Humans have a long history of tapping the Earth’s heat. It warmed the waters of the spa towns of Britain, where the Roman’s came to bathe. Today, natural hot-water spas around the world attract millions of visitors seeking the soothing comfort of that healing heat. Its fury has bewildered humans throughout history, with violent eruptions spewing hot ash and lava from giant pores in the Earth’s surface. Less dangerous – but no less impressive – are its displays of contained energy, such as those that entertain tourists in Wyoming’s Yellowstone Park, where geysers spout with startling regularity and force. It ranges in temperature from the extreme heat of the Earth’s core to the constant (and much more comfortable) temperatures found just a few feet beneath the planet’s surface.
Geothermal energy is one of the only meaningful sources of renewable energy available to us that is not ultimately reliant on the sun.
Although the Earth’s core is about 12,000 F (7,000 C), the heat near the surface – the upper crust of rock that’s about 60 miles (100 kilometres) thick, and below which we’ve never explored 2 – has a nearby, nuclear source. Radioactive elements like thorium and uranium are spread throughout the upper crust, and are constantly decaying and releasing heat. Thus, the heat in the ground comes from a massive, but very weak, nuclear furnace.
Generally speaking, the deeper you go, the hotter it gets. There are exceptions, like geysers, hot springs and volcanoes – all examples of Earth’s extreme inner heat poking through to the surface via ruptures in the Earth’s crust. Think of geothermal energy as mining the heat in the ground. Today, that energy comes from two kinds of mining operations. We mine high-temperature heat – from volcanic activity and hot springs – where it’s easy to find, along the Earth’s fault lines. We mine low-temperatureheat3 where it sits, just a few yards beneath our feet. Think of the high-temperature stuff as digging up a rich vein of gold, and the low-temperature stuff as panning for gold flakes.
Let’s call the first kind hot geothermal. It’s limited to places where the high-temperature stuff is close to the surface, near volcanoes or along cracks in the Earth’s crust – where the Romans built their baths. The second kind is often called geo-exchange, or ground-source heating. Although it’s nowhere near as dramatic as the high-temperature stuff, it has enormous potential for carbon-free energy production. Best of all, you can mine it pretty much anywhere.
Tomorrow’s mining will be a hybrid of the two. It’s called Enhanced Geothermal Systems (EGS), and it revolves around the simple idea that high-temperature heat can be found pretty much anywhere – if you only drill deep enough. The potential of geothermal energy, once EGS is brought into commercial operation, cannot be overstated – it is simply colossal.
A recent study4 by the Massachusetts Institute of Technology (MIT) noted that the total geothermal energy available within six miles (10 kilometres) of the Earth’s surface is 130,000 times the entire energy needs of the United States. Obviously, not all of it can be tapped, but even conservative estimates of recoverable energy indicate that between 3,000 and 30,000 times the total energy needs of the US are just sitting down there, waiting to be captured. This isn’t intermittent power that depends on the sun or wind; this stuff is available all day, every day, year-round.
So, EGS could provide for all of our energy needs, all over the world – and it’s both constant and reliable. At first glance, geothermal seems to be a bit of a magic bullet. Let’s see if that’s really the case.
Whether we’re walking down a city street, strolling through a park or sitting in our own backyard, there’s a reliable, clean and renewable energy resource just a few feet below us. Although we’ve known about it for decades, it’s a resource that’s scarcely been tapped.
The temperature of the Earth just beneath the surface – starting at about 10 feet (three metres) and continuing down for hundreds of yards – is roughly constant, year-round. It stays somewhere between 46 F and 60 F (8 C to 16 C), depending on geography, depth and time of year. 5 Geo-exchange is the art of using that energy to heat and cool buildings throughout the year. Think of the ground as a “heat battery,” and think of a “heat pump” as a way to get the heat in and out of that battery.
How does it work? Let’s look at an example for heating: First, you pump liquid – normally a glycol solution – through a length of pipe6 (called the “geo loop”) that’s buried or drilled into the ground. 7 The liquid absorbs heat from the surrounding earth as it travels through the pipe. Let’s say the glycol goes in at 46 F (8 C) and comes out at 52 F (11 C). The heart of the system is the heat pump,8 which acts like a refrigerator in reverse. It takes heat out of the liquid and transfers it to the building. The liquid returns to its original temperature, and the process repeats. The net effect is to mine the heat from the ground and transfer it to the building. How do you cool a building? The same process in reverse.
