Front. Energy DOI 10.1007/s11708-017-0455-9
RESEARCH ARTICLE
Li JIANG, Liandong ZHU, Erkki HILTUNEN
Large-scale geo-energy development: Sustainability impacts
© Higher Education Press and Springer-Verlag Berlin Heidelberg 2017
Abstract Geothermal energy is a renewable and alternative energy with the potential to replace fossil fuels and help mitigate global warming. However, the development of geothermal energy has environmental, economic and social-cultural consequences, which needs to be predicted beforehand and then mitigated. To guarantee a sustainable development, it is, therefore, essential to consider the relative potential impacts. From a sustainability point of view, in the present study, a comprehensive analysis of consequences of geothermal energy development is conducted, including environmental, economic and societal & cultural dimensions. The geothermal energy industry will prosper only if sustainable aspects can be integrally considered. Keywords geothermal energy, sustainability, impact, development
1
Introduction
The thermal energy used for heating or cooling accounts for approximately 47% of the total global energy demand [1]. The heating and cooling systems are usually powered by electricity which is generated by coal or gas. Renewable energy sources only contribute a small proportion to the global heat demand, where the share of geothermal and solar heat is only 0.5% [2]. Among all energy sources, geothermal energy, also called geo-energy, presents one of the most environmentally friendly energies mainly due to its lowest emission of greenhouse gases, and also a costeffective energy source with the potential to replace conventional fossils for heating [3]. Received March 15, 2016; accepted June 23, 2016
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Li JIANG ( ) Huazhong Agricultural University, Wuhan 430070, China; Vaasa Energy Institute, FI-65101 Vaasa, Finland E-mail:
[email protected] Liandong ZHU, Erkki HILTUNEN Vaasa Energy Institute, FI-65101 Vaasa, Finland
Geothermal energy, which is thermal energy generated and stored in the Earth, is a clean and abundant energy source. Represented as a directly usable type of energy [4], it originates from radioactive decay of minerals including uranium, thorium and potassium [5]. The difference in temperature between the core of the Earth and its surface can form the geothermal gradient, continuously generating thermal energy in the form of heat from the core to the surface. There are two most compelling advantages to use geothermal energy. First, low or zero carbon emissions exist in the geothermal energy production process, making it one of the cleanest energy sources. It is suggested that only 13 to 380g of CO2-equivalent per kWh electricity will be emitted from a geothermal energy plant, while 1042, 906 and 453g of CO2-equivalent per kWh electricity will be emitted from coal-, oil- and natural-gas-based power plants [6]. Second, geothermal energy can provide power for 24 hours in a continuous manner. This is advantageous, compared to solar energy which is diminished with cloud coverage and can only be produced during sunny daytime. Likewise, wind energy relies on wind speed which is changeable constantly. Geothermal resources including potential reserves for future development range from shallow ground to the hot spring and rock below the Earth’s surface [5]. Usually, geothermal energy is used directly for its heat or to generate electricity. In Iceland, almost 99% houses and buildings are heated by natural hot water [6]. Other applications of geothermal energy are in fermentation, heating in industrial process, industrial and crop drying, refrigeration, ice melting, desalination and distillation. Currently, geothermal energy contributes only a small proportion to world primary energy consumption. Countries such as the US, the Philippines, Indonesia, Mexico, Italy, Iceland, New Zealand and Japan are using substantial amounts of geothermal energy (Table 1). For example, electricity produced from geo-energy in Philippines and Iceland accounts for 27% and 30%, respectively [7]. As of August 2013, 11765 Megawatts of gross geothermal power are operating globally [7]. In the US, the installed geothermal capacity increased from 3086 MW in 2010 to 3389 MW in 2013. In the next three years, the US plans to
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Table 1 Established geothermal market installed capacity in Megawatts Country
Capacity in 2007/MW [8]
Capacity in 2010/MW [9]
Capacity in 2013/MW [7]
US
2687
3086
3389
Philippines
1970
1904
1884
Indonesia
992
1197
1333
Mexico
953
958
980
Italy
811
843
901
New Zealand
472
628
895
Iceland
421
575
664
Japan
535
536
537
develop additional 2511–2606 MW geothermal power plants for electricity generation [6].
