1. Introduction
EU legislation is moving at pace to ensure a clean and fair energy transition at all levels of the economy. The final Clean Energy Package makes the EU’s electricity market more interconnected, flexible, and consumer-centred [
1]. The Clean Energy Package measures aim to make different actors in the energy field more competitive and innovative. Member states must respond and transpose the directives into national law to ensure this happens. The Electricity and Renewables Directives are transposed into Irish law to allow Renewable Energy Communities to participate in the electricity market. Similarly, other jurisdictions are considering what legal, regulatory, grid, and market codes need to be amended to comply with the directives and unlock the potential of energy communities.
The Electricity Directive is consumer-focused and outlines requirements for Member States and Regulatory Authorities to develop frameworks that allow for consumer participation in energy markets [
2]. The Directive contains two definitions of an energy community: Citizen Energy Community, which is contained in Directive (EU) 2019/944 (recast Electricity Directive), and Renewable Energy Community, which is contained in Directive (EU) 2018/2001 (the recast Renewable Energy Directive). In both cases, the communities are autonomous legal entities based on open and voluntary participation with the purpose of providing environmental, economic, or social community benefits for its shareholders or members rather than financial profits. Energy communities are entitled to generate, consume, store and sell renewable energy and may be allowed to participate in cross-border electricity exchanges. In this paper, we use the term “renewable energy community” interchangeably with the term “local energy community”.
Energy communities can be realised in various legal forms, which depend on national and regional regulations. For example, Community Benefit Societies (CBS) are a legal structure for community-led initiatives and exist to serve the broader interests of the community. Any profit made by a CBS must be used for the benefit of the community. The appropriate use of the CBSs model in Community Renewable Energy projects is to sell electricity directly to the national grid and reinvest the profits generated for the benefit of the community.
Social Enterprises combine different economic, social, and environmental goals at the core of their activities. Social enterprises are incredibly diverse across Europe, encompassing a range of organisational and legal forms and statuses [
3]. These enterprises express their commitment to their social goals by limiting the distribution of surplus income to members and instead reinvesting this for future development.
Cooperatives are community-owned social and economic enterprises. They are the dominant institutional architecture for community renewables in Europe and are gaining popularity. There are a growing number of energy cooperatives in the EU, notably in countries like Belgium, Denmark, Germany, France, and Spain but increasingly also in the other Member States. In Greece, the 2018 law on energy communities adopted cooperatives as the basis for its definition of energy communities. In Sweden, Renewable Energy Communities must take the legal form of an Economic Association, which is their adapted form of a cooperative. There are many other forms and interpretations of energy communities, the review in [
4] synthesises 183 definitions across three dimensions of meanings (interpretations of the community concept rather than legal forms or definitions), activities, and objectives of the community. The authors note the foremost meaning ascribed to an energy community is a community associated with a “place”, and this is particularly prominent for community wind where locally owned, utility-scale wind development interconnected to the grid is anticipated. We adopt this interpretation that an energy community is expected to conduct projects located in the vicinity of where they live.
There are many challenges to the success of local energy communities (LECs), including policy support, social acceptance, financing, management and market structures, and smart grid technologies [
5]. LECs must decide the mix of renewable energy generation and storage, where to locate, and how best to manage the assets to achieve the LEC objectives. Energy communities are not just about technical smart energy systems innovations, but they cannot succeed without technological and decision support. Likewise, the Clean Energy Package and National Energy and Climate Plan (NECP) ambitions of EU Member states cannot be achieved without energy community and energy citizen participation.
In Ireland, the Renewable Electricity Support Scheme (RESS) supports community social enterprise and community participation in the electricity market through a competitive auction-based framework [
6]. Through a community enabling framework supported by the Sustainable Energy Authority of Ireland (SEAI), citizens can form a Renewable Energy Community and then apply for a license at RESS auctions. The auctions are designed to support progress toward the 80% renewable electricity target in Ireland’s NECP [
7].