Here’s the key to energy production: The heat pump can get three to five times more energy out of the ground than it consumes. That means it runs at 300% to 500% efficiency and can lower a building’s energy use by up to 75%. Depending on the source of the electricity, the carbon footprint can be almost completely eliminated.9
Simply put, geo-exchange is the holy grail of heating and cooling – no other technology can touch it. High efficiency furnaces, modern air conditioners, baseboard heaters – none of these come close. As a bonus, the entire heating system gets pushed to the electrical grid, which will one day be powered by clean, carbon-free, renewable energy. There’s no way a natural-gas furnace can ever go carbon-free.
Sounds great-so why isn’t a geo-exchange system installed in every building?
Mainly, it costs more. A typical house would face about $10,000 in additional costs, above and beyond the price of a furnace and air conditioner. You’ve got all those pipes to bury in the ground, and maybe some holes to drill. Why go to all that bother and expense? It does pay for itself over time, 10 but we don’t always think long-term.
Plus, there’s often a disconnect between paying for the geo-exchange system and getting the savings. A typical condominium or housing developer doesn’t pay the ongoing energy bills, and they’re motivated to minimize construction costs. Again – why go to the extra expense? Despite these hurdles, geo-exchange is catching on. There are more than a million installations in North America alone, and we’ve barely scratched the surface. The easy installs are in buildings with a big yard where you can bury the pipes – but now, geo is going downtown.
A building development of my own, called Planet Traveler – a hotel in a dense part of downtown Toronto – has been designed to be the greenest11 hotel in North America. We wanted to prove that buildings in dense urban cores, with little or no land for the geo-loop, can still use geo. We have literally no ground to bury pipes-the building takes up the entire footprint of the property. So how did we do it?
We forged an agreement with Toronto city council that allowed us to bury 4,000 feet (1,200 metres) of pipe in 10 holes drilled into the publicly owned laneway that runs alongside the building. Not only did the city give the go-ahead, but it’s now looking at opening up all public lands – parks, laneways, everything – to geo-exchange. That would make Toronto the first city in the world to formalize this kind of relationship, allowing its citizens to be their own geo-exchange utility.
The technology may not be new, but as Paul Mertes, CEO of Canadian geo-exchange provider Clean Energy Developments, puts it: “Geo-exchange makes existing heating and cooling technologies look like an 8-track player.” Bring on the iPod!
If geo-exchange is like panning for gold flakes (mining lots of low-temperature heat), then hot geothermal is like finding a rich vein of gold. The heat is more intense – sometimes hot enough to make steam and produce electricity – but it can only be found in a few places. Areas around volcanoes, geysers and other perforations in the Earth’s crust are all places the hot stuff – normally buried much deeper underground – has poked its way close to the surface.
Hot aquifers are formed when water seeps close to one of these areas, and some gets sealed under a rock cap. Geysers are examples of that cap being punctured, releasing gasps of the hot steam. Hot geothermal makes use of that heat by tapping into hot aquifers located close to the surface.
Iceland is famous for its hot springs, geysers and volcanic activity. About a quarter of the country’s electrical production is geothermal, and almost all of its buildings are heated by geothermal sources. Iceland has so much of the stuff, they even heat their sidewalks. Paris is a long way from Iceland, but even there, geothermal energy is used to heat entire neighborhoods.
How does it work? The idea is simple: Drill down to the hot aquifer, pump hot water to the surface, then either use the heat directly or – if it’s hot enough to make steam – to generate electricity.
Waters of different temperatures are treated differently. If it’s really hot – like superheated steam at 57 5 F (300 C) – it will be under a lot of pressure and can be run directly though a turbine. Tapping that resource at the surface, if exposed to the open air, can sound like a jet engine. Lower temperatures – say, 300 F (150 C) – are still used for electrical production, but it takes an extra step. Heat from the geothermal water is extracted and used to boil a second liquid – butane or pentane – that has a lower boiling point. It’s the vaporized second liquid that drives the turbine. Finally, if the temperature is low enough – between 140 F and 160 F ( 60 C to 70 C) – then the heat can be used directly.
