geothermal electricity and combined heat & power - European ...

EuropeanGeothermalEnergyCouncilGeothermal Electricity andCombined Heat & PowerContentPageIntroduction 3Geothermal Power Systems 4Dry steam and Flash power plants 5Binary cycle power plants 6Geothermal CO 28Geothermal electricity history 9Geothermal electricity in Europe 10Geothermal electricity worldwide 12Combined Heat and Power 13EGEC | Geothermal Electricity and Combined Heat & Power

Dry steam andFlash power plantsDry steam power plants utilise straightforwardlysteam, which is piped fromproduction wells to the plant, then directedtowards turbine blades. The first, ever exploited,geothermal field, still in operation, at Larderelloin Italy, is among the very few drysteam fieldsrecorded worldwide.Flash steam power plantsConventional drysteam turbines require fluidsof at least 150°C and are available with eitheratmospheric (backpressure) or condensingexhausts. In the backpressure system steam ispassed through the turbine and vented to atmosphere.This cycle consumes twice more steamper produced kilowatt-hour (kWh), at identicalturbine inlet pressure, than a condensing cycle.However, backpressure turbines may proverewarding as pilot or/and stand by plants in caseof small supplies from remote isolated wells andfor generating electricity in the early stages of fielddevelopment. They become mandatory in caseof high non condensable gas contents, in excessof 12% in weight, in the vapour phase.The steam, separated from the water, is piped tothe plant to drive a turbo-alternator. The separatedleft over brine, together with the condensedsteam, is piped back into the source reservoir, aninjection process meeting waste disposal, heatrecovery, pressure maintenance and, last but notleast, resource sustainability requirements.Berlin 44 MWflash power plant -El Salvador.Condensing units are more complex in design,requiring more ancillary equipment and space andup to twice long construction/installation delays.Turbine specific steam consumption varies from8 to 10 t/h depending on temperature and pressure.55 to 60 MW eplant installed capacities are quitecommon but, recently, 110 MW eplants have beencommissioned and are currently operating.Flash steam plants, by far the most common,address water dominated reservoirs and temperaturesabove 180°C. The hot pressurised waterflows up the well until its pressure decreases tothe stage it vaporises, leading to a two phasewater-steam mixture and a vapour lift process.Larderello standard unitof 20 MW dry steampower plant - ItalyEGEC | Geothermal Electricity and Combined Heat & Power 5

Binary cycle power plantsBinary, known also as organic Rankinecycle (ORC), plants operate usually withwaters in the 100 to 180°C temperaturerange. In these plants, the heat is recoveredfrom the geothermal fluid, via a heat exchanger,to vaporize a low boiling point organic fluidand drive an organic vapour turbine. The heatdepleted geothermal brine is pumped back intothe source reservoir, thus securing sustainableresource exploitation. Since the geothermaland working fluids are kept separated duringthe process there are little if any, atmosphericemissions. Adequate working fluid selection mayallow to extend the former design temperaturerange from 180°C to 75°C.Upper and lower temperature limits depend onthe organic fluid stability and techno-economicconsiderations respectively. At low temperaturesthe size required by the heat exchangers coulddefeat project economic viability. Apart from lowto medium temperature utilisation, geothermaland waste fluid binary processes can be contemplatedto avoid well scaling damage further toin-hole flashing, in which case submersiblepumps are used to produce the geothermal fluidunder pressure.Binary powerplants.Binary processes are emerging as a cost effectiveconversion technology for recoveringpower from, water dominated, geothermalfields at temperatures below 180°C. Recently,a new candidate binary process, known as theKalina cycle, has been developed, displayingattractive conversion efficiencies. It’s distinctivefeatures address an ammonia-water workingfluid mixture and regenerative heating. In brief,it takes advantage of the low boiling point of thewater-ammonia mixture to allow a significantfraction of it to be vaporised by the excessheat available at turbine exhaust. The gainsover conventional ORC plant efficiencies havebeen estimated at 40%, although its reliabilityand performances are yet to be demonstratedon long term plant service.Reclamation of low temperature geothermalsources, achievable via binary cycles, can significantlyincrease the overall worldwide exploitationpotential. Small scale geothermal binary plants(< 5 MW eratings) can be widely implemented inrural areas and, more generally, respond to anincreasingly disseminated human demand.6 EGEC | Geothermal Electricity and Combined Heat & Power

