Vol. 23, No. I, pp. 1-6, 1998 Association for Hydrogen Energy Elsevier Science Ltd All rights reserved. Printed in Great Britain 036&3199/98 $19.00+0.00
:C 1997 International
Pergamon PII: SO360-3199(97)00021-9
U. WAGNERt, B. GEIGER? and H. SCHAEFER1 tlnstitute for Energy Technology and Power Engineering, Technical University Munich, P.O. Box 20 24 20, D-80290, Munich, Germany fResearch Institute for Energy Technology, Am Bltitenanger 71. D-80995, Munich, Germany
Abstract--In any overall balance of hydrogen energy systems it is the way in which this energy is generated and the primary energy required to produce the equipment that are of decisive importance. Excerpts from the results of a study entitled “Process Chain Analysis for a Hydrogen Energy System”, commissioned by the Bavarian State Ministry of Economics, Transportation for Hydrogen Energy
INTRODUCTION The German government decided in 1990 to reduce energy-related CO2 emissions by 25% by the year 2005 (based on 1987 levels). This extremely ambitious goal presupposes signiticant savings to be made at the consumer end and, to the same extent, great efforts in energy generation and conversion. The most important measures to cut CO, emissions in the field of energy conversion include further optimization in conversion efficiencies and an increasing use of renewable sources of energy where it makes economic and energy sense; it also involves greater use of nuclear energy to the extent acceptable to politicians and the public at large. A widely discussed concept to conserve fossil primary energy and to reduce emissions in energy conversion and usage could be the introduction of a hydrogen energy system. Hydrogen, as a secondary source of energy, is similarly versatile in terms of its production and applications as electric energy, it is as easy to handle, but easier to store. The study [l] defines several technically interesting variations of hydrogen production, storage, transport and selected applications and estimates its energy efficiency and costs. Distinctions are made between the fundamental technical principles (e.g. liquid hydrogen LH2 or gaseous hydrogen GHJ, and estimates are made for the years 1995 and 2020 for different design sizes, from distributed plants of under 1 MW to large central plants with several hundred megawatts. With a view to the required process components and processing stages, the following areas are covered: ~ availability of power and/or fuel for the production of H,;
production of H,; conversion and storage of GH2; transport (and distribution) of GH, and LH2; power generation from HZ; distribution of making GH, or LH, available to the consumer.
ANALYSIS OF PRIMARY CONSUMPTION
The cumulative energy demand KEA  states the entire demand, valued as primary energy, which arises in connection with the production, use and disposal of an economic good (product or service) or which may be attributed respectively to it in a causal relation. This energy demand represents the sum of the cumulative energy demands for the production (KEA,,), for the use (KEA,) and for the disposal (KEA,) of the economic good. It has to be indicated for these partial sums which preliminary and parallel stages are included. The cumulative energy demand for production (KEAb,) denotes the sum of those energy expenditures valued as primary energy which result from the production of an object or a service itself as well as from the acquisition, processing, fabrication and disposal of the production and auxiliary materials, the consumables and the production facilities including the demands for transport. The cumulative energy demand for use (KEAN) denotes the sum of those energy expenditures valued as primary energy which result from the use of an object or a service, renewable energy inputs are not taken into account in this study. In addition to the energy con-
