The elements of direct uses

Direct uses of geothermal energy are important in many countries of the world. Well-known examples are district heating (hitaveita) in Iceland, industrial processing in New Zealand, greenhouse heating in Hungary, and traditional bathing uses in Japan. Although direct uses are also called non-electrical applications, they span the whole range of geothermal temperatures, as evident from the Lindal Diagram shown in Fig. 1. A recent paper on direct uses is that of Gudmundsson and Lund (1985). Because of the many possible applications of geothermal energy, there is a need to identify the main elements that make up direct use projects. The purpose of this paper is to consider these elements, in an attempt to better organize the field of geothermal engineering. The paper concerns the technologies needed to bring geothermal fluids from resource to user. However, corrosion and water quality matters are not discussed, neither are environmental issues. Geothermal drilling, production and reservoir engineering are also outside the scope of this paper.     

Geothermal space heating

The use of geothermal resources for space heating dominates the direct use industry, with approximately 37% of all direct use development. Of this, 75% is provided by district heating systems. In fact, the earliest known commercial use of geothermal energy was in Chaudes-Aigues Cantal, France, where a district heating system was built in the 14th century. Today, geothermal district space heating projects can be found in 12 countries and provide some 44,772 TJ of energy yearly. Although temperatures in excess of 50 °C are generally required, resources as low as 40 °C can be used in certain circumstances, and, if geothermal heat pumps are included, space heating can be a viable alternative to other forms of heating at temperatures well below 10 °C.     

Direct heat utilization of geothermal resources

Direct utilization of geothermal energy consists of various forms for heating and cooling instead of converting the energy for electric power generation. The major areas of direct utilization are (1) swimming, bathing and balneology, (2) space heating and cooling including district heating, (3) agriculture applications, (4) aquaculture applications, (5) industrial processes, and (6) heat pumps. Major direct utilization projects exploiting geothermal energy exist in about 38 countries, and the estimated installed thermal power is almost 9,000 MWt utilizing 37,000 kg/s of fluid. The world-wide thermal energy used is estimated to be at least 108,100 TJ/yr (30,000 GWh/yr) - saving 3.65 million TOE/yr. The majority of this energy use is for space heating (33%), and swimming and bathing (19%). In the USA the installed thermal power is 1874 MWt, and the annual energy use is 13,890 TJ (3,860 GWh). The majority of the use (59 %) is for heat pumps (both ground coupled and water source), with space heating, bathing and swimming, and fish and animal farming each supplying about 10%.     

Geothermal energy utilization in Turkey

This paper investigates the status of geothermal development in Turkey as of the end of 1999. Turkey is one of the countries with significant potential in geothermal energy. Resource assessments have been made many times by the Mineral Research and Exploration Directorate (MTA) of Turkey. The main uses of geothermal energy are mostly moderate‐ and low‐temperature applications such as space heating and domestic hot water supply, greenhouse heating, swimming and balneology, industrial processes, heat pumps and electricity generation. The data accumulated since 1962 show that the estimated geothermal power and direct use potential are about 4500 MW_e and 31 500 MW_t, respectively. The direct use capacity in thermal applications is in total 640 MW_t representing only 2 per cent of its total potential. Since 1990, space heating and greenhouse developments have exhibited a significant progress. The total area of greenhouses heated by geothermal energy reached up to about 31 ha with a heating capacity of 69.61 MW_t. A geothermal power plant with a capacity of 20.4 MW_e and a CO₂ factory with a capacity of 40000 ton yr^?1 have been operated in the Denizli‐Kizildere field since 1984 and 1986, respectively. Ground source heat pumps have been used in residential buildings for heating and cooling for approximately 2 years. Present applications have shown that geothermal energy in Turkey is clean and much cheaper compared to the other energy sources like fossil fuels and therefore is a promising alternative. As the projects are recognized by the public, the progress will continue. Copyright © 2001 John Wiley & Sons, Ltd.     