10 MW eRibeiraGrande binaryunit - AzoresIslands.Binary systems represent a means for upgradingoverall plant efficiencies of “conventional” flashcycles. Contrary to dry steam plants, where thewater phase reduces to steam condensates,flash units produce large amounts of separatedwater and waste heat, which remains lostunless otherwise utilised as heat proper (spaceheating/process heat for instance) or as binarypower downstream from the flash steam turbine.This power cascading scheme produces lowcost energy extras at zero mining costs.200 kW eChenahot spring binaryunit using 74°Cgeothermalresource- Alaska2 MW eHusavikKalina binaryunit- IcelandEGEC | Geothermal Electricity and Combined Heat & Power 7

Geothermal CO 2Geothermal systems are located in areasexhibiting high CO 2fluxes inherent tothe geology of geothermal host structures.In volcanic environments much higherCO 2fluxes are the rule.Natural generationof CO 2in geothermalsystemsFor instance, in Italy, in the Central West Tyrrhenianregion, large amounts of CO 2are producedat depth as a consequence of marine carbonaterock metamorphism. During their ascent, gasesget trapped in deep seated structures includingpermeable mesozoic limestones overlain byimpervious capping terrains, which becomesources of high CO 2upward flows. For thisreason, deep ground waters are enriched indissolved CO 2. Metamorphic processes affectingcarbonate phyllites can also contribute toCO 2production from shallow crustal levels atca 8 km depths and 400-500°C temperatures,higher than those (3-4 km; 200-300°C) of theoverlying geothermal reservoir.LarderelloNoteworthy is that natural CO 2production is independentfrom geothermal exploitation. Actually,surface manifestations, characterised by hotwater and steam discharges from springs andfractures, can create an environment hostile tohuman settlements (Larderello, Yellowstone).Thanks to industrial geothermal exploitation,deep, eventually toxic, geothermal fluids could bechannelled, via geothermal wells and collectinglines, to power plants concentrating on a singlepoint (the plant chimney) natural emissions, whichwould otherwise contaminate the surrounding soilsand atmosphere over much larger areas.Summing up, geothermal CO 2emissions arenot generated by the industrial exploitationprocess.CO 2emission in electricity productionGeothermal,natural emission122Natural Gas315Oil760Coal9150 100 200 300 400 500 600 700 800 900 1000CO 2emission g/kWh8 EGEC | Geothermal Electricity and Combined Heat & Power

First experimentto producegeothermalpower, donein Italy in 1904by princeGinori ContiGeothermal electricity historyIn the early 1900’s, geothermal fluids werealready exploited for their energy content. Achemical industry was set up in Italy duringthat period, in the area known now as Larderello,to extract boric acid from natural hot water outletsor from purposely drilled shallow boreholes. Fromyears 1910 to 1940 the low pressure steam,in that area of Central Tuscany, was utilisedto heat industrial and residential buildings andgreenhouses. In 1928, Iceland, another pioneerin the utilisation of geothermal energy, beganexploiting its abundant geothermal resources(mainly hot waters) for domestic heating.This application, exemplified by Italy, was followedby several countries. In Japan, the first geothermalwells were drilled in 1919 and, in 1929, at TheGeysers, California, in the USA. In 1958, a smallgeothermal power plant started operating in NewZealand, in 1959 in Mexico, in 1960 in the USA,and in many other countries the following years.The first attempt to generate electricity from geothermalsteam dates back to 1904 at Larderello.The success of this experiment (see illustration)proved the industrial value of geothermal energyand marked the beginning of an exploitation routethat was developed significantly since then. Actually,electricity generation at Larderello was acommercial success. By 1942 the installed geothermoelectriccapacity had reached 128 MWe.GeothermalBook - Italy.PanoramaLarderello -TodayEGEC | Geothermal Electricity and Combined Heat & Power 9

