The context.

In the last three decades considerable concern has emerged regarding limits to the future availability of energy in the quantities required by industrial-affluent societies.  More recently Campbell (1997) and others (Fleay, 1995, Ivanhoe, 1995, Gever, et al, 1991, Hall, Cleveland and Kaufman, 1986) have argued  that the energy source on which industrial societies are most dependent, petroleum, is more scarce than had previously been thought. They argue that non-conventional sources such as tar sands and shale oil will not make a significant difference to the situation.  The world discovery rate is currently about 40% of the world use rate.  The USGS (2000) has recently arrived at a much higher estimate for ultimately recoverable petroleum, but this would only delay the peak by some 10 years.

If the discussion is expanded to take into account the energy likely to be required by the Third World the situation becomes more problematic.  If the present world population were to consume energy at the rich world per capita rate world supply would have to be 5 times its present volume.  World population is likely to reach 9 -10 billion  by 2070.  If 10 billion were to consume fossil fuels at present rich world per capita consumption rates all probably recoverable conventional, oil, gas, shale oil, uranium (through burner reactors), and coal (2000 billion tonnes assumed as potentially recoverable), would only last about 20 years.  (Trainer, 1985.)   As will be discussed below, when the universal commitment to economic growth is added, the problems associated with the future availability of conventional energy sources become much greater.

Given this context in which there are grounds for expecting increasing energy scarcity in coming decades, there has been a strong tendency to assume that renewable sources can substitute for fossil sources.  Because Australia receives more solar energy than most other developed  regions of the world it is  also  commonly assumed that Australia will be more able than most to meet its energy demand from solar sources.  The following analysis concludes that with respect to the two crucial energy forms, electricity and liquid fuels, this assumption is mistaken, both in relation to existing costs and to those likely to be achieved in the foreseeable future.

 Solar electricity.

The potential for solar electricity supply must be examined primarily in relation to the task of meeting winter demand. The following derivation assumes an ideal Australian site, at the tropic of Capricorn where the average daily solar incidence in winter is approximately 4.25 kWh/ squ.m.  (University of Lowell Photovoltaid Program, 1991.)  This means that the sun would approximately  35-40 degrees from vertically overhead throughout most of winter.  Thus the incidence of solar energy on panels set at optimum inclination would be 5.18 kWh/d in winter.   It will be assumed that for 8 hours a day electricity from solar PV plants will be supplied directly, and for the other 16 hours it will have to be stored before being supplied to consumers.  Night time electricity demand is about one-third lower than daytime demand (Mills and Keepin, 1993) so in the following discussion supply from a power plant will be assumed to be at the rate of 1000MW for 8 daylight hours  and 670MW at other times of the day.

Although efficiencies in the region of 24% are being achieved in the laboratory the efficiency of PV cells in use is reported by Kelly (1993) to be approximately 13%.   (Evidence that actual performance is lower than this is given below.) At 13% efficiency each square metre of PV collection area would produce .67 kWh   per day in winter in central Australia.  A  15% loss of this output in transmission from the inland generating site to the coastal consuming areas will be assumed (derived from Ogden and Nitsch, 1993), along with a 7% loss for inversion from DC to AC current.   The overall efficiency of delivering electricity directly to consumers in the daytime would therefore be 10.27%. In other words to deliver 1000MW, solar energy would have to be collected  at the rate of 9737MW.  Therefore to deliver 8 hours x 1000MW directly, 77,896MWh of solar energy would have to be collected each day.

The most significant problems for solar electricity supply are set by the need to store energy for supply at night.   (The problems deriving from the occurrence of a series of continuously cloudy days will be ignored in the following analysis; obviously greater storage capacity would be required.)   Storage in the form of hydrogen will be assumed here.

The energy efficiency of producing hydrogen gas from electricity is approximately 70%.   (Commercial supply in the US is currently via methane reforming at 65% efficiency.)  Again a 15% loss in transmission and a 7% loss in inversion will be assumed.   Generation of  electricity by burning the hydrogen gas will be assumed to be 40% energy efficient.  A higher figure for future fuel cell technology is discussed below.  (Note that any plan to convert the hydrogen into electricity after storage would involve construction of a generating plant comparable in magnitude and cost to a  coal-fired plant.)  The combined  effect of these efficiencies would mean that for each kWh of solar energy collected only .029 kWh  would be delivered in the form of electricity after storage; i.e., the process would only be about 2.9% energy efficient. Thus the need to store a unit of energy increases the collection area by a factor of 3.7.

To meet the 670MW demand for the 16 hours of the day when the sun is not shining via a 2.9% efficient process, 373,519MWh of solar energy would have to be collected each day.  Adding the direct and the night time figures indicates a need for a total collection of 451,416MWh per day.  At 5.18kWh per square metre the collection area would have to be 87 million  square metres.  Each square metre of collection area would deliver .2 kWh of electricity per day.

The current wholesale cost of PV panels is approximately $5 per watt (half the retail cost.)  The “balance of system” cost, i.e., the cost of mounting panels, connecting wires, control devices etc.,  typically doubles this cost. This is for a non-tracking systems.  Systems in which the panels change their angle throughout the day to track the sun collect some 30% more energy, but have much higher balance of system costs.  If we assume 75 Watt panels, i.e., 150 peak watts per square metre, the cost per square metre would be $750 for the panels, and the cost for the whole system would be $1500 per square metre.  Therefore the cost of a generating plant 87 million square metres in area would be  $130.6 billion.

How does this figure compare with the cost of a coal fired plant?  To construct a coal fired plant of 1000MW capacity would probably cost $800 million.  (This is the cost of the recently completed Mt. Piper power station in N.S.W., Australia.  Pacific Power, 1993, p. 104.)  Coal for 20 years will be assumed to cost $2 billion.  Therefore the total cost of the fossil fuel option would be approximately $2.8 billion.  Thus the PV solar option would cost approximately 47 times the cost of the coal option. (Taking into account externalities, especially the environmental costs of coal use, would reduce this figure.)  If a 30 year plant life is assumed the multiple would be 33.

