What Is Geothermal Energy? A Career and Community Primer

Geothermal energy is heat from inside the Earth, used directly for warmth or converted into electricity. Global installed geothermal power capacity reached 15.4 GW at the end of 2024, up from roughly 13.0 GW in 2020, according to IRENA's geothermal technology assessment. That's small. Solar can add that much in a matter of weeks. But geothermal does something solar and wind can't do on their own: it runs at night, in winter, and through a storm.

That single property is why the technology keeps coming back into fashion, and why it deserves more attention from students planning a career than it usually gets.

What Is Geothermal Energy?

Geothermal energy is thermal energy stored inside the Earth's crust, produced by heat left over from the planet's formation and by the ongoing radioactive decay of elements in the rock. People use it two ways: directly as heat for buildings, greenhouses and industry, or indirectly by converting it into electricity at a power plant.

The word comes from the Greek geo (earth) and therme (heat). The US Energy Information Administration describes the crust as roughly 15 to 35 miles (24 to 56 km) thick under the continents and only 3 to 5 miles (5 to 8 km) thick under the oceans, which starts to explain why some places have usable geothermal resources and most don't.

Here's the part textbooks tend to skip. Heat is everywhere under your feet. A geothermal resource is something much narrower: heat you can actually get out at a rate and a cost that make sense. Those are different problems. Confusing them is the single most common error we see in student energy plans.

Where Does Geothermal Energy Come From?

A conventional geothermal resource needs three things at once: a heat source, permeable rock, and water. Stanford's Understand Energy Learning Hub puts it plainly. Heat has to flow up by conduction or as magma. Fractured rock has to hold and move the heated water. And water has to carry that heat to the surface.

Miss any one of the three and you don't have a project. You have a warm rock.

This is why the map of global geothermal power looks the way it does. Resources cluster where the crust is thin, faulted, or volcanically active, which usually means tectonic plate boundaries. Kenya's Rift Valley. Iceland. The Ring of Fire through Indonesia, the Philippines, New Zealand and the western Americas. Turkey and Italy.

If your community sits on thick, cold, tight sedimentary rock, no amount of enthusiasm changes the geology. We'd rather a student team hear that early than spend six weeks modeling something the ground won't support.

How Does Geothermal Energy Work?

Geothermal energy works along two separate paths. Direct use takes hot water straight from the ground and moves the heat where it's needed, through pipes and heat exchangers, with no conversion step. Power generation uses that heat to make steam, spin a turbine, and produce electricity.

Direct use is older and, in most places, easier. Romans heated public baths this way at Aquae Sulis, now Bath in England. The physics hasn't changed much since.

Power generation is where the engineering gets interesting. IRENA notes that medium or high temperature resources are needed to make electricity, and that most plants in operation today are dry steam or flash plants working with temperatures above 180 °C (356 °F). Binary cycle technology has opened up cooler fields.

Plant type	Typical resource	How it works	Maturity
Dry steam	Steam-dominated field, above about 180 °C	Steam from the well drives the turbine directly	Mature, but rare geology
Flash steam	Pressurized hot water, above about 180 °C	Pressure drops at the surface, water flashes to steam, steam drives the turbine	Mature, most common design
Binary cycle	Medium temperature fields	Geothermal fluid passes through a heat exchanger and boils a second fluid with a lower boiling point, in a closed loop	Mature and growing
Enhanced geothermal systems (EGS)	Hot, dry, low-permeability rock	Engineers fracture the rock to create a reservoir, then circulate fluid through it	Demonstration stage, per IRENA

Plain version of the table: if the ground gives you steam, use the steam. If it gives you hot water, drop the pressure and make steam. If it only gives you warm water, use that warmth to boil something else. And if the rock is hot but won't flow, you have to build the reservoir yourself, which is the hard problem the industry is still working on.

How Is Electricity Generated From Geothermal, and Why Does Capacity Factor Matter?

Electricity from geothermal comes from a turbine, same as a coal or gas plant. The difference is the fuel is free and the plant almost never stops.

That last point is worth sitting with. Capacity factor is the share of a year a plant actually produces compared to running flat out the whole time. Solar farms typically land somewhere in the tens to mid-twenties percent. Wind does better. Geothermal plants run at high capacity factors year-round, which IRENA identifies as one of the technology's main advantages, along with low operating cost.

IRENA also makes a point that matters more every year: as solar and wind take a bigger share of the grid, firm dispatchable output becomes more valuable, not less.

So a 20 MW geothermal plant and a 20 MW solar farm are not the same asset. Not close. The geothermal plant might deliver three or four times the annual energy from the same nameplate number.

Nameplate capacity is the number students reach for first, and it's the number that misleads them fastest. If you're building an energy plan and you're adding up megawatts without multiplying by capacity factor, your plan doesn't balance. It just looks like it does.

Is Geothermal Energy Renewable or Nonrenewable?

