Editor's note: Bill and Dorte Griswold were part of a Clean Power Now (CPN) sponsored fact finding trip to Denmark in 2004 to learn about land and offshore wind farms. The couple recently returned from a trip to Denmark, a country which remains dedicated to using and improving renewable energy sources. Dorte is a native of the country.
By Bill and Dorte Griswold
Denmark is another world
On final approach to Copenhagen’s Kastrup Airport, we saw our first wind turbine. By the time our two week visit was over, we would see many more.
As of December 2011, Denmark had 4,555 wind turbines, both on land and offshore. In 2000, this figure was 6,125 wind turbines. Earlier wind turbines, now obsolete, averaged 0.2 MW. Today’s replacement wind turbines are rated at from 2.5 to 3.0 MW. This means that, as obsolete wind turbines are scrapped, one modern wind turbine can replace roughly 12 scrapped wind turbines. The result is that, even as many older wind turbines are being scrapped, the output of the wind turbine fleet in Denmark has continued to increase. Quite simply, fewer wind turbines are now producing more electricity. An estimated 85% of the steel in a scrapped wind turbine can be recycled.
From the airport, we took an electric train to Copenhagen’s Main Station. From there, we took a 20 passenger battery powered bus to our hotel. The next afternoon, we took a guided tour of some of Copenhagen’s many canals, riding in a 120 passenger battery powered tour boat.
On batteries, both the bus and the tour boat have a 12 hour endurance. They are recharged overnight, when the cost of electricity is at its lowest, using RECs (Renewable Energy Credits) from wind.
So here is a country which is on its way to becoming CO2 neutral. The plan forward is to add 3,900 large scale wind turbines by 2020, so that about 50% of Denmark’s electricity demand will then be generated from wind power. This will put Denmark in the forefront of the renewable energy sector. For Denmark this means cleaner air, more employment, and more exports.
The sound of the wind
With 4,555 wind turbines now in service, both on land and offshore, it is rare to find yourself at a location where you can not see at least one wind turbine somewhere on the horizon.
Denmark is roughly the size of Massachusetts, Connecticut and Rhode Island combined. With 4,555 wind turbines now in service, both on land and offshore, it is rare to find yourself at a location where you can not see at least one wind turbine somewhere on the horizon.
In older wind turbines, now obsolescent, there is a transmission or gearbox which connects the blades in the front to the generator in the back. If the main shaft carrying the blades is turning at, say, 20 rpm, this shaft is connected by a complex series of gears to the drive shaft, which may turn at as much as 2,000 rpm. This higher shaft speed is connected to the generator, which delivers electricity to a cable leading to the ground. This tried and true arrangement has one disadvantage. The multiple gears in the transmission, some of them turning at comparatively high speed, can generate noise.
A solution has been found in the form of a wind turbine design which does not use a transmission. Power in the main shaft is delivered to the generator directly. With no gears in the power path, there is almost no noise. For peace of mind, when considering the purchase of a new wind turbine, whether by an individual, a business or a unit of government, the buyer should make certain that the wind turbine being considered does not have a transmission.
With 4,555 wind turbines now in service, Denmark currently produces 20% of its electrical demand from wind. Work is underway to increase this percentage to 50% by 2020. This is an almost unprecedented approach. However, the wind does not continue to blow during every hour of every day. A group of backup natural gas power plants, most of them already existing, are used to generate electricity during the hours when the wind is not blowing. When the wind is blowing, the natural gas plants are either at idle or generate at a very low output.
Consider the following hypothetical situation:
In the above scenario, the natural gas plants are needed to generate electricity for 12 hours per day. But, if there were no wind turbines in the mix, the natural gas plants would have been needed to generate electricity for 24 hours a day. Thus, for the 20% of the electrical load being covered by wind, the availability of multiple wind turbines cuts the daily consumption of natural gas in half. Because the fuel not used comes in the form of natural gas, it can easily be stored for use at a future date.