Professor Philip Lloyd works at the Energy Institute at the Cape Peninsula University of Technology. He recently sent me a copy of a paper he had written, entitled ‘An Assessment of the Impact of Wind Energy on Energy Supply’.
The paper addresses a number of concerns that power system engineers have with wind energy. Putting aside the visual and noise impact of wind turbines (and bird and bat strike), there is the matter that wind energy is often referred to as being ‘nondispatchable’ – the output of a wind farm can go from maximum to near zero, and there is nothing that the grid operator can do.
To keep the power supply to the load going, wind turbines then have to be backed up by ‘spinning reserve’ in the form of a generator that can be brought on line, if necessary, in a few seconds. Spinning reserve in this context refers to gas turbines. It is well known that gas turbines run up very quickly and consume great quantities of hydrocarbon fuel. Thus, using a gas turbine to back up a wind turbine is hardly a combination which can be described as being green.
Another characteristic of wind turbines is that they have a load factor which is low, compared with other generation. ‘Load factor’ is the ratio of the energy supplied by the wind turbine divided by the total possible energy that could be supplied by the wind turbine. It has been widely claimed by wind turbine suppliers that this load factor can reach 50% – at least half the total installed capacity.
What Lloyd has done is to examine the power output of the UK grid. This information is available from the UK Gridwatch (www.gridwatch.templar.co.uk) and shows, with five-minute updates, what energy is being supplied by nuclear, coal-fired, hydro, wind, gas turbine power stations (as I am writing this, Gridwatch records that 10% of the UK grid is being supplied by wind and a third is being supplied by gas turbine).
Lloyd examined the figures for a four-year period. He found that the number of shifts in wind power supply where the shift was greater than 200 MW and lasting longer than five minutes is increasing and went from 10 shifts in 2011 to 80 shifts in 2014. He also found that, while in the last five years a 20% load factor is attainable in the UK, it is unlikely that this will ever improve.
Further, the maximum production from Britain’s wind system is 55% to 60% of installed capacity. This is a vital piece of information because it allows developers and investors to understand exactly what financial model applies to wind power development. What’s more, the UK wind farm capacity is about 1 000 MW. The figures indicate that it is quite possible on some days for this entire capacity to be unavailable owing to a lack of wind.
Lloyd notes: “Clearly, while it is true that the wind always blows somewhere, there are times when that ‘somewhere’ is a very small region in a very large system.”
He adds: “The implications of this are that it is essential to increase the spinning reserve as the proportion of climate-dependent renewable energy feeding a grid increases. Moreover, the increase in spinning reserve should be proportionately greater than the increase in the renewable energy. As spinning reserve is more costly than other sources of energy, the costs can mount rapidly. This needs to be taken into account in planning the expansion of renewable sources of energy.”
It is very unlikely that Energy Minister Tina Joemat-Pettersson even grasps this concept distantly. However, it must be understood, and understood clearly, that this very important piece of research by Lloyd has shown us the following: no wind farm will ever operate at a load factor greater than 20%. The maximum production from any one system cannot exceed 60% of installed capacity. The faster one grows renewable energy, which is climate based, still faster must one grow spinning reserve in the form of gas turbines. This paper is a landmark publication by the professor. I take off my hat and I bow.
Edited by: Martin Zhuwakinyu
Creamer Media Senior Deputy Editor
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