How does the Wave Energy Prize calculate ACE?

The goal of the Wave Energy Prize is to stimulate the development of innovative wave energy converters (WECs) that have the prospect for becoming commercially competitive with other forms of electricity generation.  Specifically, the Prize seeks to double the state-of-the-art performance of WECs. As mentioned in a previous blog, 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 WEC technologies that are at low TRLs.

With support from Sandia National Laboratories and the National Renewable Energy Laboratory, the Prize team derived a new metric to determine effectiveness of low TRL concepts that is a modification of existing WEC metrics. Importantly, this metric allows for robust analysis of innovative WEC devices using novel methods and materials.  ACE is a benefit to cost ratio, and 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.

Wave Energy Prize ACE Metric Slide

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. Below is a detailed description of how to calculate ACE.

Average Climate Capture Width

The average climate capture width (ACCW)—the numerator of ACE—represents an expected yearly average capture width for a WEC operating in typical West Coast wave climates. ACCW is calculated from a set of WEC capture widths for a select set of irregular wave conditions that are either measured in sub-scale physical model testing or calculated from numerical simulations.  The full scale capture widths are weighted by the yearly occurrence of the specified test wave conditions at select locations and summed to yield the ACCW.  This means that a device that performs very well in one sea state but poorly in other sea states may have a relatively low ACCW when compared with the maximum capture width.  Alternatively, a device that has modest performance over a wide range of sea states and wave directions may have a higher ACCW.

Calculating ACCW

ACCW is calculated in two steps, first by calculating the average annual capture width (AACW) for each wave climate of interest through weighted absorbed power measurements in the sea states of each wave climate, and then by averaging the AACW values to give ACCW.  For more details on these calculations, see Appendix I of the Wave Energy Prize Rules.  Below is a description of the approach for determining which tests to perform to determine ACCW, followed by a simple illustration of calculating AACW and ACCW.

Both tank testing and numerical simulations must cover enough sea states to represent a realistic wave climate. Simulations should be performed in enough irregular sea states that the power in every bin of the resource matrix, or joint probability distribution (JPD), at the wave climate can be approximated. For tank testing, testing at every sea state bin at the wave climate would be over burdensome, but enough sea states should be tested to represent the characteristics of that climate.

In both cases, the sea states that are tested should be weighted so that average annual power absorbed for a particular wave climate can be estimated. (This scaling is represented by Ξ in Appendix I of the Wave Energy Prize Rules.)  The resulting dataset will be a power ma­trix of device power absorbed for significant wave heights and energy periods that cover the range of sea states experienced at the wave climate of interest.  Multiplying the power matrix by the JPD and summing the values of the matrix yields the average device power absorbed for a particular wave climate. The average power absorbed is then used to determine the average annual capture width.

For example, for a particular wave climate, if the average power absorbed by a WEC is 90 kW and the average annual wave resource is 30 kW/m, the WEC would have an AACW of 3m.

P average absorbed = 90 kW

P resource = 30 kW/m

AACW = ( P average absorbed (kW) / P resource (kW/m) ) = 3 m

Per Appendix I of the Wave Energy Prize Rules, ACCW will then be given simply by averaging the AACW for all wave climates of interest.

Characteristic Capital Expenditure

Prior analysis performed at NREL shows that the largest contributor to wave energy LCOE is the structural cost of a WEC, and in the Prize, the Characteristic Capital Expenditure (CCE) is used to estimate the structural cost of a device (CCE and RST were discussed in a previous blog post, and are discussed in more detail here). The device structure accounts for the mass of any and all load bearing structures that are critical to the power conversion path. This includes:

  1. Any structure that interacts with the wave environment
  2. Any supporting structures used to resist forces in the power conversion chain in the load path/force flow path
  3. Any significant load-bearing foundation components

This implies that for a heaving buoy, for example, not only must the structure of the buoy be used to calculate CCE, but the structure of the gravity base itself must also be used. For offshore devices that require substantial structures, such as jack up barges, those structures must be included as well.