The discussion to this point has dealt only with the cost of constructing the collection area. The cost of construction plus fuel accounts for only about 28% of the present price of electricity generated by coal-fired plants. There are several additional factors which would significantly increase the cost of the solar plant.

a) Operations and management costs, especially the cost of regular cleaning of the large collection area.

b) No provision has been made in the above estimate for the extra capacity needed to cope with extended cloudy periods. On clear days the home lighting system referred to at c) below generates around twice as much energy as is required, yet difficulties experienced in cloudy periods would not be totally eliminated if generating capacity was doubled. In large scale systems the problem might be avoided if there was sufficient alternative generating capacity available in cloudy weather, such as hydro power.  However this solution generally involves the problem of duplication of plant which will remain idle some of the time.

c) The actual performance of systems in the field can be well below expectations deriving from theoretical expectations, when all extraneous factors capable of affecting output have had an opportunity to operate.  Theoretically electricity generated from wood should be produced at c 33% efficiency, but  Hohenstein and Wright (1994, p. 162) provide figures showing  that for  the entire US electricity via wood system the actual performance was only 22%.  PV panel performance can be lowered by imperfect alignment, dust and water vapour in the atmosphere, dust on panels, ageing of the cells, losses in wiring and inverters, and the heating effect of sunlight on the cells.   Nominal ratings derive from tests in  ideal laboratory conditions which eliminate all the above factors.  Especially important for systems not connected to the grid is the fact that when output exceeds demand or storage capacity much of the energy being generated can’t be used and has to be dumped.   Similarly, a large scale system capable of meeting all demand in mid-winter would have approximately twice the required capacity in mid-summer, given that solar energy is about twice as great in summer.

A home lighting system monitored in Sydney, at 34 degrees South,  with a nominal rating of 11% efficiency delivers on a cloudless summer day only 5.7% of the solar energy falling on its surface.  (Winter performance is even lower, because the sun is on a lower angle, shines for a shorter period, and its energy has  to travel through more atmosphere.)  This is a tracking system.  Systems involving stationary panels would be around  30% less efficient.  These figures do not include losses due to energy dumping.

Data published in 1999 by BP Solarex  (Corkish, undated, Ferguson 2000a) on a 390 square metre system in the UK,  a 805 square metre system in Switzerland, and  a 7960 square metre system in Toledo, Spain,  show that over approximately three years the output of these systems was around 6-7% of the solar energy received by the respective  collection areas.

 A 1.26kW PV system installed in Melbourne, with panels normal to the sun in mid winter, delivered as electricity only 8% of the solar energy falling on the panels, averaged over the 2.5 mid winter months. (Renew, 2001.)

d)  The energy cost of constructing the plant must be subtracted from its lifetime output before we can discuss the amount of energy it would actually deliver.

Ferguson’s estimates that for the Toledo system referred to above the energy needed to produce the panels would be .25 of the energy the system will produce (over an assumed 30 year lifetime in this analysis.)  For the UK site the fraction was .38.  Energy payback times stated by manufacturers are derived from performance under ideal laboratory conditions.  As is noted in c) above many factors reduce panel performance below these levels and this means that real payback time in the field will in general be much longer than might be expected from the manufacturers' statements.

This inclusion of “emergy” (embodied energy) costs should take into account more than the energy content of the construction materials.  It should include all the energy required to build the panel factories, and all the trucks, worker’s  clothes and transport etc. that went into producing the plant.  In other words the total emergy cost of the PV plant includes the energy cost of all the work and production that would not have taken place had the plant not been built.

e)  The basic cost calculation above does not take into account the plant’s capacity factor.  If it is assumed that it would be out of operation 30% of the time due to breakdowns and maintenance, a typical figure for coal fired stations, then the necessary area and cost for a plant to deliver 1000MW constantly would have to be multiplied by 1.43.  However PV plant capacity factors are likely to be much higher than for coal-fired generation.

f) The cost of building and operating the hydrogen production, pumping and storage systems would be considerable.    To store the hydrogen to meet night time demand  would involve a huge storage volume given the low energy density of hydrogen.  To retrieve the 10,560MWh from hydrogen via a process that is .7x.4% efficient would require storage of 37,700MWh of hydrogen.  At 3kWh per cubic metre, the volume of hydrogen would be approximately  12 million cubic metres, or a mine shaft some 1,300 km long. Compression would reduce the volume but increase energy and plant costs.   Even liquid hydrogen has only 25% of the energy density of petrol.

 g)  The cost of the plant to convert the stored hydrogen to electricity would have to be added.  This would be comparable to the cost of a coal-fired power station (assuming the hydrogen is used as fuel to generate steam; fuel cells are more expensive.)

h)  The cost of the capital that would have to be borrowed to build the plant, i.e., the interest to be paid,  might double the cost figure from all the above factors combined.   A coal-fired plant produces around 122.6 million MWh in its lifetime (assuming it is out of operation .3 of the time; i.e., a .7 capacity factor), so for a $2.8 billion construction plus fuel cost the cost of the electricity produced per kW is  2.28 cents.  However, the 1998 Australian retail price of domestic electricity was 10.1 cents per kWh, which suggests that profit, operation and management and interest costs (and distribution costs, which PV can avoid) can be expected to much more than double the cost of electricity due to plant construction cost.

i)  A decision to build large scale solar generating plant with the sort of costs under discussion here will obviously not be made until the cost of energy from other sources ceases to be cheaper than the energy generated by these solar plants.  We must assume therefore that the cost of the energy required to build the solar plant will be approximately the same as the price of the energy it will generate, which it has been indicated would be very high.  Given that energy-intensive  materials make up much  of the construction cost, the cost of the plant would be far higher than the $1500 per square metre assumed in the above derivations, which assume present energy costs for construction and materials.

Combining these eight factors would indicate that the initial $130.6 billion cost estimate might have to be multiplied several times.

 What difference might technical advance make?

