Geothermal Energy; A review of its nature,distribution and utilization.

Heriot Watt University: ICIT, Orkney Campus

MSc Renewable Energy Development

Energy in the 21st Century

November 2015


So what is this article about and who is it for? 

If a source of electrical power to society existed that was carbon free and relatively clean to extract, offered all year round sustainable and scalable home or national grid size ‘baseload’ power (primary electricity source), had little inherent risk to nearby life and already had the technology and knowledge in place to utilize – why would society not be using it to replace dirty, climate change inducing fossil fuels for power generation?

Geothermal Energy is a unique renewable resource in many ways which I will go on to explain. The article is tailored towards a secondary school and early University years students.

Lets start by understanding the difference between energy and power?

This article will refer to Power and Energy throughout using the most common terms for each. Power is just “Energy flow per time” and is measured in “Watts”, most of us are aware our electrically appliances like kettles are sold with power labels in Watts. Energy units are in “Joules”, so 1 Watt is equal to 1 Joule per second. Hence a Watt is a measure of power, or rate at which a Joule is converted. In the electrical power generation industry these two terms are used interchangeable, however it’s important to be aware of the difference.

When we refer to the Energy usage, for example by a ‘typical household’, we do not use Joules. Instead we multiply back by time and refer to it as a “kilowatt Hour” (kWh), i.e. 1000 (kilo) Joules per second X 3600 seconds (an hour) = 3,600,000 Joules (3.6 Mega Joules). Hence why a kWh is an industry measure for Energy.

To get a grasp on tangible examples of power and energy, consider the following examples according to Alyson Kenward at;

A 100W incandescent light-bulb burning for 1 year continually will consume the same amount of electrical energy (100W x 8760 hours = 876kWh) as that generated by 700lbs of average coal (assumed each ton of coal generates 2500KWh of energy, so 876kWh/2500kWh = 0.35 ton or 700lbs), which is roughly equivalent to around 3 large suitcases of coal. So don’t leave the lights on all day when you go out!

Stepping up in scale to a typical home, The EIA (USA Energy Information Administration) estimates on average that 10932kWh is the residential electricity energy consumption in a year per US home (2014). Using the same calculation as earlier, this equates to 4.4tons of coal per home a year which would fit into approximately 44 large suitcases.

Stepping up in scale still further to a single wind turbine that you may see in the countryside, it has a typical generating maximum power of 2MW (M – million). If we assume the winds blows only 25% of the year to generate electricity, then in a year it provides 4,380,000kWh of energy (2MW x 8760hours x 25%). The same usage as 401 average homes in the US, or equivalent to 1752 tons of coal (that’s a lot of suitcases and a lot of nasty CO2 not emitted into the atmosphere).  A typical wind farm array maybe made up of 10’s to 100’s of individual turbines on one site!

As a final example, the largest power station in the world is the Three Gorges Hydro Electric Dam in China which is a 22.5 GW facility (Giga – billion). Its energy generation a year varies depending upon water levels, so in 2014 it reportedly generated 98.8TWh (Terra – Trillion) of energy (Chinese Three Gorges Corporation figure). That’s equivalent in the US to just over 9 million homes a year and replaces the burning of 39.5 million tons of coal. I’m not going to calculate how many suitcases that is!!!!

This installed MW power generation to ‘average’ home conversion can vary wildly depending upon country, electrical consumption patterns as well as which type of energy resource provides the energy. It’s important to remember that not all MW’s of power are equal so be mindful of the conversion approximations you see on websites (including this one).

One final small point to note here is that Energy is not destroyed, it is changed from one form to another and conserved but diluted in form – the first law of Thermodynamics. For example a boiling kettle dilutes electrical energy into heat, sound and kinetic energy. This dilution in energy form is called Enthalpy and will be referred to later on.

So why is Geothermal power important and how does it fit into the worlds energy mix?

Geothermal Energy is the only renewable energy source independent of the sun’s energy or gravitational attraction provided by the sun and moon. It’s been used for centuries for different purposes – ancient Romans kept themselves clean with geothermal heated spa waters and Maori New Zealanders cooked food in buried ‘hangi’ ovens. The most modern use however has been to use deep, hot pressurized fluids in the earth’s crust to convert hot water into high pressure steam to spin turbines that generate electrical energy. The first official geothermal power station operated in Lardello, Italy over a century ago. Shallower, lower temperature geothermal fluids that cannot ‘flash’ hot water into steam instantly can still be utilised for smaller ‘binary’ power plants and heat pump systems via heat exchangers to create power, more of which I will explain later.

