Wave energy converters are always specially designed to ensure that they generate maximum possible electricity from the movement of the waves around them. The design and adaption are made on the basis of data from the past.
However, according to Alain Ulazia, lecturer at the UPV/EHU’s Faculty of Engineering, the timescale taken into consideration is short and the year is regarded as typical in this period. This means that expectations of behavior during this typical year are the basis for adjusting the wave energy converters.
Alain and other two researches in collaboration with the Irish Centre for Ocean Energy Research tackled a longer-term study to explore wave energy as a resource. Using a simulation, they calculated what response or behavior a converter would have displayed when faced with the level of wave energy recorded during the last century, divided into periods of 20 years (the average useful service life of wave energy converters).
They analyzed two datasets of the European Centre for Medium-Range Weather Forecasts (ECMWF): ERA-Interim and ERA20. Both of them were fed by a whole host of observations and measurements before. ERA-Interim brings together a multitude of data coming from satellites, but its limitation is that it only has data on the last 40 years. ERA20 is fed by far fewer data, is much more irregular from the time and spatial perspective, but provides data on the whole 20th century.
Therefore, the team used the overlapping period they have to calibrate the datasets. And then they validated them against the measurements made in the buoys in the Atlantic.
They divided the last century into 5 periods of 20 years (Lifespans of wave energy converters) and adapted the converters for the level of energy corresponding to each of these periods. The level of marine energy has increased by 40% between the first and the last period. Additionally, the biggest increase occurred in the last 20 years (18%). The main hypothesis for this is climate change, but the team has not analyzed what the reason for this increase was.
The result from the study also showed that the wave energy converters did not take full advantage of all the energy they had available and additionally, extreme events, such as periods of waves over seven meters high or phenomena like El Niño, that became more frequent, caused the converter to go more frequently into survival mode, or to stop producing energy.
Ulazia says the information obtained should be useful in optimizing the design of the converters to ensure they achieve maximum output in conditions that are increasingly more active.