Wind energy development usually presents greater challenges in terms of planning and engineering. However, in the case of Ireland, which lies at 53° North and has an extensive coastline and temperate maritime climate, wind projects are likely to provide a higher Community Benefit Fund (CBF) return compared to solar. The CBF is a mandatory contribution of €2/MWh for all generation projects to be used for the wider economic, environmental, social, and cultural well-being of the local community.
Figure 1 shows estimated wind speeds at 20 m elevation over Ireland based on measurements taken during 2001–2010 [
8].
Micro wind generation means a wind turbine or turbines with a nominal output of 300 watts or more but no more than 50 kilowatts with hub heights of 10–15 m. Planning permission is required for the installation of all but the smallest turbines. While lower turbine heights may be allowed in urban settings, the technology to date has not been cost-effective [
9]. Very low performances are observed for a micro-wind turbine in an urban area in Italy for most of the year, and the technology is deemed not to be suitable or cost-effective [
10]. A possible case for micro wind turbines in agricultural farms is made in [
11] but is dependent on a longer than usual payback period of 12 years and state grants. The same team of authors at the University of Southampton outlined the “Boom-to-bust” history of micro wind in [
12] and concluded that half of the urban turbines evaluated in their study have a negative load factor, that is, they consume more power than they generate over the year.
The turbines for commercial wind farms are 100 m or higher, where wind speeds are higher than those measured at ground level. Community-led projects in the RESS scheme have an upper limit of 5 MW, effectively restricting the design choice to one or two wind turbines [
13]. Wind farm technology is constantly improving, and investment costs are reducing. The estimated costs are around €1.4 million per megawatt installed for the types of wind turbines a LEC would use (1.5 to 3 MW in size) [
14]. The wind turbine itself incurs the most significant costs (~€1.25 M–€2.5 M). Additional costs include groundworks, grid connection, planning, and consultancy costs.
Evidence of long-term wind speed trends is required to secure financial backing for a project. Wind speed is the most significant factor in determining the amount of wind power that can be produced, but wind speeds are difficult to predict and highly variable. The wind at coastal locations is strongly influenced by changes in sea-surface temperatures (breeze circulations), friction, as well as local topography. Furthermore, wind resources at a specific site are difficult to quantify with any level of confidence without undertaking field trials. Potential LECs are advised to first utilise the best available wind speed data and estimation tools and then install anemometry to determine the observed wind speed distribution at a particular site.
Reanalysis provides a picture of past weather and climate. Reanalysis blends observations with past short-range weather forecasts rerun with modern weather forecasting models. Reanalysis data is produced by running a numerical weather prediction (NWP) model in hindcast mode, i.e., a projection back in time rather than a forecast prediction of future values. The reanalysis models assimilate historical observations and produce a time series of historical weather variable values. Three reanalysis data sets are evaluated in [
15]. The authors conclude that the choice of dataset depends on the type of renewable energy and the location; there may not be a single best source for wind and solar at all locations.
The authors in [
16] note that ideally, wind speed should be measured at a typical turbine hub height. However, there are no long-term records of hub height wind speed available at different locations around Ireland, and anemometry equipment can be expensive. Therefore, their study focuses on 10 m wind speed observation records from synoptic stations, using extrapolation to estimate the wind speed at 100 m hub height.
Reliable historical wind speed and solar irradiance databases are fundamental for policymakers and the distribution system operator (DSO). Rapid variations in wind and solar power availability may compromise the secure operation of the grid. The intermittent nature of renewable energy can result in voltage fluctuations and a decrease in power quality. Even with the high penetration of renewable energy, the low voltage (LV) network must be able to keep the voltage levels and system frequency within the allowable limits while the balance between power generation and demand remains stable. Renewable energy scenarios provide a framework for exploring future energy perspectives, give insight into the behaviour of complex systems, and demonstrate both benefits and challenges associated with the increased integration of renewables into the LV network.
Additionally, data-driven management strategies will determine the short-term decision-making of prosumers in local energy markets. The design of markets and policies such as grid usage pricing heavily depends on modelling prosumers’ behaviour [
17,
18]. The design of such policies as a function of minute-based operation may bring opportunities for coping with the rapid variations of the uncertainty. The data used to feed those models should capture the complex spatiotemporal correlations found in actual scenarios [
19]. A higher sampling frequency (in the order of the seconds) is required to perform out-of-sample simulations of real-time operations.
