Marine
Predictability of Wave Energy and Electricity Markets a report by Julia Fernández Chozas PhD Student, Civil Engineering Department, Aalborg University
Ocean energy is one of the largest renewable energy resources available on the planet and includes four different energy conversion principles: wave energy, hydrokinetic energy (i.e. the energy of ocean currents and tides), osmotic energy and ocean thermal energy.
Wave energy refers to the surface and subsurface motion of the waves. These movements are the result of winds hitting and transferring part of their energy to the ocean´s surface. Once formed, surface waves travel thousands of kilometres with little energy loss. High wave potentials are found between 30° and 60° latitudes in both hemispheres, induced by the prevailing westerly winds blowing in these regions.
Experts estimate wave energy can technically cover the entire world’s primary energy demand. When the economics are taken into account, this number is reduced to 10 % of the world’s electricity consumption – still a significant percentage. In fact, wave energy can also bring the following benefits: it is an abundant, inexhaustible and free resource with high-energy fluxes, it allows different final energy uses, it is close to heavily populated areas along coastlines, it has low visual and acoustic impact and, above all, it works towards energy diversification and increasing security of supply.
Nevertheless, this resource still remains untapped. It is expected that in 10 to 15 years’ time wave energy will reach the commercial stage, when some financial and technical barriers are overcome. Among these, the integration of the electricity generated by wave technologies into the grid, including offshore grid connections, quality of the power output, power variability and production predictability.
Throughout the present article the latter is examined, i.e. wave energy predictability, particularly with regard to the integration of wave energy into day-ahead electricity markets. The article provides an indication of how accurately wave energy can be predicted, with regard to wave parameters, such as wave height and wave period, and the power output of wave energy converters (WEC).
Julia Fernández Chozas is a PhD candidate at the Civil Engineering Department of Aalborg University, Denmark. She has been involved in wave energy research for four years, three of them as part of the Marie-Curie FP7 funded project of the European Commission ‘The Wavetrain2 Project’ (
www.wavetrain2.eu). She is also a member of the Steering Committee of the International Network of Offshore Renewable Energy (INORE), a worldwide
network of offshore renewable energy researchers. She has participated in several conferences, workshops and lectures, and has published around 10 papers.
E:
jfch@civil.aau.dk
This study comprises a collaborative project between Spok ApS (by HC Sørensen), Energinet Denmark (by NE Helstrup Jensen) and the Department of Civil Engineering at Aalborg University (by JP Kofoed). It represents the first approach of the Danish transmission system operator (TSO) towards analysis of the predictability of wave technologies’ power output. The main results were presented at the European Wave and Tidal Energy Conference (EWTEC) 2011.1
Predictability and Day-ahead Electricity Markets The importance of predicting wave energy derives from the current functioning and rules of day-ahead electricity markets.
The day-ahead market in Denmark falls under the Nord Pool spot market, also integrated with Norway, Sweden and Finland. The market closes at noon of the day before, which demands that power producers and consumers make their bids 12–36 hours before the actual generation and consumption time. Hence, wave electricity producers require accurate predictions of the power output of their converters for the following 12–36 hours. Any deviations in the estimated power lead to economic losses due to balancing costs.
The current problem is the increasing percentage of not fully predictable energy sources in day-ahead generation estimates. Uncertainties are causing TSOs, electricity producers and/or users large expenditures to cope with balancing mechanism costs. This is a particular hurdle for wind energy integration into electricity markets and can become a less significant, but still important, issue for wave energy. Consequently, there are two fields of interest in the analysis; firstly, the predictability of the environmental conditions at the deployment site of the wave converter, which dictate the power production and secondly, the estimations of this power production.
Methodology
The research site was Hanstholm, on the west coast of Jutland, Denmark, in the Danish part of the North Sea. It is characterised by a windy sea on top of a non-constant swell, with 6 kW/m of mean energy flux. The location was selected due to data availability and increasing interest in the characteristics of the area from the established Danish Wave Energy Centre (DanWEC).
The investigation was based on simultaneous and co-located forecast and buoy-measured wave data, as well as on theoretical power productions of three WEC, during a five-month winter period (October 2010 to February 2011).
Buoy measurements were provided by a Datawell Waverider buoy from the Danish Coastal Authority, whereas forecast data were calculated by the spectral wave module of MIKE 21 from the Danish Hydraulic Institute (DHI). Data records include half-hourly values of the spectral estimates of significant wave height Hm0, zero crossing period T02 and maximum wave
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