Geothermal electricity in EuropeAs far as geothermal electricity is concerned,the vast majority of eligible resources,in Continental Europe at large, isconcentrated in Italy, Iceland and Turkey; thepresently exploited potential represents so far0.3% of the whole renewable energy market.There are two major geothermal areas in Italy,Larderello-Travale/Radicondoli and Monte Amiatarespectively, achieving a 810 MW einstalledcapacity.They represent two neighbouring parts of thesame deep seated field, spreading over a huge,ca 400 km 2 , area, which produces superheatedsteam. On the Larderello side, the exploited areaand installed capacity amount to 250 km 2 and562 MW erespectively. On the Travale/Radicondoliside, to the Southeast, the installed capacity is160 MW eand the exploited area 50 km 2 . Thesteam condensates recovered from Travale arereinjected into the core of the Larderello field,via a 20 km long water pipeline.The Monte Amiata area, in Northern Latium,includes two water dominated geothermal fields,Piancastagnaio and Bagnore. On both fields a deepresource has been identified under the shallowproducing horizons. Weak social acceptance fromthe local communities are slowing down the fulldevelopment of the promising, high potential, deepreservoir. Presently, five units are operating, one inBagnore and four in Piancastagnaio, totalling a 88MWe installed capacity. Projects, adding a further100 MW ecapacity, have been commissioned andwill be completed in the near future.Geothermal resources in Iceland relate to the activevolcanic environment of the island, located onthe mid-Atlantic ridge and its sea floor spreadingattributes. Iceland has proved a leading countryin direct uses of geothermal energy, mainly ingreenhouse and district heating (89% of the totaldomestic heating demand) and is increasing itselectricity production, which reached (@2006) a420 MW einstalled capacity. Although significant,this capacity ought to be compared to the hugepotential of the island, estimated at ca 4000 MW e,a figure far above national power requirements,ca 1500 MW e, among which hydropower holdsthe dominant share (1300 MW e).Turkey’s geothermal resources are mainly locatedin Western Anatolia on the Aegean sea façade.District heating stands presently as the mostimportant utilisation with 65000 heated homes.This, in spite of mild climatic conditions which stillmakes geothermal heat competitive as a resultof the high cost of electric heating, 8 to 10 timeshigher than geothermal heat. Electricity productionin the Kizildere water dominated field is suppliedby a 15 MW edesign plant (start up, 1988) capacity,actually standing at 12 MW e. Binary plantshave been commissioned. The largest geopower(flashed steam) plant, rated 45 MW e, is presently inadvanced construction stage at Germencek. Thenational geothermal electricity potential has been(conservatively) estimated at 200-300 MW e.In Greece, high temperature geothermal resourcesare located in the Aegean volcanicisland arc, in the Milos (Cyclades) and Nisyros(Dodecanese) islands, thanks to direct drillingand testing assessments. Electricity generationfrom a 2 MW erated pilot plant ceased further tothe strong opposition of the local community andmismanaged communication by the geothermaloperator. The country potential in the Aegeanarchipelagos and, at a lesser extent through, inthe northern, mainland located, grabensis estimated at ca 200 MW e. Otherwise,several low temperature fields areexploited, on presently limited bases,for greenhouse heating and processheat applications.In Russia, geoelectric development tookplace in the Mutuovski field of Kamchatkawhich, although belonging politically toEurope, ought to be regarded as geogra-IcelandKrafla, Iceland10 EGEC | Geothermal Electricity and Combined Heat & Power

approximately from 2 to 4.5 €/MW,and very attractive generation costs,from 40 to 100 €/MWh. It is a resourcesuitable for base load power.GeothermalelectricityworldwideThe growth of developing countries willresult in a two fold increase of the globalelectricity demand over the next 25 years,from 15,000 TWh in 2005 to 30,000 TWh in 2030.The present renewable energy quota is 21.5%(mainly hydro), while the projected share will be25.8% in 2030.Geothermal Energy provides approximately 0.4%of the world global power generation, with a stablelong term growth rate of 5%. At present, the largestmarkets are in the USA, Philippines, Mexico, Indonesia,Italy and Iceland. Future developments arelimited to areas worldwide, particularly under currenttechnologies. The present installed capacity of 9GW will increase up to 11 GW in 2010. It displaysinvestment costs, depending on the quality of theresource (temperature, fluid chemistry and thermodynamicsphase, well deliverability,..), rangingIt can be considered as broadlycost-competitive, despite relativelyhigh capital investment costs forthe development of the geothermalfield (resource assesment, miningrisk, drilling and piping), owing toits very high availability and stableenergy production. The next generationshould be able to benefit fromthe implementation of the Enhanced GeothermalSystem (EGS) production, alongside an intensiveincrease of low-to-medium temperature applicationsthrough binary cycles and cascading uses.Geothermal electricity potentialEstimating the overall worldwide potential is adelicate exercise due to the many uncertaintiesinvolved. Nevertheless, it is possible to identify arange of estimates, by taking into considerationalso the possible impacts of new technologies (permeabilityenhancements, drilling improvements,EGS, low temperature electricity generation).Minimum: 35,000/70,000 MWMaximum 140,000 MWIt is deemed possible to produce up to a maximumof 1,000 billion kWh of electricity annually, i.e.8.3% of total world electricity production, serving17% of the world population. 39 countries (mostlyin Africa, Central/South America and the Pacific)can be wholly geothermally poweredWorld Geothermal PotentialInstalled Capacity Wordlwide150,000 MW12 GW10 GW100,000 MW8 GW50,000 MW0 Current Today’sTechnology EnhancedTechnology6 GW4 GW2 GW01980 1990 2000 2010Installedcapacity from1975 up toend of 2007(light blue) andto 2010 (red).12 EGEC | Geothermal Electricity and Combined Heat & Power

