Analysing the effect of the sliding feed-in premium scheme to the revenues of a wind farm with the use of mesoscale data - case study of Greece

One of the main challenges of the wind industry is the accurate prediction of the revenues that a developing project is expected to produce during its operation lifetime. The European Commission’s Guidelines on State Aid for Environment Protection and Energy 2014-2020 (2014/C 200/01) (European Commission, 2014), enforced the transition from the Feed-in Tarif (FiT) scheme to a market-oriented Feed-in Premium remuneration mechanism. This evolution creates additional uncertainty when evaluating the revenues of a wind energy project, since the remuneration of the produced energy is now market depended instead of stable, as it was under the FiT scheme. The present study attempts to estimate the level of uncertainty that the change of support scheme creates. The expected revenues under both schemes are calculated for three (3) continuous years in the Greek market with the assumption that the strike price of the new FiP scheme coincides with the fixed tariff of the FiT scheme and the results are compared in an annual and total period. The study takes into account the revenues from the day-ahead market (i.e. the only wholesale market currently exists in Greece) and from the support mechanism. The results of the comparison reveal small fluctuation in the annual revenues of the wind stations examined between the two schemes, which does not seem to increase when examining the total 3-year period


Introduction
Greek wind energy market was operating under a feed-in tariff scheme (hereinafter "FiT") up to the end of 2015. The FiT scheme formulated a protected environment for investors, since wind energy plants were compensated according to a constant, pre-defined tariff for the 20-year validity period of the Power Purchase Agreement (PPA) of each project.
The European Commission's Guidelines on State Aid for Environment Protection and Energy 2014-2020 (2014/C 200/01) (European Comission, 2014), hereinafter "EEAG 2014-2020", enforced the transition from the FiT scheme to a market-oriented feed-in premium mechanism (hereinafter "FiP"). Law 4414/2016 (OG 149A, 9.8.2016) -which enforced the new supporting scheme in Greece -determined that new wind projects will receive a premium on top of their income from the market, in the form of a variable (sliding) premium. In practice the sliding premium is calculated, on a monthly basis, as the difference between a Reference Value ("RV") and the hourly market price (the System Marginal Price or "SMP"). Moreover, from 1.1.2017 onwards, the RV is determined through auctions announced and executed by Regulatory Authority for Energy (RAE).
The present study investigates the abovementioned schemes for the case of the Greek wind energy market, with respects to estimating wind farm revenues under both schemes.
The scope of the present study is to evaluate and quantify the effect that the change of the supporting scheme will have on the revenues of wind projects in various locations in Greece.

Basic principles of the two remuneration schemes
The following paragraphs briefly describe the remuneration schemes, previous and existing, that have been applied in the Greek wind energy market.

The previous remuneration scheme: Feed-in tariff (FiT)
Until 2015 the development of wind energy in Greece was governed by a feed-in tariff (FiT) scheme, according to which the investors were compensated a by-law pre-defined tariff for a 20-year period, according to a Power Purchase Agreement (PPA) between project company and the market operator.
The FiT had a value of 73 €/MWh on 2006, where at the end of 2015 was 105 €/MWh. Both values refer to projects located in the interconnected system. Further, the value of 2015 refer to projects that don't receive state subsidy for their construction.

The new remuneration scheme: Feed-in premium (FiP)
In compliance with the European Commission's Guidelines on State Aid for Environment Protection and Energy 2014-2020 (Official Journal of EU, 2014/C 200/01, par. 124-131), wind projects in Greece which had not signed a Power Purchase Agreement (PPA) until the end of 2015, will be remunerated through a Feed-in premium (FiP) mechanism. The basic provisions for the operation of the FiP scheme in Greece, have as follows: i) The wind projects receive a premium in the form of a variable (sliding) premium, on top of their income from the market. The premium is calculated on a monthly basis and its sum with the hourly market price, practically targets a strike price, the so-called Reference Value (RV). For year 2016, the RV for wind projects was defined by law at 98€/MWh. From 1.1.2017 onwards the RV is defined per project through auctions organized by the Regulatory Authority of Energy (RAE). The first auction, held on 2.7.2018, determined RVs between 68,18 €/MWh and 71,93 €/MWh. As long as the RV is being defined for a project, it remains valid for 20 years (contract with the Electricity Market Operator).
ii) The wind projects will sell their electricity directly to the market, while they will be subject to balancing responsibilities, unless no liquid intra-day market exists. In order to meet these market obligations, the wind projects receive, on top of their remuneration, a management fee equal to 2€/MWh. Finally, the wind projects have the option to outsource their market obligations to other entities, the Aggregators, while the Electricity Market Operator has been defined as a Last-resort Aggregator.

