CMIP6 projections for global offshore wind and wave energy production (2015–2100)

Three-hourly CMIP6 projections have been used in conjuction with the CSIRO WaveWatchIII wave model to calculate the global trends in offshore wind and wave energy for the SSP585 and SSP126 scenarios until 2100. The results indicate that moderate yet significant changes are expected in the theoretical electricity generated from wind and waves at fewer than 10–15% of coastal locations. While this implies a generally stable outlook for the future, certain coastal regions with existing or planned wind farms may experience a slight reduction in production by 2100. Regarding wave energy, given its early stage of development, a more cautious approach is advisable, although a similar conclusion may be reached. Considering the decreasing installation costs on the horizon and accounting for both climatic scenarios, this provides a reliable context for most ongoing feasibility studies, technological developments, and offshore facility investments.This study is part of project PID2020-116153RB-I00 funded by the Spanish Ministry of Science and Innova- tion/National Research Agency MCIN/AEI/ 10.13039/501100011033. The authors acknowledge funding for the research groups by the University of the Basque Country (UPV/EHU, GIU20/08). All the authors have contributed equally to this paper

Extension and improvement of synchronous linear generator based point absorber operation in high wave excitation scenarios

[EN]The exploitation of marine wave energy resource has led to the design of numerous Wave Energy Converter (WEC) configurations. The power absorption of a WEC is tightly related to its physical properties and the characteristics of the incoming wave front. Additionally, the operational range of a WEC is limited to certain characteristics of the incoming waves. These restrictions are usually related to limitations in the maximum force of the Power Take-off (PTO) system and the safety of the WEC. As a result, the power production of the WEC must be stopped during sea states of high wave elevation. With the objective of improving the operation of a WEC during these sea states, a Field Weakening (FW) control functionality is proposed to be implemented in the control system of a single-body linear in heave oscillating point absorber with a Permanent Magnet Synchronous Linear Generator (PMSLG) based electrical PTO system. The aim of the aforementioned functionality is to attenuate the magnetic flux in the PMSLG during sea states of high wave elevation. The influence of the size of a WEC on the benefits of the proposed FW functionality is also studied. To that end, two point absorbers with different size are analysed with NEMOH and a wave-to-wire (W2W) model of each WEC is developed. This W2W model enables analysis of the performance and power production of the WECs at different sea states of interest. The obtained results show a remarkable improvement of the operation of a WEC with the implementation of the FW strategy during sea states of high excitation, which leads to an extension of its operation and subsequent additional energy/hydrogen generation.Authors acknowledge financial support by the Spanish Ministry of Science and Innovation, Agencia Espanola de Investigacion (grant PID2020-116153RB-I00/AEI/10.13039/501100011033) and the University of the Basque Country under the contract (UPV/EHU, GIU20/008)

Floating wind turbine energy and fatigue loads estimation according to climate period scaled wind and waves

Offshore wind power is one of the fastest-growing renewable energy sources, as it is expected to play a major role in the transition towards sustainability and net zero emissions. Despite its potential, the interaction of the turbines with the oceanic waves, especially in case of floating turbines, is one of the main drawbacks associated to it. In fact, mechanical oscillations caused by the waves could potentially alter the operation and lifetime of the turbines. Hence, while the characterization of the wind is sufficient for the long-term design of onshore wind turbines, the procedure is more complex in case of offshore turbines, since the height, period and direction of the waves will affect the lifetime of the turbine. In this paper, a methodology for the evaluation of the energy generation and fatigue mechanical loads of a Floating Offshore Wind Turbine (FOWT) considering a 30-year period is proposed. To that end, meteorological data from 1991 to 2020 are characterized using a cluster analysis and reduced into a computationally affordable number of simulation cases. Results show negligible energy loss of a FOWT due to interaction with the oceanic waves. However, a substantial increment of the mechanical fatigue in the side-side and fore-aft bending moments of the tower are detected. Such analyses might be applied for the predictability of the lifetime of an offshore wind turbine, as well as the selection of potential optimal wind farm locations, based on climatic patterns and the evolution of meteorological data.The authors acknowledge grant PID2020-116153RB-I00 funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by “ERDF A way of making Europe”, by the “European Union” or by the “European Union NextGenerationEU/PRTR”. Additionally, financial support by the University of the Basque Country under the contract (UPV/EHU project GIU20/008) has been received

Optimal strategies of deployment of far offshore co-located wind-wave energy farms

