An important article "Flere Vindmøller Skaber Kaos" by Niels Sandøe was published in the Danish newspaper, Jyllands Posten, on 4th June 2003. Herewith is a short summary :
Electrical power supplied must balance the power demand plus transmission losses at every second of the day. If this balance is not achieved, either there will be an automatic disconnection of either supply (to prevent physical damage to generating plant) or of loads (blackouts). Conventional plant has to be run in conjunction with the unpredictable wind generators and their output varied in order to provide a cushioning effect.
When large changes in wind power occur, beyond the capability of such conventional plant to compensate, then the assistance of neighboring systems has been called upon.
With excess wind power the surplus has to be dumped somehow. Help is secured from Germany, Sweden or Norway by offering zero-priced electrical energy. Unfortunately it appears that Germany has, at times, the same problem because of its own wind-turbine concentration in the same region. When the wind blows strongly, the problem is to dispose of the excess wind electricity. Hence the price drops -- which is why Denmark has been known to export electricity at zero economic benefit.
What is very interesting in this article is the statement that because the turbines in Northern Germany and Denmark operate at much the same time and rate there is keen competition between these two countries to sell power to each other! Hence the frequent big drops in price. Both need to get rid of their uncontrollable excess of wind electricity at whatever price they can get!
As to pricing, Eltra is the Transmission System Operator, and is an entirely different company from Elsam, the main electricity generator. Both companies are trying to optimize their operations, so when the supply of electricity from wind, coal and gas generators is suddenly reduced by a deficiency of wind, the other (coal and gas fired) generator companies, such as Elsam, must be on-line to take up the demand and charge a premium for this service.
The whole system is crazy, and could only operate because Denmark has neighbors who are only too willing to receive cheap electricity, and the previous "green" government was willing to support the vast costs involved! The present Danish government is trying to sort out the mess!
PS: The UK faces a far greater problem than Denmark since it cannot trade power with neighboring countries. The need for more fossil-fuel back-up increases both cost and CO2 emissions.
