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May 6, 2011
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Geothermal heat

Geothermal heat

Heat from the hot core of the earth can be extracted and used in various ways (including ground source heat pumps described separately)

Hot dry rocks

One form of geothermal energy is produced using hot rocks, a few kilometers beneath the earth’s surface. Water is pumped into this hot, crystalline rock using an injection well. As it flows through fractures in the rock the water heats up and is returned to the surface through another well, known as a production well. At the surface the heat is extracted from the water and using a steam turbine, generates electricity. The water is then recalculated to mine more heat.

Geothermal energy not only has little impact on climate or the environment but it is also clean, quiet and virtually inexhaustible. One cubic kilometer of hot granite at 250 degrees centigrade is said to have the stored energy equivalent of 40 million barrels of oil.

Hot dry rock (HDR) energy is increasingly becoming an important source of energy but only a small number of locations currently have the right conditions for cost effective production. The granite rock must be no deeper than 5 kilometers, the current capability of drilling equipment, and it must be covered by around 3 kilometers of insulating rock which prevents the heat escaping to the surface.

Geothermal aquifers

Unlike hot dry rocks, where water is pumped through the underground rocks, an aquifer is an underground layer of permeable rock in which water already naturally occurs. As the hot water flows through the rock it can be extracted using a borehole.

Water temperatures between 50 and 150 degrees centigrade can be used for heating and higher temperatures are used to produce electricity. Those areas with the best geological conditions for producing electricity usually occur close to crustal plate margins.

After the heat has been extracted the cooled water is then pumped back into the ground. Whilst geothermal aquifers are not completely renewable as heat is usually extracted at a rate quicker than it is replenished by the surrounding rocks, geothermal energy is much less environmentally damaging than fossil fuels.

Geothermal power plants emit 1000-2000 times less carbon dioxide than fossil fuel power plants and take up a much smaller area of land.

 

May 5, 2011
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How many turbines are required?

At the end of 2005, an estimated 47,000 wind turbines were installed in Europe, generating 83 TWh of electricity, equal to about 2.8% of European electricity demand.

The average size of turbines delivered to the European market in 2004 was about 1.3 MW onshore and 2.1 MW offshore. Under the assumption that by 2030, the average size of a wind turbine will be 2 MW onshore and 10 MW offshore, this will result in a total of 90,000 turbines (75,000 onshore and 15,000 offshore machines) to fulfi l the 300 GW target.

In 2030, 90,000 wind turbines would generate 965 TWh, and provide 23% of European electricity demand in 2030.

This takes into account rising demand, so the 90,000 machines would meet 32% of current European electricity demand.

By doubling the number of turbines in Europe from 2005 to 2030, 12 times more electricity can be generated.


 



May 5, 2011
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The myth of intermittency

It is widely perceived that because the wind resource is intermittent, the wind technology is not ‘reliable’ enough to be a major power source.

Watching a single wind turbine stop and start, it might seem logical to conclude that, as more of these machines are built, the result can only be an unreliable supply.

The entire electricity system is variable, like wind energy. Both supply and demand of electricity are infl uenced by a large number of planned and unplanned factors. The changing weather makes millions of people switch on and off their supply. Millions of others expect instant power for lights, TVs, computers.

Conventional power sources are intermittent.

On the supply side, no power station of whatever type is completely reliable. Large power stations that go off-line, whether by accident or for maintenance, do so instantaneously, causing immediate loss of power. When a fossil fuel or nuclear power plant trips unexpectedly, it takes a capacity of up to 1,000 MW off the network instantly. That is true intermittency.

Power systems have always had to deal with these sudden output variations, as well as variable consumption, and the procedures put in place by network operators can be applied to deal with variations in wind power production as well.

Variability and intermittency are different concepts.

Variations in wind energy are smoothed by the fact that there are hundreds or thousands of units in operation, making it easier for the system operator to predict and manage changes as they occur. The system will not notice the shut down of a 2 MW wind turbine, but it will have to respond to the removal of a 500 MW coal fi red plant or a 1,000MW nuclear plant. Wind energy does not suddenly trip off the system.

So the issue is not one of variability in itself, but how to predict, manage and ameliorate electricity variability and what tools can be utilised to improve effi ciency. Wind power is variable in output, but this can be predicted to an increasingly accurate extent.

The electricity system, not the turbine is what matters.

It is the net output of all wind turbines on the system or large groups of wind farms that matters for electricity needs. Wind power has to be considered relative to the overall variability of demand and the intermittency of other power generators.

  • The wind does not blow continuously in one place, yet there is little overall impact if the wind stops blowing somewhere – it is always blowing somewhere else.
  • Therefore wind can be harnessed to provide reliable electricity even though the wind is not available 100% of the time at one particular site. In terms of overall power supply it is largely unimportant what happens when the wind stops blowing at a single wind turbine or wind farm site.
  • The more wind farms that are built over a wider geographical location, the more reliable wind energy is.

The EWEA report “Large scale integration of wind energy in the European power supply” analyses these issues in depth. The report’s main conclusions are that the capacity of Europe’s power systems to absorb signifi cant amounts of wind power is determined largely by economics and regulatory rules rather than technical or practical constraints. Already today, it is generally considered that wind energy can meet in the region of 20% of electricity demand on a large electricity network without posing any serious technical or practical problems – as proven by the example of Denmark.

May 5, 2011
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European Wind Energy Association-Official scenarios

The electricity production from wind energy and its contribution to meeting European electricity consumption is:

83 TWh in 2005 (2.8% of European electricity demand),
to 188 TWh in 2010 (5.5%),
to 523 TWh in 2020 (13.4%),
to 965 TWh in 2030 (22.6%).

EWEA Targets

In 1991 EWEA set a target to install 4,000 MW of wind in 2000. This was revised in 1997 to 8,000 MW. In 2000 the actual wind installed in Europe was 12,887 MW three times higher than the fi gure set nine years previously.

In 1997 EWEA set a target of 40 GW installed in 2010 (the same target as the Commission White Paper) and 100 GW in 2020. In 2000 EWEA set a target of 60 GW in 2010 and 150 GW in 2020.

Three years later in 2000 EWEA revised its target to 60,000 MW by 2010 (including 5,000 MW offshore) and 150,000 MW by 2020 (including 50,000 MW offshore).

In 2003, EWEA further revised its target to 75,000 MW by 2010 and 180,000 MW by 2020 (including 70,000 MW offshore).

Today in 2005, EWEA has updated this target and extended the period to 2030, resulting in a total installation of 300 GW, 150,000 MW of this offshore.