The assumptions made within the above analysis are apparent and enable derivation of  the conclusions that would follow if different assumptions about efficiencies and costs were made.  If it is assumed  a) that cells with  20% actual operating efficiency in the field (as distinct from nominal peak watt rating), compared with the 13% taken above, b) a cost of $2 per watt for PV cells, i.e., a 60% reduction, (it is not clear the balance of system costs will fall significantly), c) fuel cells producing electricity from stored hydrogen at 60% efficiency, then the cost of the plant to deliver 1000MW would only  fall by about 60%, i.e, to the region of 20 times that of a coal fired plant plus fuel or a of nuclear plant.  (This ignores the fact that at present fuel cells are 4-6 times as costly per kW of capacity as conventional energy generating plant.)

If the cost of PV cells fell to zero the cost of the large collection area required in the above discussion would still be very high.  If the PV material was sprayed at zero cost onto 6 mm toughened glass at the current wholesale price of approximately $60 per  square metre, the cost of the  glass for the 87 million square metre collection area would be $5220 million.

PV roof cladding systems.

Integration of PV cells into roofing etc. material would significantly reduce balance of system costs, e.g., for support structures (and roofing replaced.)  It would also avoid transmission loses which make up one-third of the retail cost of US electricity, but only if systems are large enough to be completely independent of the grid and therefore involve the excess generating and storage capacity needed to cope with long cloudy periods.  Decentralisation would probably increase some costs, especially for storage in many small units each with its own power conditioning equipment such as inverters and regulators.

However replacing roofing with PV panels sets the problem of whether the solar incidence where the house is located is adequate.  For instance in Sydney, 34 degrees South, in winter the solar incidence is 2.78 kWh per day, 2/3 of the 4.25kWh per square metre per day  in central Australia where large scale centralised PV systems would be ideally located.

Rooftop collection surfaces are fixed in orientation and on average rooftops differ considerably from ideal orientation, and are subject to shading by other structures.   It is likely that only about 40% of the surface of an average house  roof would have an orientation enabling effective use as a solar collector in winter.  In mid winter in Sydney the mid day sun is 56 degrees from vertically overhead, so a roof surface facing North with a 12 degree slope will be 44 degrees from ideal inclination.  However because it is angled somewhat towards the sun it would  intercept about 1.2 times the 2.78kWh/m/d
falling on a horizontal plane in Sydney in mid-winter, i.e., 3.3kWh/m/d.  This is only .78 of the amount collectable in Central Australia at the Tropic of Capricorn at that time of the year.

To supply the same amount of power as was assumed above  for centralised PV supply (i.e., 1000MW   for 8 hours without storage, and 660MW for 16 hours via storage), a rooftop collection area of 111 million square metres would be required.  Thus each square metre would deliver .17kWh(e) per day. This is approximately 5 times the area likely to be adequately oriented on all Sydney domestic rooftops.  The panels would cost $84 billion.  Costs associated with the above 8 additional factors would also have to be taken into account.  At this stage it is difficult to estimate the combined effect due to savings likely because supporting structures and roofing are not required, and remaining normal balance of system costs, such as power conditioning equipment, wiring etc.

If we assume a  house roof area of 100 square metres, 40% of which is covered with PV panels delivering electricity, at the above rate of .17kWh/m/d the system would deliver 6.7kWh/d.  The average residential electricity consumption for Australia is .76 kW, or 18.2kWh per day.  Thus the roof would only meet 1/3 of the house's electrical needs, at a panel cost of $90,000.  To meet Australia's total electrical demand, 175GWh/y, would require the equivalent of about 20 power stations each of 1000 MW capacity, and therefore 2720million square metres of collection panels, which is approximately 13 times the area available on all residential roofs (making the above 40% assumption and again ignoring factors a-i. above.) (To also fuel a car via rooftop PV panels would be to more or less double the magnitude of the task.)

The costs and efficiencies associated with solar thermal generation of electricity do not differ greatly from those outlined above for PV systems. (Trainer, 1995a.)  Energy storage via thermochemical processes would seem to be about as efficient as  hydrogen gas storage (possibly somewhat less; Kaneff, 1992, p. 43.), although for large scale generation there would be a significant problem of storing very large volumes of gas temporarily. Storage of energy via methane reforming or ammonia recombination is more energy efficient than storage via hydrogen,  yet these processes would require one cubic metre of gas storage per 1.54kWh, at normal pressure.  Thus to store the energy from a power station for the 16 hours when the system was not generating would require a mine shaft  approximately 1500 km long, assuming 60% energy storage efficiency.  Compression of the gas would reduce the necessary volume, but impose a further energy loss.

There is far too little storage capacity for pumped water storage on the required scale and the energy efficiency of this process is not greatly different from that of hydrogen storage.  (Trainer, 1995a.)  The vanadium battery promises a higher storage efficiency, initially 87% but this will deteriorate with recharge  cycles.  However current estimates of world potentially recoverable resources indicate far too little vanadium exists for a world supply and storage system, especially when automobile demand is added to electric power  demand. (Erickson, 1973, Trainer, 1995.)

 Liquid fuels.

The second crucial energy source for industrial societies is liquid fuel and the potential solar source of this is biomass.  The production of liquids from biomass usually has a low (sometimes zero or negative) net energy return on energy invested; i.e., it might require more energy to be put into the harvesting and distillation etc. than is available in the resulting fuel.  Pimentel and Pimentel, (1998) conclude that for ethanol produced from corn “...about 71% more energy is used to produce a gallon of ethanol than the energy contained in a gallon of ethanol.” (See also Pimentel  1984,1991.) Ferguson says the net energy capture of biofuels is “..so low that these methods are barely viable.”   (Ferguson, 2000b.)  Ulgiati (2001) concludes that the energy return from ethanol produced from maize in Italy is .59, rising only to 1.36 when energy credits from waste are maximised.
 

