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January 2015: reasonably good energy production and operational time


by Kieran Monk

Production total January = 5734.1 kWh
Operational hours January = 203 Hrs

January saw a consistent wave activity and reasonably good energy production and operational time as seen in figure 1. There were some on-going issues with accelerated ware of the RPM sensor leading to inaccurate readings. This causes control issues because the RPM sensor feeds the controller which decides the level of generator power take-off. Ultimately this meant some down-time for the machine whilst the issues were being dealt with.


Figure 1 Power delivered to grid (January 15 minute averages)


As seen in figure 1 the mean power levels have strong oscillations on a time scale shorter than the change in sea state. In the following a discussion is given on the root cause of the oscillating performance.

By considering: the local wave climate at Pico (from monitoring), original design chamber water depth, specific system specification and turbine characteristics, and by using an optimised power take-off control curve, it was projected in (falcão, 2002)(Falcão, 2002), from stochastic frequency domain analysis, that the Pico OWC should achieve time averaged power take-off levels of up to 190 (kW) in the most energetic sea states and around 100 (kW) over all operational periods (annually). In reality the Pico plant achieves maximum short-term (1 hour) average power take-off levels of about 60 (kW) and about 30 (kW) when all periods (that are chosen for operation) are averaged. This is a significant shortfall of about 70%. As such, it is important to establish the origins of this deviation and to determine if and how corrections/improvements can be made.

The disparity between theoretical and achieved power production levels is at least in-part due to a number of deviations from the original optimised design methodology that were incurred in reality and some of these (relating to the focus of this research) are discussed in the following.

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News January 2015

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