Once the structure is defined the CCE of a device is calculated using the following equation:

CCE = RST * Asurf * ρ * MMC

where:

  • RST = representative structural thickness [m]
  • Asurf = total structural surface area [m2]
  • ρ = material density [kg/m3]
  • MMC = manufactured material cost [US$/kg]

If more than one structural material is used in a device, the individual CCEs for each material are summed to give a total CCE.  Below are details on calculating each of the variables above for a single material in a device.

Representative Structural Thickness

The representative structural thickness (RST) mentioned in the above equation is a scalar that is used to determine the total structural mass when multiplied by the surface area of the material. The RST can be visualized as a single uniform thickness obtained by “melting down” all of the structural components of a material, and then “casting” the shape of the WEC with a constant wall thickness, the RST. This means that all stiffeners and support structures are “lumped” together. A simple representation of the RST is shown below with a flat plate. The original structure includes a grid of stiffeners with a thin hull. That same quantity of material is then represented by a solid plate with the thickness given by the RST.

plate1.png

Manufactured Material Cost

The last critical variable to calculate CCE is the manufactured material cost (MMC). This value represents the total cost to manufacture the material used in a device at full production scale. Therefore, the MMC includes the raw material cost, any fabrication, forming, and assembly.

In practice, the value of MMC will fluctuate due to material suppliers, complexity of device, number of devices, along with many other market factors. For example, the raw cost of structural steel may be approximately 1 $US/kg but by the time any forming, cutting, or welding is made the MMC may be closer to 3 $US/kg at full production. For a device already built, one can back out the MMC by dividing the total cost to build the device using a particular material by the mass of that material used.

Summary and Example Calculation of RST, CCE, and ACE

Once all the above variables have been defined, one can calculate the RST, CCE, and ACE values for any wave device. Below is an example calculation using cost and performance estimates from the DOE MHK Reference Model #5 which is made of steel and is assumed to operate offshore of Humboldt Bay, Calif.  The absorbed power for Reference Model #5 was simulated at each sea state using the numerical code WEC-Sim developed by the National Renewable Energy Laboratory and Sandia National Labs:

eq1.png

Using this method one can estimate and compare the economic viability of different devices at an early stage. However, one must be careful when employing this method for devices that have different percentage breakdowns with regards to structure, power take-off, mooring, etc. In these situations, and when comparing devices, a more reliable method would be to include all capital costs in the CCE. If all the initial capital costs were included, the CCE would increase from $2.4M to $4.97M, yielding an ACE of 0.84 m/$M.

 

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Wave Energy Prize Finalist Teams and Alternates Showcased at Waterpower Week

Photocollage_640x480_V2Wave Energy Prize Finalist and Alternate Teams recently had a unique opportunity to showcase their technologies and network with industry, academic, and government stakeholders during Waterpower Week 2016 in Washington, D.C.

The week’s events kicked off during the National Hydropower Association Annual Conference’s opening plenary session on Monday, April 25 when José Zayas, Director of the U.S. Department of Energy’s Wind and Water Power Technologies Office, highlighted the work of the teams to the more than 700 conference attendees.

Jose Cristin Finalists.jpg

On Monday and Tuesday, the teams had their 1/50th-scale WEC models on display, meeting with Zayas, Cristin Dorgelo, Chief of Staff of the White House Office of Science and Technology, and other event attendees during the conference’s coffee breaks. On Tuesday afternoon, teams switched gears and took part in a Wave Energy Prize Team Summit, a key part of Waterpower Week, where they were able to meet each other and share ideas; learn about the requirements of upcoming Technology Gates 3 and 4; and participate in on-camera interviews discussing their thoughts on the role of government in innovation, their teams’ successes so far, and the challenges they are overcoming in the upcoming final phase of the Prize. The teams then traveled to the MASK Basin at Carderock, Md., on Wednesday morning to better understand the logistical and technical requirements related to 1/20th-scale testing, and to tour the world-class facility where they will test their prototype devices beginning in August.

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Thanks to all those who joined us for Waterpower Week and the Team Summit, as well as all those who helped make the event a success!

U.S. Department of Energy’s Wave Energy Prize Announces Finalist Teams

Meet the Wave Energy Prize Finalist Teams

The U.S. Department of Energy (DOE) announced Tuesday that nine teams have been named finalists in the Wave Energy Prize, a 20-month design-build-test competition, and will proceed to the next phase of the competition.