However Lynd (1996) claims that the energy output to input ratio for ethanol from cellulosic material could be 4.6, when outputs not in the form of ethanol are included.  From his account the ratio for ethanol alone appears to be 1.94 (when the 19% of ethanol output required for biomass harvesting etc is also taken into account.)  It is not clear how the  energy required as a liquid fuel to deal with the large volume of waste water has been taken into account. Giampietro, Ulgiati and Pimental, (1997, p. 591.)  state that there would be 13 litres of high BOD sewage for each gross litre of ethanol produced, (1997, p. 210), requiring energy for treatment equivalent to 50% of the energy in the ethanol.  Ulgiati (2001) says the figure rises to 33. 58 litre per litre of net ethanol, i.e.,  after the energy cost of producing the ethanol have been deducted from the output. (Lynd assumes a very high 21 tonnes per ha yield for the input material (discussed below.)  The differences between Lynd and Pimentel seem to remain unreconciled at this point (personal communications) but are probably due in part to the fact that Pimentel’s reference is mainly to corn as the feedstock and to existing production systems whereas Lynd is discussing cellulosic inputs and theoretical possibilities as no plants of this kind are in commercial operation. (Lynd, 1996, p. 431.)

Lorenz and Morris (1995) argue that recent technical improvements now enable a positive net energy ratio for ethanol from corn, but only if energy credits for non-ethanol outputs are taken into account.  Giampietro, Ulgiati and Pimentel (1997) conclude from their review that the net energy return ratio for ethanol ranges between .5 and 1.7, again apparently without taking into account energy needed to deal with the waste water.  (Ulgiati, 2001, estimates this at only 1.7% of the ethanol energy.)

It would appear therefore that  the net energy return ratio for ethanol production  can be positive but at best is quite low.  (It should be noted that a full accounting which dealt with emergy costs would yield a less promising picture.) The  closer the ratio is to 1 the more problematic the energy source is, being subject to disruption by fluctuation in conditions such as droughts and poor harvests and  the  costs of inputs, which can push the yields, dollar and energy costs above the critical line.

The limits to liquid fuel production are  not primarily to do with the energy return ratio.  They are to do with quantity, i.e., the areas of land available and the associated  yields.  Giampietro, Ulgiati and Pimentel, (1997) find that to produce only 10% of US energy via ethanol would require 37 times the commercial livestock feed production.  They say that providing US food plus energy via biomass would require 15 times the existing cropland, 30 times the agricultural water consumption, and 20 times present pesticide use.  For Japan the land multiple is 148.  (p. 591.)  "...none of the biofuel technologies considered in our analysis appears even close to being feasible on a large scale due to shortages of both arable land and water..."  (p. 593.)  Their discussion does not take into account pollution control measures required to deal with ecological impacts, notably the large quantities of nutrient-rich waste water.    Giampietro, Ulgiati and Pimentel conclude "...biofuels are unlikely to alleviate to any significant extent the current dependence on fossil energy..." (1997, p. 588.)  Ulgiati (2001)also concludes from a detailed analysis of ethanol from maze that this is “…not a viable alternative.”
 

Lynd estimates that idle US cropland could provide only 14% - 28% of current US transport fuel (1991), even making the very optimistic assumption of 21 t/ha biomass production.  (US corn achieves 15 t/ha with intensive application of fertilizer, water and pesticides on good soils.  US average forest growth is only around 3 t/ha/y.) Di Pardo (undated) says that only 10% of US cropland is the maximum amount that could be used to produce cellulosic biomass inputs.  Lynd estimates that 186 million tonnes of waste biomass (dry) could be collected in the US (at under $56/t, 1994 dollar, the higher of two costs examined).  Lynd . (1996, p. 412.) says this would yield 20 billion gallons of ethanol, which is only equivalent to 6% of US petroleum consumption

The general limit on biomass growth and therefore on energy production from biomass is set by photosynthesis.  In natural ecosystems only about .07% of the solar energy input becomes stored as energy within plant material, although in special agricultural situations such as sugarcane growing the figure can rise to .5%.  (Pimentel, 1997, p. 14.)   For a region averaging 5kWh/m/d of solar energy, natural vegetation would be storing energy at the rate of approximately  only 1.4 kW/ha  ( i.e., average continuous flow over 24 hr).   Pimentel notes that not all of this will be  harvestable as the plant will need to use perhaps 40% for its growth processes. (1997, p. 14. )  The gross available energy flow (without the significant losses due to biomass processing, conversion and storage) would  therefore be around .84kW/ha.  (This might be compared with the average per capita US energy consumption rate of approximately 10 kW, indicating the need for 12 ha per person to meet energy demand (ignoring all energy costs of producing the energy), whereas the global amount of productive land per person (i.e., “footprint”) at present is approximately 1.2 ha, and world population is likely to increase by 50%.  (Wachernagel and Rees, 1996.)

 This .84kW/ha general flow of “potentially retrievable energy” into the feedstock,  equivalent to  an annual quantity  of 26,490 MJ/ha, would seem to set the upper limit for the energy output from a liquid fuel production process.  This is the energy content of 1.65 tonnes of wood, or 212 gallons of petrol. From this must be subtracted the energy cost of fuel production, and the non-liquid output energy, some of which will be waste and some will be useful.

These figures roughly align with the conclusions others have come to.   Giampietro, Ugliati and Pimentel (1997) say that the best gross ethanol  yield likely to be achieved in temperate conditions is 30,000MJ/ha, equivalent to 265 gallons of petrol/ha/y, i.e., excluding energy required for harvest, processing etc.  Lynd (personal communication) predicts that it will be possible to convert up to 56% of the energy in the biomass to  ethanol (although the current figure is 33%.)  This corresponds to 72 gallons of petrol per tonne of feedstock, or 42 gallons from current technology. Lynd had previously concluded that the gross yield could be 107 gallons of ethanol per tonne of inputs, equivalent to approximately 81 gallons of petrol.  (Lynd, 1996.)

From Foran and Mardon (1999) it can be estimated that ethanol and methanol can be produced at a net energy yield equivalent to 26 and 68 gallons of petrol per tonne of dry wood feedstock.  These figures are equivalent to 78 and 204  gallons of petrol/ha per year assuming a 3/t/ha  dry feedstock yield.