Geothermal energy in Turkey: the sustainable future

Turkey is an energy importing nation with more than half of our energy requirements met by imported fuels. Air pollution is becoming a significant environmental concern in the country. In this regard, geothermal energy and other renewable energy sources are becoming attractive solution for clean and sustainable energy future for Turkey. Turkey is the seventh richest country in the world in geothermal energy potential. The main uses of geothermal energy are space heating and domestic hot water supply, greenhouse heating, industrial processes, heat pumps and electricity generation. The district heating system applications started with large-scale, city-based geothermal district heating systems in Turkey, whereas the geothermal district heating centre and distribution networks have been designed according to the geothermal district heating system (GDHS) parameters. This constitutes an important advantage of GDHS investments in the country in terms of the technical and economical aspects. In Turkey, approximately 61,000 residences are currently heated by geothermal fluids. A total of 665 MW_t is utilized for space heating of residential, public and private property, and 565,000 m² of greenhouses. The proven geothermal heat capacity, according to data from existing geothermal wells and natural discharges, is 3132 MWt. Present applications have shown that geothermal energy is clean and much cheaper compared to the other fossil and renewable energy sources for Turkey.     

Direct application of geothermal energy: 2005 Worldwide review

This paper is a review of worldwide direct applications of geothermal energy. It attempts to update the surveys presented at and after the World Geothermal Congresses of 1995, 2000 and 2005. Seventy-two countries report direct utilization of geothermal energy. In May 2005, the direct-use projects had an estimated installed thermal capacity of 28,268 MWt. The thermal energy usage is 273,372 TJ/year (75,943 GWh/year), a 43% increase over 2000; the annual compound growth rate is 7.5%.The distribution of thermal energy used by category is approximately 32% for geothermal heat pumps, 30% for bathing and swimming (including balneology), 20% for space heating (of which 83% is for district heating), 7.5% for greenhouse and open-ground heating, 4% for industrial process heat, 4% for aquaculture pond and raceway heating, <1% for agricultural drying, <1% for snow melting and cooling, and <0.5% for other uses. The equivalent annual savings in fuel oil amounts to 170 million barrels (25.4 million tonnes) and 24 million tonnes in carbon emissions to the atmosphere.     

U.S.A. experience in direct heat use

Direct heat use of geothermal energy in the U.S.A. occurs mainly in the western states. A total of 216 projects is operational, with six under construction and 21 planned. The operational projects account for about 2100 TJ/yr (233 MWt-peak) with an average load factor of 29%. The under-construction and planned projects would approximately double the energy use. Not included are an estimated 10,000 TJ (400 MWt-peak) used in enhanced oil recovery. Space and district heating account for almost half (45.8%) of the annual use, whereas greenhouses account for 20.2%, fish farming for 20.7%, industrial processing for 6.7%, and pools and spas for 6.6%. Future growth is expected to be greatest in district heating, where eight proposed projects will produce 1360 TJ annually (149 MWt-peak). Future growth of all direct heat uses in the U.S. is estimated at 8% annually.     

The USA geothermal country update

Geothermal energy is used for electric power generation and direct utilization in the United States. The present installed capacity (gross) for electric power generation is about 2020 MWe, with 1902 MWe net delivering power to the grid, producing approximately 16,000 GWh per year for a 96% capacity factor. Geothermal electric power plants are located in California, Nevada, Utah and Hawaii. The two largest concentrations of plants are at The Geysers in northern California and the Imperial Valley in southern California. The latest development at The Geysers, due to recent declines in steam output, is the injection of recycled wastewater from two communities into the reservoir, which has at present permitted the recovery of 70 MWe of power generation. The direct utilization of geothermal energy includes the heating of pools and spas, greenhouses and aquaculture facilities, space heating and district heating, snow melting, agricultural drying, industrial applications and ground-source heat pumps. The installed capacity is about 4350 MWt and the annual energy use is 22,250 TJ, or 6181 GWh. The largest application is that of ground-source (geothermal) heat pumps (60% of the energy use), and the largest direct-use is that of aquaculture pond and raceway water heating. Direct utilization is increasing at about 6% per year, whereas electric power plant development is almost static. The energy savings from electric power generation, direct uses and ground-source heat pumps amount to 6.6 million tonnes of equivalent fuel oil per year and represents a reduction in air pollution of 5.8 million tonnes of carbon annually (compared to fuel oil).     

