THE PROBLEM WITH UNCONTROLLABLES by Andrew R.B. Ferguson

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1 THE PROBLEM WITH UNCONTROLLABLES by Andrew R.B. Ferguson Abstract. David MacKay, in his admirable book Sustainable Energy without the hot air, 1 believes that there may be a renewable energy plan that will work: he thinks that we, in the UK, with some help from Concentrated Solar Thermal electricity from North Africa, can support ourselves with extensive use of electricity from renewable sources. But electricity is a tricky business: demand has to match supply for every fiftieth of a second for 24 hours of every day. This paper argues that it would be impossible to introduce so much uncontrollable input into an electrical system without providing an amount of controllable backup that because of the low power densities of all controllable renewable energy sources there is no evident way of providing. His book contains the data for others to have a try to solve the as yet unsolved problem of how to provide from renewable sources adequate energy to support civilized life. To some extent, the problems associated with uncontrollables have been brought into focus in previous editions of the OPT Journal (The Meaning and Implication of Capacity Factors, pp , OPTJ 4/1). 2 There are two reasons to take another look at the subject. The first is that objections have often been raised to my analyses on the grounds that one possible solution, that of greatly oversizing the uncontrollables, has not been adequately considered. The objectors suggest that were they to be oversized (i.e. accepting some waste), uncontrollables could contribute a greater proportion of the whole. The second motivation arises from the publication of David MacKay s remarkable book Sustainable Energy without the hot air. On page 18 he says, This book is emphatically intended to be about facts, not ethics. I want the facts to be clear, so that people can have a meaningful debate about ethical decisions. I want everyone to understand how the facts constrain the options that are open to us. Hear! Hear! Such sentiments accord with the philosophy of the OPT Journal. On page 250 Mackay says, We need to choose a plan that adds up. It is possible to make a plan that adds up, but it is not going to be easy. It is the last sentence that warrants further investigation. The plan that the book suggests as plausible is to run our society almost exclusively on electricity (although some of the heat captured is ambient heat, electricity is needed to operate the heat pumps). My view is that this plan has an Achilles heel, namely that it is not possible to produce so much electricity from uncontrollables because they need to be backed by controllable renewable energy sources, and renewable controllables have very low power densities. The problems stem from low capacity factors (also called load factors). The capacity factor is the amount of electricity actually produced, as a fraction of the amount of electricity that would be produced if the source operated steadily at full capacity. Wind has a low capacity factor, but nearly all other uncontrollables are even lower. Photovoltaics is in the range of 10% to 19% depending on insolation. Tidal barrage is 25%. Concentrated Solar Thermal (CST) electricity, which is only possible in places with very high insolation, has a capacity factor of about 22%, 3 (and immense seasonal variation problems). 4 Thus looking at wind, and assuming a capacity factor of 30%, will provide a general indication of the problems associated with all uncontrollables. For simplicity, we will choose round numbers as an illustrative scenario. As that scenario will encompass about double the UK s current use of electricity, we will merely need to halve the scenario results to take account of the current use of electricity in the UK. Since 1 From OPT Journal Vol.10, No 1, April 2010

2 only about 40% of fossil fuels are used to produce electricity, producing all the electricity from renewable sources will only solve 40% of the problem, but if we could solve it, it would be a start. Can we solve it? Figure 1 shows a wind capacity of 100 gigawatts (GW). Jim Oswald 5 has shown that even with wind turbines spread over the entire UK, it will sometimes be windy everywhere, and peak output will rise to 98% of total wind turbine capacity. However that will occur rarely, and it would not be too wasteful to assume that we plan to make use of only the electricity that is made available when the wind turbines are producing 80% or less of their total capacity. This smoothing out of the output helps the prospect for using renewables, as does another smoothing out that we will now address. Demand varies each day, being low at night and high in the day. Renewable energy optimists think that various devices (e.g. turning off deep-freezes for a while when there is high demand, and running heat-pumps during the night to store heat) will alleviate this problem. For present purposes, let s indulge ourselves in this optimism, and assume that this program is so successful that in our scenario, system demand is held steady at 80 GW. Thus in the system we are considering (Figure 1), the annual demand for electricity is 80 GWy and, by our choice of 100 GW wind capacity, 80 GW is also the effective peak output of the wind turbines. The electricity produced by the wind turbines will be 30% of their 100 GW capacity, 30 GWy/y (i.e. the area below the curve in Fig. 1). Since the total demand is 80 GWy/y, this leaves 50 GWy/y to be produced from controllables (i.e. the area above the curve in Fig. 1). Before going on to consider the possibility of storage, let us look at the area of land that is likely to be required to supply this 50 GWy/y of controllable electricity. Although hydroelectricity is an excellent power source for working in harness with uncontrollables, its potential is very small compared to the scale of electrical demand in the UK, so unless storage is possible we have to fall back on the only other form of controllable renewable energy, namely producing it in power stations similar to those currently used for fossil fuels, but using, as fuel, wood or other dry plant material. MacKay correctly estimates the power density of plants as 0.5 W/m 2. But this is a measure of the heat energy they produce. If we use them to produce electricity, it would be on the high side to expect a 35% conversion efficiency, because it is hard to make the conversion as efficiently as with pulverised coal or gas. That makes the power density of producing electricity from plants 0.5 x 0.35 = 0.17 W(e)/m 2. The small area of 1 square metre is easily altered, because there are 1 million m 2 in 1 km 2, so the power density is also 0.17 MW(e)/km 2. So to produce the required 50 GW will need an area of / 0.17 = km 2. As mentioned, the UK demand is about half of the amount of this scenario, so for the UK that reduces to km 2. The area of the UK s fertile land is about km 2, so in order to produce this electricity we would need another 0.8 UKs to provide the fertile land. We should remind ourselves that the present UK does not have sufficient fertile land to allow us to feed ourselves or produce more than a fraction of the timber we use for construction purposes, but even without that problem, it is clear that this plan is not going to work. Perhaps we could improve the outlook by using more uncontrollable input at least it has a better power density. Suppose that, instead of installing wind turbines with a capacity of 100 GW, we double the capacity to 200 GW. With the same capacity factor of 30%, this will produce 60 GWy/y. However, as Figure 2 shows, approximately 7 GWy/y will be surplus to requirements. Thus, unless we can store the electricity, the amount of useful electricity provided by the wind turbines will be 60-7 = 53 GWy/y. This leaves = 27 GWy/y to produce from uncontrollables. With the first scenario, we needed 50 GWy/y, so we have 2 From OPT Journal Vol.10, No 1, April 2010