The average geothermal plant is smaller than a coal plant and will produce enough energy to power about 50,000 homes. But several can be scattered over the same geothermal resource. The Mammoth Pacific plant in California, operating since the late ’80s, is typical, producing enough power for 40,000 homes. A large plant in Larderello, Italy – the world’s first geothermal electrical installation, built back in 1913 – now provides 10% of the world’s geothermal supply, powering over a million homes.
Geothermal plants are not environmentally pristine, since the geothermal water can contain contaminants – including carbon dioxide. But geothermal plants release far fewer13 of these contaminants per unit of power than do their fossil-fueled counterparts.
There are hundreds of geothermal plants worldwide, producing enough electricity to power about 11 million homes. That’s actually not much-less than 1% of world electrical production. The problem is geology – there just aren’t that many rich veins of hot water near the surface – and production is limited mainly to a few places like the US, Costa Rica, Indonesia, Italy, Japan and Mexico.
If we had to stick to the stuff close to the surface, geothermal would remain a bit player on the world energy stage. But geothermal is ready to hit the big leagues.
To get a feel for enhanced geothermal, think geo-exchange, only bigger and deeper, with more complicated pipes and used for electrical production instead of just heat. In most of the world, the ground six miles (10 kilometres) beneath our feet is dry, but as hot as the hottest aquifer. That heat can be mined, brought to the surface and used to generate electricity.
Enhanced geothermal systems (EGS) represent the great hope of geothermal. If geo-exchange is the holy grail of heating and cooling, EGS is the holy grail of electrical production. Available around the clock, all year long and almost anywhere, it could be the workhorse of the world’s electrical system, with a constant baseload supply. It’s got colossal potential – the ground beneath the US could easily provide all of the country’s energy needs for the foreseeable future. EGS is the real deal.
How does it work? Drill down 2.5 to six miles (four to 10 kilometres), until you reach hot rock approaching 400 F (200 C). Drill another hole some distance away. Push water down the first hole at high pressure, creating a network of cracks between the two holes. Essentially, you’re creating a big, complex and very deep geo-loop. To mine the heat, pump liquid down one hole, and let it seep through the cracks in the rock and up the other. Grab the heat at the surface and use it to generate electricity. If you ever run out of heat, just move over a mile or two and start again, allowing the first area to heat up again.
To get a sense of how much energy is stored in the ground, imagine a 70,000-metric-ton pile of coal. Extracting enough heat to lower the temperature of a chunk of rock measuring just one-quarter of a cubic mile (one cubic kilometre) by just one degree will give you as much energy as burning that pile of coal. It could provide electricity to 14,000 homes for a year. 14 Ten degrees gets you 140,000 homes. The real magic of EGS is that you can drill for it pretty much anywhere – London, Adelaide, Toronto or New York, it doesn’t matter. We’re not limited to those few, thin veins of heat close to the surface.
Thanks to experimental projects in the 1970s at Los Alamos National Laboratory in the US, and at Cornwall, in the UK, in the 1980s, researchers developed methods of making fractures in hot, dry rock deep below the surface. A full-scale international collaboration is underway in Soultz, France. Small experimental holes 2.2 miles (3.5 kilometres) deep were drilled back in 1997, and the site has now been expanded into a full-scale pilot project, using three holes 3.1 miles (five kilometres) deep. Water pumped into one hole emerges from the other at about 400 F (200 C). A power plant big enough to power 1,500 homes is currently in operation.15
1. Drill an “injection well” 2.5 to six miles deep (four to 10 kilometres), until you reach hot rock approaching 400 F (200 C). Pump down cold water at high pressure, creating fissures in the low – permeability basement rock.
2. The water flowing into the fissures of the hot, dry rock creates a reservoir of very hot geothermal fluid. This essentially creates a massive, complex and very deep geo-loop.
3. Drill a nearby production well to roughly the same depth and pump the heated fluid back to the surface. As it rises, the pressure decreases and it turns into steam.
4. At the surface, the steam is captured and runs a series of turbines to generate electricity. At various steps in the process, excess water is captured and returned to a reservoir, creating a “closed loop” system.
Soultz is not the only project on the way. Drilling has started at two locations in Australia – one at Paralana, and a massive second project at Cooper Basin. There has been an operational plant in Landau, Germany, since 2007 that produces enough power for more than 6,000 homes. Sweden and Japan are also in on the action. And the first commercial plant in the US, partly funded by the US Department of Energy, is planned for Desert Peak, Nevada.