The foregoing varying yield figures cannot be taken with great confidence, especially as most are predictions as distinct from actual yields.  It will be assumed below that under favourable agricultural conditions a net production equivalent to 66 gallons of petrol per tonne of feedstock, or 200 gallons  per ha per year will be possible from a 3t/ha/y gross biomass yield,  (although again the sustainability of such a  yield over time must remain problematic), i.e., assuming approximately 66% improvement on the present ratio of .33 for liquid fuel output to feedstock energy content.

US petroleum  use (in the mid 1990s) was approximately 6.6  billion barrels or 277 billion gallons per year.  (Youngquist, 1997, p 187.)  Transport was taking approximately 212 billion gallons. (Department of Energy, 2000.)  At  200 gallons/ha 1385 million ha of land producing biomass would be required if total petroleum demand were to be met from biomass sources.  This is about 1.5 times the total land area of the US.  US forest area totals 290 million  ha, all cropland 162 million ha, and pasture and grazing 300 million ha.  These figures align with Pimentel's conclusion that present US energy use is 30% greater than the total solar energy captured by all US vegetation.  (Pimentel, 1998, p. 197.)  Note that this discussion has ignored the problem of also replacing gas via biomass.  US gas consumption is equal to 74%  of US petroleum consumption.  The previous discussion also ignores the approximately 174 million tonnes of wood currently being used p.a. for domestic heating.

The Australian situation, involving poorer soils and growth rates than the US, is probably much less promising (although Australia has about twice the per capita area of farmland.)   In 1998-9 Australia used 1681 PJ of petroleum and 881 PJ of gas.  (Australian Bureau of Statistics, 2000.)    Combined petroleum and gas consumption is the equivalent of 20.5 billion gallons of petroleum.   If a gross biomass yield equivalent of  200 gallons of petrol  per ha per year is assumed,  and the predicted .56 of feedstock energy can be converted into liquid fuel, this task would require 100 million ha of land producing biomass with  a yield comparable to the Australian cropland average (i.e., around 3 tonnes per ha, achieved at considerable cost in fertilizer, water and pesticide inputs; see below.) For petroleum use alone the area would be 66 million ha., when the energy costs of production have not been dedudted.  (Note that extrapolating the long term growth trend to 2001 raises these figures by 5%.)

Roughly similar figures can be arrived at when wood production is considered.  20.5 billion gallons of petroleum is equivalent to the energy content of 145 million tonnes of wood (at 16 GJ/t.).  If Lynd’s predicted .56 ratio is taken an energy input of  at least 258 million tonnes of wood would be required, again ignoring inputs necessary to provide  collection and processing energy.  World average forest growth is around 2 t/ha/y and the Australian average forest growth rate is probably well below the world average rate.  However Mason (1992) says pine grows in Australian plantations at around 4t/ha/y and Bartle (2000) reports mallee harvest at 7.5 dry t/ha/y. At the world average forest growth rate of 2 t/ha/y some 129 million ha of forest would have to be constantly harvested to provide Australia's present petroleum and gas demand (and more to cover processing etc costs.).

Ellington (1994) estimates that whereas the methanol produced could contain 53% of the energy in the feedstock, taking into account all production and infrastructure costs reduces this to 41%.  In other words production costs reduce energy yield by 29%.  This indicates that to produce Australian petrol plus gas would require harvesting of 163 million ha of forest.

 Australia's forests total approximately 41 million  ha and are probably already being harvested at an unsustainable rate.  The potentially harvestable area might be only 20- million ha  when water catchments, national parks and the wishes of private owners are taken intro account.  Nilson et al (1999) conclude that possibly 40% of existing forest areas might  not be accessible to biomass harvesting, being on steep slopes, near creeks or on private land.  (These restrictions would not apply to plantations for biomass use.)  In addition note should be taken of the fact that if Australia were to be self-sufficient in forest products local production might have to be increased by approximately 50%. Also, approximately 6 million t/y of wood are presently being harvested p.a. for domestic heating in Australia.  Current Australian and world timber and fuelwood demand are probably well beyond maximum sustainable quantities.

These figures indicate that Australia’s existing forests are not likely to be capable of contributing significantly  to the large quantity of biomass required.  Plantations for energy production are not likely to solve the problem.   Currently there are only about 1 million ha under plantations in Australia and the relatively poor soils would probably place severe limits on the extent to which this area could be increased and continuously cropped.  Mercer says Australia might increase  plantations to 10 million  ha. (1991, p. 81.)  The required area should be considered in comparison with the 23 million ha of pasture and the 21 million ha of cropland presently in  use.

Optimistic conclusions on the potential for biomass typically make very high assumptions regarding achievable biomass yields.  For example Lynd (1996) and Foran and Mardon, (1999) assume dry weight yields can be  20-21t/ha/y, and these can be maintained year after year.   Such discussions  usually make reference to instances where yields of this order and greater have been achieved in specific locations or experimental conditions.  For instance the Oak Ridge National Laboratory reports on switchgrass, willows and poplars in the US growing in experimental plots at 11-15 t/ha/y. (McLaughlan, 1999.)  However for very large scale biomass production large areas of land would be required and it is not plausible that large areas with such yields can be found in the US, let alone in Australia with its poorer soils.  (American agricultural yields are around twice Australian yields.) Personal communications from ORNL state that these high yields are likely from only about 20 million ha of US cropland. Hohenstein and Wright (1994, p. 187) found  that only 91 million ha of US farmland could yield 5 t of biomass per ha per year.  Graham (1994, p, 187) concluded that  88 million ha of US farmland will be available by 2030, but 75% of this will not be suitable for bioenergy production, meaning that only 16.2 million ha will be available.