The nine finalists and two alternates, identified from the 17 remaining official qualified teams, will continue their quest to double the energy captured from ocean waves and win a prize purse totaling more than $2 million. Each of the finalists and alternates will now receive seed funding from DOE to develop 1/20th scale models of their wave energy converter (WEC). These models will be tested at the nation’s most advanced wave-making facility, the Naval Surface Warfare Center’s Maneuvering and Seakeeping (MASK) Basin at Carderock, Md., beginning in the summer of 2016.

Official finalist teams are:

Alternate teams are:

“The qualified teams’ efforts resulted in some very promising technologies for the judges to evaluate,” said Wes Scharmen, principal investigator at Ricardo, Inc. and chief judge of the Wave Energy Prize. “Based on our preliminary evaluation, the data indicates that many of the teams identified as finalists have the potential to achieve the ACE threshold, and thus the potential to exceed DOE’s program goal. We’re looking forward to further verifying their designs performance at 1/20th scale in the MASK Basin at Carderock this summer.”

ACE—a benefit-to-cost ratio—was selected by the Wave Energy Prize as a metric appropriate for comparing low Technology Readiness Level WEC concepts when there is not enough data to calculate the levelized cost of energy —itself a cost-to-benefit ratio—from a device. ACE is determined by dividing, in essence, the wave energy extraction efficiency of a WEC by its structural cost. Finalists were determined based on their potential to achieve the doubling of the current state-of-the-art ACE value of 1.5 meters per million dollars (m/$M) to 3 m/$M during 1/20th scale tank testing at the MASK Basin, making them eligible to win the grand prize.

A panel of expert judges evaluated each qualified team based on their revised technical submissions, numerical modeling results, Model Design and Construction Plans, and the results of small-scale tank testing of their 1/50th scale models, and determined aggregate scores to identify the finalist pool.

The Wave Energy Prize is encouraging the development of game-changing WECs that will reduce the cost of wave energy, making it more competitive with traditional energy solutions.

Congratulations to the finalist teams, and thanks to all who have participated in theWave Energy Prize to date!

Technology Gate 2 Requirements

wep-tg2

The purpose of Technology Gate 2 is to evaluate the likelihood of each team’s success in achieving the ACE threshold if they were to test a 1/20th scale model of their device in the MASK Basin. As a first step in this evaluation process, judges will consider each Qualified Team’s Model Design and Construction Plan to determine if the team exhibits a reasonable understanding of the effort, tasks, timeline and materials that will be needed to design and build a 1/20th scale model. The team will not proceed and will be eliminated from the Wave Energy Prize if the plan is deemed not credible.

If the judging panel determines that a team’s plan is credible, it will then use the following information to evaluate the likelihood of the proposed WEC technology concept in satisfying the required threshold value for ACE during the 1/20th scale testing:

  • The capture width of the physical 1/50th scale model from the 1/50th testing, scaled up to full scale.
  • Numerical modeling results of the 1/50th scale wave environment (at full scale) and the determination by the judging panel of how well the numerical model predictions correlate with scaled-up experimental measurements. This includes absorbed power, motions, and forces.
  • Revised Technical Submission and its re-evaluation using the TPL.
  • Predictions of ACE (in m/$M) that can be expected in the MASK Basin testing, as determined by the judges, with support from the National Laboratories.

The judges will score each of the above four criteria on a scale of 1 to 9. Then, they will calculate an overall combined score by computing a weighted average of the four individual scores. Qualified Teams will then be ranked from the highest overall combined score down to the lowest; up to 10 will be named Finalist Teams and up to two Alternate Teams will be identified. If the judges and/or Small-Scale Test Facilities are unable to test, measure and analyze the 1/50th scale WEC device in order to adequately determine absorbed power, the device will be eliminated from the Wave Energy Prize.

For more information on the assessment of the construction plans, evaluation of the four criteria, and the weighting of each as part of the overall combined score, please see the Wave Energy Prize Rules.