U. WAGNER et al.
sumptionfor operation itself, this sumalsoincludesthe cumulative energy demandfor the production and disposalof replacementparts, auxiliary materialsand consumables,as well as of production facilities which are required for operation and maintenance.The operating and servicelives taken asa calculationbasisalwayshave to be indicated.The energy demandfor transportsis to be included. The cumulativeenergydemandfor disposal(KEA,) is the sumof thoseenergyexpendituresvalued asprimary energywhich result from the disposalof an object or of parts of the object, i.e. from the final removal from the utilization cycle. This sum includesin addition to the energy usefor the disposalitself the cumulative energy demand for the production and disposalof auxiliary materialsandconsumables aswell asof production facilities which are required for the disposal.The energy demandfor transportsis to be included. No data is available on the disposalof many of the new technologiesunder review. Basedon current experience,this can be neglectedin relation to the estimates presentedhere. Figure 1 showstwo selectedprimary energy balances includingthe primary energyrequiredto producevarious plant components,one for a combinedcycle plant (combinedgassteampower station), and the other for a photovoltaic plant in North Africa. The underlying systematicapproachis identical in this figure and in the following energyflow charts. The primary energy required for the production of equipmenthasbeenplotted for both plants,incomingat the top left-hand side.The useof fossilenergy,adjusted for primary energy, is shownas an arrow flashingver-
tically from the top, whereasrenewableenergy sources enter the picture from the top right-hand side. The numbersin thesearrows refer in eachcaseto the demandper “functional unit” of the plant underreview, in this casea 1kWh,, net powergeneration. Under the given conditions,the combinedcycle plant consumes1.922kWh of primary energyfor every kWh,,. In the samevein, Fig. 2 illustratesthe KEA to provide 1kWh GH, both for alkaline high-pressurewater electrolysisand steamreforming. Figure 3 isthe flow of KEA for producingpower from hydrogenin moltencarbonatefuel cells,an alternative to the conventional type of cogeneration. The exampleof a processchain for the provision of liquid hydrogenin Germany is shownin Fig. 4. It covers the various stagesfrom the photovoltai~ production of the requiredelectric energyin Bavaria, an alkalinehighpressurewater electrolysissystem,to liquefaction and distribution. All figuresrefer to providing 1kWh of liquid hydrogen at the consumerend. The following statementscan be made. -- The primary energy required for the production of equipment in upstreamdistribution is 0.03kWh,,,/ kWhi,u2. In order to obtain 1kWh LH2 at the consumer end, 1.22kWh LH, must be distributed, for which 1.52kWh GH2 must be processedin the liquefier. - The generation of 1.525kWh GHZ in an alkaline high-pressure water electrolysis system requires 0.034kWh of KEA for the production of equipment and 2.388kWh of electric power. As, in addition, approximately 0.37kWh of electricity is consumedin
PRIMARY ENERGY FOR PRODUCTION ;; ;Ql;lPMENT
PRIMARY ENERGY 1,920 kWh PRIMARY ENERGY FOR PRODUCTION OF EQUIPMENT 0,002 kWh COMBINED GAS/STEAM POWER STATION 700 MW 5000 h/a; 40 a g=52% KEA “= 400 k~(~m)/kW KEA p(= 384000 k~(p~rn)~W
PHOTOVOLTAIC POWER STATION IN NORTHERN AFRICA 300kW 2000 h/a; 20a g=fO% KEA, = 20005 k~(p~m)/kW VogbB IICONVERSION
ELECTRIC ENERGY 1.0 kWh
Fig. 1.Cumulativeenergydemand for electricpowergeneration.
PRIMARY ENERGY FOR PRODUCTION OF EQUIPMENT 0,004 kWh
SYSTEMS ELECTRIC ENERGY 1,533 kWh PRIMARY ENERGY FOR PRODUCTION OF EQUIPMENT 0,022 kWh
NATURAL GAS 1,428 kWh
-4-l ALKALINE HIGH PRESSURE WATER-ELEKTROLYSIS 1000 h/a; 20 a; (750 Nm’ H dh) g=65% 11xea.m LOSSES 0.432 kWh
g5-E GASEOUS HYDROGEN 1,0 kWh