 Consider the following yields for Australian agriculture.  Wheat, 1.9t/ha/y (i.e., grain; total plant biomass might be 3 t/.ha/y), fodder, 3.5t/ha/y, overall agricultural production excluding sugar cane, 2 t/ha/y.  In other words biomass yield from Australian cropland, which is obviously the best growing land available, is under 4t/ha/y,  (...after the application of 3.5 million  tonnes of fertiliser, and considerable pesticide and irrigation inputs.)  (A.B.S., 1997-8.) It should also be noted that c15% of biomass harvested is lost in six month storage (Wright, 1994) and that biomass energy production is likely to take fertilizer applications comparable to   those in agriculture.  US corn production takes c 135 kg of nitrogen per ha per year, and wheat 60 kg.  Panney and Mason (1994)estimate that biomass energy plantations will require 50-60 kg of Nitrogen per ha per year.  These energy cost equivalents have not been included in the following derivations.
 

The Australian CSIRO Beyond 2025 Report (Foran and Mardon, 1999) argues that biomass energy for Australia could come from the areas that need to be replanted to remedy Australia's dryland salinity problem.  However dryland could be expected to have biomass yields that are a small fraction of those for average Australian cropland. Nevertheless Bartle (2000) expects coppicing of Eucalyptus mallees to yield 5-7.5 dry tonnes of feedstock per ha per year, although there is at this stage no evidence on how yields will stand up over time.  Continued harvesting from nutrient poor soils could be expected to lead to deterioration in growth rates, or to require fertilizer application thereby adding to the energy costs of production.

 Methanol.

Foran  and Mardon (1999) conclude that the methanol option will yield approximately 2.6 times as much gross energy in liquid form per ha as ethanol, i.e., not taking production energy costs into account.  From their figures, for an energy input of 68.6GJ, including the energy in the 2.2t of feedstock, a net 13 GJ of methanol can be produced, on the assumption that 2.2 dry tonnes of wood yield 1 tonne of methanol, and on the assumption that it is reasonable to deduct the whole 9.4 GJ needed to produce the methanol.  ( Not all of the energy inputs required are in liquid form but they must come from some source and biomass and solar are the most likely options.  Some use can be made of waste heat from processing.)  At this net yield, i.e., 40 gallons of petrol per dry ton of wood feedstock,  to meet Australia’s oil and gas demand would require some 512 million tonnes of dry wood.  The areas of land required  assuming 7.5, 5, 3 and 2 tonnes yield per ha respectively would be  68, 102, 171, and 256 million  ha respectively.

The magnitude of the problem is made clear when expressed in “footprint” terms.  (Wachernagel and Rees, 1996.)  At the above assumed output of 200 gallons of petrol equivlent per ha per hear, Australia’s per capita petrol consumption of 708 gallons per year would require 3.54 ha.  (Per capita oil plus gas consumption would require 5.4 ha.  In addition Pimental and Pimentel (1997) estimate that 2.2 ha of forest would be needed to yield the 10,000kWh of electricity used by one person in a rich country per year.  This per capita liquid fuel plus  gas plus electric energy production from biomass would require 7.6 ha.  However the total global amount of productive land per capita available to  meet food, fibre, water, settlement, energy and all other demands (e.g., plllution absorption is usually not included in footprint analysis) is approximately 1.2 ha.  If population rises to 9 billion and the present rate of productive land loss continues by 2070 the area will be approximately .8 ha.

These considerations indicate that although a large volume of liquid and gas fuel could be produced from biomass, it is not plausible that this source could provide more than a small fraction of current demand.  It should also be noted that if petroleum becomes scarce there will be feedback effects making the biomass situation more difficult.  For instance if there is  less fuel available then irrigation, fertilizers and pesticides will become more scarce and costly and  agriculture will tend to become more labour and land intensive, and agricultural produce will become more costly, reducing the availability and increasing the costs of inputs to biomass production.  There will tend to be a shift from energy-intensive building materials such as kiln-fired brick, aluminium, steel and plastics to timber, again increasing pressure on biomass sources.  Looming water shortages and the impact of the greenhouse problem will probably significantly reduce biomass production.  Also global economic development is accelerating the rate at which people are moving to cities, where per capita energy and resource consumption is higher.
 

 The significance of economic growth.

The situation becomes much more difficult when the significance of economic growth is taken into account.  An economy growing at 3% or 4% p.a. will double its output each 23 or 17 years respectively.  It is not plausible that increases in production and consumption of this order can continue without significant increases in energy               demand, meaning that the magnitude of the energy supply task and the associated costs discussed above can be expected to multiply greatly.

Two common counter arguments here must be briefly considered.  The first is the common assumption that economic growth will increasingly take place in the service and information sectors and not in energy-intensive sectors such as mining, agriculture and manufacturing.  However many services are remarkably energy-intensive.  Consider transport, travel and tourism.  Services actually account for 27% of Australian energy consumption.  (Common, 1995.)   Many services such as retailing, insurance, construction, transport and security deal with industries that are energy and resource intensive, e.g., producing and selling goods.  It is not plausible that an economy can treble or quadruple its service activity without significantly increasing its demand for energy.

The second counter argument is that modern economies are “dematerialising”, i.e., reducing the amount of materials and energy they require.  Crude figures on “energy intensity”, i.e., energy consumed in the economy per unit of GDP, seem to confirm this.  However there are good reasons for concluding that this is misleading and that dematerialisation is not taking place.

Firstly Gever et al. (1991) conclude that a significant proportion of the apparent effect is due to change to fuels of higher quality, e.g., gas rather than coal.  (More economic value can be derived from a MJ of energy in the form of petroleum than coal, or electricity than gas, because the former sources are more flexible, transportable etc.)  Secondly there is a strong tendency for rich countries to import goods they used to manufacture, meaning that the energy used in their production is not tallied as having been used in their economies.  An examination of US trade figures provides impressive evidence for this claim. (Adrianse, 1997, US Department of Commerce, 1995.)  This energy is taken into account when “emergy” accounting is carried out (i.e., analysis of the energy costs of production, especially important in the production of energy.).  Finally, the amount of garbage thrown out would seem to be an important indicator of the volume of materials and energy consumed and garbage generation per capita in rich countries is not falling.

