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The limits to solar thermal energy

It is very commonly assumed that we can move from fossil fuels to renewable energy sources without significant change in the lifestyles and systems of rich countries. People might think that some things would have to be quite different, such as the kinds of cars they drive, but it seems to be taken for granted that the transition could be made without any threat to the growth economy, the free enterprise market system, or affluent living standards.

I do not think this is so and for some years have been trying to clarify the situation. My 2007 book (Trainer 2007) set out the situation in the light of the evidence I was able to find to that point in time. A shorter and updated 60 page summary of the situation as I now see it is available at

Whether or not renewables can save consumer-capitalist society depends heavily on solar thermal electricity, because unlike wind and photovoltaic energy it can be coupled with large scale storage and so can deal much more effectively with the problem of the intermittency of wind and sun. But can it enable total dependence on renewables?

My analysis of the situation is given in the 40+ paper available at It is rather dense, being an attempt to deal with all the relevant information I have been able to find. It is not possible to be very confident re conclusions, mainly because the few commercial generating companies will not make public the data on the actual performance of dishes and central receivers. However I believe there is enough information from which to draw some important indicative conclusions. Following are the main points arrived at.

  • The crucial issue is what can solar thermal systems do in winter. We know they will be major contributors in summer but can they sustain us through those months when solar resources are at their weakest? They will have to take most of the load because there will be times when both wind and PV are contributing almost nothing, and electricity cannot be stored in very large quantity except via ST heat tanks.
  • Troughs will not be able to do the job. Their geometry means that their winter output typically goes down to the region of 20% of summer output.
  • Dishes seem to be the most efficient solar thermal devices. However dish-Stirling systems can’t solve the winter problem because they do not involve storage, and dish-steam systems seem to involve major difficulties in transporting heat long distances to power blocks. Turbines must be relatively big to maximise efficiency, but that means big collection fields and long distances and greater losses. (One large dish field might involve several thousand km of pipe to connect all dishes to the power block.)
  • The most promising approach seems to be the 400m2 Big Dish developed at the Australian National University using an Ammonia dissociation process for heat storage. This is only in the experimental stage so efficiencies and costs are far from firmly established at this stage. If the experimental and theoretical figures are taken a dish located at the best Australian(and therefore world) sites, where winter monthly DNI averages 5.7 kWh/m2, would deliver at long distance perhaps 25 W per square metre of collector, net of most energy costs, including a 15% long distance transmission energy loss (e.g., from North African deserts to the UK.)
  • Central receivers seem to be capable of around the same performance, but seem to be more costly.
  • However the issue of likely future plant capital costs is quite problematic. There is little evidence, technologies are immature, and it is by no means certain that capital costs will fall (some are rising at present), especially given that the price of energy and therefore all inputs into production seem bound to rise in future.
  • I use the estimate that the future cost of a Big Dish will be $(A2010)240,000. This is to take the prediction made in 2000 that costs estimated at that point in time will fall by 2/3.
  • Despite their capacity to store heat solar thermal systems suffer a significant intermittency problem, though far less than for wind or PV. There can be several days in a row in winter when an entire continent is under cloudy and calm conditions, so if the solar thermal sector was to continue to carry its load through such periods its storage capacity would have to be maybe 13 times that being built into systems now. That much storage would cost more than the collection plant.
  • If we assume that global energy demand in 2050 will be 1100 EJ, solar thermal systems will provide 3/4 of it (66 EJ/month in winter), a Big Dish in winter delivers at distance 20.7 GJ/month (i.e., 25 W/m2), then we would need 3.188 billion of them. At the above unit cost the total capital expenditure would be $756 trillion, and therefore the annual cost would be $30 trillion. This would be 17% of world GDP assuming it grows at 3% p.a. from now to 2050. At present only about .7% of world GDP goes into total energy investment. In other words it would seem that we could not possibly afford the cost, especially when the cost of a lot of extra storage, and the capital cost of the other 25% of demand are added.

The basic Simpler Way claim is that consumer-capitalist society cannot be saved. It is already consuming resources and causing environmental damage at rates that are far beyond sustainable, or reversible by plausible technical advance. Yet this society is committed to constantly and limitlessly increasing production, consumption, and GDP; i.e., economic growth is the supreme goal.

The alarming and probably fatal global problems we are encountering are generated by the quest for greater affluence and GDP and can only be solved by moving to systems, ways and values which do not create these problems. The Simpler Way project is intended to show that there are alternative ways that could easily defuse the problems, and cut resource and environmental impacts to very small proportions while greatly improving the average quality of life even in the richest countries. However these ways involve shifting to zero-growth economies with much lower GDP per capita than we have now and not driven by profit or market forces, mostly small and highly self-sufficient local economies run by participatory democratic systems. Above all, these alternative ways cannot work unless there is immense cultural transition away from preoccupation with competitive, individualistic acquisitiveness. That the prospects for such a transition are miniscule need not be pointed out, but it must be the goal to be worked for since no other option can enable a sustainable future. The case is detailed in Trainer 2010, and at the website given above.

Trainer, T., (2010), The Transition to a Sustainable and Just World, Sydney, Envirobook, 320 pp.

Editorial Notes: Ted Trainer is a professor in the School of Social Work, University of New South Wales. His main interests have been global problems, sustainability issues, radical critiques of the economy, alternative social forms and the transition to them. He has written numerous books and articles on these topics, including, The Conserver Society: Alternatives for Sustainability, Saving the Environment: What It Will Take, and What Should We Do?. He has been working on the problems of energy and sustainability for many years. For online versions of his documents, see -BA

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