A prime duty of government is to make sure that its energy policy is correct, that the supply of energy, particularly electricity, is secure into the future. Unfortunately during the last 12 years our government in the UK has been more interested in other issues and has only at its last hour addressed the problem

For years it has been glaringly obvious to energy experts that Britain will soon be facing a colossal energy gap, as the ageing power stations which currently supply 40 percent of our electricity are forced to close down

Eight of our nine nuclear power plants are coming to the end of their life. And half of our coal and oil-fired power stations are rapidly running out of the hours they are allowed to keep running under the EU’s Large Combustion Plants directive, designed to stop the pollution blamed for acid rain

By 2015, or even earlier, we shall thus begin to lose two-fifths of our present electricity supply, and the question energy experts are asking is: how do we propose to fill this yawning gap?

The government’s answer is wind power, much of it onshore

But wind energy has major problems

At present there is effectively no means of storing really large quantities of electrical energy. So the fundamental rule for the electricity grid is that the supply from the generation companies and the demand by consumers must balance EXACTLY, every minute of the day, every day of the year

Failure to do so results in unacceptable variations in voltage and/or frequency, leading to failure of the computer and other systems on which our society depends. Power cuts are the last resort to avoid this disaster

Obviously the wind does not blow full strength all the time. As a result, the total energy produced by a windfarm over the course of a year is only a small fraction of its capacity. In the north of Scotland, where winds are more constant, load factors of 35% are achievable, whereas in Cornwall the figure is about 25%

It is of course true to say that any energy produced from wind replaces that from fossil fuels. But that is not the whole story

It is the fluctuation in wind power supply that causes the difficulty

When the wind strength increases from zero, a turbine starts up when the wind reaches a certain speed. At some point it reaches its maximum output which is maintained until the wind exceeds a certain maximum speed at which point the turbine automatically shuts down in order to prevent damage to itself

The British Wind Energy Association (BWEA), which represents the wind industry as a whole, also advises the government on wind policy. It says that the variability in wind power supply is a relatively small addition to the existing variability in demand, which can more than double from a minimum at 4 am on a summer’s morning to peak at 6 pm on a cold winter’s evening. They also say that the wind will always be blowing somewhere in the UK, so no need to worry

In fact, on a number of occasions in recent years, a cold winter spell has coincided with an anti-cyclone covering the whole of the UK. (For example several times in the period Dec 2008 – February 2009)

So really the only effective way to reduce the probability of power cuts to an acceptable level is to provide back-up plant, somewhere on the electrical grid, roughly equal to the capacity of the total wind power supply connected.

BWEA (who obviously have a vested interest) deny this. They also say that the necessary back-up plant already exists (even though much of this will have been closed down before 2020)

National Grid have been responsible for successfully maintaining the continuous balance in consumer demand for electricity and its supply from generating stations since 1947. So concerned are they about the effect of the increasing amount of uncontrolled wind-power on system stability, that they have commissioned a UK wide consultative document that identifies a significant increase in the cost of reserve generation

We leave it to you to decide whom to believe

However, it is clear at this stage that it will not be cheap. Not only are windfarms themselves relatively expensive to construct (per megawatt of capacity) compared to thermal plant, they require a similar capacity of thermal plant as back-up

But that is not the whole story either. This back-up plant would in practice be gas turbines and as already mentioned these will also have to be built. It should however be borne in mind that, as the percentage of electrical wind power increases, the profitability of this plant drops off. So in order to persuade companies to build, maintain and run this plant the price paid to them will be very large indeed

One further consideration is that this back-up plant, when used in this way, is not running in a thermally efficient manner and, as a result, its carbon emissions are higher than their optimum value

To see how this works out in practice take the case of Denmark (with more than 6,000 turbines generating 19% of its electricity - compared to 2% in the UK - It has the highest per capita wind power capacity in the world). Yet It also has the highest consumer electricity prices in the developed world - even though their supply is heavily subsidised (more)

Because Denmark is not as windy as the UK, the average load factor achieved is only about 22%. On the other hand they have the advantage of proximity to their neighbours Norway, Sweden and Germany. They can sell their excess electricity (at very low prices) at times of high wind and low demand and buy it back (at higher prices) at times of low wind and high demand. This arrangement with Norway is particularly beneficial as the latter has large hydropower resources, which provide an environmentally friendly load-balancing function. This is good for the world but not so good for the Danish economy

The informed Danish public naturally object to their taxes in effect subsidising the electrical supply of other countries. But what is particularly sad is that, according to the UN Human Development statistics, Danish annual per capita CO2 output is actually greater than that of the UK