GLOBAL DEPLOYMENT PROJECTIONS OF SUSTAINABLE & RENEWABLE
GEOTHERMAL ENERGY - THE GOOD, THE BAD AND THE OUTRAGEOUS – FROMAN IEA-GIA PERSPECTIVE
Chris Bromley1
1

GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealandc.bromley@gns.cri.nz

Keywords:
deployment
renewable, IEA-GIA

projections,sustainable,

ABSTRACT
Geothermal energy may be ubiquitous, but being ‘out-ofsight’ (subsurface) can also mean ‘out-of-mind’ for many
people. This paper explores the legacy of past deployment
projections, and how to increase confidence in future
projections and awareness of global geothermal resource
potential, while remaining cognisant of its technical,
economic and social deployment challenges, and theadaptive strategies necessary to sustain utilisation in thelong term.
1. INTRODUCTION
In the future, geothermal could become the cheapest andsafest source of non-polluting, base-load heat and power(without subsidies) for as much as 15% of the global
population (those living near active volcanic zones), andcould make a significant contribution (with subsidies) to therenewable energy mix for the rest.
For example,
geothermal could become a sizable base-load component ofmany isolated electricity grids on poorly-developed
volcanic islands. But away from these tectonic areas,
geothermal could also play a larger role throughdeployment of more-efficient ground-source heat-pumps
and advanced technologies such as enhanced geothermal
systems (EGS). Other development ideas might include
tapping super-critical temperature reservoirs, hot brines indeep sedimentary basins, or even heat sources alongoceanic spreading-ridges where near enough to the coast.
Truly innovative ideas are needed to popularize geothermal
technology and to accelerate our existing, somewhat
sluggish, global geothermal growth rate. More could belearnt from countries where recent geothermal growth rates
have exceeded 20% per year. Knowledge and resourcesfrom the shale-gas drilling industry could be applied to
EGS to reduce costs and accelerate deployment. Moreinnovative ideas could surface in the area of geothermal
direct use, for heating and cooling of building spaces,
energy-intensive industrial processes, agricultural foodprocessing, or better technologies for efficient bulk heattransfer.
In preparing resource assessment protocols and undertaking
deployment projections we should also be addressing theconcepts of sustainable development and renewability inorder to attain an optimum long-term geothermal utilisation
rate. The focus should be on establishing what is technicallyfeasible as well as realistic and good for the environment.

Also, the legacy of publishing unattainable deployment
targets can end up as a source of public scepticism and aconsequent reluctance to invest. So, in order to truly
accelerate global geothermal growth to mitigate climatechange effects, what are needed are more forward-thinking,perhaps even somewhat outrageous ideas. These should be
more effective than relying on optimistic deployment
projections to gain attention and stimulate enthusiasm.
Commentators such as Mearns (2015) have posed thequestion : why does ‘geothermal energy’, as a replacement
for significant amounts of carbon-emitting, fossil-basedenergy sources, remain a ‘minor player’ in the global fieldof renewable energy politics, despite being a ‘major player’in some economies such as New Zealand and Iceland ? One
reason might be the economic disadvantages of long project
lead times (delays between conceptualizing a good project
and finally achieving it). Another reason might be riskaverseness, through lack of knowledge, by potential project
investors. An investigation of such barriers could be
fruitful.
Mearns (2015) succinctly summarised the virtues ofgeothermal electricity relative to alternative sources in a
July 2015 article:“Geothermal electricity is about as close to a perfect sourceof renewable energy as one can get. It’s (almost) carbonfree, doesn’t emit large quantities of noxious gases orgenerate radioactive waste, doesn’t require the clear-cuttingof virgin forests, doesn’t take up lots of room, doesn’t
blight the skyline (at least, not by much), doesn’t decapitate
or incinerate birds, is replenished by the natural heat of theearth, delivers base-load power at capacity factors usuallyaround 90%, and can even, if necessary, be cycled to follow
load. It’s also one of the lowest cost generation sources
available. No other renewable energy source can match thisimpressive list of virtues or even come close to it.”Despite these ‘virtues’, the barrier that Mearns saw as themain reason for sluggish growth rate at present was that thelocation of favourable geothermal sites is often far frommajor centres of energy consumption. Large areas of theworld, that are heavily populated, simply don’t have directaccess to the high temperature resources needed to produce
electricity at economically favourable prices.
In a panel discussion on Climate Change and Society; The
Age of Resilience, held in Auckland on 26th August 2015,
participants saw the issue of socio-economic drivers forrenewable energy differently. Their theme was a plea to‘think holistically’ through innovation and was expressed asfollows:
Proceedings 37th New Zealand Geothermal Workshop
18 – 20 November 2015
Taupo, New Zealand“Economic production systems and consumption patterns
are both the problem and the solution to climate change. A
resilient economy is not just about reducing our ecologicalfootprint through producing and consuming less –economics can be used to drive change:aligning
incentives, sparking innovation and encouraging
transformation throughout the production/consumption
chain. Humankind has irrevocably altered the planet’s
natural systems – can we use that same human power tounleash true “Green Growth” and achieve a high andsustainable level of human well-being?”