The 2014 IEA World Statistics report assimilates annual world energy data, it’s a really useful place to look for how the planet utilizes energy and not to be confused with its American cousin the EIA which offers similar data. The Figure 1 pie chart shows the percentages of different fuels used for mankind’s total primary energy supply (TPES) between 1973 and 2012. ‘Other’ refers to renewable fuels usage (not including hydroelectricity). As you can see as an energy source, ‘renewables’ as a whole remains low at around 1% in 2012 from almost nothing in 1973. Fossil fuels however (Coal, Gas and Oil) make up 72% in 2012 of mankind’s primary energy resource! It’s these carbon intensive fuels we need to remove from the primary energy supply to limit climate change and geothermal energy is one of those abundant natural and clean resources that can help to do this.

Figure 1        Figure 1: Total Primary Energy Supply by fuel shares 1973 – 2012(IEA World Statistics, 2014)

The Figure 2 pie chart identifies more clearly where geothermal, as part of the renewables primary energy resource fits into the global energy usage mix. Geothermal and other electricity generating resources combined are overwhelmingly (greater than 98%) focused on industrial and other uses (commercial, residential etc.…), with a very small direct supply to the carbon fuel dominated transport sector. The key point here is that transport makes up only 1.6% of direct electricity consumption.

A combined renewable resource power generation AND electrically powered transport sector solution is needed for a truly carbon free society in the future. For the immediate future however, the more realistic aim is for renewable’s to retire coal, oil and finally the transition fuel, gas as feed sources to electrical power generation to reduce mankind’s impact upon the environment.

Figure 2  Figure 2: World electricity consumption between 1973-2012 (IEA World Statistics, 2014)

So how exactly is Geothermal Energy created?  

Geothermal Energy is the potential energy stored as heat beneath the Earth’s surface. It’s a significant resource, the British Geological Survey states that 99.9% of the planet is at a temperature greater than 100 degrees Celsius – so as hot as boiling water needed to cook an egg!

As shallow as 10m-15m, the ground has enough stored potential heat energy to be used directly for heating purposes by small scale users. During the day, the suns direct heating slowly warms up the ground. At night, the reverse situation occurs with the ground cooling more slowly than the surrounding air. This temperature differential in the soil can be used to extract heat energy via differential heating.  The ground can work in a similar way to a chemical battery. At 15m depths, ground temperatures are no longer influenced by seasonal changes in air temperatures and remain a stable heat resource all year round. So in the summer the ground at this depth remains cooler than the air, in the winter the ground is warmer than the air.

As you travel deeper – many of kilometers down, the deep, dry rock formations potential heat energy increases. Its this potential heat energy that can be tapped into by large scale geothermal power stations. Heat energy from the Earth’s inner mantle which  is composed of hot, molten rock (magma) is continually produced; mostly from the radioactive decay of potassium, uranium and thorium elements but also from the planets primordial heat. The Earth’s crust acts as a thick insulating blanket pierced by heated fluid conduits from the mantle. You may well have seen surface eruptions of geothermally heated waters from vents called geysers or the more gentle manifestation as hot Spa bath waters in Iceland, North America and Japan.

Increasing geothermal potential heat energy occurs with increasing depths according to the local geothermal gradient. This can vary immensely depending upon geographical location; away from tectonic boundaries (crustal plate joins) it can average 25 degrees Celsius per km of depth, but along the Mid-Oceanic ridge tectonic boundaries the gradients can increase to 200 degrees Celsius per km (Figure 3). The oceanic crustal plates are a lot thinner (ca.7km) than continental crustal plates (10-65km) – since they are closer to the mantle this means they are hotter too. Remember the 100W incandescent lightbulb – it has a surface temperature of around 100 degrees Celsius, the Earth’s core is estimated to be 7200 degrees Celsius!

Just as an aquifer stores and transmits water, a body of geological material that stores and transfers heat is termed an ‘aestifer’. These can exist within permeable or impermeable rock. Importantly the two physical heat transfer processes are ‘conduction’, which involves a substances energized molecules rebounding off each other, and ‘convection’ which is the physical transport of heat from one place to another by fluids. An aestifer needs to be delineated and its intrinsic thermal properties understood prior to any geothermal energy extraction system being put in place. Being a subsurface resource this creates difficulties in estimating its properties. Geological wells are drilled and geophysical surveys undertaken to gather the subsurface data in a similar way to buried oil and gas resources estimation.

Figure 3  Figure 3: Earths composition and temperature gradients (Various web sources)

So how can shallow and deep Geothermal Energy be harnessed?  

A geothermal resource is defined as the thermal energy that could reasonable be extracted at a competitive cost to other forms of energy at a specified future time (Muffler and Cataldi, 1978)

Geothermal energy can be utilized at the small, medium and large scale and is termed a ‘scalable’ resource (think of Lego bricks which can be stuck together to form different scale models). You may remember I remarked earlier that the deeper into the Earth you go the hotter it gets, well generally this equates to the deeper you go, the bigger the power creation potential. You will also remember the term ‘Enthalpy’ from earlier used to describe system energy changes. Geothermal energy sources can be described as low (<180C) and high (>180C) enthalpy systems. A newer refined resource categorization based on domains and different energy conversion technologies exist, but essentially it simply further segregates low and high enthalpy nomenclature systems already in conventional usage.