It is therefore not plausible that the Australian economy could continue to increase  production and consumption at normal rates, for example rising to 8 or more times present levels of output by 2070, without seeing its present energy consumption multiply many times in coming decades.  If all the world’s expected 9-10 billion people were to rise to the per capita “living standards”  Australia would have by 2070 given 3% growth, total world economic output would be more than 60 times as large as it is today.

These are the sorts of considerations which lead those within the “limits to growth” school to conclude that there is no realistic possibility of sustaining industrial consumer societies committed to economic growth.  (Trainer, 1995a, 1998, 1999.)

 Conclusions.

The foregoing estimates are imprecise but the magnitude of the numerical conclusions arrived at  are so large that very different and quite implausible assumptions would have to be made before it could be claimed that Australia could meet its probable electrical and liquid fuel demand from solar sources in the coming century.

It should be emphasised that this is not to reject the development of renewable energy sources.  A large literature on the limits to growth predicament and alternatives to industrial consumer society concludes that a sustainable society can only be sensibly defined in terms of a) much simpler material living standards, b) high levels of social and economic self-sufficiency at national, local and household levels, c) more cooperative and participatory ways, d) a new economy that is not driven by profit maximisation, market forces  or  growth and e) heavy reliance on alternative technologies including renewable energy, earth building and  Permaculture.  (For a detailed discussion of this option see Trainer 1995b and 1995c.)  The position on  energy adopted within  this  “Simpler Way” vision is that all could live well on renewable sources, but not at anything like current rich world per capita rates of consumption.
 

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1.    No environmental costs are factored into the discussion so I do
not accept the economic argument.  A carbon tax could easily reverse the
resulting conclusions.

2.    No decrease in usage due to upgraded efficiency of plant and
equipment is factored into the discussion and as this is occurring I
conclude that argument is flawed.

3.    Adaptation of building stock can substantially reduce heating,
cooling and lighting requirements so I query the basis of the whole
discussion
 
Date: Mon, 8 Oct 2001
From: Chris Mardon
 
· The conclusion is probably over-pessimistic in the long term, especially
from the technical point of view. We could meet most of our needs using
renewable energy within about 50 years, but a lot depends on how we manage
the transition. The conclusion depends on how ‘material living standards’
and ‘economic activity’ are defined. The Genuine Progress Indicator for
Australia is not rising, despite continued GDP growth.
· Energy consumption is linked to population, so we will need to stabilise
our population and restrain the fall in average household size in order to
limit the growth in the overall demand for goods and services, including
energy.
· This is not just a technical problem. Unless the government is prepared to
tackle the difficult institutional and political issues of how to phase out
energy-intensive industries, how to change the behaviour of the energy
supply industries and energy consumers, and how to ensure that more
energy-efficient appliances, buildings and transport systems are available
here, little real change can be expected.
· We will need to stop subsidising the consumption of energy and resources,
reform our flawed energy markets and impose taxes on energy corresponding to
the external costs of the environmental impacts and greenhouse emissions.
· We will need to reverse the shift in taxes and subsidies in favour of road
transport that occurred with the GST, stop the rush to build roads and
freeways, and structure our urban areas so that they can more easily be
serviced by public transport and rail freight.
· In the overall economy, the current emphasis on Mining, Agriculture,
Tourism and finance is driving still further increases in the consumption of
resources, so we should shift to a less resource-intensive economy if we are
ever to make it ecologically sustainable.
· Ethanol from sugar crops could be an option for rural fuels in some areas,
but generally it would not compete with methanol from wood or other sources
of biomass. Ethanol would not be a viable source of transport fuel for the
major urban centres where most fuel is consumed. Methanol or CNG produced
from natural gas are more likely contenders for this purpose. The paper
concentrates too much on ethanol which is least likely to be the major
source of urban transport fuel. Also, we will need to switch to more
fuel-efficient vehicles so that the cost of providing the fuel and our
greenhouse gas emissions can both be reduced. It is pointless to invest in
the massively expensive infrastructure which would be necessary to support
our existing consumption patterns.
· Unless we look at the whole picture for the provision of particular energy
services, we are likely to come up with the wrong answers. Passenger
transport is really about access to work and community facilities, not just
about moving people. We need to think through the options more carefully
than in the past, not just substituting one source of energy for another.
· Unfortunately, governments are vulnerable to influence from business
pressure groups and are so lacking in impartial policy advice that they are
unlikely to come up with sensible solutions. Perhaps we need to reform the
political system first so that governments are really answerable to us
rather than to the markets and the multinationals.
 
Date:         Mon, 8 Oct 2001 21:10:05 +0100
From:         Heiko Gerhauser
 
To start off with I should say that I think that even greater taxation
of fossil fuels or subsidies for renewables are wrong and should be
strongly opposed.

Nevertheless, renewables, phased in slowly, would only make us
poorer in the sense that we'd grow richer at a more leisurely pace.

The following two links provide data on Australia's GDP and
electricity consumption:

http://www.lonelyplanet.com/destinations/australasia/australia/

http://www.uic.com.au/nip37.htm

Supplied electricity 160 TWh

Population 19.2 million                   GDP: US$ 418 billion

Per capita electricity consumption: 8300 kWh

Per capita GPD: US$22000

Hydro is 8.7% of consumption and 18% of capacity, while fossils
provide the rest.

Criticisms of Ted Trainer's approach:

Assessment based on winter demand:

Currently, about 2 tcf or 10% of annual US natural gas demand are
stored during the summer and used in the winter months (actually
this year it's nearly 2.5 tcf). This would be done in Australia, as
well, but with hydrogen and would not require mine shafts of several
thousand kilometers of length.

Assessment based on current night time demand:

This is wrong, as demand is actively managed via differential
pricing to achieve higher night time demand. Even pricing would
move night time demand to 50% of daytime demand, while a
simple daytime economy tariff would move it to 30%.

