In
Table 2 the 1995, 2000, 2005 and 2010 data are divided among the various uses in terms of capacity, energy utilization and capacity factor. This distribution can also be viewed as bar charts in
Figure 2.
Figure 3 presents the 2010 data in pie-chart form in percentages. An attempt was made to distinguish individual space heating from district heating, but this was often difficult, as the individual country reports did not always make this distinction. Our best estimate is that district heating represents 86% of the installed capacity and 85% of the annual energy use, similar to WGC2005. Snow melting represents the majority of the snow melting/air-conditioning category. “Other” is a category that covers a variety of uses: frequently the data sources do not provides details; but include animal husbandry.
Figure 2.
Comparison of worldwide energy in TJ/yr for 1995, 2000, 2005 and 2010 [
1].
Figure 3.
Geothermal direct applications worldwide in 2010, distributed by: (a) percentage of total installed capacity; and (b) percentage of total energy use [
1].
3.1. Geothermal Heat Pumps
Geothermal (ground-source) heat pumps have the largest energy use and installed capacity, accounting for 68.3% and 47.2% of the worldwide capacity and use. The installed capacity is 33,134 MWt and the annual energy use of 200,149 TJ/yr, with a capacity factor of 0.19 (in the heating mode). Almost all of the installations occur in North American, Europe and China, increasing from 26 countries in 2000, to 33 countries in 2005, to the present 43 countries. The equivalent number of installed 12 kW units (typical of US and Western European homes) is approximately 2.76 million, over double the number of units report for 2005, and four times the number for 2000. The size of individual units; however, ranges from 5.5 kW for residential use to large units of over 150 kW for commercial and institutional installations.
Table 2.
Summary of the various categories of direct use worldwide, referred to the period 1995–2010 [
1].
Table 2.
Summary of the various categories of direct use worldwide, referred to the period 1995–2010 [1].
| | 2010 | 2005 | 2000 | 1995 |
|---|
| Capacity (MWt) | | | | |
| Geothermal Heat Pumps | 33,134 | 15,384 | 5,275 | 1,854 |
| Space Heating | 5,391 | 4,366 | 3,263 | 2,579 |
| Greenhouse Heating | 1,544 | 1,404 | 1,246 | 1,085 |
| Aquaculture Pond Heating | 653 | 616 | 605 | 1,097 |
| Agricultural Drying | 125 | 157 | 74 | 67 |
| Industrial Uses | 533 | 484 | 474 | 544 |
| Bathing and Swimming | 6,700 | 5,401 | 3,957 | 1,085 |
| Cooling / Snow Melting | 368 | 371 | 114 | 115 |
| Others | 42 | 86 | 137 | 238 |
| Total | 48,493 | 28,269 | 15,145 | 8,664 |
| Utilization (TJ/yr) | | | | |
| Geothermal Heat Pumps | 200,149 | 87,503 | 23,275 | 14,617 |
| Space Heating | 63,025 | 55,256 | 42,926 | 38,230 |
| Greenhouse Heating | 23,264 | 20,661 | 17,864 | 15,742 |
| Aquaculture Pond Heating | 11,521 | 10,976 | 11,733 | 13,493 |
| Agricultural Drying | 1,635 | 2,013 | 1,038 | 1,124 |
| Industrial Uses | 11,745 | 10,868 | 10,220 | 10,120 |
| Bathing and Swimming | 109,410 | 83,018 | 79,546 | 15,742 |
| Cooling/Snow Melting | 2,126 | 2,032 | 1,063 | 1,124 |
| Others | 955 | 1,045 | 3,034 | 2,249 |
| Total | 423,830 | 273,372 | 190,699 | 112,441 |
| Capacity Factor | | | | |
| Geothermal Heat Pumps | 0.19 | 0.18 | 0.14 | 0.25 |
| Space Heating | 0.37 | 0.40 | 0.42 | 0.47 |
| Greenhouse Heating | 0.48 | 0.47 | 0.45 | 0.46 |
| Aquaculture Pond Heating | 0.56 | 0.57 | 0.61 | 0.39 |
| Agricultural Drying | 0.41 | 0.41 | 0.44 | 0.53 |
| Industrial Uses | 0.70 | 0.71 | 0.68 | 0.59 |
| Bathing and Swimming | 0.52 | 0.49 | 0.64 | 0.46 |
| Cooling/Snow Melting | 0.18 | 0.18 | 0.30 | 0.31 |
| Others | 0.72 | 0.39 | 0.70 | 0.30 |
| Total | 0.28 | 0.31 | 0.40 | 0.41 |
In the United States, most units are sized for peak cooling load and are oversized for heating, except in the northern states; thus, they are estimated to average only 2,000 full-load hours per year (capacity factor of 0.23). In Europe, most units are sized for the heating load and are often designed to provide the base load with peaking by fossil fuel. As a result, these units may be in operation up to 6,000 full-load hours per year (capacity factor of 0.68), such as in Nordic countries. Unless the actual number of full-load hours was reported, a value of 2,200 hours was used for energy output (TJ/yr) calculations, and higher for some of the northern countries, based on reports by Curtis
et al. [
7].