Low enthalpy systems are at the shallowest levels, so right beneath your feet and can be harnessed by open or closed loop systems to heat or cool homes and offices. Open loop systems exchange heat with subsurface ground waters requiring a water bearing and flowable aquifer at shallow depths. Closed loops systems exchange conduction heat directly from the bed rock via installed heat exchangers in shallow horizontal trenches or vertical boreholes. Abandoned subsurface mine systems can also provide a permeable water storage network from which heat can be extracted. For example flooded coalmines acting as ‘aestifers’ in Mieres (Spain) and Springhill (Nova Scotia, Canada) already function as geothermal open loop systems.

Personal homes can install small scale closed loop conductive ground source heat pump systems 2-3m under the soil. By pumping water or a refrigerant through buried pipes called ‘ground loops’, heat or cold can be concentrated and transferred from outside the home – into the home (Figure 4). This heat can be used in radiators, hot water or home heating systems. These systems however do need external electricity to run compression pumps.

Figure 4               Figure 4: Illustration of small scale home based GHP system

Urban Geothermal District Heating systems (Open Loop Ground couple heat-pump systems, GCHPS) heat and cool individual buildings through a geothermal distribution network. The GeoDH European information hub state that over 240 geothermal district heating systems exist in Europe (2015). Figure 5 Below illustrates the concept of a dual well strategy where deeper, geothermally heated hot water is pumped (via electrical pumps) to the surface and ‘convection ‘heat extracted via a mechanical heat exchanger consisting of a low boiling point, circulating fluid or gas. In some hotter climates, this system can also provide building cooling systems as a revere heat engine system.

Figure 5  Figure 5: Illustration of medium scale GCHPS system (

By drilling wells many of kilometers (1km-3km) into the Earth’s crust, larger scale conventional high enthalpy geothermal power plants can be constructed to access the convection heat of mobile heated fluids. High enthalpy geothermal resources used today consist mostly of hydrothermal dry steam (greater than >100C), steam-water (temperature mixed)  and hot liquid resources (less than <100C). Most of the geothermal energy (57%) is produced by Single/Dual flashing units, 27% by Dry steam units and the rest from Binary cycle units. Three other geothermal systems that technology and economics are yet to allow development of are termed; hot dry rock, geopressured and magmatic. This article mainly focuses on existing systems exploitation.

A typical countries geothermal resource development progresses in stages. Stage 1; the highest temperature Dry steam resources are developed first. Stage 2; high liquid-water temperatures using Flash units is then developed. Finally Stage 3; the lowest temperature liquid-water temperature resources are developed using Binary cycle units.

The world’s largest geothermal energy development in California is called ‘The Geysers’ and it’s a dry steam unit project. It is made up of 14 operating power plants drawing superheated steam from 327 steam wells. The source of the heat for the steam reservoir is a magma chamber 6.4km below the surface, supplied by magmatic flow through an active tectonic system. Geothermal wells are drilled into a permeable sandstone reservoir that allows superheated steam to escape and be evacuated to the surface. The steam reservoir is geologically capped by impermeable rocks which insulates and stops the steam from escaping naturally. Thermal energy in the form of pressurized steam flows from the wells, through pipelines and then to the power plant where it enters the steam turbine. As the steam cools and expands heat energy is converted to mechanical energy. The turbine is coupled to a generator which then transforms the energy to AC electrically energy sent to the external power grids and onto households. The steam field is pressure recharged by injecting treated sewage effluent via 56 injection wells – this is a novel way to dispose of municipal waste waters as well as the very salty brine waters produced from hte geothermal plant (Figure 6). The current installed power capacity is 1517MW. This is enough to power over a year, with a 95% capacity factor  over 1.15 million homes (based on the earlier US statistics of 10932kWh consumption annually per home).

Figure 6   Figure 6: The Geysers Dry Steam geothermal power station, California, USA (

What is the current uptake in geothermal power generation systems?

Geothermal energy is in direct competition with other power generation sources like solar photo voltaic cells, wind turbines, wave/tidal turbines, nuclear fission, and  the fuel burning of biomass, coal and gas. The growth of geothermal energy in countries has been very slow by comparison. This can primarily be blamed on the financial risks involved and perceived social impacts of the projects. Uncertainty in describing subsurface geothermal resources means the capital and operating expenditures involved compared to other renewable’s can be high whilst being designated as a riskier investment.