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Objective and dimension
In the last few years, geothermal energy has received dramatic attention in its development, capabilities and application. Geothermal energy development has been witnessing a rapid growth globally. An installed capacity of 18500 MW by the year 2015 has been estimated, representing an increase of about 73% from 2010 [10]. Still, there is 11766 MW planned capacity additions of geothermal power under construction or in the early stages of development. Besides, developers are ambitiously interested in building 27 GW of geothermal power worldwide [7]. Countries such as France, Chile, Tanzania, Uganda and Rwanda are establishing geothermal projects and will operate their first geothermal power plants in the coming years. Based on the above introduction, it can be concluded that geothermal energy development is booming. Many studies have been conducted on the economic feasibility and the thermodynamic efficiency of geothermal energy applications using different methods such modeling. However, the sustainability impacts related to large-scale geothermal energy development is too often overlooked, or too easily taken for granted, which is not beneficial for the development of geothermal sector in the long run. Since the identification of potential sustainability impacts associated with geothermal energy development on a large scale is the first step in supporting a sustainable industry, the potential sustainability impacts must be predicted beforehand and then minimized or even eliminated to some degree. From a sustainability perspective, this paper explores the potential risks related to geothermal energy development, including environmental, economic and social-cultural dimensions (Fig. 1). This is an exploratory study with systematic and explicit investigation, where particular impact focuses on environment, economy and social-culture are discussed in detail and some of the key issues are highlighted as well.
Fig. 1 A framework for sustainability impact analysis of largescale geothermal energy development
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Potential sustainability impacts
In this part, the detailed potential sustainability impacts related to geothermal energy development will be discussed, and the dimensions include environmental, economic, and social and cultural impacts. 3.1
Environmental impacts
The environmental impacts related to geothermal energy development include the concerns on land, water, air and biodiversity. 3.1.1
Land
Geothermal plant establishment requires land use ranging from 160 to 290 m2/(GWh$a) excluding wells, and this number can reach up to 900 m2/(GWh$a) if wells are included [11]. The development of geo-energy involves a lot of drilling activities [12]. Boreholes need to be built for measurement of the geothermal gradient in the exploring
Li JIANG et al. Large-scale geo-energy development
phase, and geothermal wells are required to be produced as well. Inevitably, a lot of earth or rocks need to be removed, which might harm the physical and chemical composition of earth, causing soil erosion and even some geological hazards. Due to construction activities, soil can be compacted, thus reducing soil aeration, permeability and water-holding capacity. Soil compaction can also affect the feasibility of future vegetation [13]. Especially in the areas where there are steep slopes and high precipitation, soil erosion and geothermal hazards such as landslides and ground subsidence might potentially happen. In addition, it may trigger or increase the frequency of seismic events in certain areas. However, these are primarily micro-seismic events that can only be detected by means of sensitive instruments. Hence, such risks should be fully evaluated before development occurs in these areas [14]. The geothermal development might also cause some direct or indirect land use changes. Geothermal plants can be located on lands with multiple uses, and thus aquaculture operations, agricultural activities, and hunting can be regularly mingled with the power plants at the same site. Still, the construction of additional roads, pipeline system and transmission line also give rise to some potential land use changes [15]. Geothermal projects may also be established in forestland, which might result in some deforestation or impact the surrounding ecosystems. Developers should be aware of their responsibility for the protection of the forestland around geothermal power sites. 3.1.2
Water
Drilling itself has potential risks in groundwater if the location of boreholes or wells is not properly chosen. Once the groundwater layer is damaged, it will trigger several impacts on water, such as water quality, water availability, water resources usage and the previous construction of the groundwater layer. In addition, the original hydrologic cycles will be interrupted to some degree, reducing the biological activity in the soil below [16]. Water is a critical element in geothermal resource development. There are two systems for geo-energy operation: closed-loop circulation geothermal systems and open circulation systems. As to the closed-loop circulation geothermal systems, impacts such as arsenic accumulation and groundwater contamination or degradation can be reduced. In contrast, groundwater can be degraded in open circulation systems. The intensive pumping of deep thermal groundwater will cause the deep fractures to lose their artesian pressure and the upper shallow fractures will be encroached by shallow, cold waters. In other words, this will cause the introduction of shallow groundwater into the deeper fractures, degrading water quality by the downward flow of the shallow, cold water [17]. This case has happened in the Onyang Spa area in Republic of Korea, and in Nevada and Memphis region in the US [17].