MIT estimates that an EGS plant capable of powering 100,000 homes would take up less than a square mile (two square kilometres), and use a 1.2-cubic-mile (five-cubic-kilometre) underground reservoir of rock. When that plant runs out of heat – every six years or so – you simply drill new holes a few miles away. The Earth will gradually reheat the original area. This is truly renewable energy.
EGS is still in the early stages of commercial development, and there remain technical uncertainties related to the geophysics of deep-earth rock fracturing, water flow and loss rates. Plus, all sorts of engineering issues are sure to pop up. But these are mere engineering problems – the sort of challenges engineers face all the time.
Bob Potter is one of those engineers. Mr. Potter, now 88, was a cofounder of EGS while working at Los Alamos National Laboratories back in the 1950s. Not one to hang up his hat, just five years ago, Mr. Potter founded Potter Drilling. Now, backed by money from Google, he’s working on (literally) cutting-edge technology to lower the cost of drilling those deep holes. He and his son have invented a new type of drilling technology that fractures the rock by spraying superheated 1,500 F (800 C) water out of a nozzle, instead of using traditional drill bits. They figure they can bring the cost of drilling down by half and get it done faster. Drilling is a big part of the cost of EGS, and proving that it can be done cheaply would go a long way to establishing the commercial viability of the technology.
There’s no real question about the long-term potential of EGS. That MIT report clearly established that there’s more than enough accessible EGS energy to power the entire planet for thousands of years.
There’s not much downside to geothermal exchange – it really is one of the lowest-hanging fruits on the carbon-reduction tree. It can cut heating and cooling energy use in all our buildings – office towers, hospitals, houses – by between 50% and 75%.
Buildings account for more than half of greenhouse gas emissions in large urban areas, so geo-exchange can take a really big bite out of city emissions – easily one-quarter. There are no real impediments to large-scale geo-exchange, either. It takes no high-tech factories or long-term planning – just simple commodities like pipes and compressors, and some local labor.
It does take capital, however, and as long as building developers don’t have a stake in the energy costs of a building, they’ll continue to avoid the added expense.
So how do we get there? We need a new, well-funded utility – a geo-exchange utility – that pays for geo-exchange systems (for both new buildings and retrofits) in return for the right to charge for the energy delivered. Everybody wins. Developers win, since they deliver state-of-the-art buildings at no extra cost. Condo owners win, since they pay less for their heating bills. The new utility wins, since it generates a long-term, stable return on capital. The rest of us win because we lower our collective carbon footprint.
Hot geothermal, the easy-to-reach stuff, is limited and will remain a marginal contributor to world energy production.
The big stuff, the real promise of geothermal, is EGS. As noted earlier, conservative estimate of the accessible geothermal energy in the US is 3,000 to 30,000 times the total energy needs of the US. Similar abundance exists everywhere in the world. The energy is there – we just need to get at it.
MIT estimates that what EGS needs is a $1-billion R&D kickstart (spread over 15 years) to establish the engineering know-how. At that point, market forces would take over. They estimate that by 2050, enough EGS systems would exist in America to satisfy 100 million homes, or 10% of the total expected US electrical demand.
That’s a conservative estimate of the potential, since it relies heavily on market forces and a natural rate of uptake. I saw nothing in the MIT report that talked about what will happen when there’s a hard price-or cap-on carbon, other than to note that EGS will “gain an economic advantage.” You bet it will – the installation rate would be even higher. What’s the total upside for EGS? It’s truly open-ended, since
more energy than we need is right there and – unlike other renewables – there are no constraints on when or if it’s available. EGS plants could replace, one-for-one, existing and planned coal plants.
There are pitfalls, of course. In order to exploit this resource effectively and economically, we need to know a lot more about using and expanding the natural fissures in deep rock formations. We must also learn more about how that structure will respond to having large amounts of heat extracted over time. In other words, we need to know more geology. In Basel, Switzerland, there were reports of seismic disturbances when an EGS system was activated, so we certainly need to be aware of potential earthquakes or other possible disturbances.
But these are the sorts of challenges the engineering and scientific communities solve all the time. The real barrier to widespread deployment is economic incentives. What EGS really needs is a market signal that says: Ready, set – go!
A not-so-modest proposal: Start drilling EGS holes beside every existing coal plant. Replace the furnace with a heat-exchanger, and keep the rest of the infrastructure, including turbines and transmission lines.