studies (Fridleifsson, 2000, Zheng et al., 2015, Bertani,
2015, and GEA, 2015) are plotted in Figure 1. The legend
gives the base year that the projections started from. Theyshow a wide variation in trends. Relative to the realized
installed capacities (for example, 12.63 GWe at the start of2015, Bertani, 2015) the previous predictions of both
Fridleifsson (2000) and Goldstein et al. (2011) havesubsequently proven to be too optimistic. However, theprediction of Zheng et al. (2015), based on data up to 2012,
proved to be too pessimistic.

This message was echoed at a recent world energy summit
for students in Bali (Indonesia) http://www.ises2015.com/
where innovative ideas for helping replace fossil fuels withrenewable energy sources were canvassed and some novel
suggestions involving geothermal in hybrid combinations
were discussed.
It is timely and appropriate, therefore, to review the historyof geothermal deployment projections and perhaps to draw
conclusions on strategies to improve awareness and to help
advocate for sensible growth through innovation. In thefollowing sections we explore this legacy and suggest betterways to increase awareness of global geothermal resource
potential, whilst remaining cognisant of its technical,
economic and social deployment challenges.
2. IPCC DEPLOYMENT PROJECTIONSThe energy capacity from the global geothermal resource(that portion of the earth’s crustal heat that is potentiallyaccessible and extractable) is estimated to be about 5000
EJ/yr (Rybach, 2014). This is about three times that of solarand eight times that of wind. A smaller portion of thisresource is considered to consist of ‘reserves’ that could besustainably and economically developed. This has been
estimated to be in the range of 300 to 500 EJ/yr (UNDP,
2000). Such a rate is similar to the continuous rate of heatflux through the earth’s surface, and would therefore
theoretically be indefinitely sustainable, while meeting thecurrent total annual energy needs of all mankind.

Figure 1: Predictions of global geothermal power
capacity. Legend shows author and prediction date.
Figure 2 shows a similar plot for projected direct use
installed capacity growth in GW(thermal). In this case, theearliest prediction (Fridleifsson, 2000) was relatively
conservative and significantly under-estimated the actual
realized values. In retrospect, the main difference can be
attributed to the unexpectedly high growth rate in groundsource heat pump (GSHP) installations that occurred inseveral countries over the past 15 years.

Geothermal deployment projections out to 2100 were
published by Goldstein et al., (2011a, 2011b) and Bromley
et al. (2010) in conjunction with preparation and review ofa geothermal chapter for the Intergovernmental Panel on
Climate Change (IPCC), Special Report on Renewable
Energy (SRREN).
Technically-recoverable and accessible global stored-heat
reserves were assessed using a log-normal probability
approach in Goldstein et al (2011a). A conservative
estimate of 0.7 * 106 EJ (90% probability, and 1.34% heatrecovery factor), applies to stored heat within 5 km depth
beneath the continents. At an extraction rate of 567 EJ /yr(total world energy consumption in 2012), this would last
about 1200 years, even without any consideration ofcontinuous heat recharge from below 5 km depth (which
would theoretically be at or greater than the rate of natural
surface heat loss from the continents (12.5 TW or 400
EJ/yr). Therefore, the issue for geothermal in terms of
future capacity is not so much the global resource size, butrather deployment constraints from economics andindividual project feasibility.
Comparisons between deployment projections of installedcapacity (GWe) for geothermal power from the IPCC report(Goldstein et al, 2011a and 2011b) and those from otherFigure 2: Predictions of global geothermal direct-use
heat capacity. Legend shows author and prediction date.

