Utilisation of geothermal energy in Iceland

The present and future uses of geothermal energy in Iceland are reviewed. The classification of geothermal areas is mentioned and their potential estimated. High temperature areas may be able to sustain the production of 20 MW/km² of electricity for at least 50 years. The potential of the 17 high temperature areas is almost 6000 MW, which is substantially greater than that of the 250 low temperature areas. However, practically all the hot water used for district heating and greenhouse farming is supplied by low temperature areas. About half the population of Iceland enjoys geothermal district heating at the cost of 35% that of comparable fuel oil heating. Utilisation of high temperature areas is relatively recent. Saturated steam from these areas is used for industrial purpose and a 60 MW geothermal power plant is being constructed.     

Low-temperature geothermal utilization in Iceland – Decades of experience

Geothermal energy plays a key role in the economy of Iceland and it supplies about 89% of the space heating requirements. A large fraction of the country's district heating services (hitaveitas) use energy from low-temperature geothermal systems, which are mostly located outside the volcanic zone. Many of the geothermal district heating services have been in operation for several decades and much can be learned from their operation, in particular regarding long-term management of low-temperature geothermal resources. In most cases down-hole pumps are used, but there are examples of large-scale artesian flow still being maintained. The Reykjavík geothermal district heating service is the world's largest such service. It started operation on a small scale in 1930, and today it serves Reykjavík and surrounding communities, about 58% of the total population of Iceland. The Reykjavík district heating service utilizes three low-temperature systems. The production and response (pressure, chemistry, and temperature) histories of these systems and six other low-temperature geothermal systems are discussed. Four of the systems are very productive and reach equilibrium at constant production. Two are much less productive and do not attain equilibrium, while three are of intermediate productivity. Groundwater inflow has caused temperature decline and chemical changes in two of the systems. Several problems have faced the Icelandic low-temperature operations, such as excessive pressure drawdown caused by overexploitation, colder water inflow, and sea water incursion. None of the district heating systems has ceased operation and solutions have been found to these problems. The solutions include improving the energy efficiency of the associated heating systems, deeper and more focussed drilling (e.g., directional drilling), finding new drilling targets (even new drilling areas), and injection, as well as technical solutions on the surface. The long utilization case histories provide important information pertaining to sustainable management of geothermal resources.     

The geothermal industry in Iceland

Direct (non-electrical) uses of geothermal energy in Iceland in 1984 amounted to 5517 GWh and the installed power was 889 MW_t, assuming 35°C discharge temperature. The bulk of this thermal power was for district heating, called hitaveita in Icelandic. In recent years this utilization has increased moderately. The installed geothermal electric power is currently 41 MW_e and is unlikely to change in the near future. Icelandic personnel have participated in many geothermal projects of the United Nations during the last 35 years. Contract work has been carried out by Icelandic consulting firms in several developing countries.     

Industrial use of the high-temperature geothermal field at Theistareykir, Iceland

The Theistareykir high-temperature geothermal field is located in the region Thingeyjarsýsla about 32 km from the coast and its principal town, Húsavík in northern Iceland. The paper shows that geothermal steam from the Theistareykir field can be piped to an industrial area close to Húsavík having a temperature of 170°C – 180°C at a cost of approximately US$ 4 per tonne while a steam cost of US$ 10 a tonne is quite common in steam consuming industries.The production of alumina is used as an illustration of the possible industrial use of geothermal steam. It is probable that the requirements for aluminium smelter capacity in Iceland may exceed 500,000 tonnes per annum within a decade. One million tonnes of alumina would be needed to achieve this annual aluminium production rate.     

Thermodynamic assessment of geothermal energy use in hydrogen production

In this study, geothermal-based hydrogen production methods, and their technologies and application possibilities are discussed in detail. A high-temperature electrolysis (HTE) process coupled with and powered by a geothermal source is considered for a case study, and its thermodynamic analysis through energy and exergy is conducted for performance evaluation purposes. In this regard, overall energy and exergy efficiencies of the geothermal-based hydrogen production process for this HTE are found to be 87% and 86%, respectively.     