[EN] The most profitable offshore energy resources are usually found away from the coast. Nevertheless, the accessibility and grid integration in those areas are more complicated. To avoid this problematic, large scale hydrogen production is being promoted for far offshore applications. The main objective of this paper is to analyze the ability of wave energy converters to maximize hydrogen production in hybrid wind and wave far offshore farms. To that end, wind and wave resource data are obtained from ERA5 for different locations in the Atlantic ocean and a Maximum Covariance Analysis is proposed for the selection of the most representative locations. Furthermore, the suitability of different sized wave energy converters for auxiliary hydrogen production in the far offshore wind farms is also analysed. On that account, the hydrodynamic parameters of the oscillating bodies are obtained via simulations with a Boundary Element Method based code and their operation is modelled using the software tool Matlab. The combination of both methodologies enables to perform a realistic assessment of the contribution of the wave energy converters to the hydrogen generation of an hybrid energy farm, especially during those periods when the wind turbines would be stopped due to the variability of the wind. The obtained results show a considerable hydrogen generation capacity of the wave energy converters, up to 6.28% of the wind based generation, which could remarkably improve the efficiency of the far offshore farm and bring important economical profit. Wave energy converters are observed to be most profitable in those farms with low covariance between wind and waves, where the disconnection times of the wind turbines are prone to be more prolonged but the wave energy is still usable. In such cases, a maximum of 101.12 h of equivalent rated production of the wind turbine has been calculated to be recovered by the wave energy converters.This paper is part of project PID2020-116153RB-I00 funded by MCIN/AEI/ 10.13039/501100011033. Authors also acknowledge financial support by the University of the Basque Country under the contract (UPV/EHU, GIU20/008)

Paradigmatic case of long-term colocated wind–wave energy index trend in Canary Islands

Previous studies based on remote sensing data and reanalysis have identified strong historical increments of wind speed in the area around the Canary Islands (Spain) without appreciating any increment of wave height. This decoupling of long-term trends for wind and wave data is not very common, and can be considered paradigmatic for an innovative study, with important implications for wind and wave hybrid or co-located energy production. In this study, wind and wave data from ERA5 reanalysis in the area around the Canary Islands have been used to compute a wind–wave energy co-location feasibility index between 1981–2020 showing an increment of the index above ＋5%/decade. Furthermore, realistic wind and wave energy production has been calculated at an interesting hot-spot using a specific floating wind turbine co-located aside a oscillating buoy type wave energy converter. The corresponding capacity factor trend for wind energy (＋0.8%/decade) and capture width ratio evolution for wave energy (−1.5%/decade) shows also the wind–wave decoupling, which constitutes a significant result for an original approach.This paper is part of project PID2020-116153RB-I00 funded by MCIN/AEI, Spain/10.13039/501100011033 and has also received funding from the University of the Basque Country, Spain (UPV/EHU project GIU20/08)

Long-Term Freezing Temperatures Frequency Change Effect on Wind Energy Gain (Eurasia and North America, 1950 & 2019)

The persistent freezing conditions in cold regions are the cause of ice accretion on mechanical and instrumental elements of wind turbines. Consequently, remarkable Annual Energy Production (AEP) losses are prone to occur in those wind farms. Following global expansion of wind energy, these areas have had increased study interest in recent years. The goal of these studies is an improved characterisation of the site for the installation of turbines, which could prevent unexpected high AEP losses due to ice accretion on them. In this context, this paper provides an estimation of the freezing temperatures frequency (FTF) at 100 m over latitudes and evaluates the changes during the last 70 years. To that end, hourly surface temperature data (2 m above surface) from the ERA5 reanalysis is used in the [50∘ N, 75∘ N] latitudinal belt for the period 1950–2019. The obtained results show an average reduction of FTF hours of 72.5 h/decade for all the domain, reaching a maximum decrease of 621 h/decade on the southeast coast of Greenland and a 60% annual reduction at a specific location in Scandinavia. In terms of AEP a maximum gain of more than 26% would be projected, as categorised by the the International Energy Agency.This paper is part of the project PID2020-116153RB-I00 funded by MCIN/AEI/10.13039/ 501100011033, and also received funding from the University of Basque Country (UPV/EHU project GIU20/008)

Performance variations of wave energy converters due to global long-term wave period change (1900–2010)

Long-term ocean climate effects on wave energy are often analysed from the viewpoint of the well-known increment of wave height over the decades. However, this increment associated with the increase of wave energy flux and absorbed power does not consider the influence of variations in the wave period, whose contribution is more important according to an adimensional performance analysis given by the capture width ratio. This study identifies significant past variations in wave periods during the 20th and 21st centuries using the reanalysis ERA-20C globally and at specific locations, such as Ireland, via calibration with ERA5. A more specific analysis developed in this area shows very significant performance variations (up to 20%) for two types of wave energy converters: oscillating water column devices and a floating body, in which laboratory empirical equations have been used to compute their performance loss due to the deviation from its natural resonance frequency or optimum working wave period. Thus, the performance measured as capture width ratio is highly sensitive to wave period changes, even losing productivity for regions where the wave energy potential is being incremented during the last decades.This study is part of project PID2020-116153RB-I00 funded by Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, Spain MCIN/AEI/ 10.13039/501100011033. The authors acknowledge the funding of the research groups by the University of the Basque Country, Spain (UPV/EHU, GIU20/08)