Assessment solely based on PV:

Hydro and wind would also be used. Hydro can be assumed to be
mainly stored hydro. It can therefore produce at night, while water
is allowed to accumulate behind the dams during the daytime. 18%
of capacity is represented by hydro and could be be fully used for
roughly half the time. That would cut the need for night time
storage from 30% to 15% roughly. There is plenty of wind potential.
This is irregular, but when it is blowing during the night, it'll relieve
the need for storage and the use of hydro. Assuming an average
wind contribution of 30%, should cut the need for night time
storage by about half, leaving an average storage need of about
7.5% of daytime demand at night.

Wrong numbers for the conversion efficiency of hydrogen and plant
costs:

For the conversion of hydrogen to electricity, modern combined
cycle plants would be used. These only have a third of the capital
costs of coal plants (not the same, as implied by Ted Trainer) and
have a conversion efficiency of 60%, not 40%, as again wrongly
assumed by Ted Trainer.

Wrong application of the net energy concept:

Panels would be constructed in the desert in an ideal location.
Mirrors would be used to provide process heat.
The advantage of using residential panels with a nominal net
energy ratio of 4 would be that solar energy from that ideal location
could be converted into electricity in Melbourne with a gain of a
factor 4, rather than with a loss of 60%. That's a an order of
magnitude.

Wrong suggestion that capital costs would be a minor fraction of
total cost:

Administration, the grid, billing will cost the same and not scale
according to the higher capital costs. Maintenance costs will be
fairly small compared to capital costs. The vast majority of the
costs will be the capital costs for PV (assuming the current price
for panels).

Likely capacities and capital costs (US Dollars/Euros billions):

Wind: nominal 30 GW                    60

PV: nominal 150 GW                  1125

Hydro: nominal 9 GW                      0

Combined Cycle: 30 GW                18

Storage and electrolysis:                60

This is around three times present GDP. Phase-in would be over 50
years or more, while coal plants are slowly being phased out.
Storage would only become necessary after the first few decades.
The means of phasing out coal would presumably be harsh
taxation. A fair estimate for a fifty year phase in would assume no
growth in electricity consumption (the high taxes) and reduced
economic growth of 1.5% assuming a stable population. In 2050
that would give an economy of about 800 billion US Dollars, with an
annual investment in electricity generation of about 40 billion
Dollars, mostly for PV. These are highly conservative numbers.
Should PV/solar thermal electricity generation become cheaper by
a factor 10, annual expenditure on electricity would dive below 1%
of GDP. This would easily allow for a doubling of the population and
a doubling of electricity consumption to account for transportation
requirements and still keep energy production quite low as a
percentage of GDP.

Kind regards,
Heiko Gerhauser
 

   Date:         Sun, 05 May 2002 16:40:12 -0400
   From:         Graham Cowan
 
Let me belatedly add to Heiko Gerhauser's insightful comments.
The dismissal of solar-powered production of liquid motor fuels
refers only to biofuels, and so knocks over a strawman.

What must really be refuted is the prospect that
the inefficiency of photosynthesis will be bypassed
through the use of concentrated sunlight
to drive thermochemical fuel production.
So, for instance,

1.  Hydrogen iodide, HI, is thermally cracked to H2 and I2
    at 400 Celsius. The hydrogen is extracted through a
    selectively permable membrane and cooled.

2.  Sulfuric acid vapour is cracked to water, SO2, and O2
    at 1,000 Celsius. All three substance are cooled
    and the oxygen is released.

3.  Water, SO2, and iodine (I2) react at normal environmental
    temperature to regenerate the hydrogen iodide and
    the sulfuric acid which were consumed in steps 1 and 2.

This has been demonstrated, and heat-to-hydrogen
efficiencies of 51 percent are projected.
This makes the hypothetical large-scale solar production
of hydrogen through PV cells followed by electrolysis
very unlikely.

Liquid fuels -- gasoline and diesel -- would require the
solar thermochemical hydrogen to be further combined with
carbon dioxide, by processes such as this,

    CO2 + 3H2       --100 bar, 200 C -->    H3COH + H2O

and possibly further processing of the methanol.
This would reduce the final efficiency well below 50 percent,
but still it would end up well above the efficiency
of inexpensive PV cells, and vastly more than that of
the oil crop plantations that are putatively proposed
for the same purpose -- liquid fuel production using sunlight.
 

yours sincerely,
 
 

-- Graham Cowan
 
Date:         7/3/05
From:         Nathan Hurst
 
I started reading your post at: http://www.aie.org.au/material/trainer.htm

but you lost all credibility with this paragraph:

"The energy efficiency of producing hydrogen gas from electricity is
approximately 70%.   (Commercial supply in the US is currently via methane
reforming at 65% efficiency.)  Again a 15% loss in transmission and a 7%
loss in inversion will be assumed.   Generation of  electricity by burning
the hydrogen gas will be assumed to be 40% energy efficient.  A higher
figure for future fuel cell technology is discussed below.  (Note that any
plan to convert the hydrogen into electricity after storage would involve
construction of a generating plant comparable in magnitude and cost to a
coal-fired plant.)  The combined  effect of these efficiencies would mean
that for each kWh of solar energy collected only .029 kWh  would be
delivered in the form of electricity after storage; i.e., the process
would only be about 2.9% energy efficient. Thus the need to store a unit
of energy increases the collection area by a factor of 3.7."

Assuming your figures are right then the round trip efficiency is
22% (0.7*0.85*0.93*0.4).  I'm not going to bother reading any further when
you start off with this doozy.

njh
 

Date: November 07, 2006
From: Trevor Whittle

hi ted

interesting article, big  job!

i had an idea that the most effective way to store electricity was as water behind a dam (scientific american, last century) since most aussie capitals have dams and all have a water problem for us perthites and maybe a few other capitals, pumping water by day and reaping its energy by night might reduce significantly the infrastructure cost associated with hydrogen technology.

clearly this immediately spins solar power into a size bracket determined more by existing infrastructure than a global proposal as suggested in your paper; but most punters see p/v as only a pat of the final picture, anyway.

did you consider water/dams as a storage device in any context?

cheers

tw