Wave Energy Prize winner(s) to be announced Nov. 16

carderock2

It has been a long road for our teams since registering for the Wave Energy Prize back in the spring of 2015. In 18 months, they have written technical submissions, test plans, and build plans; constructed 1/50th-scale models, completed small-scale testing, and numerically modeled their WEC’s performance; and finally, after building 1/20th-scale WEC prototypes, tested their devices at the Navy’s Maneuvering and Seakeeping (MASK) Basin in Carderock, Md. Nothing remains but to find out how many teams were able to meet or exceed the Prize’s goal of doubling the energy captured from ocean waves, and to ultimately announce whose technology met or exceeded the required ACE value and produced the highest HPQ.

The U.S. Department of Energy will announce the winner(s) during the Wave Energy Prize Innovation Showcase to be held at Naval Surface Warfare Center Carderock on Nov. 16. Attendance at this event will be by invitation only.

For our teams, whether they are the winner of the $1.5 million grand prize or not, Nov. 16 is not the end, but rather a new beginning. In the months following the Prize, the teams will analyze the data obtained during testing at the MASK Basin to help bring their innovative technologies to the market.

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Team Technical Summaries

It has been more than two months since the 20 Qualified Teams in the Wave Energy Prize were announced, and you are probably wondering what they have been working on. Well, they have been developing their 1/50th scale wave energy converter (WEC) models; preparing for testing these scale models; and starting to numerically model their innovative WEC designs. Below, in their own words, the Qualified Teams provide a glimpse into the breakthrough technologies they are developing (we present them alphabetically based on team name, and will do so for all Qualified Teams).

Advanced Ocean Energy @ Virginia Tech
Hampton Roads, Va.

AOE@VT WEC Technology Image for Publication FINAL 20150921

Virginia Tech’s MULti-body LinEar Terminator (MULLET) is a self-contained array of Bundled pIpe Terminator Wave Energy Converters (BITWECs). Each BITWEC is a floating bundle of large-diameter high-density polyethylene (HDPE) pipes. The basic MULLET building block is a “tandem BITWEC” whereby two pipe bundles are arrayed one behind the other in the down-wave direction.

Each bundle is tethered by a pair of flexible fiber matrix composite tube pumps to the deeply submerged deck of a pontoon barge, which also is fabricated from large-diameter HDPE pipe sections, as shown in the conceptual diagram above, seawater output from the tube pumps is piped to an underwater habitat housing an accumulator and Pelton turbine-generator.

The MULLET barge is assembled while floating in calm water at dockside and then towed to its offshore installation site. Once on site, the barge is connected to a pre-set catenary anchor-leg mooring (CALM) buoy. The barge pontoons and CALM buoy are then flooded with seawater, submerging the barge to its mid-water operating position, where the barge deck acts as an inertial reaction plate for the floating bundles to work against, stretching the tube pumps. For inspection and maintenance, the barge and CALM buoy are re-floated to the surface by reversing the installation procedure.

AquaHarmonics
Portland, Ore.

aquah

AquaHarmonics’ Wave Energy Device is a point absorber device consisting of a simple Power Take Off (PTO) system mounted in a cone/cylinder shaped hull with a single mooring line that has a power cable at its core.

The PTO System consists of a sheave fixed to a shaft mounted in bearings within a sealed compartment and directly coupled to a pair of axial flux generators. The device only generates power on the rise of the wave, and during the fall of the wave the generators are operated as motors to reel in the mooring line for the next wave cycle.

During reel in, the control system of the device can provide additional energy input to achieve phase locking with any wave frequency. This control method is known as “de-clutching,” which has been shown to effectively increase the operational bandwidth of a wave energy device.

The generated power is far greater than that consumed during the wave cycle with some energy stored on board for periods of low wave activity. The power is conditioned on board and sent to shore via a slipring on the shaft connected to the power cable located at the core of the mooring line.

AquaHarmonics. Clean.Simple.Energy.

Atlantic Wavepower Partnership
Newport, R.I.

awp

The AWS-III is a large-scale surface floating multi-absorber wave energy converter. Each absorber cell comprises a partially submerged air-filled chamber, one face of which is covered with a rubber diaphragm which flexes in response to the incoming wave actions. The movement of the diaphragm pumps air to and from the cell via an air turbine-generator set where the energy is converted to electricity. The cells are inter-connected via a ring-main such that air is exchanged between cells rather than with the outside environment.