Historical Evolution of theWave Resource and Energy Production off the Chilean Coast over the 20th Century

The wave energy resource in the Chilean coast shows particularly profitable characteristics for wave energy production, with relatively high mean wave power and low inter-annual resource variability. This combination is as interesting as unusual, since high energetic locations are usually also highly variable, such as the west coast of Ireland. Long-term wave resource variations are also an important aspect when designing wave energy converters (WECs), which are often neglected in resource assessment. The present paper studies the long-term resource variability of the Chilean coast, dividing the 20th century into five do-decades and analysing the variations between the different do-decades. To that end, the ERA20C reanalysis of the European Centre for Medium-Range Weather Forecasts is calibrated versus the ERA-Interim reanalysis and validated against buoy measurements collected in different points of the Chilean coast. Historical resource variations off the Chilean coast are compared to resource variations off the west coast in Ireland, showing a significantly more consistent wave resource. In addition, the impact of historical wave resource variations on a realistic WEC, similar to the Corpower device, is studied, comparing the results to those obtained off the west coast of Ireland. The annual power production off the Chilean coast is demonstrated to be remarkably more regular over the 20th century, with variations of just 1% between the different do-decades.The authors with the Centre for Ocean Energy Research in Maynooth University are supported by Science Foundation Ireland under Grant No. 13/IA/1886. It is also supported by grant CGL2016-76561-R, MINECO/ERDF, UE. Additional funding was received from the University of Basque Country (UPV/EHU, GIU17/002)

Long-term changes in offshore wind power density and wind turbine capacity factor in the Iberian Peninsula (1900–2010)

This study analysed temporal and spatial changes in offshore wind power density (WPD) and capacity factor (CF) around the Iberian Peninsula during the 20th century by analysing data from ERA20 and ERA5. Both WPD and CF were calculated using reanalysis data considering a wind turbine with a hub height of 90 m and incorporating the effect of air density changes. Since ERA5 assimilates more observations, the data from ERA20 was bias-corrected using quantile matching, with ERA5 reanalysis data as the reference. As both variables are based on wind speed (WS), this variable was also corrected and analysed. The results show that the mean values for WPD, CF, and WS during the 20th century were highest in the Atlantic zone and the Gulf of Lyon and lowest around the Balearic Islands. The results of the assessment of decadal trends using the Theil–Sen estimator show that all indicators increased significantly in the waters of the Iberian Peninsula during the study period (1900–2010). Considering the mean slope over this period, the change over the entire period could amount to 174 Wm-2 for WPD, 8.8% for CF, and 1.1 ms−1 for WS. Based on these changes, offshore wind turbines would have increased their returns by approximately 20% over the 11 decades.This work was financially supported by the Spanish Government through the MINECO project CGL2016-76561-R (MINECO/ERDF, UE) and the University of the Basque Country (UPV/EHU, GIU 17/002). Reanalysis data were downloaded at no cost from the ECMWF. All calculations and plots were carried out in the R framewor

Combining random forests and physics-based models to forecast the electricity generated by ocean waves: A case study of the Mutriku wave farm

This paper combines random forests with physics-based models to forecast the electricity output of the Mutriku wave farm on the Bay of Biscay. The period analysed was 2014-2016, and the forecast horizon was 24 h in 4-h steps. The Random Forest (RF) machine-learning technique was used, with three sets of inputs: i) the electricity generated at Mutriku, ii) the wave energy flux (WEF) prediction made by the ECMWF wave model at Mutriku's nearest gridpoint, and iii) ocean and atmospheric data for the Bay of Biscay. For this last input, extended empirical orthogonal functions (EOFs) were calculated to reduce the dimensionality of these data, while retaining most of the information. The forecasts are evaluated using the R-Squared, Mean Absolute Error (MAE), and Mean Absolute Percentage Error (MAPE). The model easily outperforms a persistence forecast at 8-10 h and beyond. The most accurate forecasts are achieved by using all three of these inputs. This approach may help to effectively integrate wave farms into the electricity market.This work has been financially supported by the Spanish Government through the MINECO project CGL2016-76561-R, (MINECO/ERDF, UE) and the University of the Basque Country (UPV/EHU, GIU 17/002). ERA5 hindcast data have been downloaded at no cost from the MARS server of the ECMWF. All the calculations have been carried out within the framework of R (R Core Team, 2018). Special thanks to the Basque Energy Agency (EVE www.eve.eus) for kindly providing the data from the Mutriku wave farm used in this study