SvartsengiPower Plantaerial viewCombined Heat& PowerGeothermal CHP is nothing new. As amatter of fact, a low temperature (81 °C)geothermal resource has been exploited,since the late 1960’s, at Paratunka, Kamchatka,Russia, combining power generation (680 kW einstalled capacity) and direct uses of the (huge)waste heat for soil and greenhouse heatingpurposes. Such a temperature cascading use iswhat geothermal CHP is all about. Actually,heatmay be regarded as a by product of geothermalpower production in terms of either waste heatreleased by the generating units or excess heatfrom the geothermal source. The latter opportunityhas been exploited by the Sudurness GeothermalDistrict Heating Corporation in Iceland.Here, steam from the nearby high enthalpy, liquiddominated, field heats, up to 95-105°C, coldground water, which is piped to nine surroundingcities and the Kevlafik International Airport. Thiscogeneration scheme, unique of its kind, secures45 MW eand 150 MW thpower and heat capacitiesrespectively, indeed a true geothermal paradise,combining, equally shared, power generationand heating issues.Sudurnes Regional HeatingSystem LayoutPower generation from medium enthalpy sources,standing in the 100-150°C temperature range,by using a low boiling point working fluid andan organic vapour turbine, a conversion processknown as the Organic Rankine Cycle (ORC), canhardly seek economic viability, unless a heatingsegment be added to the utilisation grid.EGEC | Geothermal Electricity and Combined Heat & Power 13

What can we do with geothermal energyOver the last decades a growing concern on environmental issues has been spreading aroundthe world’s people, and, contemporaneously, the demand of energy was shooting up too. It isalso evident that energy sources are not equally distributed among the countries and quite oftendeveloping nations cannot afford buying fossil fuels abroad to supply their industries and to warm theirdwellings. It is clear that an indigenous and easily exploitable energy source is needed in many countriesaround the world to give a boost to local activities and support a self-sustaining economic growth.Geothermal energy can then represent a viable, local and environmental friendly solution for many suchcountries. In fact, geothermal energy is almost ubiquitously available and could be used to spare fossilfuels in dealing with different processes. Moreover, no burning is involved and no manmade emissions willaffect the area (any geothermal area is already characterised by gas emissions which escape naturallyfrom the ground, but no combustion is involved and the clouds over geothermal plants are made ofsteam). Also, there is no radioactive waste.In a few words, geothermal is a clean, reliable and baseload energy (available year round and roundthe clock), that save money at home (no fuel to be imported from abroad), and can create jobs in localcommunities. In addition, it helps the implementation of the Kyoto Protocol and of the EU objectives.EuropeanGeothermalEnergyCouncilContact:EGEC - European Geothermal Energy Council a.s.b.l.Renewable energy House63-65 rue d’ArlonB-1040 BrusselsT : + 322 400 10 24F : + 322 400 10 10W : www.egec.orgE : info@egec.orgThe sole responsibility for the content of this publication lies with theauthors. It does not necessarily reflect the opinion of the EuropeanCommunities. The European Commission is not responsible forany use that may be made of the information con-tained therein.Supported byPhoto and graphical elements credits : EGEC, Geotec Consult,Geothermal Education Office - California, ENEL, IGA, ORMAT, Enex,GRC, Orkustofnun, Geoheat Center (OIT), City of Altheim, GTN,Geofluid, G.E.I.E. Exploitation Minière de la Chaleur.Published in December 2007 - Text: Ruggero Bertani andPierre Ungemach - Design: ACG Brussels - Printed onecologically friendly paper (chlorine-free paper)