GEOTHERMAL HYDROGEN A VISION?

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1 PAPER PRESENTED AT EUROEPAN GEOTHERMAL ENERGY COUNCIL S 2 ND BUSINESS SEMINAR, EGEC 2001, MARCH 8 9, ALTHEIM, AUSTRIA GEOTHERMAL HYDROGEN A VISION? Werner Zittel, Werner Weindorf, Reinhold Wurster, L-B-Systemtechnik GmbH, Daimlerstr. 15, D Ottobrunn (info@lbst.de) and Werner Bußmann, Geothermische Vereinigung, Gartenstraße 6, Geeste (info@geothermie.de) Abstract With the progresses in geothermal electricity production by means of the hot-dry-rock (HDR) method electricity might be produced at cost of between ECU/kWh, depending on systems sizes of between 5 20 MW e. The electricity can be used to produce hydrogen from electrolysis and water. This method of electricity production offers high availability with operating hour of between 7,600 8,000 hours per year. The 40 GWh eletricity production per year from one 5 MW e geothermal plant are sufficient to produce enough hydrogen for the operation of an average fueling station with about 400 refuelings per day at cost of about percent higher than today s gasoline (including taxes). In this contribution some details of the analysis are presented as well as a general discussion of geothermal hydrogen production as a future energy vector. 1 Introduction: Why Hydrogen? - We need a carbon free fuel for mobile applications in the mid-term future (beginning in the next years and to be implemented to a certain degree at about 2010) - The European automotive industry has reached a self-commitment through ACEA which aims at reducing the average CO 2 emission of the entire European car fleet for sale in 2008 to 140 g/ km and to 120 g/km in If this selfcommitment would not be met the European Commission would enforce it via legislative measures. At present, car manufacturers do not know how they can achieve these requirements with existing propulsion technologies or conventional fuels while maintaining the present mix of vehicle classes. - Hydrogen offers the most promising perspectives since it can be produced from various sources such as conventional electricity, renewable electricity, conventional steam reforming and regenerative steam

2 reforming following a biomass gasification process and thus has the highest energy source flexibility of any alternative fuel and therefore offers the most robust strategy to clean transportation fuels it is suited for a broad spectrum of applications: from caloric burning as gas via chemical processes to electrochemical conversion in fuel cells - Short to mid-term: Hydrogen as fuel for fuel cells. But in addition, via electrolysis and fuel cells, hydrogen offers a perspective to store large quantities of electricity without raw materials limitations as, e.q., batteries do. Therefore it will be introduced as buffer storage of electricity for smoothing the load profile. The perspective is short to midterm (presumably within the next five years) for local applications as off-shore wind energy or smaller sized stand- alone systems based on renewable energies. Why Geothermal Energy? In front of severe basic problems to mankind such as increased carbon emissions mainly from fossil fuel combustion and its impact to global climate, and resource restrictions of fossil fuels which we will have to face with very soon we need fast, clean and cost efficient alternatives. Among other renewable energy technologies, the world s geothermal potential offers a good perspective, for both thermal applications as well as electricity production. Its advantages might be described as - huge potential (of up to 12,000 TWh/a of sustainable power generation potential, of which about 10% are estimated to be utilized by 2020 [Source: Bjornsson et al. 1998]) - available around the clock, independent from weather or climatic influences - using engineered geothermal systems (HDR, HWR, DHM etc.) geothermal energy is available everywhere - clean and inexhaustible energy source - comparable economics also for small-scale applications Why geothermal Hydrogen? - Hydrogen might be produced from various sources. One option might be the production from geothermal resources via electrolysis. In countries, rich of geothermal sources, certainly geothermal hydrogen will become a major energy vector (e.g Iceland is already on the way to realization).. If this option will take its place in relation to others within a hydrogen economy will depend on availability, and prices. General concept The hydrogen is stored at high pressure (above 30 MPa) and distributed via several dispensers to refuel vehicles with internal combustion engine or with fuel cell drive system at demand. Hydrogen supply of the fuelling station has a broad range of supply options, as sketched in figure 1below.

