Why the world can't rely on renewable energy if we want to remain affluent

Can sun and wind provide base-load power? The answer is, of course they can! But that’s the wrong question. The right question is, can they provide enough 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 and I believe there is a strong case that our world 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 and many others have argued that this does not prevent renewables from providing all the energy that 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 many days. Weather comes across 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 (Current State of Electricity Generating Technologies 2009) includes a plot for the whole of Germany showing hardly any wind input for several days in a row.

Germany's not in a good wind region but several studies show that the same problem applies to the U.K, probably the world’s best inhabited wind region.

Coppin and Davey (2003) make the same point for Australia, indicating that for 20 per cent of the time a wind system integrated across 1500 km from Adelaide to Brisbane would be operating at under 8 per cent of peak capacity. Mackay (2008) found that data from Ireland between October 2006 and February 2007 had a 15-day lull over the whole country. For five days output from wind turbines was 5 per cent of capacity and fell to 2 per cent on one day.

What’s more at these times of low renewable energy demand can peak. Most renewable energy enthusiasts make the mistake of discussing the issues only in terms of averages. What matters are: minima in available renewable sources (the solar radiation over a whole mid winter month for a particular year and place can be 40 per cent below the average level for that month and place, and lower than that on specific days (NASA, 2010); and maxima/peaks in demand. What matters even more is the fact that the two can coincide in time, for example, Victorian demand peaks in stable 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 most of demand from other sources.

All the renewable-optimistic reports I have read, including those by Stern (2006), The World Wide Fund for Nature (2010), Greenpeace, Zero Carbon Britain and Zero Carbon Australia 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 per cent of annual demand. He then proceeds as if we will only have to build enough wind plant to generate 8 per cent of annual demand. 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 100 per cent of demand. When there is no sun, and we might also need to build enough solar capacity to meet 100 per cent of demand. When there is no wind, it means total system capital cost might be several times what we thought it would be. 

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 build in that region enough capacity to provide it all. And what if tomorrow the wind is only blowing well in region ‘B’? Obviously we 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. We will have to build far more windmills than would contribute that 8 per cent of total 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. 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 per cent of world electricity, and 6 to 10 per cent of Australian electricity (i.e., only 2 per cent 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 four times as much as a coal-fired power station.

The options?