With regards to energy planning, the problem of unit commitment is historically one of the most important tools in power systems. This is a challenging optimisation problem in planning which thermal and hydro generation units to “commit” to serve the electricity demand. Recently, renewable energies have been incorporated. The conventional generation is only required to serve the net demand. The problem becomes more difficult to solve when variable wind generation is included [
20]. Renewable energy scenarios play a fundamental role in obtaining robust planning and production schemes [
21].
In this paper, we focus on identifying the most suitable publicly available wind speed data for LECs to evaluate the potential for renewable wind as part of an Initial Viability Study. We demonstrate the approach at a sample set of locations in Ireland. The paper is organised as follows:
Section 2 gives a detailed overview of the data and methodology used for the quality assessment.
Section 3 presents the results of the quality and accuracy assessment.
Section 4 discusses the insights on identifying the best data source. Finally, conclusions are highlighted in
Section 5.
2. Materials and Methods
Since micro-wind has been shown to have limited potential, we focus on a scenario of a LEC that wishes to install a single commercial wind turbine. We consider wind speed at a hub height of 110 m for a potential community-owned onshore wind turbine. We first evaluate two important reanalysis datasets, ERA-5 and MERRA-2, one high-resolution mesoscale data (NEWA), and four PVGIS datasets (two satellite and two reanalysis datasets) by comparing them with the Met Éireann hourly wind speed data observations at four locations in Ireland over a common data period 2009 to 2016. The objective of this step is to identify the best wind speed data source for LECs in Ireland.
Once the best data source was identified, we then assessed the energy potential at a sample of 13 locations in Ireland as a case study to demonstrate the methodology. Seven of the 82 licensed projects in the first RESS auction in 2021 are majority-owned by communities, and the revenues from their operation will be cycled back into those communities.
Table 1 shows a summary of the five solar energy and two onshore wind community projects that were successful.
In addition to the types of locations where community projects were licensed, we consider six additional locations taken from [
15], based on the availability of continuous records of hourly data.
Figure 2 shows the 13 locations in our study that span the island of Ireland geographically. These stations represent the longest available record of wind and shortwave radiation covering different regions of Ireland. The locations include eight coastal locations (Galway, Wexford, Mayo, Clare, Belmullet, Dublin Airport, Malin Head, and Valentia Observatory) and five inland stations (Kilkenny, Cork, Birr, Clones, and Mount Dillon).
In the final step, we extract wind speeds for the sample of 13 locations in Ireland from the best data source. Wind speed is then converted to wind power using a sample manufacturer’s turbine power curve.
2.1. Data Sources
The availability of wind speed data at hub height is limited. The Met Éireann “ground truth” wind observations are available at 10 m height only. Therefore, we use 10 m wind speed records for the quality assessment. The global reanalysis (ERA-5 and MERRA-2), satellite datasets (SARAH and CMSAF), regional reanalysis (ERA-5 and COSMO), and station data (Met Éireann) were available at a one-hour temporal resolution, whereas the NEWA data was available at 30 min resolution, all freely available.
Table 2 shows a summary of the data sources which were assessed in our study. In the following sections, we describe the data sources in more detail.
2.2. Met Éireann Observational Data
Met Éireann is the Irish Meteorological service and has an observation network that gathers weather data across the country for use in weather forecasts, aviation, and meteorological research. Their aim is to produce data of the highest quality that is widely available and very easy to access; they also have researcher-friendly access. The weather observations (for example, temperature, relative humidity, wind speed, wind direction, shortwave radiation, and rainfall) record day-to-day changes in the atmosphere and are quality controlled and archived in the Met Éireann database [
22]. This historical data is available at different temporal scales such as hourly, daily, or monthly for various weather variables. The Met Éireann dataset was considered the “ground truth” in this paper against which the reference data were compared to check their quality and accuracy.
