By Philip Michael, Ricardo Inc.
What is ACE?
When comparing the economic attractiveness of power generating technologies, levelized cost of energy (LCOE) is a common metric frequently used in the power generation sector. LCOE is the ultimate expression of the ratio between effort (cost) to benefit (energy generated).
Unfortunately, LCOE cannot be used in the Wave Energy Prize because the data needed to determine LCOE are either not available or are very unreliable at low Technology Readiness Levels (TRLs), and the Wave Energy Prize is fundamentally expecting to be operating with wave energy converter (WEC) technologies that are at low TRLs.
The Wave Energy Prize needs a more fundamental metric that expresses the effort to benefit ratio using data generated in a wave tank testing program, and derived from technical analyses of designs.
While some existing metrics that have been developed by the wave energy research community express an effort to benefit ratio that can be determined at low TRLs, these existing metrics were derived using a body of research and experience on traditional approaches to exploiting wave power. Thus, they may not be wholly valid for the kinds of novel designs and materials that we can foresee as contestants in the Wave Energy Prize.
With support from Sandia National Laboratories and the National Renewable Energy Laboratory, the Prize team derived a new metric that is a modification of existing metrics. Importantly, this metric allows for robust analysis of innovative WEC devices using novel materials. The ACE metric is a proxy for LCOE, appropriate for comparing low TRL WEC designs.
The two components that comprise the ratio ACE are described in full in the Wave Energy Prize Rules. In summary they are:
- Average Climate Capture Width (ACCW) = a measure of the effectiveness of a WEC at absorbing power from the incident wave energy field.
- Characteristic Capital Expenditure (CCE) = a measure of the capital expenditure in commercial production of the load bearing device structure.
ACCW and CCE—the most important LCOE drivers for WEC devices—are calculated values derived from measurements in the wave tank at 1/20th scale (scaled up to full scale), and from structural and cost analyses of full scale drawings.
Other parameters that are ultimately influential in determining LCOE of a WEC are accounted for in the Prize through the Technology Performance Level (TPL) Assessment of the Technical Submission and in the Hydrodynamic Performance Quality (more details coming in the next newsletter).
How will ACE be used in the Wave Energy Prize?
The goal of the Wave Energy Prize is to stimulate the development of innovative WEC concepts that have the prospect for becoming commercially competitive with other forms of electricity generation.
Analyses of the current state of the art reveals that existing WEC concepts achieve an ACE value of 1.5 m/$M (meters per million dollars). For WEC technologies that emerge from the Wave Energy Prize to be on a development trajectory to become commercially competitive, our analysis shows that in the Prize, WECs must achieve a minimum threshold value for ACE of 3 m/$M. Thus, only WECs that achieve this threshold value for ACE following 1/20th wave tank testing at Carderock’s MASK Basin will be considered as candidates for prizes. Prize winners from among these candidates will then be decided using the Hydrodynamic Performance Quality metric.