60m underground, MRT tunnels which go down to 43m and the Jurong Rock Caverns, which are 150m below the ground. 

What the scientists found were rocks hot enough to cook a soft-boiled egg. Based on data extrapolation and modelling, the team calculated that the site could have a temperature of around 200 degrees Celsius or more at depths of 4km to 5km.

That's hot enough to generate electricity and hydrogen, and hotter than other rocks found at the same depth in other non-volcanic regions. 

On where the heat came from, the researchers pointed to the Earth's core, and more surprisingly, to the rock itself. 

Simpang granite contains heat-producing elements – referring to elements that produce heat naturally – and more so than other rocks. 

It also has a high heat flow, which is the ability to store and transfer heat. The team said Simpang granite has twice as much heat flow as the global average, excluding those found in the vicinity of volcanoes. 

Geothermal energy can be harnessed from the ground through a closed loop system, where water ported from the surface into pipes underground is heated by the rocks. The water is pushed back to the surface and as the hot water boils into steam, it can power a turbine or a generator. 

Research engineer Anurag Chidire is one of the scientists studying the feasibility of a system that would work for Singapore and to find the optimal utilisation for heat factoring in cost, and the social and environmental impact. 

For a country lacking in natural resources, geothermal energy to Mr Chidire represents a promising opportunity for Singapore to finally have its own sustainable source of energy with minimal carbon emissions. 

Mr Chidire, who is from TUMCREATE's Energy and Power Systems Group, said that the carbon emissions from a geothermal power plant would come from the preparation and construction of the site, rather than the operation of the plant. 

By his calculations, the carbon footprint from bringing in materials for the plant would still be significantly less than burning natural gas. 

The findings also gave him hope that in finding its own energy source, Singapore will no longer be called a "resource-deficient country" or one that doesn't have any renewable resources. 

Mr Chidire echoed lead scientist Tobias Massier's sentiments on the potential of geothermal energy to cover part of Singapore's cooling demand. Dr Massier said that every gigawatt of geothermal power produced could cover about 12 per cent of Singapore’s current cooling demand. 

Around 60 per cent of energy consumption in a building is used for air conditioning. In Singapore, an overall 30 per cent of electricity consumption is for cooling. 

More than just the potential for geothermal energy, the data gained from the study provided new insights into Singapore's underground landscape. 

For Assoc Prof Wu Wei, the co-investigator of the project, the study presented him with the chance to satisfy his curiosity about Singapore's geology. 

"All (the information) we have is just maybe down to 200m deep ... That affects future development because in Singapore we plan underground in multiple layers," said the cluster director for geothermal at the NTU's Energy Research Institute.

Apart from limited subsurface temperature measurements, there are no deep boreholes and temperature measurements on the western, eastern and southern sides of the country. 

When the time came, however, Assoc Prof Wu was surprised by what he found. He had expected to find dense and high-quality granite, instead, the site at Admiralty Lane has fractured granite. 

The second surprise was that, unlike Sembawang Hot Springs, the borehole did not produce pressured water which would have indicated higher temperatures underground. 

Hot springs are formed when groundwater comes into contact with hot rock underground. The water is heated to high temperatures and the high pressure causes the water to seep upwards through cracks, forcing itself out of the ground and onto the surface.

However this did not happen at the study site, which means the next drilling area should be closer to the Sembawang Hot Springs, Assoc Prof Wu said. 

NTU research fellow Jonathan Poh said the project is his first job after completing his PhD studies. 

"Considering that I'm a geologist by training and I focus on mineral resources, finding a job that is close to my discipline is very very rare, especially in Singapore."

Dr Poh ran experiments on a small sample of rocks, crushing and milling them to measure their elemental concentration. This was to find out the amount of heat-producing elements, such as potassium, thorium and uranium, in the sample.  

He was involved in the numerical modelling of data using data points obtained from the drilling. 

"I did these measurements for the entire borehole length, so I have many, many data points. Of course you can try and extrapolate it to a certain degree of confidence.

"Maybe the trend suggests that there might be more of the Simpang granite down there but to actually know, to confirm whether there is Simpang granite down there you either have to drill, or you employ some non-invasive method to determine how thick the rock is."

While the team had targeted to drill to 1.5km, they could not proceed past 1.1km due to the difficult rock conditions and technical constraints of the equipment they worked with. 

Dr Hendrik noted that the team used machines which started with a smaller borehole, which limited the depth it could drill to. 

"When drilling with a small borehole diameter (slimhole), at some point – where the rocks are weak, we will struggle to continue drilling deeper without increasing the risk of losing the borehole, because the rocks keep collapsing into the borehole," he said.

The senior research fellow, who is responsible for managing the budget and coordinating the team, said the results were promising enough to progress to more expensive equipment that could start with larger boreholes to reach lower depths.

The thought that Singapore's rocks could have high heat flows sprouted in the late 2000s and nagged at Dr Hendrik for more than a decade.

Without its own data, Singapore only had statistics from neighbouring countries to work with, he said.

"We thought that Singapore could have high heat flow. This thought, together with the existence of the hot springs, started the geothermal research project in Singapore," Dr Hendrik. 

"The high heat flow remained a guesstimate for years, from the beginning in 2009 and, only recently in 2023, we know from measurements that Singapore indeed has high heat flow at Admiralty. That, to me, is exciting.”

Even then, the project got off to a rocky start in October 2020. Lead scientist Alessandro Romagnoli found that there was a dearth of geothermal research and talent in the area, making it a struggle to even begin. 

"We had to bring geothermal energy from ground up, there was no geothermal research in Singapore before. It was very hard to find people that wanted to work on this project," said Prof Romagnoli, who is cluster director of multi-energy systems and grids at NTU's Energy Research Institute.

"It was a big effort from the beginning. Basically from scratch to develop a team that could eventually deliver the project, which is challenging on its own, right? It's the first of its kind."

Even as the right expertise came together, its members had to find contractors with the capability to deep drill. By the time the actual drilling started at Admiralty Lane, it was October 2022. Drilling was completed in March this year. The same process at another site in Gambas Avenue site began in June this year and is still ongoing. 

But the long process was worth it. The study's findings and the attention it garnered were "beyond expectation", said Prof Romagnoli. 

The findings have provided a basis for further investigation into harnessing geothermal energy as a potential source, and the team recommends more geophysical surveys aside drilling to deeper depths. 

These will provide more data to evaluate the total amount of heat stored in Singapore's deep subsurface rock, the speed of heat transfer, and the amount of energy generation it may support.

So far, results have been shared with the Energy Market Authority, which has asked for proposals for a non-invasive geophysical study to assess the potential for power generation up to depths of 10km.

Prof Romagnoli also sees the study as an opportunity to create public awareness, to educate and to dispel misunderstandings about geothermal energy.

"So that is important, to get that sort of visibility. Because we don't want to stop this project. We would like really to push the bar even further."