Can sun and wind provide “base-load” power?

19.5.11

Ted Trainer

The answer is, of course they can!  But that’s the wrong question. 

The right question is, can they always provide enough power when we want it and the answer to that question is, no they can’t.

There are several impressive studies and reports “proving” that the world could indeed run entirely on renewable energy sources.  As this is what everyone wishes to believe it is not surprising that there has been almost no examination of the possible limits to renewable energy.  For some years I have been attempting to clarify the situation (Trainer 2007, 2010, 2011a, 2011b) and I believe there is a strong case that our society cannot run on renewable energy. 

The main problem for renewables is to do with the variability of the two major sources, sun and wind.  For years Mark Diesendorf (2010, 2011) and many others have argued that this does not prevent renewables from providing all the energy energy-intensive societies will demand.  Following is a brief indication of the reasons for thinking that this conclusion is mistaken.

First, the obvious point that even on a sunny day PV panels can provide no energy for about 16 hours of that day.  Similarly there are times when there is close to no wind blowing in your region, and these times can last for a many days.  Weather comes across from the west in very large “synoptic patterns” and these can leave the entire continent of Europe under conditions of intense calm, cloud and cold for a week at a time. Lenzen’s review of renewable energy (2009) includes a plot for the whole of Germany showing hardly any wind input for several days in a row. (See also E.On Netz, 2004.)

Germany is not in a good wind region but several studies show that the same problem applies to the UK, probably the world’s best inhabited wind region, (Oswald, Coelingh, 199, Fig. 7, Sharman 2005, Lenzen, 2009, Mackay, 2008, p. 189.)  Coppin and Davey (2003) make the same point for Australia, for instance indicating that for 20% of the time a wind system integrated across 1500 km from Adelaide to Brisbabne would be operating at under 8% of peak capacity.  Mackay (2008, p. 189.) reports data from Ireland between Oct. 2006 and Feb. 2007, showing a 15 day lull over the whole country.  For 5 days output from wind turbines was 5% of capacity and fell to 2% on one day.

What’s more at these times of low renewable energy sources demand can peak. Most renewable energy enthusiasts make the mistake of discussing only in terms of averages.  What matters are firstly the minima in available renewable sources.  The solar radiation over a whole mid winter month for a particular year and place can be 40% below the average level for that month and place, and lower than that on specific days; NASA, (2010.)  Secondly maxima/peaks in demand are crucial.  What matters even most is the fact that the two can coincide in time, e.g., Victorian winter demand peaks in stable and calm winter cold snaps.  On these occasions you might need more than twice the generating capacity that would meet annual average demand, and you might be able to get none of it from wind and PV.   That means that on these occasions you will have to meet about 100% of demand from some other sources.

All the renewable-optimistic reports I have read, including those by Stern, 2006, The World Wide Fund for Nature, 2010, Zero Carbon Britain, Jacobson and Delucci, 2011a and 2011b,Greenpeace, Zero Carbon Australia, 2010, make the same fundamental and fatal mistake.  They fail to recognise the need for massive redundancy in generating capacity, caused by the fact that often one or more component systems will not be contributing much if anything.  When the solar energy is low you will need enough wind or some other capacity to make up that deficiency.  Stern for instance proposes wind will provide 8% of annual demand.   He then proceeds as if we will only have to build enough wind plant to generate 8% of annual demand but this fails to recognise that there will be times when all that wind capacity is contributing almost nothing and will have to sit idle while PV or some other source fills the gap.  Similarly there will be times when there is no sun and you will need to have enough windmills etc., to meet all the demand.  So we might have to build enough wind capacity to meet around 100% of demand, when there is no sun, and we might also need to build enough solar capacity to meet 100% of demand, when there is no wind, meaning total system capital cost might be several times what at first we thought we would need. 