Methodology applied
In order to calculate the revenue of a wind farm under the FiP regime, energy production information for each and all of the wind projects of the country would be needed. Since production data from the existing wind farms are not available to the public, the approach was to investigate whether the use of mesoscale wind data in representative locations (where wind farms are located) would provide accurate enough results so that a comparison between the two schemes could be made.
Given that the main purpose of the study is the comparative assessment of the two different remuneration schemes, the absolute energy production values are not indispensable, as long as the wind resource assessment provides valid and consistent results in both cases to be compared. Moreover, in the case of the FiP calculation, it is essential to know the variation of the energy production in an hourly basis, since this is needed to be combined with the hourly System Marginal Price (SMP) (Hellenic Transmissions System Operator, n.d.) values in order to estimate the premium for every station. Hence, it was decided to use mesoscale wind data (EMD International A/S;, n.d.) because of the high correlation factors they have shown in the past, when compared with actual wind measurements (Foussekis & Gkarakis, 2014).
The regions of the country where wind farms are located have been identified from the official data from the Greek Regulatory Authority for Energy. A total of 45 representative locations were eventually selected for which the mesoscale data sets were acquired. In each of these locations a representative nominal capacity was assigned, derived from the annual wind statistics report of the Hellenic Wind Energy Association (HWEA) (Hellenic Wind Energy Association, n.d.), so that eventually each of these locations represent a virtual wind station (see Appendix 1) which is representative of the actual spatial distribution of the total operating wind capacity in Greece. A calculation model was created, in order to match, for each wind station, the hourly wind data with the power curve of a typical 3 MW wind turbine. The calculated total energy production was then compared to the official data from the Hellenic Electricity Market Operator (Hellenic Electricity Market Operator, n.d.) on a monthly and yearly basis, in order to verify the accuracy of the results. Based on that comparison, a correction factor was applied to the calculations, so that the calculated production was adjusted to match the official total wind energy production on an annual basis.
The results of the energy calculations confirm the initial assumptions, since the monthly calculated results present indeed high correlation with the actual production figures on an hourly basis (R 2~ 0,9, see following graphs). Finally, the calculated energy production values were used to estimate the revenue of each wind station for both FiT and FiP schemes, with the fair assumption that the tariff of the FiT coincides with the strike price of the FiP scheme.

Selection of representative locations for wind stations
The first step was to determine representative wind stations for which to estimate the revenues under both FiT and FiP schemes. Due to the lack of analytical public data for the energy production of the operating wind farms in Greece, it was inevitable to define virtual wind stations, hereinafter the "wind stations", for each one of them the remuneration was then calculated for the above-mentioned schemes.
In order to obtain accurate results, a large number of candidate locations were selected, spread in all over the country in representative location according to where the operating wind farms are located. Particularly, 51 locations were initially selected for the virtual wind stations.
For each one of the locations, hourly mesoscale wind speed data at 100 m a.g.l. from EMD & ConWx were used, covering the period 01.01.2014-31.12.2016. Due to the fact that 6 locations presented extremely low wind potential (<4m/s @ 100 m a.g.l.), they were finally rejected and no further analysis was conducted from them. Thus, 45 locations constitute the final list of wind stations' locations used for the present study. The basic information (coordinates, wind speed and map) for the abovementioned locations are presented in Appendix 1.

Power capacity allocation to wind stations
The next step was to allocate the power capacity for each one of the 45 selected wind stations at the locations of the actual distribution of the total installed wind capacity in Greece, the following methodology was performed (it is noted that the methodology described represents year 2014, while similar methodology was used for the years 2015 and 2016 accordingly).
The first step was to calculate the annual average wind capacity for all the country. In order to estimate an annual average wind capacity in Greece, the monthly reports of EMO (LAGIE) for the RES Special Account were used. The following Table illustrates the total installed wind capacity in Greece (interconnected system & non-interconnected islands) at the end of each month of the year 2014. The corresponding data for whole examined period are presented in Appendix 2. The second step was to allocate the wind capacity to each wind station accordingly.
In order to allocate the aforementioned average capacity to the wind stations, the annual "wind statistics report" of Hellenic Wind Energy Association (HWEA) for the period 2014-2016, were used. Due to the fact that HWEA reports present the installed capacity per administrative region, as an intermediate step, the annual average capacity of step 1 was primarily allocated per region. The actual capacity per region derives from the data of HWEA report for 2014 (see Table 2).
Subsequently, the values of actual capacity per region were normalized according to the mean annual capacity of 1885,50 MW calculated. Hence, new normalized values for wind capacity per region were calculated for year 2014. Finally, it was assumed that the normalized wind capacity of each region is equally distributed to the virtual wind stations selected in that region. Table 2 consolidates the aforementioned calculations. The complete HWEA reports and relevant calculations for the capacity of each wind station for the whole period (2014-2016) are presented in Appendix 3.

