Wind energy data are distorted

Wind power has grown enormously in Europe and worldwide. In 2015, wind turbines with a capacity of 350 gigawatts were installed around the globe, 135 gigawatts of which were in Europe, distributed across around 87,000 wind turbines. At 13 percent, the share of wind energy is now greater than that of nuclear power plants. In countries such as Spain, Denmark or Germany, enough wind power has already been installed to theoretically cover the respective national electricity demand under ideal conditions - maximum wind production and low electricity demand.

Changing production

However, the installed capacity says little about how much electricity a country's wind turbines actually fed into the respective national grid. This is because wind energy is difficult to predict. This makes it difficult to link it to existing energy systems.

Operators and energy researchers therefore rely on simulating electricity production with high temporal resolution to estimate how high the load might be at any given time.

Only recently have researchers begun to perform such simulations with the help of so-called reanalysis models. These are global weather models that are fed with real measured data from weather stations and satellites. These reanalyses process these measurements into coherent global simulations of atmospheric conditions.

Models critically reviewed

However, data from reanalyses have a big catch: the weather models simplify the real world. As a result, factors important for wind power, such as the surface conditions around a wind farm, are not represented in sufficient detail. Thus, when such data from reanalysis models are used without corrections for simulations of wind power production, the models provide a systematically biased picture. Nevertheless, some studies of wind power production have been published that rely on uncorrected data.

Energy researcher Stefan Pfenninger of ETH Zurich and his colleague Iain Staffell of Imperial College London therefore compiled data on measured electricity production from wind farms across Europe, as well as country-specific production data collected by power grid operators. They needed this data collection to derive correction factors for each European country. Finally, they simulated wind power production in Europe over twenty years using the Virtual Wind Farm Model (VWF) they developed.

Underestimated south

Thanks to their rigorous approach, the two researchers have been able to paint a more realistic picture of wind power production in Europe. Their simulations reveal that the uncorrected simulations used in other studies overestimated wind power production in northwestern Europe by up to 50 percent, while underestimating production in southern Europe by 30 percent.

The researchers also recalculated the utilization rates for Europe: the current European average is 24.2 percent; in the UK it is 32.4 percent and in Germany 19.5 percent. The European average varies by only a few percent from year to year. "This deviation is much smaller than that of any single country," Pfenninger says. "The larger the wind fleet and the greater the geographic dispersion, the smaller the fluctuations in supply." He says it is therefore important for national power grids to be even better interconnected to compensate for production shortfalls in one area with excess production in another country.

The simulation also shows that utilization rates are on the rise, thanks in part to better technology and better offshore locations. The UK's wind farms are now a quarter more productive than they were ten years ago.

North Sea states make gains

At the current planning stage, Pfenninger and Staffell expect that the average utilization rate for Europe could increase by one-third to more than 31 percent. "North Sea countries in particular are likely to see strong gains in the near future," Pfenninger says. The United Kingdom could reach a utilization rate of nearly 40 percent, and Germany could reach one of nearly 30 percent.

To enable planners, grid and power plant operators, as well as other scientists, to continue using the simulations developed by the energy researchers, Pfenninger and Staffell created the interactive web application www.renewables.ninja, where the European data sets are available for download. The two researchers have been testing the platform for six months. It already counts users from 54 institutions in 22 countries, including the International Energy Agency.

The platform also grants access to data developed with a comparable simulation of photovoltaic electricity production in Europe. The study on photovoltaics appears at the same time as the one on wind power production and was also written by Pfenninger and Staffell.

Text: Peter Rüegg, ETH Zurich