2.3. ERA-5
ERA-5 is a fifth-generation reanalysis by the European Center for Medium Range Weather Forecasts—ECMWF. Hourly data of many atmospheric, land, and oceanic climate variables such as wind speed at 10 m and 100 m elevations from 1979 to the present at a spatial resolution of 0.25° × 0.25°, i.e., a ~31 km grid [
23]. ERA-5 includes information about uncertainties for all variables at reduced spatial and temporal resolutions. The data covers the entire Earth. Studies have shown ERA-5 data fit the ground measurements for Ireland well [
15] and have found its usage satisfactory for energy system modelling [
24]. ERA-5 can be accessed from the climate data store. The downloading procedure is through the web interface of CDS. A procedure to download the ERA-5 data is outlined in [
25].
2.4. MERRA-2
The second version of Modern-Era Retrospective analysis for Research and Applications (MERRA-2) data is produced by NASA [
26] using an upgraded version of the Goddard Earth Observing System Model version 5.12.4 (GOES-5) based on three-dimensional variational data assimilation system. MERRA-2 is one of the few global reanalyses that assimilate the data from the entire constellation of NASA satellites. MERRA-2 data is available from 1980 to the present day, with global coverage of 0.5° lat × 0.625° lon (horizontal grid resolution). MERRA-2 data can be downloaded from NASA Goddard Earth Sciences (GES) data and information service center. This procedure is outlined in [
27].
2.5. NEWA
The New European Wind Atlas (NEWA) is a joint research effort from eight European countries and is a combination of downscaling of ERA-5 data and Weather Research Forecast (WRF) model data. It is a comprehensive mesoscale model with a spatial coverage of the whole of Europe and Turkey, extending at least 100 km from any known coastlines. Data are available at 30 min temporal resolution for 2009–2018. It is driven by ERA-5 with special nudging over a domain. Nudging, or Newtonian relaxation, is a simple form of data assimilation that adjusts dynamical variables of free-running Global Climate Models (GCMs) using meteorological reanalysis data to give a realistic representation of the atmosphere at a given time. All mesoscale simulations in NEWA use three nested domains with a 3 km horizontal grid spacing for the innermost grid and a 1:3 ratio between inner and outer domain resolution, leading to three different resolutions: 27 km for the outer domain and 9 and 3 km for the inner nested domains. The model details can be seen in [
28]. The temporal coverage of the sensitivity simulations is 1 year (2015 or 2016), based on data availability. WRFs over 10 domains cover most of Europe. NEWA data can be accessed via a web interface that includes interactive maps, time series of wind speed and direction at different heights, as well as other information of relevance to the wind industry. Full details of the NEWA model are described in [
29,
30].
2.6. PVGIS
While the focus of this paper is on wind energy assessment, we mention here sources that provide additional focus on solar irradiance as many LECs will be interested in selecting the best mix of renewable energy sources to meet their goals. In other works, we evaluated the reference data sources with respect to temperature and solar irradiance. PVGIS version 5.2 is a tool developed at the European commission joint research center that provides meteorological data. The main focus of PVGIS is solar resource assessment and photovoltaic (PV) performance studies, but hourly wind speed at 10 m at high spatial scales is also available. Data is available on the website [
31]. PVGIS 5.2 provides three different sub-datasets (a) PVGIS SARAH, (b) PVGIS SARAH2, and (c) PVGIS-ERA5.
2.6.1. PVGIS-SARAH
The Surface Solar Radiation Data Set-Heliosat (SARAH) is a satellite-based climatology of the solar surface irradiance, the surface direct normalised irradiance, and the effective cloud albedo derived from satellite observations of the visible channels of the MVIRI and SEVIRI instruments onboard the geostationary Meteosat satellites. The data are available from 2005 to 2016 and cover the region ±65° longitude and ±65° latitude. The products are available as monthly, daily, and hourly averages on a regular latitude/longitude grid with a spatial resolution of 0.05° × 0.05°. For more detailed information, see [
32].
2.6.2. PVGIS-SARAH2
The Satellite Application Facility on Climate Monitoring (CMSAF) solar radiation product SARAH-2.1 (PVGIS-SARAH2) provides data from 2005 to 2020. The CMSAF solar surface irradiance retrieval is based on radiative transfer calculations using satellite-derived parameters as input. It is a part of the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) ground segment and part of the EUMETSAT network of Satellite Application Facilities.