This exposes the common fallacy expressed as “...but the wind is always blowing somewhere.”   Sometimes there is hardly any wind anywhere you can tap, but more importantly if it is blowing strongly today in region A and Stern is going to provide his wind quota from that region today, then he will have to have built in that region enough capacity to provide it all.  And what if tomorrow the wind is only blowing well in region B?  Obviously he will need to build sufficient capacity to meet the wind quota in every region where the wind might be blowing well on a particular day.  He will have to build far more windmills than would contribute that 8% of total annual demand.

            “We’ll store it.”

This problem of intermittency and redundancy would not exist if electricity could be stored in very large quantities.  But this can’t be done and it is not foreseen.  Pumping water up into high dams is the best option, but Mackay (2008) shows that even in Britain where it rains a lot development of all possible sites couldn’t plug gaps in wind supply.  Hydro electricity provides only about 15% of world electricity, and 6 -10% of Australian electricity (i.e., less than 2% of all our energy), so it couldn’t meet anything like total demand when there is no wind or sun, (even if all dams could be adapted to it, and few can be  because you need a low and a high storage space.)  Using electricity to compress air is viable, but you have to burn gas to heat the compressed air or efficiency is quite low and the availability of caverns is a problem. New batteries are being used to store wind energy, but at present only on a minute scale (30 MW compared with what would be needed, e.g., 96,000 MWh to get a solar power station through a four day cloudy period.  Exetec is aiming for batteries costing $500/kWh, but that means storing for night time supply from a  1000 MWPV power station would cost you $8b, about 4 times as much as a coal-fired power station.  (On the reasons why using car batteries will not help much see Trainer, 2011a.)

The options?

Lenzen’s review of renewable (2009, p. 88) concludes that it is not possible for wind to contribute more than 20 – 25% of electricity demand, because integration difficulties increase steeply after that point.  He suggests that a slightly higher figure for PV (but this is debateable; see Trainer, 2011a.)  This means that wind and PV can at best supply 55% of that 20% of energy that takes the form of electricity.  Where are we going to get the other 89%?

Lets briefly consider the options.

1.     Biomass. In an era when land is being lost and a food crisis is developing, the world is very unlikely to find as much as 1 billion ha on which to plant biomass energy crops.  The loss of habitat is the cause of the holocaust of extinctions we are now causing so we should be returning vast areas nature, not thinking about taking more.  If that area was put into producing ethanol we would probably get 50 EJ (Trainer, 2007,2011a), which is around 5% of the world energy demand figure we are heading for by 2050 (Moriarty and Honnery, 2009.)

2.    Geothermal.  Even the renewables-optimistic WWF Energy Report, (2010), and  Jacobson and Delucci, 20911a and 2011b, only assume geothermal can contribute about 4% of world energy.  Australia has much better hot dry rock heat resources than the rest of the world but it is anything but clear how effectively they can be tapped, if at all.  How much energy will it take to bore holes 5 km deep through rock, fracture rock down there, pump water down and force it 500 metres across to the nearest rising hole? What will be the temperature and rate of flow of the water that comes up, and what generation efficiency will that enable?  And what will be the dollar and energy costs of constructing very long transmission lines from the deserts where the hot rock is? The answers are not known yet.  The only operating plant in Australia (not at the most promising location) achieves a mere 6% efficiency, one sixth the value for a coal-fired power station. Early in 2010 the much-publicised Geodynamics venture in South Australia abandoned its efforts, writing off $350 million. 

3.    Solar thermal. Here’s the back-of-envelope calculation.  The world is heading towards needing 700 EJ/y of final (not primary) energy by 2050. (Moriarty and Honnery, Trainer, 2010, Trainer, 2011a.)   Let us assume a 33% reduction in demand due to energy efficiency effort.  My review of solar thermal systems (Trainer, 2011b) erstimates that in mid-winter both central receivers and Big Dishes using ammonia for heat storage could probably deliver at distance a continual flow of about 25W/m2 of collection area.  Probably the best strategy, Big Dishes, might cost $600 per square metre in future (Luzzi, 2000.)  This means we’d need 1,980 million of them, the total cost would be $475 trillion, i.e., $19 trillion p.a. assuming a 25 year lifetime (Jacobson and Delucci assume 20 years.)  If we assume world GDP will treble by 2050 this sum would be13 times the present ratio of energy investment to GDP in developed countries. (Pfuger, 2010.) 