3. IGA DEPLOYMENT PROJECTIONS
Bertani (2015) produced an update for the start of 2015 on
global geothermal installed power capacity and annual
generation for the World Geothermal Congress. These weresummarized from country reports prepared byrepresentative members of the International Geothermal
Association (IGA). The average growth rate of installed
electrical capacity over 2010-2015 was 3.2% per annum.
His forecast growth for 2015-2020 is 12.6-21.4 GWe, or an
average of 14% per annum growth rate, implying that a
Proceedings 37th New Zealand Geothermal Workshop
18 – 20 November 2015
Taupo, New Zealandsignificant acceleration in deployment is anticipated.
However, as noted by Bertani (2015), the 2020 forecast is atbest ‘hopeful’. It follows an exponential growth curve andassumes that all 8 GWe of projects that are ‘on paper’
transform into reality. This will be a challenge.
Bertani (2015) also provided a projected global target out tothe year 2050 of 70 GWe from conventional hydrothermal
resources plus 70 GWe from EGS and non-conventional
geothermal resources. The combined target of 140 GWe is
similar to the IPCC 2050 target value from Goldstein et al.
(2011a) of 150 GWe. If achieved, this would provide up to
8.3% of total world electricity, serving 17% of the world
population. A total of 40 countries could potentially be
relying on geothermal for the bulk of their electricity needs.
Such numbers should get the attention of renewable energy
analysts and policy makers, but only if they are found to bebelievable.
Lund & Boyd (2015) updated global direct utilization data
for the World Geothermal Congress. By the start of 2015
installed thermal power amounted to 71 GW(th) producing
165 GWh(th) per annum, and growing at about 7%
compounded annually since 2010. Approximately 55% of
this energy use was for heating and cooling using GSHP
(the fastest growing category), 20% for bathing, 15% forspace heating (including district heating), 4.5% forgreenhouses, 2% for aquaculture and 1.8% for industrial
process heat. If the growth rate continues at a similar pacethen another 46% increase can be estimated for the next 5
years (to 2020).
Figure 3 illustrates a range of predictions of global
geothermal power generation and direct heat utilization interms of TWh/yr. Arguably this is a more reliable indicatorof actual trends in deployment than the installed capacity
figures because it takes into account changes in capacity
factor or energy utilization factor. The values for each five
yearly measurement refer to the accumulated generation orheat utilization over the previous year. (Heat value for Lundin 2020 uses a linear projection of the current growth rate.)

Figure 3: Predictions of global geothermal power anddirect-use heat generation (TWh/yr). Legend shows
author and prediction date.
In terms of power generation, both the Fridleifsson (2000)
and Goldstein (2011) predictions were optimistic comparedto the actual 2015 value (from Bertani, 2015) of 73.6
TWh/yr. In terms of heat utilization, the actual 2015 value(from Lund & Boyd, 2015) of 165 TWh/yr lies midway
between the predictions of Fridleifsson and Goldstein.

4. IEA-GIA TREND REPORTS
Weber et al. (2015a) and Mongillo & Bromley (2015)
describe the organisation and preparation of annual trend
reports under a working annex (Annex X) of the IEAGeothermal Implementing Agreement (IEA-GIA). The
purpose of these is to analyse and disseminate annual dataand commentary that indicate deployment trends in thegeothermal industry, particularly within the 15 countries
that are represented by the IEA-GIA through government –sanctioned membership or through industry associations.
The intention is to provide a more regular update on such
trends than is currently accomplished through the morecomprehensive 5 yearly updates undertaken by the IGA for
World Geothermal Congresses. Over time it is planned toseamlessly merge the IEA-GIA and IGA efforts in thisregard. So far two IEA-GIA trend reports have been
published (see Weber et al., 2015b, and http://ieagia.org/category/publications/ for the latest).
Figure 4 shows a trend plot in geothermal power generation
since 1995 using data from Weber et al. (2015b),
supplemented by data from Bertani (2015), other World
Geothermal Congress summary papers, and the UnitedStates Energy Information Administration (EIA) online data
depository. From this it can be seen that IEA-GIA
membership currently represents approximately 55% of the
global geothermal electricity generation, a decrease from2000 when it was 67%. The USA (an IEA-GIA member)currently produces 23% of the total, but this is a decrease
from 1995 when it was 37%. The trends in terms of growth
rates tell a compelling story. A reasonable fit is achieved
using a linear gradient to all three sets of data between 1995
and 2015. There is no evidence yet of a significant switch toexponential growth rates. Growth rates in USA geothermal
generation have been relatively flat at 1% or 0.12 [TWh/yr]
per annum, compared to the 2% or 0.67 [TWh/yr] perannum across all IEA-GIA member countries and 5% or
1.88 [TWh/yr] per annum across the world. Clearly
deployment growth has been occurring at a faster pace
within countries that are not yet represented within themembership of the IEA-GIA.