Details on the Hydrodynamic Performance Quality (HPQ) Metric

The Hydrodynamic Performance Quality (HPQ) of a Wave Energy Converter (WEC) Technology

By Diana Bull, Sandia National Laboratories

The two components that comprise the Average Climate Capture Width per Characteristic Capital Expenditure (ACE) metric are the most important levelized cost of energy (LCOE) drivers for WEC devices, however there are many other influential parameters. Although a scaled wave tank test cannot provide information on all influential parameters (system availability, installation, etc.), it can provide substantial useful information beyond ACE.

ACE requires knowledge of the power absorbed by the device in a West Coast deployment climate and the Characteristic Capital Expenditure needed to build the device. By requiring additional sensors to monitor other aspects of the devices performance, processing the data to obtain alternative views beyond averages, and subjecting the devices to additional wave environments, much more can be learned about a device’s overall performance. In addition to monitoring averaged absorbed power, the devices will be outfitted with sensors that measure mooring forces, accelerations, and the position of the device. This data will be processed to reveal statistically significant peak values, ratios between peaks and means, as well as identifying events like end-stop impacts. Lastly, all of the sensors and processing will occur not only for the irregular wave spectra used to establish average climate capture width (ACCW), but also for two large irregular wave spectra (LIWS) and two realistic wind swell spectra (RWS).

This additional data will be processed into six performance-related quantities for each device tested in the MASK basin. These performance-related quantities are:

  • Statistical peak of mooring watch circle (WCHPQ)
  • Statistical peak of mooring forces (MFHPQ)
  • Statistical peak-to-average ratio of absorbed power (APP2A,HPQ)
  • End-stop impact events (ESHPQ)
  • Absorbed power in realistic seas (RSHPQ)
  • Adaptive control effort (ACHPQ)

These quantities relate to aspects of the techno-economic performance not addressed by ACE and will allow devices to distinguish themselves on more levels then the ACE metric alone provides.

Each of these hydrodynamic performance-related quantities will be allocated to a factor (in the range of 0.94 – 1.06) and the HPQ of a device will be established by multiplying the ACE metric by the factors allocated to each performance-related quantity.

HPQ = ACE * ( MFHPQ * WCHPQ * APP2A,HPQ * ESHPQ * RSHPQ * ACHPQ )

Each of these factors may have limited beneficial, non-beneficial or no influence on the HPQ. The allocation of the factors from the performance-related quantities will be the responsibility of the judging panel.

The HPQ will establish that the winners’ designs will more effectively address key aspects of the techno-economic performance. The HPQ continues to encourage teams towards a systems-level engagement through the end of the competition. At the end, the device with the highest HPQ that has surpassed the ACE threshold will be declared the winner of the Wave Energy Prize.

The Wave Energy Prize Purse and Seed Funding

Wave Energy Prize Cash Purse

Why participate in the Wave Energy Prize? Teams will be competing for more than $2 million in prizes and seed funding.

The prize purses available to the winner(s) of the Wave Energy Prize will be:

  • Grand Prize Winner: Team ranked the highest after testing of the 1/20th scale WEC device model at the Carderock MASK Basin – $1,500,000
  • 2nd Place Finisher: Team ranked second after testing of the 1/20th scale WEC device model at the Carderock MASK Basin – $500,000
  • 3rd Place Finisher: Team ranked third after testing of the 1/20ht scale WEC device model at the Carderock MASK Basin – $250,000

To be eligible to win a monetary prize purse, a team’s 1/20th scale device must achieve a threshold of 3m/$M Average Climate Capture Width per Characteristic Capital Expenditure. The judging panel will rank all teams whose devices achieve the threshold and assess their overall performance using the Hydrodynamic Performance Quality (HPQ), outlined in Section 6 of the Wave Energy Prize Rules.

The Wave Energy Prize will also provide seed funding to the Finalists (up to $125,000) and Alternates (up to $25,000) determined at the end of Technology Gate 2. This seed funding will be provided to the Finalists and Alternates for costs associated with the building of the 1/20th scale model to be tested at the MASK Basin, as well as costs associated with the shipment of the 1/20th scale model and participation in the testing process.

10 Teams Registered for the Wave Energy Prize

Wave Energy Prize - 10 Registered Teams

As of today, there are now 10 REGISTERED TEAMS! U.S. corporations, small businesses, professional engineers, students, entrepreneurs and innovators are encouraged to compete for more than $2 million in cash prizes: http://waveenergyprize.org/teams