2.6.3. PVGIS-ERA5
Data from the ERA-5 ECMWF are processed to higher resolutions. The original ERA-5 data is gridded into a higher spatial resolution, 4 by 4 km. The PVGIS ERA5 data covers the Earth over a time frame from 2005 to 2020 and provides 137 elevation levels from the surface up to a height of 80 km.
2.7. Methodology for the Quality Assessment
Four skill scores are used to compare the reference data sets in
Table 2 to the Met Éireann ground truth measurements. The statistical metrics are; correlation coefficient (
R), mean error or bias (ME), root-mean-square error (RMSE), and index of agreement (IOA).
xi are the estimates and
yi are the Met Éireann observations.
N is the number of data points for analysis.
and
are the average of the estimated and observed values, respectively. We define each metric next.
Equation (1) is the correlation coefficient. The numerator of Equation (1) is the covariance of two variables, and the denominator is the product of standard deviations of two variables.
Equation (2) is the difference between model-predicted and observed values i.e., the mean model error or “bias”. Bias is the tendency of a statistic to overestimate or underestimate a parameter. A positive value signifies that the model has overestimated the actual value. A negative value signifies that the model has underestimated the actual value of the period.
Equation (3) is the root mean squared error (RMSE).
Finally, the Index of Agreement (IOA) is a standardised measure of the degree of model prediction error which varies between 0 and 1 [
33]. It represents the relative covariability of the estimates and observations about the ‘true’ mean. The agreement value of ‘1′ indicates a perfect match, and ‘0′ indicates no agreement at all. The IAO can detect additive and proportional differences in the observed and simulated means and variances; however, IOA is overly sensitive to extreme values due to the squared differences. The IOA is given in Equation (4).
2.8. Wind Power Model
Wind speed is the most significant variable in estimating wind to electrical energy transformation. The validity of wind power estimates is significantly affected by the quality of the input wind speed data. Wind speed measurements are rarely available to Local Energy Communities without the installation of anemometry equipment and present a challenge to long-term strategic decisions. Hence we recommend the use of sources such as those in
Table 2 for the initial evaluation of site suitability.
We follow the approach in [
34] to generate wind power energy for a particular type or set of turbines. The steps to transform wind speed into wind power are:
Acquire wind speed records for at least two heights;
Extrapolate the wind speeds to the turbine hub height;
Convert hub height wind speed to power output using the manufacturers’ power curve.
A common approach is to extrapolate the vertical wind speeds (
WS) at 10 and 100 m to hub height (
HH).
is the rate of change of
WS with height
z between 10 m and 100 m heights in Equation (5).
Equation (6) allows us to estimate the wind speed at hub height,
WSHH.
Once the wind speed records at hub height are derived from Equations (5) and (6), the wind speed time-series values are converted into wind power energy using the appropriate power curve for the selected turbine.
Power curves depict the relationship between wind speed and power and the range of operation of the turbine [
35]. The system of equations in Equation (7) shows the relationship. No power is produced when the wind speed is below a cut-in threshold,
Vc. Power is produced rated according to a polynomial function
Pn up to the rated speed
Vr. The turbine operates at full capacity up to the furling speed
Vf—the speed at which the turbine cuts out to protect the blades in strong winds. The system is normalised by the capacity factor, the average power output divided by the rated power of the turbine. Hence full production is shown with a capacity of 1.
Several power curves for commercial turbines are available from renewable ninja [
36]. In this paper, we have chosen a Vestas V110 2.0 MW IEC IIIA turbine as it is suitable for low-wind sites with a cut in wind speed of 3.0 m/s. It has a capacity of 2 MW, in the range suitable for the RESS scheme in Ireland. The hub height is 110 m. Technical information is available at [
37].
The power curve from “Ninja Renewables” is in the form of a discrete series of power values versus wind speeds between 0 and 40 m/s with a resolution of 0.01 m/s.