The energy use reported for the heat pumps was deduced from the installed capacity (if it was not reported), based on an average coefficient of performance (COP) of 3.5, which allows for one unit of energy input (usually electricity) to 2.5 units of energy output, for a geothermal component of 71% of the rated capacity [
i.e. (COP-1)/COP = 0.71]. The cooling load was not considered as geothermal, as in this case, heat is discharged into the ground or groundwater. Cooling, however, has a role in the substitution for fossil fuels and reduction of greenhouse gas emissions and is included as discussed in
Section 8.
The leaders in installed units are the United States, China, Sweden, Norway and Germany.
3.2. Space Heating
Space conditioning includes both heating and cooling. Space heating with geothermal energy has widespread application, especially on an individual basis. Buildings heated from individual wells are popular in Klamath Falls, Oregon; Reno, Nevada, USA, and Taupo and Rotorua, New Zealand. Absorption space cooling with geothermal energy has not been popular because of the high temperature requirements and low efficiency. However, newer units recently placed on the market report to use temperatures below 100 °C efficiently. Geothermal heat pumps (groundwater and ground-coupled) have become popular in the U.S., Canada and Europe, used for both heating and cooling.
Downhole heat exchangers have been used for heating individual buildings using a closed loop of pipe in a well extracting only heat in Klamath Falls, Oregon, Reno, Nevada, Rotorua, New Zealand and Ismir, Turkey (see the Heat Exchanger section for more details). An example of space heating and cooling with low-to-moderate temperature geothermal energy is the Oregon Institute of Technology in Klamath Falls, Oregon. Here, twelve buildings (approximately 70,000 sq. m of floor space) are heated with water from three wells at 89 °C. Up to 62 L/s of fluid can be provided to the campus, with the average heat utilization rate over 0.53 MWt and the peak at 5.6 MWt. In addition, a 541 kW (154 tons) chiller requiring up to 38 L/s of geothermal fluid produces 23 L/s of chilled fluid at 7
oC to meet the campus cooling base load (recently decommissioned) [
8,
9].
District heating involves the distribution of heat (hot water or steam) from a central location, through a network of pipes to individual houses or blocks of buildings. The distinction between a district heating and space heating system is that space heating usually involves one geothermal well per structure. The heat is used for space heating and cooling, domestic water heating and industrial process heat. A geothermal well field is the primary source of heat; however, depending on the temperature, the district may be a hybrid system, which would include fossil fuel and/or heat pump peaking. An important consideration in district heating projects is the thermal load density, or the heat demand divided by the ground area of the district. A high heat density, generally above 1.2 GJ/hr/ha (33.3 W/m
2) or a favorability ratio of 2.5 GJ/ha/yr (0.0079 W/m
2) is recommended. Often fossil fuel peaking is used to meet the coldest period, rather than drilling additional wells or pumping more fluids, as geothermal can usually meet 50% of the load 80 to 90% of the time, thus improving the efficiency and economics of the system [
10]. Geothermal district heating systems are capital intensive. The principal costs are initial investment costs for production and injection wells, downhole and circulation pumps, heat exchangers, pipelines and distribution network, flow meters, valves and control equipment, and building retrofit. The distribution network may be the largest single capital expense, at approximately 35 to 75% of the entire project cost. Operating expenses, however, are in comparison lower and consists of pumping power, system maintenance, control and management. The typical savings to consumers range from approximately 30 to 50% per year of the cost of natural gas.
