Uncertainty in wind energy
Uncertainty in wind energy
Uncertainty in meteorology
An analysis of the data collected on the different sites during the wind resources measurement with anti-icing system (AIS) should be performed in order to find possible deviation of the flow model and thus calculate correction factors to affect the results. The uncertainty is around the data from meteorological icing, instrumental icing, incubation time and recovery time (Battisti, 2015). It is difficult to make a universal model of meteorology uncertainty, as data varies greatly between geographic areas, and is further affected by other conditions which are difficult to assume (Laakso et al., 2010b).
The duration of the technical perturbation of the instrument due to icing with time as unit is defined as instrument icing (Battisti, 2015). It is normal to use an anemometer as the instrument. But there is uncertainty around an anemometer, because it may be affected by icing as well and not work optimal. For example, heated sensors can have ice build-up during heavy ice snowfall, and this may disturb the measurements. By using AIS, the incubation time may be extended.
The description of the icing characteristics of a site are based on Wind Energy in cold climates (Energy & Systems, 2012), where the incubation time is set to zero. It is assumed that the meteorological and instrumental icing start at the same time. The described duration of meteorological and instrumental icing in this report refers to unheated anemometers.
Figure 11 Definition of meteorological icing and instrumental icing from IEA Wind Report (Energy & Systems, 2012)
Figure 13 shows a timeline for the icing process and the important parameters of the process; icing rate, ice accumulation per time [g/hour], maximum ice mass accreted on a structure [kg/m] and the type of ice.
In cold climate there is an uncertainty in how long ice may remain on a structure after meteorological icing has taken place. It is defined by performance index. And the formula is:
Wind speed carries unsystematic uncertainty, and thus affects projects individually. The unsystematic uncertainty denotes the consequence of conditions that accompany random fluctuation and are turned both ways (Jordanger, n.d.).
AIS is a fairly recent technology applied to wind turbines and these systems are now being implemented on operational wind farms. The first installation (except for on test turbines) was in 2012 (Nordex, 2012). Currently, there is a lack of track-record information and data on the performance of these systems.
Production loss due to ice
There are a lot of contextual uncertainty due to production loss, project environment, nature and the project’s basic conditions. These have in common that they entirely or for a large part are outside the project’s control and are difficult to predict.
Estimation of power production
Air density is an important part of the production and to adjust the power curve a time series of air density calculated from WRF should be utilized to perform a correction. The correction shuld be done according to IEC 61400 -12-1.
In the wind industry the price of electricity is one of the most uncertain factors in investment projects. Figure 14 shows great variations in the spot price since 2012. The price has ranged from 9.55 EUR/MWh in July 2015 to 49,06 EUR/MWh in January 2012. It is difficult to estimate a future price, because it depends on the demand of electricity and supply of energy from other sources. This type of uncertainty is known as systematic uncertainty. It acts in the same direction in several projects and is not diversified even in large portfolios (Jordanger, n.d.).
Figure 13: Monthly average price of electricity and certificates in EUR in Norway (January 2012 – July 2015). Source: Swedish Energy Agency (SEA) and Nordpoolspot
Electricity certificate price
The electricity certificates prices have historically been more stable than spot prices. There are different tax regimes between Sweden and Norway, and therefore the output of the investment will be different. The largest uncertainties with the electricity certificate scheme are political risk for changes to the scheme. The government is currently getting advice from the experts: if Norway should continue with electricity certificate or not (Vindkraftnytt, 2015). The future of the certificate after 2020 is very unclear. The other risk is, if there will be under or oversupply of certificates after 2020 (Lind & Rosenberg, 2014).
Other financial uncertainties can be taxes and legislation risk, as well as regulation at national and international level for cold climates sites. The technology related uncertainties are geographical location, wind conditions, wake losses, grid connection and the different component in the turbines. This uncertainty is also known as event uncertainty. It expresses the probability with which the incident will happen and the size of consequences due to it.
Adding to regulatory uncertainty, the economic reality of a slow recovery in Europe has also impacted on investment plans and decisions, new orders and the financial health of existing assets.