Fig. 2. Cumulative energy demand for hydrogen production liquefaction, in total approximately 2.7 kWh,, is necessary. - The photovoltaic plant in Bavaria has a KEAH of 1.0 kWh/kWh,, and generates 1 kWh of current per 10.0 kWh of solar radiation energy. All in all, 2.7 kWh of current must be generated, requiring approximately 2.7 kWh,,, for the production of equipment and an input of 27 kWh renewable energy; according to the usual methods the latter is not assessed in energy terms. In this example, therefore, the KEAjkWh LH, at the consumer end is only calculated from the sum of all KEA for the production of individual process components. It adds up to 2.78 kWh,,,,/kWh,,, --a rather unsatisfactory result which, however, may be considerably better for other process chains. A summary of the results including the cost of energy generation shown in Table 1 indicates that wide bandwidths exist for the various process chains both in terms
PRIMARY ENERGY FOR PRODUCTION OF EQUIPMENT 0,051 kWh
GASEOUS HYDROGEN -1.82 kWh
MOLTEN CARBONATE FUEL CELL 550 MW: 1000 h/a; 20 a g=55% I
PROCESS HEAT 0.76 kWh
ELECTRIC ENERGY 1 ,O kWh
Fig. 3. Electric power generation in fuel cells
of energy demand and cost. Potential cost-cutting by 2020 is expected to lie mainly in the field of process chains in wind power stations and photovoltaic plants. No fundamental changes will occur in power generation in combined cycle plants and nuclear power plants, or in hydropower; nevertheless, wind-driven and/or photovoltaic plants cannot compete with thermal plants in terms of availability costs during the period under review. Table 1 also shows very clearly that the availability of chemical residual hydrogen constitutes a favourable variation on hydrogen production in terms of energy and costs. This could be used m the initial stage of a newly created general hydrogen energy supply system in niche markets where experience could be gained with its use and handling. Once a suitable source for hydrogen production is established, this experience could be applied later to enable the use of hydrogen on a wide scale. It should also be noted that only a limited amount of chemical residual hydrogen will be available. At present, Germany produces about 100millionm3 of hydrogen p.a. (under 0.01% of Germany’s current primary energy demand). Amongst all other hydrogen production processes, it is the thermal processes of steam reforming and/or gasification that provide the lowest price options. Steam reforming requires a primary energy demand of about 1.80 kWh/kWh GH,, which may decline slightly by the year 2020. Biomass as a renewable energy source for gasification is not assessed in energy terms in the present study; however, 10% of the energy content has to be consumed in the form of fossil energy in the generation process. This involves a primary energy demand of about 0.16 kWh/kWh GH2. In the Kvaerner process, a plasma beam is used to directly split CH, into the components hydrogen and carbon. In contrast to steam reforming, the Kvaerner process does not give rise to any emissions during the production of hydrogen; it requires about 82% more primary
U. WAGNER PRIMARY 2,780 FOR TRANSPORTATION
ENERGY kWh FOR PRODUCTION OF EQUIPMENT RENEWABLE ENERGY 27 kWh
BAVARIA 300 kW 1000 h/a; 20a g= 10% KEAH = 20000 kWh(p~m)~W
\ 2,704 kw ELECTRIC
kWt ELECTRIC ENERGY
@LINE HIGH PRESSURE WATER-ELECTROLYSIS 1995
kWh GH ‘I
LOSSES o.s4s Kwh
0,366 kWh ELECTRIC ENERGY
LlQillD HYDROGEN AT CONSUMER 1 ,O kWh
Fig. 4. Cumulative energy demand for production and distribution of liquid hydrogen (process chain no. 6).
energyandincursabout 73% highercosts,unlessa bonus is consideredfor the very pure coal obtained as a byproduct. At present,hydrogen production in water electrolysis combinedwith a nuclearpower plant is almost double the price of the Kvaerner process; the primary energy demandis about 80% higher at 5.9kWh/kWh GH,. At 3.38DMjkWh, gaseous hydrogenproducedby photovoltaics and water electrolysisin North Africa and transportedin pipelinesisevenmoreexpensive.However, at about 1 kWh,,/kWh final energy at the consumer end, this processchain has the lowest primary energy
consumptionand the lowest costsof a11combinations basedon photovo~taicpower generation. Becauseof the high energy demand for hydrogen fiquefaction, hydrogen produced in North Africa and transportedin liquid form is almosttwice asexpensiveas GHZ.