Figure 3 shows the “Wind Turbine Power Curves~5 (0.01 ms with 0.00 w smoother).csv” data for the Vestas.V110.2000 turbine. Then, a smoothed power curve data “Wind Turbine Power Curves~5 (0.01 ms with 0.40 w smoother).csv” is considered. Next, we fit a polynomial of sixth order to the discrete power curve data for the range
Vc ≤
WS ≤
Vr to derive the coefficients of a polynomial
Pn as given in Equation (8).
where
is the coefficient of the best-fitted polynomial.
Table 3 shows the parameters and technical details of the turbine used in our study.
Pn(
WS) is the normalised power output value. By considering Equations (7) and (8), a time series of WS at hub height is converted to wind power energy. Both the capacity factor and power in Watts are computed at one-hour temporal resolution. The capacity factor (
CF) is defined as the ratio of average power,
Pavg, and rated power,
Pr, i.e.,
CF =
Pavg/
Pr.
We then consider the 110 m wind speeds at the 13 sample locations and generate a corresponding time series of wind energy capacity factors and power (Watts) using the methodology described here to support a LEC in the initial site evaluation.
4. Discussion
This research paper assesses how good the representation of wind speed from various publicly available datasets is in comparison to observations. The objective is to support LECs in their initial evaluation of site suitability.
Table 6 shows that across Ireland, a wind turbine such as the Vestas 110 m offers the potential to a LEC to meet the electricity needs of several thousand homes. Wind assessment should be based on long-term time-series data. Short periods consisting of a few years may hide variations from the long-term average and consequently lead to inaccurate wind estimation and poor outcomes for the LEC. Longer periods yield more representative results.
Moreover, understanding the diurnal variations and their predictability is of key importance for the integration and optimal utilisation of wind in the power system.
Figure 11 shows representative electricity demand load profiles for residential consumers in Ireland. The profiles are created from a smart meter consumer behaviour trial in Ireland; the data are available from [
39]. The electricity load profiles show diurnal patterns with midday peaks that coincide with high wind capacity factors. However, the evening peaks coincide with dips in the wind capacity factors. The wind variation is largely due to the fact that temperature differences, e.g., between the sea surface and the land surface, tend to be larger during the day than at night.
Utilising the long-term measurements (2009 to 2016), we found that ERA-5 outperformed the other sources in Ireland. We found the highest correlation, IOA values, and lowest RMSE values. The choice of dataset to use is important for LECs in their initial wind energy assessment. An overestimation in wind speed during the night often changes to an underestimation in wind speed during daytime hours and vice-versa, see
Figure 5 and
Figure 6. A false representation of vertical mixing in the lower atmosphere in the models and surface friction, local topography, and many other factors are responsible candidates for these biases. After sunrise, the observed wind speeds increase faster than all other reference datasets. This increase is due to turbulent mixing between different vertical levels, where higher wind speeds are entrained from faster wind speed layers higher up in the atmospheric boundary layer, causing the wind speed at the surface to become faster.
In this paper, we only considered wind-to-power. There are times when electricity demand is low, and wind generators may be instructed to curtail production. Curtailment instructions may also be issued for technical or other operating considerations such as the system’s nonsynchronous penetration limit. There are opportunities to explore how wind energy could be stored or converted to other forms to reduce curtailment and improve the cost benefits for wind generators generally or how a renewable energy mix and storage could be combined to serve the LECs needs. As noted, the adoption of low carbon technologies is expected to significantly change both the demand value and time of occurrence. Further research is needed to understand how best to match the available renewable generation with the demand.
We have not explored the difference between the wind power estimates and the actual power produced. The actual performance may differ from that specified by the manufacturer under laboratory test conditions since each site has multiple variables that influence the wind farm performance. There is a gap that needs to be assessed as estimates are often too optimistic and decision support for long-term investments by the energy communities [
40].
In future work, we aim to explore additional datasets for the European region and to explore the biases by season, time of day, and particularly by location. Issues in using ERA-5 data at more challenging sites such as mountains, hills, or ridges are noted in [
41] in which it is shown that land-use complexity may negatively affect ERA5 wind energy prediction skills even more so than topography complexity. This will allow us to design more accurate methodologies to support LECs.