New method to identify best locations for offshore hybrid PV-wind projects

Scientists in Spain have created a new index that reportedly help project developers identify better areas in initial stages of hybrid wind-solar power plants development. The proposed approach is claimed to avoid deficiencies of previous criteria and overestimation caused by time delays.

Researchers from Spain’s Public University of Navarre have proposed a new methodology to evaluate areas for the offshore installation of hybrid wind and PV power plants. The novelty of their approach lies in its integration of a new complementarity, that evaluates how well the two energy sources balance each other.

“In general, complementarity between two concepts or variables is understood as the situation in which the joint confluence of both improves, in some aspect, each one individually,” explained the researchers. “In the context of wind and solar energy, the general consensus is that complementarity occurs when the deficiency of one resource is compensated by the availability of the other.”

The novel index for evaluating the complementarity of resources is called CIWS_align and is based on the wind and solar complementarity index (CIWS), which was developed for a hybrid project in Oklahoma in 2011, and a dynamic time warping (DTW) technique that was used to align the wind and solar curves. The inputs for this index were taken from the ERA5 dataset and the Copernicus atmospheric monitoring service (CAMS). The output is a number representing the degree of complementarity.

“The Ocean-H2 project is an industrial research project, whose objective is the design and validation of Spain’s first offshore green hydrogen generation, storage, and distribution plant,” the researchers said. “Motivated by the objectives of this project and the growing interest in offshore renewable generation, the current methodology has been developed on the Spanish offshore area.”

To show the effect of including the weight of complementarity, the team has looked for a location around Spain to install a project of 80% wind and 20% solar. Using the traditional method, this ratio also presented the weight of the solar and wind capacity. However, in compression they inserted a 15% weight into the complementarity metric, changing the weight to 68% wind, 17% floating PV and 15% complementarity.

“Changes occur when the complementarity is included, for example, the area in the North-West of Spain reduces its suitability like some areas in the Mediterranean Sea but the most suitable zones as those in North-East or South Canarian Islands maintain, as general, their ranking,” the academics stressed. “Moreover, we can identify the preferable areas by selecting the 10% locations with major value of suitability (percentile 90%) in both cases.”

A closer look was then taken at the Tarifa Gulf, the south Iberian Peninsula. The location in a rank without a complementarity metric (P1) has an annual mean wind speed of 8.88 m/s and a daily mean global horizontal irradiance (GHI) of 4.668 kWh/m2. On the other hand, the area found with the rank that includes a complementarity metric (P2) has a wind speed of 8.64 m/s and a solar radiation of 4.925 kWh/m2.

“While these values do not differ significantly in terms of resources, the situation changes when observing the long-term daily profiles simultaneously,” the group emphasized “Point 2 exhibits a high complementarity with opposing effects of both series, whereas at Point 1, complementarity is observed due to a minor delay between the resources.”

Finally, the academics conducted a sensitivity analysis focusing on the top 10% of locations where the novel approach was found. In it, they gave the complementarity metric a value of either 10%, 15% or 20%. All cases were tested with wind weight ranging from 10% to 90%, while PV was accounted for the difference. Those changes have affected the top 10% locations by 7.9% to 41.1%.

“The methodology can be seen as a start point of a more complex methodology including more than two energy sources and that could take into account different timing to analyze their complementarity,” concluded the scientists.

Their findings were presented in “A new methodology to easy integrate complementarity criteria in the resource assessment process for hybrid power plants: Offshore wind and floating PV,” published in Energy Conversion and Management: X.