THE PROBLEM WITH INTERMITTENT RENEWABLES

THE PROBLEM WITH INTERMITTENT RENEWABLES

It is hard to understate the implications of the UK’s growing exposure to wind for its electricity. According to the Royal Academy of Engineering, which is sympathetic to renewables, it requires ‘a fundamental shift in society’s attitude to and use of energy.’ Success, the Academy says, depends on the ability to manage demand to reflect the output from wind, going on to note that despite increasing efforts to research demand management techniques (to match consumption to the variability of the weather), ‘there is still much uncertainty on how effective it will be and at what cost.’ So called ‘smart grids’ will be vital, the Academy says, but their potential and effectiveness at scale ‘are yet to be proven.’

Electricity has a set of uniquely demanding characteristics:
◾It cannot be stored, except to a limited extent, with batteries and pumped hydro, and that storage is limited and incurs a cost;
◾Supply must respond almost instantaneously to demand;
◾If too little is produced, there is a danger of degraded quality and, eventually, of power cuts, which are costly to users;
◾Too much production can damage the transmission system, leading to wires becoming deformed or even melting;
◾Failing to equalise demand and supply can also lead to changes in the frequency of the power supply – too high, and it can damage appliances; too low, equipment can underperform.

Wind and solar technologies pose huge integration challenges. They are difficult to predict, particularly wind, which is highly variable – on gusty days, wind speeds can vary enormously over a few minutes or even seconds. According to Malcolm Grimston of Imperial College, London, low wind speed tends to be weakly correlated with high power demand (cold, windless winter evenings and hot, windless summer days). Depending on how wind-generated electricity is connected to the grid, large amounts of wind power can reduce system inertia and make it less stable.

 

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