Design of geothermal steam supply systems in Iceland

The role of the geothermal steam supply system is to receive the geothermal fluid from the geothermal wells, separate the steam from the water and to deliver steam and/or water to a user of the thermal energy. It may be for direct use in any kind of an industrial process, such as drying, heating, cooling, etc., or it may be intended for electric power generation. The steam supply system delivers the fluid at a specified temperature, pressure and quality to the user.The steam supply system consists of wellheads, steam collection pipelines, nowadays in Iceland normally designed for two-phase flow of water and steam, steam-water separators, main steam/water lines, moisture separators, control valves, exhaust system, and effluent disposal equipment as needed and may include compressors and/or pumps for long distance transportation.Design criteria for the system depend on one hand upon the characteristics of the geothermal field, and on the other upon the intended use and required steam quality and economy. High enthalpy fields, for example, are capable of producing high pressure steam which is relatively economical when electric power generation alone is being considered. For such systems, high quality of the steam is of utmost importance.The paper gives a general overview of the steam supply systems in Iceland and describes the main features of the Nesjavellir steam supply system where the main emphasis was laid on high steam quality in order to prevent scaling in turbines, control valves and heat exchangers. New systems or systems needing restoration should be based on the same features.     

Sulfur gas emissions from geothermal power plants in Iceland

Sulfur gas (H₂S and SO₂) emissions from geothermal fields in Iceland have been studied as part of a project, aimed at enhancing environmental research concerning effects of geothermal development. Short-term measurements of the gases have been carried out in several high-temperature geothermal fields in Iceland. In four exploited fields, baseline values for the concentration of sulfur gases have been obtained by long-term measurements. The data strongly reflect the dependence of gas concentrations on climatic factors, especially precipitation. Interpretation of the data by air distribution modeling, and by simple experiment, indicate minor, or at least very slow conversion of H₂S to SO₂ at atmospheric conditions in Iceland.     

International legal status of the use of shallow geothermal energy

Shallow geothermal energy (<400 m depth) is used in many countries worldwide, with a rising number of installations over the last decades. The use of ground source heat pump (GSHP) and groundwater heat pump (GWHP) systems results in local temperature anomalies (cold or heat plumes). Since groundwater is used in many countries as source for drinking water a balance between its use and protection has to be found. Therefore, to avoid detrimental environmental impacts it is necessary to define groundwater temperature limits for heating and cooling and minimum distances between such geothermal systems. The aim of the present study is to provide a comprehensive overview of the current international legal status for the use of shallow geothermal energy. Therefore, an international survey was performed using a questionnaire, which was sent to more than 60 countries worldwide. The questionnaire requested information on the corresponding national legislation, temperature limits and minimum distances for GSHP and GWHP systems. The answers to the inquiry showed an extremely heterogeneous outcome. Until now national and legally binding regulations only exist in few countries such as Denmark or Sweden. However, all existing regulations show a wide range for minimum distances (5–300 m) and temperature limits for groundwater. The highest inconsistency was observed for the acceptable temperature change with 3 K in Switzerland to 11 K in France. However, most countries have no legally binding regulations or even guidelines, which highlight the urgent need for further research on the environmental impact and legal management of shallow geothermal installations.     

Multiple integrated applications for low-to medium-temperature geothermal resources in Iceland

There is an increasing global demand for a faster, more expansive development in the energy sector, in order to improve the standard of living of the world's population by the creation of more jobs and better living conditions. The public is, however, well aware of the damage that has been done to the environment, in the form of deforestation, despoiling of lakes and rivers and, in particular, greenhouse effects, and it is unwilling to further sacrifice its natural environment. This decision puts pressure on scientists, engineers and developers to find ways and means of attaining “sustainable energy development”. In other words, the challenge now is to achieve the sustainable development of alternative renewable energy resources. Sustainability may be achieved in a number of ways, but the one most likely to result in a rapid increase in energy output without a deleterious impact on the environment is the revamping and integration of what we already have. This paper attempts to address sustainability as it applies to geothermal energy. We describe the concept of a multiple integrated use of geothermal energy, including the tenable benefits that can be obtained from applying this concept, such as a longer reservoir lifespan, a lower specific environmental impact, and greater marketing flexibility and profitability. The paper also emphasises the importance of achieving a maximum effective temperature drop across the application, commensurate with a minimum flow rate, optimal pumping characteristics and minimal fluid extraction from the geothermal reservoir. In geothermal house heating systems this means using large and effective radiators, dual-pipe heating systems, and thermostatic controls on each radiator. Where modifications to existing house heating systems are not feasible, e.g. by conversion from a single-pipe to a dual-pipe system or installation of larger radiators, an alternative solution is to adopt a cascaded flow of the geothermal fluid through a combination of heating systems operating at different temperature levels. For economic reasons it is always better to use the geothermal water directly if its chemical quality permits us to do so, otherwise heat exchangers made of resistant materials will be needed to isolate the geothermal fluid from the heating fluid in order to avoid corrosion or scaling in the pipes and radiators. The heat exchangers should be designed in such a way as to obtain a maximum temperature drop of the geothermal fluid. The paper also describes some heating system configurations, the characteristics of geothermal heating systems and their automatic control systems, as well as recommended geothermal field management and monitoring systems. The paper also includes a few examples of existing projects to demonstrate what has already been achieved and what could be done in the future; some suggestions are also made for new developments and innovations to make geothermal energy more generally attractive and useful worldwide.     