3 approximately halved the amount of electricity we need to produce using controllable power sources; and that means we need another 40% of one UK. By using more uncontrollables, at least we have halved the extra land needed, but in doing so created further storage problems. Let s look at dealing with lulls. It would seem a modest precaution to suppose that there will be periods of 10 days when all uncontrollables will be able to produce no more than half of their average output. This means a requirement for storing 5 days of the electricity produced by uncontrollable renewables, unless of course we are going to have extra controllable plant available for such occasions. In this second scenario, that we are now considering, that means storing 5 /365 x 53 = 0.73 GWy. As MacKay gives us figures in GWh (gigawatt hours), it is convenient to change that to 0.73 x 8760 = 6390 GWh. The relevant figures from MacKay are that although our largest pumped storage, Dinorwig, stores only 9 GWh, it might be possible, he suggests, to sufficiently ignore public outrage to expand total pumped storage to 100 GWh, perhaps even 400 GWh! Using the higher figure, and dividing the 6390 GWh into two in order to be in line with UK demand, our current plans require (6390/ 2) / 400 = 8 times as much pumped storage as can be envisaged under draconian compulsion being built in the UK. There is a remedy for dealing with lulls, but only at the extra cost of building spare controllable capacity and providing the fuel, and for that, as noted above, we require an extra 40% of one UK. In this second scenario we have considered wasting 7 GWy/y for the sake of allowing more controllables. Is there any chance of storing the electricity that is produced in excess of demand? We may need to cope with 5 days when output averages 50% above the steady 80 GW demand (i.e. 120 GW instead of 80; and = 40), necessitating a store capacity of 40 x 5 /365 = 0.55 GWy, which is 75% of the 0.73 GWy/y calculated for dealing with lulls. That is about 6 times the amount of pumped storage capacity that just might be made available in the UK. And of course it would be hard to use the pumped storage as an empty upper reservoir to accept excess output, and also to help during lulls, the latter requiring the upper reservoir to be full. Briefly, storage won t work! All these considerations are so compelling as to the problems of uncontrollables, that it is hardly necessary to draw attention to the fact that the huge changes in output that are likely to occur on occasions will mean that utility operators will be nervous wrecks! As noted at the outset, David MacKay stated, It is possible to make a plan that adds up, but it is not going to be easy. Insofar as his plan depends on extensive use of uncontrollables, the above analysis indicates that it is time to go back to the drawing board. It is easy to agree with him that it is not going to be easy. His splendid book will be a help to all those who want to emulate Don Quixote and have a try! Concentrating Solar Thermal, located in the Sahara, offers some promise for storage, but at what cost? 3 From OPT Journal Vol.10, No 1, April 2010

4 Power in gigawatts (GW) Power in gigawatts (GW) The wind profile used in these two figures is roughly modelled on the EON Netz wind report One reason for the rough modelling is that the capacity factor there in 2004 was only about 20%. Figure 1. Capacity factor problems x 100 GW = 30 GWy. Wind turbine capacity. Peak output of wind, & steady demand = 50 GWy Time in months Figure 2. Capacity factor problems Wind turbine capacity. Peak output of wind. 7 GWy. Steady demand GW = 53 GWy = 27 GWy Time in months 4 From OPT Journal Vol.10, No 1, April 2010

5 1. David J.C. MacKay Sustainable Energy without the hot air. UIT Cambridge. ISBN (Paperback 20) Available free online from 2. OPTJ 4/ Optimum Population Trust Journal, Vol. 4, No 1, April Manchester (U.K.): Optimum Population Trust. Archived on the web at 3. Hayden, H. C The Solar Fraud: Why Solar Energy Won t Run the World (2nd edition). Vales Lake Publishing LLC. P.O. Box 7595, Pueblo West, CO pp. 4. Trainer, T Renewable Energy Cannot Sustain a Consumer Society. Dordrecht, the Netherlands: Springer. 197 pp. ISBN-13: (HB); ISBN-13: (e-book). 5. The title of the report in which this is demonstrated is 25 GW of Distributed Wind on the UK Electricity System. The full twenty-one page report is available in pdf format. It is only just over a megabyte in size, and can be printed out or saved to disk without restriction. It can be found at: 5 From OPT Journal Vol.10, No 1, April 2010