Monday, 8 April 2013

Opportunities for sites with low wave resource

Many commentators have pointed out that locations with low average wave power tend to have a smaller ratio between average and extreme wave powers. This ratio between average and extreme wave powers is one of the underlying challenges of extracting wave energy. This suggests that lower energy sites could give cheaper wave energy.

There are however similar arguments for high energy sites. Wave energy converters sized for sites with lower energy waves will need to be smaller to achieve an economically viable capacity factor. For a given annual energy production, an array at a low energy site will have more individual devices than an array at a high energy site. The array with fewer larger devices will tend to be cheaper as it will have lower balance of plant (everything but the WEC) costs. The array with more smaller devices however would have better power smoothing and would probably have greater availability due to the inherent system redundancy.

The ideal site for a wave energy converter is thus an economic optimisation, much like capacity factor. We have no hope of moving in the optimal direction until we have a few years and projects worth of data for capital costs, maintenance costs, electricity revenue, component lifetimes, etc.

In the meanwhile, technologies suitable for high energy sites will be developed, because these provide the promise of the large global markets that justify the investments made by large industrial companies.

Nevertheless, there could still be opportunities for low energy sites as test sites, or in cases where the device developer has no large industrial backer. Without an industrial backer, the risks must be shouldered by the device developer and/or the prototype owner. An example is the Israeli company SDE’s sale of prototypes to utilities in 11 countries, many of which have low energy sites.

Low energy sites would make good testing locations if the goal was cost efficient collection of operational data, rather than demonstration of technology readiness by survival testing or high nameplate rating. There are strong arguments for this case if particular low energy sites had other cost advantages, such as favourable seabed conditions, low tidal currents, large weather windows, grid capacity, proximity to ports, etc.

Image credits
Bathing duck by Ladybird Cakes; photo by Denise Grayson:


  1. Ally, Maybe I am missing something here, but my question is, why would one consider an array of few larger devices when it would be so much worthwhile to reduce Balance of Plant costs which are not so proportional to the array size? Power smoothing for larger devices can also be equally good with more number of devices (Power variations coming from individual devices get averaged better over time with increasing numbers) rather than completely depend on expensive Power electronics and of course at higher power levels and capacity.

  2. Verash, I get the impression that Balance of Plant costs are one of the main targets for cost of energy reductions (for those who have specific cost of energy programs). The offshore wind industry have the motivation and the means to reduce the balance of plant costs for their technology; there is hope that wave and tidal can to borrow much from them. Technology that we need to develop ourselves, such as umbilicals, quick release moorings, and array layout, is, as you have suggested, the topic of much recent R+D.

    1. Thanks Ally,

      Just thought, Readers of this topic might also find the following report from Carbon Trust interesting:

  3. Lots more comments and discussion on the LinkedIn wave energy group:

  4. Thanks for link to the Carbon Trust report Vernash. They are obviously linking high average resource sites to low cost of energy. In last week's IET seminar I spoke to someone from the Carbon Trust who said their models also suggested larger device sizes would reduce CoE (again, balance of plant):

    I don't know what their model assumptions were, e.g. whether they express availability as a function of weather-windows; thereby linking this to resource & distance from shore. Anyhow, the Carbon Trust use data from developers to inform their models, which gives them a link to the real world. While I don't believe the available operational data is sufficient to claim with certainty that the best CoE is achieved with big devices in the biggest resource, I do however think that the first arrays will start to provide this type of information.

  5. Ally,

    I would say the difference between high wave resource (Typically 70 kW/m) and low average wave resource (20kW/m) is huge. Even at low capacity factors, the higher regime beats the low average ones even with full capacity factors, since it's the higher echelons in the matrix (figuratively speaking) that contribute a lot in terms of kWh produced per year. So, I too broadly reckon, lower CoE for larger devices after considering BoP costs, but then again like you rightly mentioned the proof of the pudding is in eating. The question is also what type of pudding (device) since capacity factor plays the major role and the ones that can resonate in a wider range within the ratings will very well win the race.