Global renewable resources, installed capacity and renewables increases between 2008-2013 for Photo Voltaic Solar Power, Wind, Hydroelectricity and Geothermal Power are compared in the Table 1 below. There was a low volume of geothermal power installed as a percentage of the global total – less than 0.5% (12GW), being by far the lowest of any of the defined renewable energy resources. Solar PV is close to 2.5% (139GW), wind 5.5%(318GW) and hydroelectric 17.5% (1000 GW). Comparing a different data source – estimated that in 2011 the global installed geothermal power capacity was 10.9GW, hydroelectric (963GW), solar (68.8GW) and wind power (240GW). Wind and Solar differ between datasets because of their high growth rates between 2011-2013.  Geothermal energy’s growth rate increase between these years is also the lowest at 9% compared to Solar PV 83%, wind power 50% and hydroelectric 12.5%.

Comparison of each renewables resource size varies widely depending upon the author in this particular study. Its fair to say that in all cases a sizeable potential resource remains undeveloped (Table 1a). Further analysis using three renewable intensive countries, Iceland (1b), USA (1d) and China (1c) as examples illustrate that on a national scale the take up of geothermal energy varies due to geographic location and the political and social situation in place. Iceland has a special geothermal location over continental tectonic plates making it ideal for geothermal power stations, as well as having a low democratic population. The United States has a high democratic population, with some west coast tectonic boundaries geographically, with a far larger energy demand and supply than Iceland. China on the other hand being a Communist country has more direct state intervention control on energy projects, but comparably less favorable high heat flux locations with an even larger energy hungry population than the USA. Iceland aside, the USA and China have installed very little new geothermal energy at a time when other technologies have shown rapid expansion.

Table 1          Table 1: Comparison of Global and three country renewable resources (Renewables 2014:”Global status report” REN21 – renewable energy policy network for the 21st Century)

Which global locations have the highest geothermal potential?

Looking at the worlds high enthalpy installed power plants only, the upper map (Figure 7) shows colour coded contours of the estimated global distribution of heat flow at the surface of the Earth’s crust (major plate tectonic boundaries drawn on also). The redder the colour, the hotter the heat flow. The hottest zones are focused around divergent and convergent plate tectonic boundaries. The lower map (Figure 8) shows the location of the worlds current geothermal power plants. It’s apparently obvious to see that globally the areas with the highest heat flow rates, with access to heated convection fluids have the most installed large scale geothermal power stations to date. Geothermal locations where crustal thinning has allowed access to resources away from tectonic boundaries are less common.

Countries having tectonic crustal plate boundaries in their territory dominate geothermal power generation. The more exact siting of these power stations along plate boundaries depends upon the location of a reachable, permeable reservoir rock formation containing large amounts of fluid, water or steam bounded by cooler impermeable layers that trap recharging surface waters which have percolated into the reservoir. The heat source, reservoir, recharge area and connecting pathways together are termed the ‘hydrothermal system’.

In 2014, a total of 24 countries were using electric power generated from geothermal. Geothermal currently provides less than 0.5% of the world’s electricity generation.

Figure 7  Figure 7: Global heat flow map in Watts per spatial area (

 Figure 8             Figure 8: World distribution of high enthalpy geothermal power stations (

The Geysers Geothermal power station in California is located close to the well known San Andreas crustal transform fault, with its heat sourced from a buried intrusion 13km in diameter. Indonesian, Filipino, Mexican, New Zealand and Kenyan geothermal power stations are all located close to tectonic plate boundaries too. Each locale possesses the potential for high heat fluxes within drillable depths, each installing 50MW-200MW individual geothermal power plants similar to ‘The Geysers’ plant principle to harvest the energy. The USA (3525MW installed), the Philippines (1915MW installed) and then Indonesia (1380MW installed) are the worlds three largest geothermal energy generators (2014) . Geothermal electrical generation as a percentage of total electricity generated however in these countries is relatively small compared to other resources.

Icelands unique geographical position makes it stand out when looking at national geothermal energy usage statistics. Its five geothermal power stations generate over an estimated 25% of the nations electricity according to the ‘Iceland Energy Portal’ (the rest being hydro-electrically generated), with geothermal supplying a large proportion of the countries domestic heating needs.

As obvious as the correlation between tectonic location versus geothermal power stations is, its equally apparent that large areas of the globe do not embrace high enthalpy geothermal power because of their location and absence of highly convective heated fluids near to the Earths surface. What is key is not that the temperature contrast, permeable aestifers or electrical infrastructure are absent, its simply that the economic potential for geothermal power is lower than other forms of power generation better suited to these locales. The potential for smaller scale, low  enthalpy systems like ground closed loop heat pump systems or binary power plants still exists, these are however uneconomical on a large scale. The British Geological Survey participates in the European Community funded wide ‘Thermomap’ project to map superficial (<10m) geothermic potential across Europe. This map is made  available to member states to optimise the locations  for low enthalpy geothermal power projects.

What are the advantages and disadvantages of geothermal power compared to other renewables projects?