Prospects and problems for geothermal use in agriculture in Europe

The agricultural uses of geothermal energy were the centre of attention during the initial stages of geothermal direct applications in Europe, e.g. in Hungary, Macedonia, Bulgaria, Serbia. The focus now seems to be on district heating systems, integrated systems, large balneological/tourist centres, etc. This paper analyses the problems involved in the development of agricultural uses in different regions of Europe and how this sector can be promoted. An analysis of the situation in Europe and in Hungary, Macedonia and Greece, in particular, has revealed different requirements and potentials, different combinations of influencing factors, and the need for different development strategies. It is, however, clear from this analysis that the agricultural uses of geothermal energy are not in collision with modern trends in direct geothermal developments in Europe. On the contrary, they can improve the economic aspects of any district heating or integrated system by offering excellent possibilities for cascade use of the geothermal water and combinations of users with different day/night and seasonal heat requirements.     

Current status of ground source heat pumps and underground thermal energy storage in Europe

Geothermal Heat Pumps, or Ground Coupled Heat Pumps (GCHP), are systems combining a heat pump with a ground heat exchanger (closed loop systems), or fed by ground water from a well (open loop systems). They use the earth as a heat source when operating in heating mode, with a fluid (usually water or a water–antifreeze mixture) as the medium that transfers the heat from the earth to the evaporator of the heat pump, thus utilising geothermal energy. In cooling mode, they use the earth as a heat sink. With Borehole Heat Exchangers (BHE), geothermal heat pumps can offer both heating and cooling at virtually any location, with great flexibility to meet any demands. More than 20 years of R&D focusing on BHE in Europe has resulted in a well-established concept of sustainability for this technology, as well as sound design and installation criteria. Recent developments are the Thermal Response Test, which allows in-situ-determination of ground thermal properties for design purposes, and thermally enhanced grouting materials to reduce borehole thermal resistance. For cooling purposes, but also for the storage of solar or waste heat, the concept of underground thermal energy storage (UTES) could prove successful. Systems can be either open (aquifer storage) or can use BHE (borehole storage). Whereas cold storage is already established on the market, heat storage, and, in particular, high temperature heat storage (> 50 °C) is still in the demonstration phase. Despite the fact that geothermal heat pumps have been in use for over 50 years now (the first were in the USA), market penetration of this technology is still in its infancy, with fossil fuels dominating the space heating market and air-to-air heat pumps that of space cooling. In Germany, Switzerland, Austria, Sweden, Denmark, Norway, France and the USA, large numbers of geothermal heat pumps are already operational, and installation guidelines, quality control and contractor certification are now major issues of debate.     

Potential of geothermal energy in the Kingdom of Saudi Arabia

The Kingdom of Saudi Arabia has rich geothermal energy resources. In Saudi Arabia, the studies on geothermal resources exploration were started in 1980. Saudi Arabia is among the most geothermally active countries in the Middle East. The geothermal power plants are not yet installed in Saudi Arabia. Some direct-use low-grade geothermal applications are already installed in the five last years. Some refreshment and swimming pools are already constructed in the Bani Malik-Jizan area. Geothermal energy can be utilized in various forms such as direct use, electricity generation, space heating, heat pumps, greenhouse heating, and industrial usage. The Kingdom of Saudi Arabia government has plans to become completely powered by difference forms of renewable energy such as solid waste, solar, geothermal, and wind.     