All mechanical moving parts are isolated from the sea and contained within the device, whilst the turbine technology is tried-and-tested and available on the commercial market. The device is moored using traditional systems for offshore structures, either catenary systems and drag-embedment anchors or tension tethers and suction anchors. Accordingly, the device is utility-scale and has low technical risk and is capable of on-board maintenance of all parts with the exception of the diaphragms. Initial systems are expected to be rated at 2.0MW.

Atlas Ocean Systems
Houston, Texas

atlasos

The Atlas Ocean Systems SQ5 Wave Energy Converter is a completely new device that captures energy primarily from pitch using two independent coupled oscillators. The SQ5 consists of three primary elements: 1) a float, 2) a new innovative submerged bag filled with air under pressure, and 3) a large submerged ballast.

The bag and submerged ballast are essentially in static buoyant equilibrium. The catamaran float provides roll stability and resonates in pitch with the waves and transfers vertical motion to the bag system which then excites a vertical oscillation of the submerged ballast. The oscillation of the ballast drives shape changes within the bag to pump air through a reversible flow turbine to generate useful energy. Pitch response of the float is adjustable in real-time using a ballasting system and coupling between the float and ballast is adjusted during design. Coupling between the two oscillating systems provides a wide dual-peak absorption spectrum providing good power output over a variety of sea states. There are no mechanical moving parts, seals, hinges, or pistons requiring lubrication or maintenance. The turbine system is protected within the pressurized pneumatic system and is suspended in a transverse mounting minimizing gyroscopic forces. The nominal system is designed for a 500kW-1MW rating.

Technical Summaries from more of the Wave Energy Prize Qualified Teams will be profiled in alphabetical order in the future. Visit the new Wave Energy Prize Team Updates page for more information.

Representative Structural Thickness (RST) and Characteristic Capital Expenditure (CCE)

In order to compare the potential cost of energy between wave energy conversion (WEC) devices at low Technology Readiness Levels (TRLs), the ACE metric was created as a proxy for Levelized Cost of Energy (LCOE) (see blog post from June 11). The Characteristic Capital Expenditure (CCE) portion of the ACE metric is determined by the following equation:

Characteristic Capital Expenditure (CCE) = Total Surface Area (m2) x Representative Structural Thickness (m) x Density of Material(s) (kg/m3) x Cost of Manufactured Material per unit Mass ($/kg) for all applicable materials.

Representative structural thickness, or RST, is the most crucial of these variables, and is described below.

What is RST?

RST is used to determine the total structural mass when multiplied by the surface area of the device. The RST can be visualized as a single uniform thickness that is obtained by melting down all of the structural components of a WEC 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.

Plate Thickness

What is considered in determining RST? How is it calculated?

The following components determine RST:

1. Structural Mass

The structural mass of the device accounts for the mass of any and all load bearing structures that are critical to the power conversion path. This includes:

  • Any structure that interacts with the wave environment
  • Any supporting structures used to resist forces in the power conversion chain central to the load path/force flow path
  • Any significant load bearing foundation components

2. Simplified Surface Area

The surface area that is multiplied by the RST is a simplified representation of the WEC device. All stiffeners and support members that do not directly contribute to the power conversion path are excluded. The following examples show how the geometries of two U.S. Department of Energy reference models have been simplified for the RST calculation (reference model reports and documentation can be accessed at http://energy.sandia.gov/rmp). In the first example (point absorber) the surface area (faces in green) is simplified by not including external stiffeners and only accounting for one side of any thin plates. In the second example (oscillating water column), the surface area excludes all external stiffeners and only one surface of any thin plate is considered.

wep-rst-original-rm3-geometry

wep-rst-simplified-rm3-geometry

wep-rst-orig-simp-geometry

How do we calculate RST?

The overall methodology that is used to calculate the RST for all contestants is the same. At the most basic level, the device geometry and wave interactions are used to estimate hydrostatic, hydrodynamic, PTO and structural loads. The loads are calculated using widely used empirical formulas as well as NREL offshore models and first principle approximations where existing standards and guidelines do not exist. These loads are fed into structural models that calculate stresses using existing offshore guidelines and standards. The diagram below represents the process that will be used to calculate the RST for each WEC.

wep-rst-calculation-diagram

What are RST Tables?

As described in Appendix D of the official Wave Energy Prize Rules (5.26.15 R1), each WEC will be assigned an RST Table by September 15, 2015. This table will include the RST value calculated based on the above process, along with additional RST values that represent different load cases. These additional RST values can be used by the Prize judges during the competition to alter the final RST value depending on results from and performance in the 1/50th and/or 1/20th tank tests. For devices that utilize more than one material, an RST table will be supplied for each material.

Why RST?