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In addition, hot water might be released into the environment during construction and/or operation of geothermal energy projects. The release of acidic or alkaline effluents might contain chlorides and sulfides or toxic chemicals, such as aluminum (Al), boron (B), arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg), and sometimes fluoride (F) [18], affecting the water quality in the area. There are many known cases that geothermal power plants have caused water pollution with heavy metals. For example, the amount of arsenic in the Waikato River has been more than doubled as of the installation of the Wairakei power plant in the late 1950s [13]. 3.1.3
Air
During the construction of geothermal power plants, the drilling of geothermal wells and boreholes will release a lot of dust. The particulate matters can flow far away from the construction site, polluting the nearby air. Air pollution may also occur especially during the operation of geothermal power plants. Gaseous emissions often result from the discharge of non-condensable gases carried in the source stream to the power plants. In many cases, however, they are relatively small compared to fugitive emissions [19]. Geothermal fluids contain a variety of gases, such as carbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4), trace mercury (Hg), nitrogen (N2), ammonia (NH3), radon (Rn), boron (B), and etc., ranging from 13 to 380 g/kWh, in contrast to 453 g/kWh for natural gas, 906 g/kWh for oil, and 1042 g/kWh for coal [20]. The amounts vary with the geological conditions of different fields, and even during the lifetime of the power plants. Carbon dioxide is usually the major constituent of the gas present in geothermal fluids, and methane, a minor constituent. Both should be paid attention to due to the fact that they are the main sources of greenhouse gases. However, less CO2 and NOx are produced from geothermal energy than those from conventional fossil fuels. IPCC suggests that geothermal power plants witness less than 50 g/kWh for CO2-equivalent emissions [11]. Hydrogen sulfide generated from the geothermal fluids probably causes the greatest concern because of its unpleasant smell and toxicity in moderate concentrations. When dissolved in water aerosols, H2S may react with oxygen and be oxidized to sulfur-bearing compounds such as SO2. Furthermore, geothermal energy plant operation will emit heat in the form of steam, which can impact local cloud formation and affect local weather conditions or patterns [21]. 3.1.4
Biodiversity
A verbal evaluation of potential biodiversity impacts of geothermal energy have been observed, as generally
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applicable indicators can seldom be quantified with the scarce information available. The visual intrusion from surface installation often disturbs or destroys the habitats of the wildlife. During the drilling and site construction, some plants and plant coverage have to be removed because of the drilling pads installation, buildings and pipelines used for operation, etc. This may block animals’ activity scope, destroy their habitats, such as breeding, feeding and resting sites, and lead to increased mitigation and surveillance in the surrounding areas. Overall, this is harmful to wildlife, vegetation, and scenic vista, especially their habitats and biodiversity. Meanwhile, the process of geothermal power plant construction also has an impact on biodiversity. Although geothermal power plants play only a minor part in electricity generation worldwide, attention must be paid to the local effects on biodiversity. Due to the unique of the intrinsic species and populations of plants, animals and micro-organisms and the dependent ecosystems are often regarded as fragile and sensitive to the external perturbations that result from geothermal development [19]. For example, in the Wairakei geothermal field in New Zealand, the production of geothermal power plants has changed local ground temperatures, pH values, and water availability, and thus influencing plant communities in hydrothermal systems. Because of the thermal and acidity stress factors on vegetation decrease, more invasive and nonnative species have thrived in the area and threatened the endemic species, causing adverse impacts upon the balance of ecological system and the stability of biodiversity [22]. In addition, toxic air emissions may cause a risk to adjacent habitats and inhabitants. Both the steam and the geothermal fluids contain chemicals, such as H2S, Hg, As, Cl, etc., that may have adverse biological effects. For example, H2S and Hg concentrations in the air have caused low or moderate environmental impacts upon the biodiversity of epiphytic lichens, and also altered the nasal quality of the air to human beings in the geothermal power plants in Bagnore and Piacastagnaio in the Mt. Amiata Area in Central Italy [23]. 3.2
Economic impacts
Geothermal energy development will generate more new job opportunities, and increased economic activities and new jobs will bring higher incomes. However, such capacities cannot be effectively commercially utilized without the well design of the development of geothermal energy. The decrease or the closing of the cost gap between geothermal energy and fossil oil still poses a great challenge. The most important cost of geothermal energy development is the capital cost in the start-up phase, although the operation and maintenance phase accounts for a small percentage of total costs. Besides, tremendous investments are needed for exploration, resource confirma-