Space heat has increased 24% in installed capacity and 14% in annual energy use over WGC2005. The installed capacity now totals 5,394 MWt and the annual energy use is 63,025 TJ/year. As stated previously about 86% of the installed capacity and 85% of the annual energy use is in district heating (24 countries). The leaders in district heating annual energy use are Iceland, China, Turkey, France and Russia, whereas, Turkey, Italy, United States, Japan and Georgia are the major users in the individual space heating sector (a total of 27 countries).
3.3. Agribusiness Applications
Agribusiness applications (agriculture and aquaculture) are particularly attractive because they require heating at the lower end of the temperature range where there is an abundance of geothermal resources. Use of waste heat or the cascading of geothermal energy also has excellent possibilities. A number of agribusiness applications can be considered: greenhouse heating, aquaculture and animal husbandry facilities heating, soil warming and irrigation, mushroom culture heating and cooling, and bio-gas generation.
Numerous commercially marketable crops have been raised in geothermally heated greenhouses in Hungary, Russia, New Zealand, Japan, Iceland, China, Tunisia, and the U.S. These include vegetables, such as cucumbers, peppers, and tomatoes, flowers (both potted and bedded), house plants, tree seedlings, and cacti. Using geothermal energy for heating reduces operating costs (which can account for up to 35% of the product cost) and allows operation in colder climates where commercial greenhouses would not normally be economical.
The use of geothermal energy for raising catfish, shrimp, tilapia, eels, and tropical fish has produced crops faster than by conventional solar heating. Using geothermal heat allows better control of pond temperatures, thus optimizing growth. Fish breeding has been successful in Japan, China and the U.S. A very successful prawn raising operation, producing 400 tonnes of Giant Malaysian Freshwater Prawns per year at US$ 17 to 27/kg has been developed near the Wairakei geothermal field in New Zealand [
11]. The most important factors to consider are the quality of the water and disease. If geothermal water is used directly, concentrations of dissolved heavy metals, fluorides, chlorides, arsenic, and boron must be identified and, if necessary, isolated.
Livestock raising facilities can encourage the growth of domestic animals by a controlled heating and cooling environment. An indoor facility can lower mortality rate of newborn, enhance growth rates, control diseases, increase litter size, make waste management and collection easier, and in most cases improved the quality of the product. Geothermal fluids can also be used for cleaning, sanitizing and drying of animal shelters and waste, as well as assisting in the production of bio-gas from the waste.
3.3.1. Greenhouse and Covered Ground Heating
Worldwide use of geothermal energy used for greenhouse heating increased by 10% in installed capacity and 13% in annual energy use. The installed capacity is 1,544 MWt and 23,264 TJ/yr in energy use. A total of 34 countries report geothermal greenhouse heating (compared to 30 for WGC2005), the leading countries being: Turkey, Hungary, Russia, China and Italy. Most countries did not distinguish between covered greenhouses versus uncovered ground heating, and only a few reported the actual area heated. The main crops grown in greenhouses are vegetables and flowers; however, tree seedlings (USA) and fruit such as bananas (Iceland) are also grown. Developed countries are experiencing competition from developing countries due to labor costs being lower—one of the main costs of operating these facilities. Using an average energy requirement, determined from WGC2000 data of 20 TJ/year/ha for greenhouse heating, the 23,264 TJ/yr corresponds to about 1,163 ha of greenhouses heated worldwide—a 16.3% increase over 2005.
3.3.2. Aquaculture Pond and Raceway Heating
Aquaculture use of geothermal energy has increased slightly over WC2005, reversing a downward trend from WGC1995; however, it is still down when compared to WGC1995. The increase over the past five years has been 6% for the installed capacity and 5% for annual energy use. The installed capacity is 653 MWt and the annual energy use is 11,521 TJ/yr. Twenty-two countries report this type of use, the main ones being China, USA, Italy, Iceland, and Israel. These facilities are labor intensive and require well-trained personnel, which are often hard to justified economically, thus the reason why the growth is slow. Tilapia, salmon and trout seem to be the most common species, but tropical fish, lobsters, shrimp, and prawns, as well as alligators also being farmed. Based on work in the United States, we calculate that 0.242 TJ/yr/tonne (7.75 W/kg) of fish (bass and tilapia) are required, using geothermal waters in uncovered ponds. Using the reported energy use of 11,521 TJ/yr, an equivalent 47,600 tonnes of annual production is estimated a 5.8% increase over 2005.