Now that we’ve described what RST is and how it’s calculated, you’re probably asking yourself, why is the Wave Energy Prize using RST instead of the actual structural design? This simple answer is to maintain consistency during the competition. Every contestant will have a structural mass that is estimated using similar standards and design guidelines, allowing lower TRL devices to be judged against high TRL devices without bias. This also allows for a quicker analysis because devices with similar geometry and similar wave interactions will be viewed as structurally similar devices.

What is Manufactured Material Cost?

Referencing back to the equation for CCE, the last critical variable is manufactured material cost (MMC). This value represents the total cost to manufacture the materials used in the WEC at full production scale. Therefore, the MMC includes the raw material cost, any fabrication, forming, assembly, etc. In addition to the RST tables, the Prize judges will be given a table that includes a range of MMC values that will allow the judges to address designs that have high or low complexity, which will result in a higher or lower MMC value.

Wave Energy Prize names 20 official qualified teams

Meet the Official Qualified Teams

Twenty teams have successfully navigated the first technology gate of the U.S. Department of Energy’s Wave Energy Prize to become official qualified teams.

The 20 qualified teams, selected from the field of 92 official registered teams announced on July 6, will continue their quest to double the energy captured from ocean waves and win a prize purse totaling more than $2 million.

Congratulations to the official qualified teams:

View the official press release: http://waveenergyprize.org/newsroom/press-release-20-teams-advancing-next-phase-wave-energy-prize

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.

Details on the Technical Submission

Technology Performance Levels (TPL): The metric used in the Wave Energy Prize to quantify the techno-economic performance potential of Wave Energy Converter (WEC) Technology

By Jochem Weber, National Renewable Energy Laboratory

Ocean wave energy has the potential to provide a huge contribution to the renewable energy mix, nationally and globally. However, WEC technology development is a challenging undertaking with respect to required development cost (over $100 million, time) up to 15 years, and encountered risk (setbacks in prototype testing). WEC technology development as a whole has not yet delivered the desired commercial maturity nor, and more importantly, the required techno-economic performance to date.

In order to identify and navigate the most time, cost, and risk efficient development trajectory that will lead to successful WEC technology outcomes, it is crucial to have metrics for both commercial technology readiness and techno-economic technology performance. Progress in technology readiness is well quantified by the Technology Readiness Levels (TRL), which are used extensively in the WEC technology development industry.

In order to quantify techno-economic performance potential of WEC systems, Technology Performance Levels (TPLs) have been introduced. The fundamental understanding of the TRL and TPL metrics are juxtaposed in Table 1.

TABLE I: FUNDAMENTAL UNDERSTANDING AND DEFINITION OF TRL AND TPL

Analogous to the TRLs, the TPLs are categorised into 9 levels quantifying the techno-economic functional and lifecycle performance of the WEC system.

An overview of the 9 TPL grades along with their primary characteristics and high level category allocation are displayed in Table 2.

TABLE II: TECHNOLOGY PERFORMANCE LEVEL CATEGORIES & CHARACTERISTICS

The TPL metric considers all cost and performance drivers in form of a large number of attributes or assessment criteria which are categorized into five groups:

  • Acceptability
  • Power absorption, conversion and delivery
  • System availability
  • Capital expenditure (CapEx)
  • Operational expenditure (OpEx)

The TPL assessments can be applied at all technology development stages and associated TRLs, but will differ considerably in assessment depth and confidence level, both dependent on TRL.

Particularly at early TRL stages (TRL 1 to TRL 4), it is crucial to identify, improve and optimize the techno-economic performance potential and achieve high TPL values (TPL 7+) in order to facilitate the most time, cost and risk effective development trajectory leading to successful WEC technology.

As opposed to the calculation of levelized cost of energy (LCOE), which is based on the summation of cost estimates over annual energy production estimates, the TPL metric is composed of technology attributes that drive techno-economic performance potential. The scores for each of the five attribute groups (see above) are combined into an overall system TPL score by means of simple arithmetic. In this sense the TPL metric and assessment process considers techno-economic performance attributes holistically while accepting a simplified functional relationship of the individual attribute to the overall techno-economic system potential and related system TPL score.

Thus, by design, the TPL metric is well suited to the evaluation of techno-economic performance potential of WEC technology concepts at early TRL stages. TPL is also able to avoid technology development trajectories that may lead into technology cul-de-sac—e.g. WEC technologies matured to high TRL while delivering low TPL, consequently requiring radical changeover of core system aspects and even conceptual system fundamentals.

Given these capabilities, the Technical Submission, based upon the TPL metric and assessment process, presents an effective choice for the WEC technology concept assessment and down-select in the first technology gate of the Wave Energy Prize.