Evidence for thermal mining in low temperature geothermal areas in Iceland

This study deals with thermal mining in several geothermal systems in Iceland. A number of 2500- to 3000-m deep drillholes have been drilled into low temperature geothermal areas in the country. The conductive gradient outside active geothermal areas has also been mapped, and shows a systematic variation from lower than 50°C/km in the outer parts of the Tertiary basalts to over 100°C/km on the borders of the volcanic zones (rift zones). The difference between formation temperatures inside geothermal systems and the surrounding conductive gradient can be computed as a function of depth. This difference is termed ΔT in this paper. The ΔT-curves show that the upper parts of the geothermal systems are heated and the lower parts are cooled compared to the undisturbed conductive gradient. In many cases the cooling of the lower part is greater than the heating in the upper part, so that a net thermal mining has occurred. This thermal mining is calculated for several geothermal systems, and the systems are compared. The net thermal mining in the top 3000 m appears to be much greater in formations of Pleistocene and Pliocene age. It gradually decreases to zero for formations older than 6 million years. However, the net thermal mining is critically dependent on the maximum depth of water convection in these systems, which is unknown.     

The ring of fire : The use of geothermal energy in Indonesia

For Indonesia's myriad smaller islands, as well as for rural locations that cannot be economically connected to the grid, electric power development strategy is increasingly seen more in terms of the country's abundant renewable energy resources. Hydro, biomass, solar and wind energy are being explored for their potential to generate power, to lessen national dependence on fossil fuels. Expert attention today is focused on exploiting the huge geothermal potential of the spectacular mountain ranges in Java and Sumatra, volcanic Indonesia's so-called “Ring of Fire”. Richard Mogg, Lanna Blue Bangkok reports on geothermal energy production and use in the region.     

CO2 emissions from geothermal power plants and natural geothermal activity in Iceland

The ratio of CO₂ emissions from power plants to natural emissions is a measure of the environmental impact associated with geothermal power production. Emissions from Icelandic geothermal power plants amounted to 1.6 × 10⁸ kg year⁻¹ in 2002. Two independent estimates of natural CO₂ emissions range between 1 × 10⁸ and 2 × 10⁹ kg year⁻¹. Thus, power plant emissions are significant compared to estimated total emissions (i.e., not less than 8–16%). However, direct CO₂ flux measurements from four of the approximately 40 geothermal/volcanic systems in the country amounted to 3 × 10⁸ kg year⁻¹, indicating that these estimates of the total natural flux may be too low.     

Economics of low temperature,direct use applications of geothermal energy

An analysis of 20 processes utilizing low temperature geothermal energy was performed to determine the cost of delivered energy to the process. The analysis indicates that the portion of the cost associated with producing and reinjecting geothermal fluids dominate the cost of direct use applications of low temperature geothermal energy. As a result, the cost of delivered energy correlates with degree of utilization of the resource rather than the type of application. Low temperature geothermal resources can be expected to provide a competitive energy source when reinjection temperatures are low and seasonal peak demands are minimal, thus yielding high utilization rates. The cost of geothermal energy was found to be competitive with fuel-oil-based energy sources at energy utilization levels above 20% of the maximum available.     

Assessment of geothermal energy use with thermoelectric generator for hydrogen production

In this work, a new model for producing hydrogen from a low enthalpy geothermal source was presented. Thermal energy from geothermal sources can be converted into electric power by using thermoelectric modules instead of Organic Rankine Cycle (ORC) machines, especially for low geothermal temperatures. This electrical energy uses the water electrolysis process to produce hydrogen. Simulation and experiments for the thermoelectric module in this system were undertaken to assess the efficiency of these models. TRNSYS software is used to simulate the system in Hammam Righa spa, the temperature of this spring is 70 °C. Obtained results reveal that in hammam righa spa in Algeria, 0.5652 Kg hydrogen per square meter of thermoelectric generator (TEG) can be produced in one year.     

U.S. department of energy support of growth in industrial use of geothermal energy

The National Energy Strategy of the U.S. is designed to expand through federal policies the fuel and technology choices available to industry, utilities, and other energy users. It also promotes policies to encourage balanced integration of energy, economic, and environmental options in the selection of technologies for application in the marketplace. Consideration of each of these factors, separately and together, favors geothermal energy in many industrial applications. It is the policy of the Department of Energy to support growth in all uses of geothermal energy through focused R & D to improve technologies for its economic exploitation.