3.4. Industrial Applications & Agricultural Drying
The oldest industrial use is at Larderello, Italy, where boric acid and other borate compounds have been extracted from geothermal brines since 1790. Today, the two largest industrial uses are the diatomaceous earth drying plant in northern Iceland [
6], and a pulp, paper and wood processing plant at Kawerau, New Zealand [
12]. Notable U.S. examples are two onion dehydration plants in northern Nevada [
13], and a sewage digestion facility in San Bernardino, California. Alcohol fuel production has been attempted in the U.S.; however, the economics were marginal and thus this industry has not been successful. With the recent increase in fossil fuel prices, there has been renewed interest in producing ethanol and bio-diesel using geothermal energy [
14].
A recent development in the use of geothermal fluids is the enhanced heap leaching of precious metals in Nevada by applying heat to the cyanide process [
15]. Using geothermal energy increases the efficiency of the process and extends the production into the winter months.
Drying and dehydration are important moderate-temperature uses of geothermal energy. Various vegetable and fruit products are feasible with continuous belt conveyors or batch (truck) dryers with air temperatures from 40 to 100 °C [
16]. Geothermally drying alfalfa, onions, garlic, pears, apples and seaweed are examples of this type of direct-use.
An example of a small-scale food dehydrator is one located in northeastern Greece where four tonnes of tomatoes are dried daily, using 59
oC geothermal water to dry 14 kg/hour on racks placed in a long tunnel drier resulting in 400 kg of dried product daily. The tomatoes are then placed in olive oil for shipment and sale. The plant is only operated by three employees [
17]. At the other end of the spectrum is the large scale onion and garlic drying facilities located in western Nevada, USA employing 75 workers [
18]. These continuous belt drier are fed 3,000 to 4,300 kg/hr of onions at a moisture content of around 85% and after 24 hours produce 500 to 700 kg/hr of dried onions at moisture contents around 4%. These large belt driers are approximately 3.8 m wide and 60 m long.
Industrial applications mostly need the higher temperature as compared to space heating, greenhouses and aquaculture projects. Examples of industrial operations that use geothermal energy are: heap leaching operations to extract precious metals in the USA (110 °C), dehydration of vegetables in the USA (130 °C), diatomaceous earth drying in Iceland (180 °C), and pulp and paper processing in New Zealand (205 °C). Drying and dehydration may be the two most important process uses of geothermal energy. A variety of vegetable and fruit products can be considered for dehydration at geothermal temperatures, such as onions, garlic, carrots, pears, apples and dates. Industrial processes also make more efficient use of the geothermal resources as they tend to have high capacity factors in the range of 0.4 to 0.7.
3.4.1 Agricultural Crop Drying
Fourteen countries report the use of geothermal energy for drying various grains, vegetables and fruit crops compared to 15 for WGC2005. Examples include: seaweed (Iceland), onion (USA), wheat and other cereals (Serbia), fruit (El Salvador, Guatemala and Mexico), Lucerne or alfalfa (New Zealand), coconut meat (Philippines), and timber (Mexico, New Zealand and Romania). A total of 125 MWt and 1,635 TJ/yr are being utilized, a decrease from WGC2005, mainly due to the shutting down of an onion and garlic dehydration plant in Nevada, USA.
3.4.2. Industrial Process Heat
This is a category that has applications in 14 countries, down from 15 in 2005 and from 19 in 2000. These operations tend to be large and of high-energy consumptions. Examples include: concrete curing (Guatemala and Slovenia), bottling of water and carbonated drinks (Bulgaria, Serbia and the United States), milk pasteurization (Romania), leather industry (Serbia and Slovenia), chemical extraction (Bulgaria, Poland and Russia), CO2 extraction (Iceland and Turkey), pulp and paper processing (New Zealand), iodine and salt extraction (Vietnam), and borate and boric acid production (Italy). The installed capacity is 533 MWt and the annual energy use 11,745 TJ/yr, a 10% and 8% increase over 2005 respectively. This application has the highest capacity factor of all direct uses (0.70), as is to be expected because of its almost year-around operation.