3 Hydrogen might be delivered to the station as liquid hydrogen coming from centralized liquefaction plants or even imported from cheap hydro power stations abroad (e.g. Iceland, Canada, Patagonia). Its thermodynamical energy content could be used for compression during gasification. Hydrogen might be produced onsite from natural gas or biomass gasification. This is a preferable option in rural areas with biomass sources and place for a reformer system. Hydrogen might be produced electrolytically by electricity obtained from conventional sources or from all types of renewable sources. Geothermal electricity production, however, offers the only choice, to produce the electricity on site. Solar Geothermal Wind Hydro Conventional Electricity Water Electrolysis Hydrogen Import Natural gas Liquid hydrogen Compressor Storage (p> 30 MPa) Waste Biomass Steam Reformer Single storage or cascade at different pressure levels Figure 1: Sketch of different supply options for hydrogen 2 Geothermal electricity production The proposed scheme is electricity generation via HDR (hot dry rock) geothermal energy use in small scale of about 5-6 MW el and MW th. The heat might be used for various purposes, e.g. to feed a local district heating system. Therefore, HDR-electricity generation might be planned efficiently only at locations where an appropriate heat demand exists. The scheme outlined in figure 2 shows the energy flows of the demonstration project in Bad Urach. From a depth of several thousand meters hot water of more than 140 C is pumped through several heat exchangers before it is re-injected at below 50 C temperature. A major part of the energy is used for thermal applications. Within an organic rankine cycle (ORC), using the evaporation energy of the organic working fluid, electricity is generated. A part of the low temperature waste heat from the cooling water might be used even further. Details of the project are given in literature.

4 The technical data are : Life expectance: Operation and maintenance cost: Peak power: Average operation hours per year: Typical daily electricity production: Electricity cost: For large assembly (> 20 MW el ): 25 years ~ 3 percent of investment 5 6 MW el and MW th 7,600 8,000 hours demand oriented (within one hour) Helmut Tenzer 0.09 Euro/kWh el < 0.07 Euro/kWh el Figure 2: Scheme of energy flows of geothermal energy production with hot dry rock technique. An artist s view of the complex is presented in figure 3

5 Helmut Tenzer Figure 3: Artist s view of of a Hot-Dry-Rock system 3 Hydrogen Fuelling station Today, Germany has about 16,000 fuelling stations. According to customers, about at least 10 percent need to offer an alternative fuel in order to provide sufficient coverage and thus to encourage customers to switch to the new fuel. Therefore within several years about 1,000 to 2,000 hydrogen fuelling stations have to be planned, constructed and set into operation. Estimates come to hydrogen specific total investment costs of somewhat more than 5 billion Euro. Technical description In the following, we describe the layout for a hydrogen fuelling station which might deliver enough energy to fuel about 400 vehicles daily, typical for an conventional average fuelling station. Figure 4 shows the systems concept.

6 Electricity generation: 5 MW e ; 8,000h/yr Compressor 150 kw ~1,000 Nm 3 /h Electrolyzer 3-5 MW e ; 3 MPa ~1,000 Nm 3 /h Storage: > 7,000 Nm MPa Dispenser 1,100 Nm 3 /h filling time 3 min [Source: Opel] On board storage ~55 Nm 3 /vehicle Depth : 4,500 6,000m Hot dry rock T = C Figure 4: Systems concept Rough cost figures are: Electrolyzer: ~ 400 /kw e Compressor: ~ 1,500 /kw e Storage: ~ 400, ,000 (depending on storage volume) Dispenser: ~ 100,000 per unit Which form of hydrogen? Energy efficient onsite generation of hydrogen for the foreseeable future can only be realized for compressed gaseous hydrogen, not for liquefied hydrogen (LH 2 ). Centralized large-scale hydrogen production is suited for LH 2 production or for distribution via pipeline systems. Vectorization of hydrogen in liquid form is especially suitable for hydrogen production over long distances and for markets where hydrogen is requested in liquid form. Distributed onsite generation of hydrogen in principle can be realized with hydrocarbon reformers (natural gas, methanol, ammonia, biomass) or with pressurized electrolysis. Both methods generate hydrogen at reasonable pressures of 2-3 MPa which save the first compression stage compared to atmospheric pressure production. Then hydrogen is compressed to onsite storage pressures of between 40 MPa and 80 MPa in order to allow vehicle storage pressures of 35 MPa to 70 MPa. Design parameters for a typical fuelling station Full scale fuelling station with about 6 dispensers and typically 410 refuellings per day (min 206; max. 607) with a peak frequency of 41 refuellings per hour. Total hy-

7 drogen requirement is somewhat less than 24,000 Nm 3 per day. The daily consumption pattern is exhibited in figure 5, showing the smooth hydrogen consumption and the typical loading/discharging cycles of the storage while supplying the daily demand. Number of vehicles Hydrogen [Nm 3 /h] Production To storage Consumption From storage Figure 5: Typical daily consumption pattern at average fuelling station To storage Figure 5 exhibits that the production capacity of an average size refuelling station required is of somewhat less than 1,000 Nm³/h of hydrogen. The peak dispensing during the afternoon hours can require up to 50% high capacities. The differences between daily low and high demand hours is usually balanced by a high pressure hydrogen storage system. The electrolyzer and the gas compression system then can be designed for the mean production of around 1,000 Nm³/h. If the refuelling station lies in areas highly frequented during vacation days and by weekend excursion traffic, the capacity of the station s electrolyzer and compressor has to be adapted accordingly, i.e. oversized in comparison to the mean capacity, in order to avoid running dry. This illustrates that each refuelling station has to be laid out according to its specific load curve (clients of a given size per time unit). If we compare hydrogen prices which can be achieved via geothermal production with today s taxed gasoline prices we see that they would match approximately as soon as today s crude oil prices would double (see figure 6). For untaxed gasoline a quadrupling of today s prices would be necessary in order to be cost competitive. Those who might think that such price developments are unrealistic should recall that in California in the year 2000 the natural gas prices quadrupled and at the spot market even reached levels which were far above a crude oil price of 100 US$ per barrel.