The majority of journal papers researching Geothermal statistics focus purely upon high enthalpy, conventional large scale power station resources which form the majority of the electrical input into national grid systems. Hence the advantages, disadvantages and impacts of geothermal power answered in the proceeding paragraphs pertain to mainly conventional geothermal sources.

Cleanliness and sustainability, how do these vary between renewable’s? The ranking in Table 2 below was based upon the following criterias; energy systems were long term and each systems relative impacts upon global warming, air pollution, water supply, land use, wildlife impacts, thermal pollution, water-chemical pollution and nuclear weapons proliferation (which is why you don’t see Nuclear power in the ranking). Based on these assumptions, Jacobson (2009) placed Geothermal energy high up for cleanliness in the energy mix for sources of long term, low life-cycle greenhouse gas emissions energy sources – even with further large scale growth in population and economic activity occurring. Geothermal power however was deemed less sustainable than existing, more prolific wind, hydro and solar PV resources.

Table 2

Table 2: Ranking of renewable resources by cleanliness and sustainability (Evans A, StrezovV, And Evans TJ.”Assessment of sustainability indicators for renewable energy technologies”)

How do power generation costs and project economics compare? The levelized costs of electricity (LCOE simply means the sum of costs over project lifetime, divided by sum of electrical energy  produced over a projects lifetime, and is a useful way to compare electricity from different sources) for geothermal energy was found to be close to wind and much less than solar photo voltaics for lower risk and well understood geothermal resources (Table 3). The main disadvantages with geothermal energy is the long payback time (the amount of time is takes to recover the total project costs) due to high initial project capital expenditure and longer construction periods compared to the other renewable energy resources. Economists and investors tend to get more nervous when it takes longer for them to see a return on their investment making it a less favorable expenditure unless a higher return is promised. So although the LOCE is low for geothermal projects, its seen as a riskier investment!

Table 3Table 3: Renewable operating cost comparison, payback and construction time  (Kenny,R. et al.”Towards real energy economics: energy policy driven by life cycle carbon emissions” 2010.)

What about operational factor comparisons? Capacity factor (percentage of time operationally producing power), thermal efficiencies (percentage of raw energy transformed converted to power), average emissions of CO2 (from standard plants), water consumption per kWh of electricity produced and finally the land ‘footprint’ of the projects development can be used for comparisons.

Compared to other renewable energy resources, geothermal energy generation technology has the highest capacity factor (Table 4). In fact, the high capacity factor is one of geothermal’s key advantages placing it in direct competition to nuclear and hydro-electric power stations. The capacity factor is a measure of the reliability of a power station to to deliver power over time. Geothermal power plants typically have high capacity factors (90-95%) which means they can deliver power daily and form whats called a ‘baseload’ power supply to homes and businesses. Nuclear power stations have a similar high capacity factor, but as we know from the Fukishima nuclear power station disaster in Japan (2011), they have less desirable operational safety and hazardous waste management issues associated with them. Similarly hydro-electric power stations like the massive Three Gorges Dam project on the Yangtze River in China can deliver reliable baseload power (as long as water levels remain high!), but like Nuclear they also have the surface potential for large scale environmental impacts. The Three Gorges Dam for example, the largest on the planet displaced 1.3 million people and caused significant ecological damage by flooding 660km upstream of the dam site. Solar PV and Wind suffer from unpredictable weather patterns incompatible with the constant, real time supply of electrical power into the electrical grid and cannot be considered as a baseload power supply. Solar, wind and wave typically have less than 30% capacity factors with  more predictable tidal power still having less than 60%.

Its noteworthy in the tables below that CO2 emissions for geothermal power plants are the highest of any of the renewable energy resource. These figures are based pessimistically on conventional power stations whilst the more modern geothermal power stations capture the CO2 and re-inject it back into the reservoirs for storage. An essential modification should future carbon taxes be introduced.

Geothermal also requires a large amount of water consumption for cooling compared to other renewable’s. In practice technologies exist to reduce markedly water usage by recycling via the re-injection of polluted and potable waters to maintain reservoir pressures in closed-loop recirculating cycles (see earlier explanation).

Geothermal plants have relatively smaller or comparable land footprints to other technologies since its major components exist underground. The wide range in footprint size is because every wellhead, however remote from the relatively small footprint of the base station needs accounting for.

Table 4

  Table 4 : Various renewable energy forms parameter comparisons  (Evans A, Strezov V, And Evans TJ. “Assessment of sustainability indicators for renewable energy technologies”)

Energy conversion efficiencies for different resources is shown in Table 5 below. Electrical energy generation from geothermal steam ranges between 10-20%, which is three times lower than fossil fuel conversion. This is due to the low temperature of the steam (<250C) and difference in chemical composition between pure steam and geothermal steam compositions which includes non-condensable gases such as CO2, H2S, CH4 etc…  that require extraction from power plant condensers.

