Historically wind turbines have been located on hilltops or throughout the relatively flat north European countryside. The efficiency of many of these turbines has been as low as 20 to 25 percent. Today efficiencies of 33% or more are typically possible for the best offshore locations and up to 40% for land locations “Efficiency” is defined as the annual average amount of kilowatts a wind turbine creates, compared to its maximum (rated) kilowatts. The efficiency depends upon turbine design, and how strong and how continually the wind blows. Higher efficiency rating have been achieved by downgrading the maximum power output.
CO2 emissions from wind turbines depend upon the CO2 used to build the turbine and its efficiency. Historical studies of CO2 emissions are worthless for analyzing future emissions. It is more appropriate to use the most recent European and American examples.
Northern Europe Off-shore Wind Farm Efficiency and Footprint:
Vlattenfall, a Swedish energy company with a large number of wind turbines in Scandinavia, claims that their new turbines emit only 13 grams of CO2 per KWh.
Siemens, Germany, claims 6 grams/kWh offshore with a 22 mph average wind in a 60,003,500 megawatt hour system (their site claims ten times more but 310% efficiency is mathematically impossible) using 80 turbines with 81 meter-long blades on a 92 meter tower made of steel. https://www.siemensgamesa.com/en-int/-/media/siemensgamesa/downloads/en/sustainability/environment/siemens-gamesa-environmental-product-declaration-epd-sg-8-0-167.pdf. So the Siemens efficiency calculates to 31%. Since the Vattenfall installation uses these exact Siemens turbines, I will use 13 grams of CO2 for a Baltic or North Sea Installation. (Note: Siemens has billions of Euros of losses , bailed out by the German government, due to to the instability of their turbines.)
Since the efficiency is 31%, and solar and nuclear are unavailable. to fill in, 69% of electricity must be made up by fossil fuel power plants. Hence I calculate 13 x .31 plus 330 x .69 = 236 for only a 29% reduction in fossil fuel use.
The footprint for the 604 megawatt installation — 72 turbines — was 132 square kilometers (50 square miles). ( The spacing of turbines in this farm is about 10 times the rotor diameter, or a turbine every mile in each direction). The Siemen’s wind farm has 80 turbines, so the footprint would presumably be 11% bigger, 147 square kilometers. This comes to 240,000 square meters per 100,000 megawatt hours.
New USA East Coast Offshore Wind Farm CO2 and Footprint:
I looked at the latest USA wind farm for which there is data: Massachusetts has been planning to install 62 General Electric Haliade-X 3 bladed turbines off Martha’s Vineyard. The turbines have a rotor diameter of 222 meters (729 feet), 35% more than the largest Siemens turbine. The technical data for the GE Haliade turbine states a survival up to winds of 160 miles per hour. The wind park would, I calculate, provide about 4% of Massachusetts’ electrical usage.
The first turbine was installed in October 2023, and five were installed by summer, 2024. In mid-July, 2024, a blade broke in two, and fiberglass shards came onto six Nantucket beaches. A few days later the rest of the blade broke offf Winds were said to be only about 40 mph. This 7% failure rate in the first few months compares to a historical Europe blade failure rate in the first year are about 3.5% (https://www.researchgate.net/figure/a-Average-annual-probabilities-for-blade-replacements-dependent-on-the-operational-the_fig3_314109509) While hurricanes occur in Northwest Atlantic waters, cyclones with equivalent winds occur in the North Sea. It is unknown whether wind shear will be greater off New England.
The capacity of these turbines is 14 MW , but the published numbers suggest that transmission losses will reduce it to 13MW after transmission to the grid. In its promotional material. No reliable data exists for efficiency or CO2. Given that the hubs come from Germany and the blades are manufactured far from the installation and require a special ship built in Texas to transport them, and also that the seabed is three time deeper off Martha’s Vineyard than in the North Sea, I will double the CO2 emitted in the North Sea to a still low 26 grams of CO2 per kWh. The wind park is privately financed, but with subsidies and a guarantee of electricity purchase over the life of the park, after renogotion, the cost per Kwh is $ 0.09
The windpark occupies 260 square miles, a square about 16 miles on a side. This suggests that the turbines will be space 2 miles apart — 15 rotor diameters. Assuming a 33% efficiency, I calculate 1,600,000 square meters per 100,000 mWh.
In North America the strongest winds, other off the Atlantic coast, are in the Great Plains — which, however, is far from the biggest electricity markets. In Europe, wind is most plentiful over and near the Atlantic Ocean and the connecting seas. The cost of electricity from the latest turbines is said to be $ 0.03 to $ 0.05. The cheapest is in the wind belt, the highest on the flatter East.
These maps and the map for wind show that to some extent the wind and the sun are complementary, but only over far-flung areas. And, the wind may not be blowing in Northern Europe while it is storming in the south.