3.6. Bathing and Swimming
People have used geothermal water and mineral waters for bathing and their health for many thousands of years. Balneology, the practice of using natural mineral water for the treatment and cure of disease, also has a long history. A spa originates at a location mainly due to the water from a spring or well. The water, with certain mineral constituents and often warm, give the spa certain unique characteristics that will attract customers. Associated with most spas is the use of muds (peoloids) which either is found at the site or is imported from special locations. Drinking and bathing in the water, and using the muds are thought to give certain health benefits to the user. Swimming pools have desirable temperature at 27 °C, however, this will vary from culture to culture by as much as 5
oC. If the geothermal water is higher in temperature, then some sort of mixing or cooling by aeration or in a holding pond is required to lower the temperature, or it can first be used for space heating, and then cascaded into the pool. If the geothermal water is used directly in the pool, then a flow through process is necessary to replace the “used” water on a regular basis. In many cases, the pool water must be treated with chlorine, thus, it is more economical to use a closed loop for the treated water and have the geothermal water provide heat through a heat exchanger [
20].
Romans, Chinese, Ottomans, Japanese and central Europeans have bathed in geothermal waters for centuries. Today, more than 2,200 hot springs resorts in Japan draw 100 million guests every year, and the “return-to-nature” movement in the U.S. has revitalized many hot spring resorts.
The geothermal water at Xiaotangshan Sanitarium, northwest of Beijing, China, has been used for medical purposes for over 500 years. Today, the 50 °C water is used to treat high blood pressure, rheumatism, skin disease, diseases of the nervous system, ulcers and generally for recuperation after surgery. In Rotorua, New Zealand at the center of the Taupo Volcanic Zone of North Island, the Queen Elizabeth Hospital was built during World War II for U.S. servicemen and later became the national hospital for the treatment of rheumatic disease. The hospital has 200 beds, and outpatient service, and a cerebral palsy unit. Both acidic and basic heated mud baths treat rheumatic diseases.
In Beppu on the southern island of Kyushu, Japan, the hot water and steam meet many needs: heating, bathing, cooking, industrial operations, agriculture research, physical therapy, recreational bathing, and even a small zoo [
21]. The waters are promoted for “digestive system troubles, nervous troubles, and skin troubles.” Many sick and crippled people come to Beppu for rehabilitation and physical therapy. There are also eight Jigokus (“burning hells”) in town showing various geothermal phenomena, used as tourist attractions.
In the former Czechoslovakia, the use of thermal waters has been traced back before the occupation of the Romans and has had a recorded use of almost 1,000 years. Today, there are 60 spa resorts located mainly in Slovakia, visited by 460,000 patients usually for an average of three weeks each. These spas have old and well-established therapeutic traditions. Depending on the chemical composition of the mineral waters and spring gas, availability of peat and sulphurous mud, and climatic conditions, each sanatorium is designated for the treatment of specific diseases. The therapeutic successes of these spas are based on centuries of healing tradition (balneology), systematically supplemented by the latest discoveries of modern medical science [
22].
Bathing and therapeutic sites in the U.S. included: Saratoga Springs, New York; Warm Springs, Georgia; Hot Springs, Virginia; White Sulfur Springs, West Virginia; Hot Spring, Arkansas; Thermopolis, Wyoming; and Calistoga, California. The original use of these sites was by Indians, where they bathed and recuperated from battle. There are over 115 major geothermal spas in the U.S. with an annual energy use of 1,500 TJ [
20].
Capacity and annual use figures for this application are the most difficult to collect and quantify. Almost every country has spas and resorts that have swimming pools heated with geothermal water (including balneology), but many allow the water to flow continuously, regardless of use. As a result, the actual usage and capacity figures may be artificially high. In some cases where use was reported, no flows or temperature drops (∆T) were known; in these cases 0.35 MWt and 7.0 TJ/yr were applied to estimate the capacity and energy use for typical installations. In other cases, 5 L/s and a 10 °C temperature change were used (0.21 MWt) for the installed capacity and 3 L/s and 10 °C temperature change (4.0 TJ/yr) were used for the annual use. Undeveloped natural hot springs are not included.
In addition to the 67 counties (up from 60 in 2005) that reported bathing and swimming pool use, the author was also aware of developments in Malaysia, Mozambique, Singapore and Zambia, although no information was available. The installed capacity is 6,700 MWt and the annual energy use is 109,410 TJ/yr, up 24% and 32% respectively over 2005. We have also included the Japanese-style inns that utilize hot spring water for bathing, as we included these figures in 2000 and 2005 [
23,
24]. The largest reported uses are from China, Japan, Turkey, Brazil and Mexico.