Estimation of wind energy production
The energy production for each virtual wind station was calculated on hourly basis for the period 01.01.2014-31.12.2016. For this purpose, the following data were used: i) hourly mesoscale wind speed data for each wind station at 100 m a.g.l covering the period 2014-2016 ii) the power curve of a 3 MW wind turbine of a dominant manufacturer in the Greek wind industry iii) the capacity in MW for each wind station derived from the previous paragraph for each year of the examined period Particularly, the hourly wind speed values were matched to the power curve of the selected WTG type and the value derived was then adjusted according to the capacity assigned for each wind station in order to calculate the hourly energy production for each one of the 45 wind stations.
The total wind energy production for 2014 for the amount of the wind stations was estimated at 4.254 GWh. This number is quite close to the value of 3.689 GWh (13,28% deviation) which was the actual wind energy production of that year, considering that mesoscale data were used instead of actual wind measurements and without taking into consideration availability and grid losses.
In order to adjust the calculated wind energy production (4.254 GWh) to the actual annual energy production (3.689 GWh), a correction factor of 86,72% was applied resulting in the normalized annual energy production for each wind station. Finally, the cumulative energy production per region was calculated, which is presented in the following table. In order to estimate the compensation of each wind station for the scenario of a FiT scheme, it was assumed a stable tariff of 98 €/MWh which is actually the Reference Value (RV) that Law 4414/2016 (OG 149A) introduced for wind projects installed either in interconnected system or non-interconnected islands. It is mentioned that according to the Ministry of Energy, the Reference Value determined for each RES technology is actually reflecting the Levelized Cost of Energy (LCOE) of the corresponding technology. Subsequently, the compensation of each wind station under a FiT scheme was estimated on an hourly basis, by multiplying the assumed Feed-in Tariff, i.e. the Reference Value with the hourly energy production (Qh), as follows:

The concept of the FiP Scheme.
According to the new RES/CHP support scheme, effective from 01.01.2016, the Total Income of the amount of the operating stations of a given RES technology is calculated on a monthly basis (calculation period). Most of the aforementioned Total Income is secured from the energy market, in the form of a Market Income. In addition to the Market Income, a new type of operating aid has been introduced for the electricity generation from RES in the form of a sliding premium (sFiP). The total monthly premium for all the stations of a given RES technology is estimated as follows:

Qws,h: the produced energy of a given wind station (ws) injected in the electrical grid at hour h AVEh: The Average Value of Energy at hour h
It is obvious from the above equations that the total monthly income for all stations of a given RES technology with the FiP scheme coincides with the expected total monthly income of those stations with the FiT scheme, as long as it is actually the product of the Reference Value with the total energy produced in the examined period (month).
However, it is underlined that while the FiP scheme distributes the same total amount, to the total RES producers, as if they were operating under a FiT scheme, the income of each one RES producer is differentiated in the FiP scheme, as analyzed in the following paragraph.

Results from the comparison
The results of the comparison reveal small fluctuation in the annual revenues of each wind station between the two schemes, which does not seem to increase when examining the total 3-year period (analytical results per station per year are presented in Appendix 7)

Conclusions
Combining hourly mesoscale wind data for selected locations (representative to the actual installed capacity in Greece) with hourly SMP data can provide accurate results regarding the energy production and hence the total revenues of wind stations for the case of Greece, as these are derived by the dayahead market and the support mechanism. The present study shows an affordable impact of the support scheme on the annual revenues of a wind plant for the period examined (years 2014-2015-2016), under the assumption that the strike value of the FiP scheme coincides with the fixed tariff of the FiT scheme. The annual income fluctuation for wind plants operating under different remuneration schemes were calculated to have a maximum value of ±1,5% per year, while for the total 3-year period the income variation does not seem to increase under the basic scenario.

Learning objectives
The present study proposes a methodology based on the use of mesoscale wind data and answers the question whether the change of the support scheme from FiT to sliding FiP in Greece creates significant uncertainty on the evaluation of the revenues of a windfarm. More calculations should be performed with longer periods of data and in other countries in order to better assess the accuracy of the energy production calculation and level of uncertainty. Moreover, the typical market obligations (e.g. balancing responsibilities) should also be taken into account per specific project in order to conclude a final investment decision.