Table 5

  Table 5 : Various renewable energy electrical generation efficiencies (Evans A, Strezov V, And Evans TJ. “Assessment of sustainability indicators for renewable energy technologies”)

What about associated social impacts for renewable’s and geothermal?. Table 6 below highlights the main social impact for geothermal projects. The biggest social impact being water re-injection induced seismic events. The injection of water back into tectonically unstable areas can cause induced seismicity – this occurred in a geothermal project in Basel, Switzerland in 2009. Up to Richter scale magnitude 3.2 events were recorded as a direct result of a hot dry rock Enhanced Geothermal Systems project which was consequently cancelled. Richter magnitudes less than 3.5 generally cannot be felt but are recordable.  Since most of the large scale geothermal projects are situated in or around active plate tectonic zones, there are difficulties in directly attributing seismic events back to the geothermal operations. None the less, operations close to urban populations will always attract attention should a seismic event occur as we know from the ongoing US gas shale fracking debates.

Water pollution from the geothermal plants water production cycles can also be an issue if this leaks since its usually high in Sulphur, CO2, salts and other minerals and gases. Hydrogen Sulphide which is deadly to humans in even low quantities does create the potential for pipework corrosion and leakage, but this already a well understood pipe design phenomena is long standing oil and gas operations. Since most geothermal power stations are enclosed circulatory systems, they inject produced water straight back underground into targeted reservoirs, thus reducing the risk of polluting nearby surface water sources or releasing dangerous gases intentionally into the environment. By targeting deep injection sites they also aim to avoid polluting residential and commercially used subsurface aquifers. All geothermal plants will have gas and water monitoring safety alarm systems to shut down the plant in the event of leakages.

All of the renewable’s technologies face government infrastructure grid improvements to be able to compete with more conventional electricity generation forms. Unlike fossil fuel burning power stations were the raw fuel is mobile and transportable to site, for renewable’s (apart from solar photo voltaic’s) the raw energy that they are harnessing is site specific – be it wind, wave or hydro electricity and are usually remote from urban high volume customer areas. This remoteness creates economic and practical land issues when needing to tie in its electricity production to national grid distribution networks. The issue of remote geothermal resource development is highly area specific for conventionals ,but potentially less so for future unconventional geothermal.

Table 5Table 6 : Various renewable energy social impacts (Evans A, Strezov V, And Evans TJ. “Assessment of sustainability indicators for renewable energy technologies”)

One last disadvantage of geothermal over other renewable’s is the difficulty in modularization of the power plants and the reliable definition of the formation temperatures at different depths and a resources spatial extent. Knowing the size of the potential resource available is critical in designing your power plant. If there is a lot of subsurface uncertainty, the project could be over designed (too much money spent) or under designed (not enough money spent), each being sub-optimal situations financially over the projects lifetime. Advanced techniques similar to the oil and gas industry are employed to properly define the size of the resource and reduce uncertainties.

Modularization is the power plants ability to be built up to maximum size via an expenditure phased number of smaller power units. For example, wind turbines and solar panel arrays, like Lego kits can be built and added together over time in standard commercially available units to reduce the up front project costs and create incoming revenue prior to the final units being installed. Geothermal plants all differ depending upon the location, resource size and depth reducing potential cost savings in equipment standardization and project modularization – since all projects are bespoke in design, they become more expensive.

So how can we speed up geothermal’s implementation in a sustainable manner?

Key to speeding up its implementation lies not only in new technologies to improve efficiencies and maximize energy conversion, but also in focusing in on why geothermal power plants are unattractive compared to other faster growing renewable energy technologies. These largely relate to initial construction and installation project costs.

New technologies have the ability to speed up and expand the growth of geothermal power by harnessing unconventional lower temperature aquifer resources or dry hot rock (hotter than expected rocks, usually above radioactive buried intrusions like granite) resources that lack sufficient heat flux or permeability’s to flow heat bearing waters. These types of ‘aestifers’ are uniformly distributed around the planet compared to those conventional resources focused around tectonic boundaries. Unconventional geothermal resources hold the key to extending geothermal’s growth to the wider world. Two examples of technology able to do this are;

Firstly – energy conversion; Thermoelectric generators (TEG). These generators are able to lower the temperature limit for converting heat to electricity to 30 degrees Celsius, hence increasing the resource harnessing range from a geothermal source. TEGs work by converting heat to electricity without the conventional mechanical intermediary stage of generation. The technology opens up further resources using Binary power units to convert low enthalpy heat energy  resources (i.e. < 150C).

Secondly – geothermal energy release; Enhanced Geothermal Systems (EGS – Figure 9). Conventional geothermal wells exploit naturally occurring heat from water flowing through natural rock permeability likes fissures and faults. Rock permeabilities can be enhanced by hydraulic stimulation. This involves using high pressure injected fluids downhole to fracture the wells rockface (e.g. buried granites).  Deeper (3-5km) and higher geothermal potential (150-200C) rocks can then be used as heat energy aestifers.