SUMMARY Basedon researchin the literature, a data collection wasstarted on technologiesin a future hydrogen energy
LIFE CYCLE OF HYDROGEN
Table 1. Comparison between the primary energy demand and the cost of the process chains under review, for the years 1995 amd 2020
4 5 6
9 10 II 12
13 14 15 16
Process chain/part chain Hydropower Windpower Photovoltaic, Bavaria Nuclear power Combined cycle PV Bavaria, electrolysis-liquefaction-distribution PV North Africa, electrolysis~liquefaction~long distance transport-distribution PV North Africa, electrolysis+storage-transportdistribution Hydropower-electrolysisliquefaction-distribution Wind power-electrolysis-liquefaction-distribution Wind power-electrolysis+ompaction-distribution Nuclear power-electrolysis
Form of final energy at consumer
Primary energy demand? 1995 (2020) (kWh/kWh)
Costs1 1995 (2020) (DM/kWh)
Electricity Electricity Electricity Electricity Electricity LK LH>
0.035 (0.035) 0.122(0.122) 1.063 (0.535) :3.455 (3.455) 2.037 (2.0371 :2.780 ;1.213j
0.094 (0.094)' 0.305 (0.305) 2.810 (1.420) 0.136(0.136) 0.222 co.2221 7.870 i3.5OOj 6.110 (2.700)
LH, Lb GH, GH,
0.121 (0.102) 0.373 (0.346) 0.219(0.217) 5.941 4.923
0.462(0.232) 1.950 (1.030)
5.941 4.923 1.803 (1.747) 0.165 (0.159) 0.012 (0.010)
0.079 0.079 0.159 0.053
C-2 GH2 GH, GH2
1000 1000 7000 5000
1000 1000 7000 7000
8000 8000 no data
1.110 (0.600) 0.276
0.079 (0.078) (0.078) (0.082) (0.052)
* Utilization period of maximum demand in hours per year. t Cumulative primary energy demand for the production, usage and disposal of renewable energy, not assessedin energy terms, in relation to the final energy. $ The cost of capital, operation, energy and disposal, in relation to the final energy.
system. This data collection comprises the current state of development and forecasts for potential new and/or further developments in this field until 2020. In all energy considerations and any related process chains, the appraisal of renewable sources of energy is always problematic. Since the renewable sources sun, water, wind and biomass provide inexhaustible potential, they are not assessed in terms of primary energy demand. However, for every process component, the use of primary energy required for the production of equipment has been considered. The main results can be summarized as follows. - The most favourable process for the generation of hydrogen is based on a thermal process, today and in the year 2020. ~ If sufficient capacities are available, chemical residual hydrogen is the most favourable variation in energy and financial terms. ~ A process favourable in energy terms is the gasification of biomass, including energy consumption for irrigation, harvesting, etc. ~ The most favourable large-scale process for the production of hydrogen is, and will remain, the steam reforming process of natural gas. However, it represents only a refinement of natural gas as a gaseous source of primary energy. ~ Hydrogen production in the Kvaerner process is
relatively expensive. It is emission-free but requires, unfavourably, much primary energy. - If hydrogen is produced via nuclear power the cost is rather high, especially if the cost is calculated on the basis of the average power generation cost rather than low load cost (marginal cost). In this consideration, the costs that arise in the production and distribution of hydrogen are approximately double as high as in the case of providing nuclear power directly to the final consumer/end user. ~ With renewable sources of energy, the most favourable hydrogen production is water electrolysis combined with hydropower, giving rise to the lowest primary energy demand under the specific conditions of the study, and the lowest cost per kWh final energy. The second best method is water electrolysis combined with wind power. The primary energy demand is significantly lower in these process chains than in steam reforming. The high primary energy demand for the production of the equipment, and the extremely high capital expenditure, lead to different results with water electrolysis in connection with photovoltaic plants depending on the place of production. ~ Wherever possible, hydrogen should be applied in gaseous form because that is the best in both energy and financial terms.
U. WAGNER - The liquefaction of hydrogen is an energy-intensive process which should only be applied in areas where liquid hydrogen is absolutely necessary, e.g. in road and air traffic. -Prices are expected to be reduced considerably by the year 2020 mainly in photovoltaics, in particular with improved plant efficiencies. The cost relationship shown here for the various process chains will be more or less maintained.
Finally, it can be stated that in the long term a general hydrogen system will raise considerable problems, some of which have not been resolved yet, mainly in the field of hydrogen production. At present it appears necessary
to promote selected pilot projects with a view to gaining further experience in the field of hydrogen production and handling. Moreover, it will be necessary to find out how hydrogen could become a suitable source of energy in the future. REFERENCES 1. Process Chain Analysis of Hydrogen Systems. Unpublished study of the Research Institute for Energy Technology, Munich and the Institute for Energy Technology and Power Engineering of the Technical University of Munich. 2. VDI-guideline4600: Cumulative energy demand-terms, definitions, methods of calculation. Draft version 1996.