8 2,000 h/yr, storage 30 percent of daily consumption 4,000 h/yr, storage 70 percent of daily consumption ,000 hours per year, storage 30 percent of daily consumption 6,000 h/year; storage 30 percent of daily consumption 8,000 h/yr; 30 % of daily consumption from storage Gasoline price including tax, July 2000 (2,05 DM/liter) ) Gasoline price without tax, July [Pf/kWh CGH2 ] 5 MW 25 MW Geothermie electricity cost [Pf/kWh] Figure 6: Hydrogen cost with respect to electricity cost and storage capacity; For comparison today s gasoline prices are also given with and without taxation [10 Pf/kWh 0.05 Euro/Wh] 4 Outlook and concluding remarks Geothermal hydrogen is one option! - It is the primary option where sources are abundantly available (e.g. Iceland) - It is an option where the huge amounts of heat can be used efficiently - In Germany its future might depend on cost relations and the cost reduction potential with respect to other renewable hydrogen options (e.g. worse than wind or biomass derived hydrogen, but much better than photovoltaic hydrogen) and their availability - It is an option for green hydrogen in the transportation sector, the equivalent to green electricity in stationary applications To develop a feeling about the volumes to be managed in a future hydrogen world we just sketch a few figures: The above fuelling station with 8 Mio Nm 3 of hydrogen supply per year is appropriate to fuel about 4,000 5,000 passenger cars completely. Therefore to fuel 10 percent of German cars would need about 1,000 such fuelling stations. 10,000 are needed to fuel all passenger cars in Germany. To supply one station with energy would require about 40 GWh electricity to be produced either by geothermal sources as sketched in this contribution, by off shore

9 wind power from about 5-7 converters each with 2.5 MW capacity, by domestic photovoltaics from about 600 x 600 m 2 area or from any other electricity source. Alternatively, to supply one station with hydrogen from hydrocarbon decomposition would require a feed gas to be produced from biomass gasification of about 1,300 ha area, from waste biomass of about 8,000 t per year, or from conventional natural gas reforming of about 3.5 Mio Nm 3 of natural gas per year. These figures may easily be summed up to estimate the efforts needed to supply the whole road traffic with hydrogen, one day. As a rough estimate, to supply all hydrogen via electrolysis would need about TWh of electricity (including heavy duty vehicles and buses). This is roughly the same amount of electricity as is needed today for all other purposes. But it is even less energy equivalent as the traffic consumes today in form of fossil fuels (~ 650 TWh). To supply all that hydrogen from natural gas reforming requires 70 billion Nm 3 per year, about two thirds of natural gas already consumed today. Finally, it should be reminded that the billion Nm 3 of hydrogen to supply the whole road traffic is three to four times the amount of hydrogen already produced and consumed today in Germany in chemical and petrochemical applications. Often it is argued that renewably produced electricity with its high exergy content shouldn t be wasted as long as fossil fueled power stations still feed the grid. But, we will argue that in real world you cannot dictate that road traffic has to wait with its carbon free propulsion until all other customers are healthy, and, finally, has to start latest. It seems to be the same discussion as whether to promote the use of photovoltaics until still any fossil generated heat is used instead of solar thermal production. We think, life (and evolution) works different in opening as many options as possible and than wait and see. Furthermore, today s world vehicle population of about 700 million internal combustion engine motor vehicles will double over the next 30 years (one generation) merely due to the foreseeable motorization of China, India and Indonesia, not talking about Latin America, Russia and Africa. These new consumers cannot be supplied by petroleum derived fuels and probably not even by natural gas derived ones. Therefore, clean fuels from renewable sources combined with an energy efficiency and lifestyle revolution are an indispensible MUST. 5 Literature Geothermal Association, Geeste ( H2T Liquid Hydrogen Delivery System, Study by L-B-Systemtechnik GmbH, February 18 th, 1999 The Potential Role of Geothermal Energy and Hydropower in the World Energy Scenario in Year 2020; J. Bjornsson et al; 17 th Congress of the World Energy Council, Houston 1998