Figure 9

Figure 9: Enhanced geothermal system model (

In China for example, 2% (conservative estimate) of the EGS resource at depths between 3km to 10km have the equivalent energy of 5300 times the total amount of energy consumed by the country in a single year (Wang, G. et al., 2013). In the USA, 2% of EGS resource would be equivalent to 2800 times the 2005 energy consumption of the country (Tester, J. et al., 2006). It’s clear this technology has the future potential to be a game changer for geothermal energy take up on a wider global basis.

One of geothermal’s biggest competitive disadvantages is the cost of installing infrastructure and drilling wells to inject and produce high temperature waters. If old oil and gas wells were re-used, this would have a significant downward impact on initial project costs. Erdlac et al. (2007) reported that onshore in the USA there are 823,000 wells already drilled, if all were converted to hot water producers then electricity generation by energy would be equivalent to utilizing between 29-46 Billion barrels of oil! In China (2005) there were 164,076 oil and gas wells, 47% of which were already abandoned. Closer to home in the UK, Geothermal Engineering Limited (GEL) announced in 2015 the initiation of feasibility studies to look at delivering deep geothermal heat from abandoned oil and gas wells onshore.

Governments can play a key part in overcoming new technologies high initial cost disadvantages. Funded breakthrough initiatives such as the UK ‘Innovate Heat Network Fund’ help to develop geothermal technologies by reducing the financial outlay risk to private companies and investors. One such example at the smaller district heating scale in July 2015 was Geothermal Engineering Limited project in the UK  to develop a deep geothermal single well heating system at the Crewe campus of Manchester Metropolitan University. This pilot aims to demonstrate how a building cluster can be heated using a 2km well system and incorporates the government funding initiative payout. The UK government also offers financial take up incentives to the general public like the ‘Renewable Heat Incentive’ scheme  for heat (expanded upon later).

In countries with an established geothermal industry such as Iceland, research is supported by the government where geothermal resources are abundant and easily accessible. The government Ministry of Finance and Economic Affairs administer Icelandic Research (RANNIS) energy related funds; the Research Fund allocates 5M Euros for basic and applied research in all Energy related topics, whilst the ‘Technology Development Fund’ allocates 4.5 M Euros annually for technology research (2015). Iceland spends 3.1% of GDP on public R&D allocated as competitive grants or funds. Figure 10 highlights possible Iceland funding routes for the predominant geothermal energy industry in country.

Figure 10

Figure 10 : Icelandic example of government created geothermal energy support  (

As with other resources, the planets Geothermal resources should be sustainably and responsibly developed. The United Nations Commission for Sustainable Development created a framework to classify sustainability issues associated with geothermal energy developments. It doesn’t just focus on renewing and sustaining resources yields such as subsurface geothermal resource pressures and temperatures, it is designed to go much further. Inclusive themes include an energy schemes impact upon poverty, health, education, natural hazards, atmosphere, land, freshwater, biodiversity, economics and consumption/production patterns. All effort should be made to reduce a projects negative impacts and enhance positive impacts of geothermal energy by the operators and governments.

How can you make a difference?

It is estimated by that conventional renewable geothermal energy could provide up to 8.3% of the worlds global electricity demand, and that 39 countries could meet their entire electrical generation needs via geothermal alone!

Although not an accurate comparison, the IEA 2011 world energy use statistics reports a global ‘calculated’ total electricity consumption of 17838TWh for the year. A conventional geothermal potential of 8.3% is equivalent to  1480TWh a year. Using the  earlier USA 2014  residential energy consumption average of 10932kWh – this roughly equates to enough energy to power 135 million US equivalent homes for a year! The potential is huge for geothermal to be a clean and safe contributory renewable energy alternative to fossil fuels and nuclear electricity generation.

So who’s responsibility is it to achieve this? Is it us – the consumer, big business – the supplier, or governments – the policy makers? In reality – its all three.

The UK based ‘Carbon Trusts’ mission statement is the acceleration of a carbon free economy. In its “Titans or Titanics?” report they conclude that industry business leaders respond to consumers wants primarily. At present, although their own awareness and conscience agrees with the need for greener business, the consumer demand does not at present justify a greener policy shift beyond corporate social responsibility programs. As an energy consumer, we all therefore have the power to shape future global energy usage by choosing to purchase greener energy, greener products and utilize greener services.

Similarly governments can be democratic  institutions that respond to public opinion. In extreme circumstances or to correct market disparities when it’s in the national interest, the government will act on peoples behalf. The Japanese government shutting down all of the nations Nuclear power stations pending safety enquiries, post the Fukushima disaster in 2011 is a good example. Governments in practice do play a big part in steering energy policy which is itself innately political – for example the nation’s energy security or energy supply mix. The German government over the past decade have invested massively in their renewable’s industry to wean themselves off their dependence on publicly mistrusted nuclear power, unclean lignite coal burning power stations and volatile imported Russian gas supplies passing across unstable intermediary countries.