Figure 4: Trends since 1995 in geothermal power
generation comparing global, IEA-GIA member
countries (15) and USA (EIA) data (modified
from Weber et al., 2015b and Bertani, 2015)
5. OTHER DEPLOYMENT PROJECTIONS
Based on observed growth rates of 9%/yr between 1975 and1995, a World Energy Assessment by the UNDP (2000)
predicted geothermal generation of 134 TWh(e) from 24
Proceedings 37th New Zealand Geothermal Workshop
18 – 20 November 2015
Taupo, New ZealandGWe installed by 2010 and 318 TWh(e) from 58 GWe by
2020. Direct use was predicted (on the basis of 6%
observed annual growth rates) to increase to 81 TWh(th)from 22 GW(th) in 2010 and 146 TWh(th) from 40 GW(th)by 2020. In retrospect, the 2010 predictions for power have
proven to be about twice what was actually achieved, while
for direct use the 2010 predictions were about half what
was actually achieved.
An observer of global geothermal deployment trends,
Romitti (2015), prepared an updated summary of theinternational geothermal market for the US Geothermal
Energy Association (GEA) in May 2015. This used anannual report (GEA, February 2015), and a list ofinternational projects compiled by GEA. Global growth
rates were assessed to have been about 5% per annum overthe previous 3 years.
Rybach (2014) has also observed that global annual
geothermal growth rates are currently about 5%. This is far
less than those of other renewable energies such as windand solar (25% to 30%). His observation was that thesolution could eventually be in tapping into ubiquitous‘petratherm’ (deep hot rock) resources. Faster (exponential)
growth should then eventuate. Enhanced Geothermal
Systems (EGS) technology for creating and maintaining
deep heat exchangers must first mature.
In the past, observers of global geothermal deployment
have sometimes relied on individual country projections forforecasts of global installed capacity. This can prove
perilously inaccurate, especially if the projections are
optimistic targets. With the benefits of hindsight, an
example of this problem can be tracked from the publishedpredictions of capacity growth over time from Indonesia(Radja, 1983 to 1997) and five-yearly World Geothermal
Congress country update reports (2000-2015). For theperiod 1985 to 2015, the 5-yearly predictions turned out, on
average, to be about twice what actually eventuated interms of the installed capacity. Also, published estimates ofpotential resource capacity across Indonesia have tripledover this period (from 10 GWe to 28 GWe). Approximately
50% of these estimates were considered of sufficientcertainty to be treated as “reserves”. The current prediction
targets for the next five year period (to 2020) are again
quite ambitious at about four times the 2015 installedcapacity. Based on previous experience with such targets,
some care is advisable in applying them to calculate
realistic global projections of future deployed capacity.
At the other, more pessimistic end of the range of publishedglobal geothermal deployment predictions, Zheng et al.
(2015) argued that geothermal power generation is a maturetechnology which reached a peak in terms of growth rate in2008. Using a statistical approach on data from 2000 to
2012, they predicted that global installed capacity would‘saturate’ and reach a maximum of only 11.5 GWe, withnear-zero growth from 2015 onwards. Clearly, withobserved growth rates of 5% per annum, reaching about
12.6 GWe in early 2015, this prediction has already provento be inaccurate (Figure 1).
6. SUSTAINABILITY AND RENEWABILITY
Axelsson et al. (2015) and Bromley & Axelsson (2015),
and references therein, provide succinct accounts of theconcepts and complex issues surrounding sustainability andrenewability of geothermal resources.