Development of geothermal energy utilization in Turkey: a review

Renewable energy is accepted as a key source for the future, not only for Turkey but also for the world. Turkey has a considerably high level of renewable energy sources that can be a part of the total energy network in the country. Turkey is located in the Mediterranean sector of Alpine–Himalayan Tectonic Belt and has a place among the first seven countries in the world in the abundance of geothermal resources. The share of its potential used is, however, only about 2–3%.The main objective of the present study is to review the development of geothermal energy (GE) utilization in Turkey, giving its historical development and opportunities. GE is used for electric power generation and direct utilization in Turkey, which is among the first five countries in the world in geothermal direct use applications. Direct use of geothermal resources has expanded rapidly last 36 years from space heating of single buildings to district heating, greenhouse heating, industrial usage, modern balneology and physical treatment facilities.Turkey presently has one operating geothermal power plant, located near Denizli City in Western Anatolia with an installed capacity of 20.4 MW_e and an electrical energy production of 89,597 MW h in 2001. Recently, the total installed capacity has reached 820 MW_t for direct use. The total area of geothermal heated greenhouses exceeded over 35 ha with a total heating capacity of 81 MW_t. Ground-source (or geothermal) heat pumps (GSHPs) have also been put on the Turkish market since 1998. Though there are no Turkish GSHP manufactures as yet, 207 units have been installed in the country to date, representing a total capacity of 3 MW.GE is a relatively benign energy source, displaying fossil fuels and thus reducing greenhouse gas emissions. So, it is expected that GE development will significantly speed up in the country if the geothermal law becomes effective.     

Geothermal rice drying unit in Kotchany, Macedonia

A geothermal field in Kotchany (Macedonia) has very advantageous characteristics for direct application purposes. Low content of minerals, moderate temperature (78°C) and substantial available geothermal water flow (up to 300 l/s) enabled the establishment of a district heating scheme comprising mainly agricultural and industrial uses.A rice drying unit of 10 t/h capacity was installed 8 years ago, using the geothermal water as the primary heat source. A temperature drop of 75/50°C enables the adaptation of conventional drying technology, already proven in practice in the surrounding rice growing region. Water to air heat exchanger and all necessary equipment and materials are of local production, made of copper and carbon steel.The use of such drying units is strongly recommended for the concrete district heating scheme because it offers a very simple geothermal application and enables improvement in the annual heating load factor without high investments in geothermal water distribution lines.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

地热资源的开发利用及可持续发展

地热资源作为一种新型能源矿产,具有分布广泛、易于开发等特点,其利用方式主要有地热发电和地热直接利用两种.我国具有良好的地热资源条件,主要为中低温地热资源.据计算,我国12个主要沉积盆地的地热可开采资源量为7500×1018J,相当于2560×108t标煤.当前,我国地热资源利用方式主要以供暖、洗浴、种植等直接利用为主;地热发电发展缓慢,主要分布在西藏;利用热泵技术开发地热资源得到了快速发展;油区地热资源的开发利用也取得了良好的经济和社会效益.但同时我国地热资源产业也面临着一些问题,包括大部分地区尚未开展地热资源勘查评价,影响了地热资源规划的制订及地热产业的发展;防腐、防垢技术还需要进一步加强研究;地热回灌率普遍过低;增强型地热系统研究有待加强等.为了促进地热资源的可持续发展,建议在加大地热资源勘查力度的同时,应以浅层地温能和热水型地热资源为主,发挥热泵技术的优势,开展地热资源的综合利用及梯级利用;重视和加快油气区地热资源的利用;在西藏等适宜地区加大高温地热能发电利用;集中全国优势技术力量,在一两个有利区域开展增强型地热系统技术探索;此外,走回灌开发道路是地热资源开发利用的必然选择.     

Experience in developing and utilizing geothermal resources in iceland

Geothermal energy plays a larger role in the energy economy of Iceland than in any other country-Iceland is The Geothermal Country. This development dates back to 1930, when the first district heating system was started in Reykjavik, and since then geothermal water and steam have been utilized for a broad range of applications. Iceland has seen an unprecedented activity of geothermal projects over the past decade; geothermal district heating systems being installed wherever possible in cities and rural areas, a 30 MW_e, electric power plant at Krafla, small scale production of salt and carbon dioxide, heat extracted from the newly erupted lava in the Westman Islands for district, heating, increased use in industry and agriculture, and now recently an explosive development in fish farming. For a number of years the investment in geothermal projects represented 1.5% of the gross national product of Iceland.The largest use of geothermal energy in Iceland is for space heating and domestic use. At the moment 85% of all houses in the country are heated with geothermal water. This is of great importance in a country where heating is required practically throughout the year. The climate is rather temperate ranging from −15 to +20°C, and with the building codes now in effect that call for double and triple glazing and 150–200 mm of roof insulation, heating demand is 20 W/m³ and the annual usage 60–80 kWh/m³. Heating of greenhouses, industrial drying, fish farming, swimming pools, chemical production and electric power generation also make use of this energy source.This development has on the whole been very successful from the economic and technical standpoint, and has contributed to the wellbeing of the population of some 240,000 persons.This review paper will focus on some of the engineering experience gained in harnessing this “unconventional” energy source.     