Geothermal energy is renewable in the sense that matters most: the Earth keeps producing heat, and the resource isn't consumed the way a barrel of oil is. The EIA classifies it as renewable for exactly that reason.

But the full answer is more interesting than a yes.

A specific reservoir is a finite thing on human timescales. Pull heat and fluid out faster than the field recharges and pressure drops, temperature drops, and output falls. It's happened at real fields. This is why Stanford's Understand Energy Learning Hub categorizes geothermal as semi-renewable rather than putting it in the same box as sunlight.

Operators manage this by reinjecting cooled fluid back into the reservoir after it's given up its heat, which maintains pressure and returns the working fluid to the system. Done well, a field can run for decades. Done badly, it declines.

On emissions, be careful with the language. Operational emissions from a geothermal plant are low, but they're not zero for every plant type. Hydrothermal fields contain dissolved gases, and flash and dry steam plants can vent carbon dioxide and hydrogen sulfide at rates that vary a lot by field. Binary cycle plants run a closed loop and vent far less. Construction, drilling and materials carry their own footprint.

If you write "geothermal is emissions free" in a competition submission, expect a judge to ask which plant type, which field, and measured over what boundary. Name your boundary. Lifecycle or operational, and against what baseline. A defensible rough number beats a confident wrong one.

Geothermal Power vs Ground-Source Heat Pumps: What's the Difference?

These are two different technologies that share a name, and mixing them up is the most common confusion we see from first-year students.

Geothermal power taps deep, properly hot rock to make electricity. Ground-source heat pumps use the shallow subsurface, which sits at a stable moderate temperature almost everywhere, as a place to dump heat in summer and pull heat from in winter. The Department of Energy describes this as using the ground as both a heat sink and a heat source.

	Geothermal power plant	Ground-source heat pump
What it produces	Electricity	Heating and cooling
Resource needed	Hot reservoir, usually well above 100 °C	Stable shallow ground temperature
Typical depth	Deep wells, often more than a kilometer	Shallow boreholes or horizontal loops
Where it works	Limited to favorable geology	Nearly anywhere, subject to soil and space
Needs electricity to run?	No, it generates it	Yes, the pump and compressor draw power

That last row trips people up constantly. A ground-source heat pump is not a generator. It moves heat rather than making it, very efficiently, but it still needs electricity to operate. So a community running heat pumps still needs a power supply plan.

Both technologies involve work that's outside DIY territory. Drilling, refrigerant handling, and anything touching a service panel needs a licensed contractor and a qualified engineer, and permitting rules are local. Don't design around an installation approach without checking what your jurisdiction actually allows.

How Is Geothermal Energy Used at Community Scale?

At community scale, the useful form of geothermal is usually heat, not electricity, delivered through a shared network rather than one machine per building.

The Department of Energy calls these networked geothermal systems, or thermal energy networks. Instead of drilling a loop for every house, you build shared infrastructure: piping, boreholes, heat exchangers, and heat pumps connected across many buildings. Water circulates between them. In winter the network delivers heat and returns cooler water. In summer it runs the other way.

The scale is the point. A network can serve a neighborhood, a campus, a city block, or a whole community.

There's real deployment behind this now. DOE's District-Scale Geothermal Energy Pilots initiative, formerly called Community Geothermal Heating and Cooling, funded 11 community coalitions across 10 states to select sites, assess the resource, work through permitting, run feasibility analysis and identify workforce needs. Three of those projects were selected to move into installation: two urban or suburban, one rural. Ball State University built what DOE describes as the largest ground-source closed-loop district geothermal system in the country.

Almost none of the popular content on geothermal covers this middle ground. Search the topic and you'll get utility-scale power plants or a single-family heat pump explainer. The neighborhood is missing.

Which is a problem, because the neighborhood is exactly the scale that matters for community energy planning, and exactly the scale of Power the Community, the international design competition Energy Mentors runs, where student teams design energy infrastructure for a livable community of 2,000 or more families.

Here's the judgment we'd offer any team looking at this. Geothermal is rarely the whole answer at community scale, and teams that bolt it on because it sounds good tend to get picked apart. The stronger submissions do the opposite. They look at the site's geology, say clearly whether a resource exists, and then explain why they ruled geothermal in or out. Showing your reasoning for a rejected option demonstrates more engineering maturity than including a technology you can't defend.

If that's the kind of problem you want to work on, you can register a team for the competition here. Teams can form ad hoc, university sponsorship is optional, and the grand prize is the Energy Innovators Award and $10,000 USD split equally among registered team members.

We keep a geothermal reference deck, "The Heat Beneath our Feet," in our geothermal knowledge page, alongside the rest of the Knowledge Resources library.

What Does a Career in Geothermal Energy Look Like?

Geothermal careers cluster into a handful of role families, and most of them don't require a geothermal-specific degree.