Note that other costs such as the transmission lines thousands of kilometres from the deserts have not been included.  And we would still have a problem of intermittency; i.e., what to do when there is little or no sun on the solar thermal fields for days at a time...pay for huge excess heat tank storage capacity?

4.Hydrogen. How about using huge numbers of windmills, the cheapest renewable source, to produce and store hydrogen.  The energy efficiencies of a) producing hydrogen from electricity, b) compressing, pumping and distributing it, and c) re-generating electricity via (very expensive) fuel cells are, optimistically, .7, .8 and.4, meaning that for each kWh your windmills generate you would end up with .22 kWh to use via this path.  So a crude estimate is that to supply 89% of that 700 EJ/y this way we would have to produce 2,832 EJ/y, and we would need 179 million windmills each of 1.5 MW peak capacity (each producing on average .5 MW or 15.8 TJ/y and costing $3 million), at a total cost of $534 trillion, i.e., about the same cost as the solar thermal option.  We would have to add the cost of the hydrogen production compression/liquefaction, distribution and huge storage capacity

Whatever option you choose, you might then have to multiply the total by 1.75 to pay the interest on the capital borrowed to build all that renewable plant.  Finally, the cost of energy and materials are now rising fast and will be much higher than is assumed in the above exercise. 

All this has been a long-winded way of saying that we couldn’t possibly afford the amount of plant required. 

By the way, if your goal was to provide all people, probably 9+ billion by 2050, the energy per capita Australians are heading for, your target would be 5 times as great as the700 EJ/y assumed in the above exercises.  Do you still think the world can all live affluently on renewables?

What then is the answer?

The point is, there isn’t one.  If the question is, how can we provide the energy to keep going the energy-intensive, growth and market driven societies we have in rich countries today, let alone to enable the continuous and limitless pursuit of ever-increasing affluent  “living standards”, then the answer is, this cannot be done.  For decades many of us in the “limits to growth’ school have been trying to get the mainstream to grasp that this quest is suicidal. 

We Australians now have a productive land “footprint” that is 10 times as big as would be possible for all people in 2050.  It is precisely the mania for affluence and ever-greater levels of production, consumption and GDP that is causing all the big global problems, most obviously resource depletion, Third World deprivation, the greenhouse problem, the destruction of the environment, and international conflict.  Such a society cannot be fixed.    For instance you cannot reform a growth-based society so that it can have a zero growth economy, let alone one producing at a small fraction of present levels.  Sustainability is not achievable without scrapping and replacing several of the fundamental structures of this society.

One of the most disturbing of those structures is the global economy.  It delivers most of the world’s wealth to the few in rich countries, because it is a market system and markets allocate resources to those who can bid most for them, not to those who need them most.  Global economic justice and satisfactory Third World development are not possible unless the rich countries agree to move way done to living on something like their fair share of world resources.  Again that is not remotely possible unless we achieve huge and radical structural and value change.

For fifty years the mainstream has refused to face up to and of this, and their delusion has been strongly reinforced by the unexamined faith that renewable energy can be substituted for carbon fuels and enable us all to go on pursuing affluence and growth. 

This has not been an argument against transition to renewable energy sources.  It is an argument that those sources can’t run energy intensive societies.  We must move to full dependence on renewables as soon as possible.  We can all live well on them... but not in consumer-capitalist societies.  For detail on the radically different path that must be taken, see The Simpler Way website; http://ssis.arts.unsw.edu.au/tsw/)

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