A renewable energy system in Frederikshavn using low-temperature geothermal energy for district heating

The Danish city Frederikshavn is aiming at becoming a 100% renewable energy city. The city has a number of energy resources including a potential for off-shore wind power, waste and low-temperature geothermal energy usable as heat source for heat pumps producing district heating.     

Direct utilization of geothermal energy 2010 worldwide review

This paper presents a review of the worldwide application of geothermal energy for direct utilization, and updates the previous survey carried out in 2005. We also compare data from 1995 and 2000 presented at World Geothermal Congresses in Italy and Japan, respectively (WGC95 and WGC2000). As in previous reports, an effort is made to quantify ground-source (geothermal) heat pump data. The present report is based on country update papers prepared for WGC2010 and other sources of data available to the authors. Final update papers were received from 70 countries of which 66 reported some direct utilization of geothermal energy. Twelve additional countries were added to the list based on other sources of information. Direct utilization of geothermal energy in 78 countries is a significant increase from the 72 reported in 2005, the 58 reported in 2000, and the 28 reported in 1995. An estimate of the installed thermal power for direct utilization at the end of 2009 is used in this paper and equals 48,493 MWt, almost a 72% increase over the 2005 data, growing at a compound rate of 11.4% annually with a capacity factor of 0.28. The thermal energy used is 423,830 TJ/year (117,740 GWh/yr), about a 55% increase over 2005, growing at a compound rate of 9.2% annually. The distribution of thermal energy used by category is approximately 47.2% for ground-source heat pumps, 25.8% for bathing and swimming (including balneology), 14.9% for space heating (of which 85% is for district heating), 5.5% for greenhouses and open ground heating, 2.8% for industrial process heating, 2.7% for aquaculture pond and raceway heating, 0.4% for agricultural drying, 0.5% for snow melting and cooling, and 0.2% for other uses. Energy savings amounted to 250 million barrels (38 million tonnes) of equivalent oil annually, preventing 33 million tonnes of carbon and 107 million tonnes of CO₂ being release to the atmosphere, this includes savings for geothermal heat pumps in the cooling mode (compared to using fuel oil to generate electricity).     

Geothermal resources in the shallow, unsaturated zone of the Wiesbaden spa district, Germany

The geothermal energy potential of the Wiesbaden spa district continues to be largely untapped. Although the thermal water is being utilized, any other activity liable to disturb the hydraulic regime of the thermal springs is prohibited. The geothermal potential of the unsaturated zone in the spa district has been mapped, although the zone must be regarded as a thermal insulator rather than a good conductor. The results of the mapping revealed the presence of a number of heat anomalies that could be exploited in the future; further economic benefits could be gained from installing the heat transfer units during road works. The modelling studies considered two possible scenarios: direct heating and heat pump usage. The results indicate that heat pumps are the more efficient option, yielding a thermal capacity of approximately 100 W/m².     

Energy and exergy analysis of Salihli geothermal district heating system in Manisa,Turkey

This study deals with an energy and exergy analysis of Salihli geothermal district heating system (SGDHS) in Manisa, Turkey. In the analysis, actual system data are used to assess the district heating system performance, energy and exergy efficiencies, specific exergy index, exergetic improvement potential and exergy losses. Energy and exergy losses throughout the SGDHS are quantified and illustrated in the flow diagram. The exergy losses in the system, particularly due to the fluid flow, take place in the pumps and the heat exchanger, as well as the exergy losses of the thermal water (e.g. geothermal fluid) and the natural direct discharge of the system. As a result, the total exergy losses account for 2.22, 17.88 and 20.44%, respectively, of the total exergy input to the entire SGDHS. The overall energy and exergy efficiencies of the SGDHS components are also studied to evaluate their individual performances and determined to be 55.5 and 59.4%, respectively. Copyright © 2005 John Wiley & Sons, Ltd.