tion and characterization (drilling and well testing), and site development (facility construction). In particular, well drilling is a requisite and the most costly phase, as demonstrated in many geothermal projects. It is suggested that the investment of well-drilling can reach up to 50%– 60% or more of the total capital costs [24]. Another study shows that it will cost US $10million to drill a typical well doublet to produce 4.5 MW of electricity, while doublet well drilling together with electrical plant construction can cost US $3–8 million per MW of electrical capacity [6]. In addition, geothermal energy projects involve high financial risks, like hydropower because of geologic factors [25]. Still, investors are also easy to perceive the lack of clarity of the country’s policy framework and institutional arrangements as a high risk. As present, economic profitability and energy efficiency is still a trade-off. Therefore, investors should be careful and cautious when planning to establish a new geothermal energy project, since they need to compare and weigh the influences of cost parameters, such as generation capacities, capital and operational costs, and other factors [26]. The expense of storage/preservation and management of geothermal energy are also very high. One of the more basic obstacles to reach the targets set by the government is that most geothermal resources are located in remote areas. And this means that it requires additional financing to connect electricity production to the main grid [27]. This will affect pricing which remains a key issue. The tariff has been raised to US $ 9.7 cents/kWh. However, some investors have requested a higher price to compensate for the high costs incurred in the development of geothermal energy, especially in remote regions. The development of geothermal energy also needs some supporting facilities in some cases. For example, rainfall diversion facilities should be established, since heavy rain or flood may threaten the geothermal energy plant. In order to minimize the risks, some extra work needs to be done. For example, to prevent land subsidence, some amount of soil should be back filled after drilling, especially in arid or semiarid areas. In order to reduce noise during the construction and operation of geothermal energy plant, mufflers or other soundproofing means should be employed, which will create some additional costs. 3.3
Social and cultural impacts
Noise pollution during the development of geothermal energy plant mainly happens during the drilling and welltesting phase, the construction phase, and the plant operation phase [28]. The drilling and well-testing can produce substantial noise, which may influence residents nearby. However, the drilling and well-testing noise is temporary and seldom exceeds 90 dB, and thus the noise pollution is not permanent [21]. For example, well-testing operations typically take place at daytime, lasting seven days a week and from 45 to 90 days per well [5]. The noise
Li JIANG et al. Large-scale geo-energy development
from discharging boreholes and other mechanical activities is high, and may exceed 120 dB with the pain threshold ranging between 2 and 4000 Hz [21]. Construction is considered as the noisiest phases of geothermal development. During the construction phase, noise may be caused by the construction of the well pads, transmission towers and power plant. For example, it can take from a few weeks or months to a few years for the well pad construction, depending upon the depth of the well. In addition, usually construction noise disturbs residents nearby only at daytime. Noise control need to be considered, for instance, by installing exhaust muffling equipment or facilities. However, noise pollution related to geothermal construction, as most construction, is a temporary impact which will end when construction is terminated. In the operation phase, the noise may be a problem to populated areas nearby, which is usually overlooked. The cooling tower, the steam ejector and turbine-generator building can generate the majority of noise [5,15]. There is the higher pitched noise of the occasional vent discharge and steam travelling through pipelines as well as the noise from cooling towers. Especially, the cooling tower is a relatively tall facility, and during routine operation the noise generated from the fans located at the top can be the primary source of noise. According to Dipippo [29], noise levels for a geothermal power plant during operation often range from 71 to 83 dB at a distance of 900 m. Presently, more importance has been attached to the surrounding aesthetics of the environment. During drilling and pipelines installation, the original natural landscape may be damaged by a series of mechanical activities for the construction of the geothermal plants and associated transmission facilities. Surface disturbances caused by excavation, construction and the creation of new roads will occur in the process of the drilling, which might reshape the landscape. Take New Zealand as an example, the development of geothermal energy has already caused the extinction of more than 100 geysers and it is not possible to get them recovered. Hence, the geysers’ decline and extinction in New Zealand provides important lessons for the environmental management [30]. In addition, long pipelines must be built to transport the geothermal fluids. Under this circumstance, some plants have to be removed, impacting vegetation in the surrounding area and thus the
