Implementation of an Energy Harvesting System for Powering Thermal Gliders for Long Duration Ocean

Research

Clinton D. Haldeman III, Oscar SchofieldCenter for Ocean Observing Leadership

Rutgers, The State University of New JerseyNew Brunswick, NJ 08901

Douglas C. WebbTeledyne Webb Research Corporation

North Falmouth, MA 02556

Thomas I. Valdez, Jack A. JonesJet Propulsion Laboratory

California Institute of TechnologyPasadena, CA 91109

I. Background – Slocum Thermal glider to Slocum-TREC

• Building on success of previous ONR funded project that resulted in 2 thermally propelled gliders

• Joint project; NASA’s JPL & TWRC integrate SOLO-TREC (Sounding Oceanographic Lagrangrian Observer, 2009) and Slocum glider. Rutgers – year 2, operational expertise.

• Testing – 15 miles offshore (trim, ballast, etc.)

• Thomas I. Valdez – Power Subsystem Analyst

• ROCKET SCIENCE!!!

Seaglider – up to 10 months durationAPEX Floats – 4 year

life

Spray Glider - ~6 months duration

Autonomous Platforms – buoyancy driven

Slocum electric glider – ~1 year w/ extended energy bay

Slocum Thermal glider

Slocum electric glider – single engine; stepping stone to the thermal

Projected endurance – 4 years or more

Uses Phase Change Material (PCM) to drive oil used for buoyancy control. Duration is limited to ability of primary battery to power “hotel load”

II. Slocum-TREC – design difference

2 thermal engines, so more oil available. PCM uses aluminum metal foam to enhance thermal conductivity - thermal response by factor of 50.

Solo-TREC

Slocum-TREC

What can we do with that extra oil?TREC!

77

Slocum-TREC Energy Storage Functional System Schematic

LP

ChargeBattery

(14.4 to 12.5V)Nominal: 13.2 V

Power Out

+

-

SW2

HydraulicMotor

P

HP

BV

Control

DAQ Sense

Power

Hydraulic

Pressure

Ball Valve

Current

Switch

DischargeBattery

(14.4 to 12.5V)Nominal: 13.2 V

AXI-

Back-upPrimaryNominal: 12 V

ControlElectronics

MotorDriver

SW4

SW3

Rectifier

SW0

Electronic

Load

SpeedControl

SW1

2 battery packs; 1 being charged, 1 being discharged (used)

Electronics Delivery: Electronics Integration

8

Control Electronics Batteries

Energy Storage System Control Electronics (JPL)

Slocum Controller (TWR)

Energy Harvesting Specifics

• Typical generation cycle – 40-45 seconds

• Generates 1.8 Wh/Dive, stores 1.7 Wh/Dive; delivers 70 Wh every 80 generation cycles

• Battery voltage – 13.2-13.4 V, an optimal operating range for a variety of scientific sensors

• Energy can be delivered at power levels as high as 800 W, opening the door to a wide array of other sensors where power levels are a concern

• Voltage levels correspond to 40-75% state-of-charge (SOC) - optimized to maximize battery cycle life, allowing 10+ years of operation!

90 generation cycles * ~4 hours/dive = ~15 days, Voltages steady

• Goals – Endurance Tests– A) Hawaii

• 2 Slocum-TREC gliders deployed (Lewis and Clark)• Lewis never resurfaced (possible large animal interaction?)• Clark – suffered issue w/ trim mechanism; recovered after 45 days

– ½ of planned initial endurance test

– B) St. Thomas, USVI• Clark repaired; redeployed Jan 2015• Oil volume issue; necessitated recovery• Recovered after 27 days; adjustments made• Redeployed for another 68 days; accumulator leak• Total of 95 days; but non-consecutive

III. Testing – Tropical Waters

• Results – What did we learn?– A) Energy harvesting/generation/storage system worked

incredibly well. Shunting energy, so increased CTD resolution while remnants of Hurricane Danny and then Tropical Storm Erika passed by. Energy budget issue is solved; perhaps bringing biofouling to the forefront

– B) Differing ballast & flight mechanics/nuances, such as twist – C) Latitudinal range of operation – still TBD. Or, how much

energy can we generate? Electric pump?– D) Environmental interaction – how to pilot this glider. Buoyancy

drive vs. power generation, etc. – E) Water Mass Layering / CTD issues

…summed up in 7 lines of text on a website…

Area of Rapid Intensification (RI)

Increase of sustained winds of at least 30 kts in a 24 hour period

• High intensity storms destructive; loss of life and property, cause economic damage…

• …National Centers for Environmental Prediction (NCEP) mission statement includes delivering climate products protecting life, property, and economic well-being.

• Real-Time Ocean Forecasting System (RTOFS) to input into hurricane and climate forecast systems

• It’s a data issue…or the lack thereof

• Working on pushing all Rutgers glider data to Global Telecommunications System (GTS) for model ingestion

• Provide continual high resolution data needed for assimilation to correct errors in model

What We Know…

What Can We Do?

Subtropical underwater (SUW) significantly deeper than shown in RTOFS

• Working on pushing all Rutgers glider data to Global Telecommunications System (GTS) for model ingestion

• Continual high resolution data needed for assimilation, else errors in model occur

• Lagrangian drifters, but only yield a profile every 10 days• Buoys, but don’t provide profiles

What Can We Do?

What Have We Done?

When zoomed in to surface of temperature profiles, cooling visible as storm passes

• Continual data collection, with a cost that diminishes over lifetime of glider; Iridium satellite communications become primary expense

• Providing high resolution data in sparsely sampled areas can correct errors in models, leading to better track and intensity forecasts. Examples include Hurricane Irene in NJ, where glider data resulted in a reduced intensity forecast due to bottom boundary layer mixing and surface layer cooling

Strengths of Slocum-TREC become apparent

• Slocum-TREC – “next generation” of ocean gliders• Harvesting thermal energy from the ocean has solved the issue of a

limited power budget – now on to the next• A few minor mechanical issues need addressed, but piloting will still

contain a learning curve. Nuances particular to the thermal design and latitudinal limits may pose challenges

• Providing continual data over an extremely long duration can increase the accuracy of models, ultimately resulting in the preservation of life and property.

• As Henry Stommel suggests, we need a fleet of “about 1,000.”

Summary