In summary, if properly managed, using flexible andadaptive injection and production strategies, supported bygood-practice monitoring and reservoir model simulationsof alternative scenarios, geothermal reservoir systems are
sustainable for very long term operation (that is, for morethan 100 years). This exceeds the foreseeable design-life of
surface plant and well casings. Their replacement is likely
to be needed long before the resource needs to besuspended because of declining temperature and pressure.
Upon production suspension, the reservoir would be rested
in order to allow for energy recovery through natural andinduced fluid and heat recharge. A long-term ‘heat-grazing’strategy could allow for sequential or rotational operation ofseveral adjacent or underlying geothermal reservoirs.
Through periodic cycles of discharge and recharge, thiswould provide for a continuous supply of renewableenergy.
Consequently, such strategies need to be taken into accountwhen undertaking projections of global geothermal
deployment and net energy extraction over long periods oftime.

7. CONCLUSIONS
Based on this brief review of past predictions of geothermal
deployment growth relative to actual achievement, it seems
that such projections have generally been too optimistic interms of power generation, overestimating growth rates by,on average, a factor of two. Using this observation tomodify the predictions of Bertani (2015), the installed
global geothermal power capacity by 2020 is more likely tobe about 17 GW(e) rather than 21 GW, representing moreconservative average growth rates of 7%/yr. This coincides
with the GEA (2015) prediction based on the sum capacityof all announced projects. For direct-use the average of past
predictions appears reasonable, but the big unknown isfuture uptake rates for GSHP technology.
To answer the question implied by the theme of thisworkshop “The Next 10,000 MW”, in a realistic manner, itis therefore likely to be 10 to 15 years before this global
milestone can be achieved. The locations where greaterthan average growth rates are likely to occur will be incountries where the economics are more favourable, accessis easiest, policies are favourable and grid connections toload centres are feasible. In the 0-5 year time-frame thisprobably includes East Africa, Turkey, Central America
and South-East Asia, whereas Japan and North and SouthAmerica may provide higher growth rates in the 5-15 year
time-frame. Deployment growth rates in island nations suchas Iceland, Hawaii and New Zealand may be constrained bydemand growth but this could change dramatically if
HVDC cable connections to United Kingdom, Oahu andAustralia, respectively, are constructed.
Environmental and social issues will also play a part inproject deployment decisions. Global warming and threatsof climate change effects may be motivators at a personallevel for involvement in geothermal projects, but they needto translate into real economic benefits (e.g. through carbon
trading, feed-in tariffs, subsidies or tax benefits) before they
will have a significant impact on private investment anddeployment growth decisions.
In summary, optimistic geothermal resource potential
assessments and deployment projections are still, in a
Proceedings 37th New Zealand Geothermal Workshop
18 – 20 November 2015
Taupo, New Zealandmanner of speaking, lurking somewhere beneath everyone’s
backyard. What is needed are more novel, even‘outrageous’, ideas to help break down the barriers to future
deployment growth, and bring the bigger picture global
issues into a better perspective. Innovation, researchcollaboration, and information dissemination, seem to be
the key elements. These already form the backbone of theobjectives of the Annex working groups within the IEAGIA (www.iea-gia.org).
Ideas that we consider most worthy of investigation
include: a) facilitating widespread deployment of EGS
through reductions in costs of deep drilling and fracture
stimulation, b) utilisation of super-critical resources deep
beneath hydrothermal systems, c) tapping into hot brines indeep sedimentary basins, and d) experimental development
of off-shore geothermal resources.
ACKNOWLEDGEMENTS
The author gratefully acknowledges ideas and concepts
from discussions with IEA-GIA colleagues, Mike Mongillo,
Brian Carey, Gudni Axelsson, Ruggero Bertani and Barry
Goldstein in particular, and research time provided under
GNS Science’s Geothermal Research programme (GRN)
funded by the Government of New Zealand.
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Proceedings 37th New Zealand Geothermal Workshop
18 – 20 November 2015
Taupo, New Zealand