Subsurface and geoscience: Geologists, geophysicists and reservoir engineers who find the resource, characterize it, and predict how it behaves once you start producing from it. Heavy on modeling and uncertainty.

Drilling and well construction: Drilling engineers, mud engineers, well site supervisors, rig crews. This is where a large share of project cost sits, and where cost reductions have the biggest effect on whether a project goes ahead.

Plant and thermal engineering: Mechanical and process engineers working on turbines, heat exchangers, binary cycles, corrosion, and scaling. Geothermal fluids are chemically aggressive, and materials selection is a real discipline here.

District and building systems: Designers and installers of thermal energy networks and ground loops, plus the HVAC trades. DOE's district-scale work explicitly identifies workforce and training needs as part of project development, which tells you where the shortage is.

Policy, finance and community engagement: Permitting, resource rights, tariff design, community consultation. Underrated, and often the reason a technically sound project dies.

Now the observation that's most useful to a student reading this. The skills that transfer into geothermal most directly are oil and gas skills. Drilling, subsurface characterization, reservoir management, well integrity, and completions are the same core competencies. Energy Mentors was started by an engineer who spent forty years in the industry, and the pattern he points to is that people don't switch industries so much as they carry a transferable technical core into a new application. If you're a petroleum engineering student who's been told your degree is a dead end, that's not what the hiring picture actually shows.

Geothermal Rising, the industry association, runs a career fair explicitly aimed at students, early-career professionals, and workers transitioning from oil and gas, construction and manufacturing. That's a signal about where the industry thinks its people are coming from.

If you're a student trying to work out whether this path fits, or which courses to take next semester, that's the kind of question our mentors answer. Professionals who want to give that time can volunteer as a mentor here.

Geothermal Energy Facts Worth Knowing

1. Global installed geothermal power capacity reached 15.4 GW at the end of 2024, up from about 13.0 GW at the end of 2020 (IRENA).

2. Geothermal supplies about 90% of Iceland's heating demand and around 30% of its electricity (Stanford Understand Energy Learning Hub).

3. In Kenya, geothermal supplies close to half of national electricity (Stanford Understand Energy Learning Hub).

4. Geothermal is much less than 1% of the world's energy mix, but it can be a major resource in the specific places where it's available (Stanford Understand Energy Learning Hub).

5. The US Department of Energy estimates domestic potential of 90 GW of geothermal electricity by 2050, plus more than 17,000 district heating systems and geothermal heat pumps equivalent to 28 million US homes.

Compare fact 2 and fact 4 and you've got the whole story of this technology. Nearly invisible globally. Dominant where the geology cooperates.

That gap between global share and local importance is the same gap we wrote about in our post on how renewable energy can help address energy poverty. National averages hide what's happening in a single valley or a single village.

Where to Go From Here

So what is geothermal energy, in one line? Heat from the Earth, usable as heat or as firm electricity, brilliant where the geology allows and irrelevant where it doesn't.

If you're a student, the most useful thing you can do with this article is stop treating geothermal as one technology. It's at least three: deep power generation, direct-use heating, and shallow ground-source heat pumps. They have different physics, different economics and different maps. Teams that keep them separate write better energy plans.

If you're planning for a community, start with your load profile and your geology before you start with a technology. The order matters more than people think.

Sitting on an idea and not sure how to develop it? That's what Energy Mentors is for. We're a 501(c)(3) public charity (Federal ID #87-2139759), and the mentoring is pro bono. Register your interest for Power the Community, or email info@energymentors.org.

Frequently Asked Questions

Is geothermal energy renewable? 

Yes, in the sense that the Earth keeps generating heat and the resource isn't burned or consumed. But an individual reservoir can be depleted if heat and fluid are extracted faster than the field recharges, which is why Stanford's Understand Energy Learning Hub describes geothermal as semi-renewable and why operators reinject cooled fluid.

How deep do you have to drill for geothermal energy? 

It depends entirely on which technology you mean. Geothermal power wells typically go deep, often more than a kilometer, to reach rock hot enough to make steam. Ground-source heat pump loops are far shallower because they only need stable moderate ground temperature, not heat.

Can geothermal energy be used anywhere in the world? 

Ground-source heat pumps work in most places, subject to soil conditions, drilling access and space. Geothermal power generation doesn't, because it needs medium to high temperature resources that are usually found near tectonically active regions, as IRENA notes.

What are the disadvantages of geothermal energy? 

The main ones are geographic limitation for power generation, high up-front capital cost concentrated in drilling, exploration risk (you can drill and find nothing), water requirements, and gas emissions that vary by plant type and field. Enhanced geothermal systems could ease the geographic limit, but IRENA still lists them at the demonstration stage.

What degree do you need to work in geothermal energy? 

There's no single required degree. Geology, geophysics, petroleum engineering, mechanical engineering, chemical engineering and environmental science all lead into the field, and drilling and installation roles often come through vocational training and certification rather than a four-year degree.