So now you know how important you are, what tangible steps can you take yourself to promote geothermal energy sources?

To a certain degree, we are bound by our geographical location with respect to geothermal energy selection. Living in California would allow consumer access to installed geothermal resources, in contrast living in Nepal with its thick crustal surface layering would make geothermal very difficult to access compared to alternate and more convenient renewable’s energy sources like wind and solar. Practically however, there are large areas of the planet away from tectonic boundaries that low enthalpy geothermal resources can provide energy.

In the UK, consumers have the choice of installing a ground source heat pump in their home. The Energy Saving Trust in the UK estimate a typical system costs between £11000-£15000 to install. As well as replacing older inefficient heat systems and reducing your fuel costs, you would also cut down your own climate warming CO2 emissions (see Table 7 below).

Table 6

Table 6: Ground couple heat pump system cost and CO2 saving comparison (

If you couple geothermal energy harnessing with other personal domestic or commercial renewable energy sources such as solar panels or wind turbines, you could take advantage of the UK governments renewable cashback schemes. The ‘Feed in tariff’ scheme for example allows you to generate your own electricity, and get paid for feeding surplus electricity back into the grid. The ‘Renewable heat incentives’ scheme pays you equivalent heat saving amounts of money for installing solar thermal panels, heat pumps or biomass boilers. Each scheme accelerates the payback of installing the technology, and your heating and electricity bills drop dramatically since you self generate both, as well as protecting you against future energy price volatility  (Figure 11).  You as a business leader or school teacher could identify the cost saving green idea and grow consumer demand for medium scale systems such as Ground Coupled Heat-Pump Systems. Make yourself aware of such support systems in your own country.


Figure 11: Cost example for 4 bedroom house installing 2.5kW solar PV, a solar thermal unit and ground sourced heat pump. This will generate 40% of annual electricity and all of the properties heat for the year (Ownenergy simple guide to renewable energy tariffs)

You can also chose green energy suppliers like ‘Good Energy’ in the UK, ‘Austin Energy’ or ‘Portland General Electric’ in the USA for example. These utilities supply electricity into the grid purely from renewable sources and focus on small and large scale independent energy generators, as well as their own renewable energy generation projects to grow supply and sell onto conscientious electrical consumers. The larger their network becomes, the greater competition they will offer to existing fossil fuel generators, thus forcing them to either diversify into renewable’s or cut production costs by retiring old, inefficient fossil fuel generation plants.

Perhaps you could become a Geothermal Engineering expert to design and develop the next generation of geothermal energy distribution systems?! Higher education establishments such as Stanford in California, Clausthal University of Technology in Germany and Chalmers University of Technology offer Masters programs that build on your science Bachelor’s degree to specialize in becoming a Geothermal extraction expert.

There are a lot individuals can do to promote geothermal renewable energy as well as governments, industry and universities.

I hope this article has equipped you with the knowledge to become a supporter of Geothermal Energy and especially make you aware that geothermal energy is good for more than Spa washes and cooking.

References/Further Reading

Internet References

Literature Journal References

  1. Evan, A. Strezov, V. Evans,T./”Assessment of sustainability indicators for renewable energy technologies”. Renewable and Sustainable Energy Review 13 (2009) p1082-1088.
  2. Jacobson, M. Delucchi, MA. /”Providing all global energy with wind, water and solar power, Part I: Technologies, energy resources, quantities and areas of infrastructure and materials”. Energy Policy (2011); 39(3):p1154–69.
  3. Kenny, R. et al. /”Towards real energy economics: energy policy driven by life cycle carbon emissions” Energy Policy 38, pp. 1969–1978, 2010.
  4. Lietal, K. et al. /”Comparison of geothermal with solar and wind power generation systems”. Renewable and Sustainable Energy Reviews 42 (2015):p1464–1474
  5. Michaelides, E. /”Future directions and cycles for electricity production from geothermal resources”. Energy Conversion and Management 107 (2015) p:3-9
  6. Shorthall, R. Davidsdottir, B. Axelsson, G. /” Geothermal energy for sustainable development: a review of sustainability impacts and assessment frameworks”. : Renewable and Sustainable Energy Reviews 44(2015):p391-406.
  7. Younger, P. /”Geothermal Energy: Delivering on the global potential “: Energies 2015, 8, p11737-11754.

Agency report References

  1. The Carbon Trust, (2015) Titans or Titanics? Understanding the business response to climate change and resource scarcity
  2. IEA World Key Energy Statistics 2014
  3. IEA World Key Energy Statistics 2012
  4. Ownergys Simple Guide to the Renewable Energy Tariff