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habitats of wildlife. Hence, it is necessary to conduct an environmental review to predict any potential effects on wildlife and vegetation prior to geothermal construction [28]. In some cases, geothermal facilities might be located on some sensitive areas, such as places of touristic importance and archeological, historical or religious areas, whose protection must be considered [31]. Moreover, public acceptance of geothermal energy development should also be considered. The geothermal resources worldwide are abundant, but it contributes only a small proportion to world primary energy consumption. Geothermal energy is not widely accepted by many countries, and substantial amounts of geothermal energy have been exploited only by several countries such as the US, the Philippines, Indonesia, Mexico, Italy, Iceland, New Zealand, and Japan [7]. For example, the survey shows that only 47% of Europeans are aware of geothermal energy as an alternative energy type [32], while another study shows that around 27% of Australian respondents report no knowledge of geothermal energy [33]. Thus, it needs time for people to adapt and accept this new energy type. In addition, negative public perception can also lead to the rejection of the geothermal project if the government would not consider the relative environmental, economic and social impacts.
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Conclusions and prospects
From a sustainability perspective, the potential sustainability impacts related to the geothermal energy development have been systematically and explicitly mapped out in this paper, as summarized in Table 2, including environmental, economic, and social & cultural dimensions. There is no denying the fact that geothermal energy plays a pretty important role in renewable energy supply. In an attempt to support the development and prosperity of this industry, it is necessary to carefully explore the sustainability concerns and thus help figure out the associated impacts. The benefits for geothermal energy as an alternative and renewable energy can potentially and significantly contribute to a sustainable industry. Nevertheless, there is still a long way to go from the cleaner production of geothermal energy together with the
Table 2 Potential sustainability impacts related to geothermal energy development Environmental dimension – Cause soil erosion, geothermal hazards and direct or indirect land use changes; – Damage groundwater, interrupt hydrologic cycles, and affect the water quality; –Dust pollution and gaseous emissions from the discharge of non-condensable gases; – Detrimental effects on local ecosystems, affecting the habitats
Economic dimension
Social & cultural dimension
– Start-up phase is expensive, requiring overwhelming investments; – The expense of storage and management of geothermal energy is also very high; – Supporting facilities might be needed, creating additional costs
– Local people might suffer from the noise in the drilling and well-testing phase, the construction phase, and the plant operation phase; – Landscape aesthetics might be damaged; – It requires time for people to adapt and accept geo-energy
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thorough consideration of the relative economic and social & cultural impacts, in light of the research advances still required. More fundamental and demonstration researches are still required, which can facilitate the creation of a more robust, prosperous and sustainable industry. The development of geothermal production for heating or electricity generation requires significant amounts of investment, in demonstration projects to show its viability, and in industrial level for commercialization. To realize these goals successfully, coherent, extensive and well-funded research and development programs should be launched, since a sustainable and continual effort from the scientists can lead to the successful development of geothermal energy for huge market deployment in the future. Besides future research and development in technology, government policy and direct support for research, development, demonstration and industrialization with commercial viability are more likely to continuously play a significant role in this process. The dissemination of the geothermal energy concept, technology and supporting policy can also be essential to develop the geothermal energy in a sustainable manner. Furthermore, it is necessary to learn lessons especially from unsuccessful projects, so that it can help predict the impacts in advance and minimize them to some extent. With the careful establishment of geothermal energy and thorough consideration of sustainability impacts, the geothermal energy industry will witness its prosperity sooner or later.
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Acknowledgements This work was supported by the Geo-energy project and the Kone Foundation project.
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