With the growing momentum towards sustainable energy sources, researchers are increasingly exploring wave energy as an environmentally friendly means of offshore energy harvesting. As an increasing number of research groups explore solutions for simple and cost-effective remote offshore water monitoring systems, a buoy device that harnesses wave energy for self-sufficiency is a promising solution. Current buoy monitoring devices are usually deployed in deep water waves and only use solar panels for energy input, requiring them to be very large to house enough panels for the power need. Our solution aims to create a small-scale self-sustaining buoy device to be deployed in shallow-water to transitional waves that harnesses both wave energy and solar energy to power a water quality device for offshore environmental testing. This device would be able to serve similar purposes but require much smaller per unit scale and cost, allowing more implementation and less disturbance to marine life. 


There are four key foundational elements to our project. Our analysis of waves, how to measure them, and the “motion of the ocean” have allowed us to formulate initial plans with a buoy and wave generator design, as well as mechanical testing for the device. In addition, analyzing potential impacts of our product in environmental testing has been key for design and testing our storage system.


Wave energy is a potential source of clean energy that has the power to operate 24/7 and harness a high amount of energy density compared to other renewable energy resources, as many scientists believe ocean waves are capable of generating 2 Terawatts per year globally [1]. In addition, wave energy technologies have many different conversions potentials with different devices that convert wave motion into electrical energy. 

When looking at waves, they can be categorized by their wavelengths, which are proportional to depth of the water at a given point offshore. While most of these technologies have shown success in deep-water waves, our project is focusing closer to shore, in shallow-water to transitional waves. Because waves can travel large distances with little energy loss, we see potential for a wave energy powered device to work closer to shore and still power a remote electronic device [1]. Nevertheless, a significant hurdle in implementing a wave system lies in the unpredictable directions of the waves and the consistent success required for a conversion device to effectively manage the inherent randomness of the waves [1]. 

Wave Types [2]

Environmental Testing

Most offshore environmental testing equipment for physical and chemical measurements are often expensive and require a high amount of maintenance because of being battery operated. And as the need is increasing to test our water, remote offshore testing is valuable to researchers and companies looking to record measurements like dissolved oxygen levels, turbidity, temperature, pH, chlorophyll, salinity, and other water quality characteristics [4]. 

Currently, Nexsens Technology has a Water Monitoring Buoy System that runs off of solar energy and measures a number of variables, such as the water quality parameters described above plus other physical water elements such as the waves and current [g]. In our project, we are using wave energy for better reliability and less maintenance as well as creating a smaller buoy that is more suitable for a classroom or lab environment. 

Nexsens Technology Water Monitoring Buoy [5]

Measuring Waves

Waves have a large variability when it comes to their energy, wavelength, frequency, and other measurable characteristics. However, they are relatively predictable, which makes them a unique clean energy source, especially in comparison to other renewables like solar and wind energy that have a higher daily and seasonal variability.

When identifying initial inputs, wave frequencies needed to be looked at in the shallow to transitional wave depths. According to the Nortek group, this distance from shore/water depth can correspond to “wind waves” [3]. 

As shown in the image below, wind waves have a wave frequency ranging from 10-2 Hz to 1Hz. The frequency of a wave, combined with knowledge about its depth/length, could be used to approximate the wave’s speed and amplitude, which determine the input energy of the wave energy harvesting device, and provide information regarding the device’s design constraints and expected energy output. 

Average Wave Frequencies for Different Wave Categories [3]

2D Circular Motion into Linear Motion

As waves move, they are generating circular motion in both the x and y directions. This circular mechanical motion can be converted to electrical energy through a generator within a buoy that floats along the surface of the water and moves vertically with the tidal motion. This type of wave energy capturing device is a “wave profile device” [6]. Most wave profiles devices are practical for near shore devices, like navigation buoys [1]. 

Movement Patterns of Waves [3]

Main Project Goals

Functional Requirements

  1. The system must harvest and convert linear wave motion in shallow-water and transitional wave patterns into rotational energy 
  2. The system must convert the rotational energy into electricity through a generator
  3. The system must have a voltage control element and store both wave and solar energy through a storage system

Performance Requirements

  1. The storage system must meet the total power input need of 24 Watts 
  2. The system must not exceed $1000 in total cost (excluding environmental testing equipment)
  3. The system must not exceed 45 cubic ft

Educational Goals for Duke Courses

  1. PHY 151 Introductory Mechanics: Buoyancy calculations and analysis of loads on transmission components
  2. PHY 152 Introductory Electricity, Magnetism, and Optics: Magnetic coupling in generators and how that affects power output of a system 
    1. Lab Idea: Analysis of correlation between magnet rating and placement and coupling torque limit
  3. EGR 244 Dynamics (syllabus): Generator basics 
    1. Lab Idea: Changing generator design and learning about effect on power output  
    2. Lab Idea: Study of conservation of energy through a transmission of system, comparison of input work and work received at the end to understand loss energy in a practical environment 
  4. EGR 224 Mechatronics (syllabus): Circuitry design and power calculations for combining a wave energy and solar energy system, usage of capacitors and bridge rectifiers with a 3 phase motor, how to discharge capacitors onto a battery for storage 
    1. Lab Idea: RC Circuits with changing loads and capacitance values and analyzing outputs 
    2. Lab Idea: Apply knowledge of diodes in building bridge rectifier, build and compare one and three phase rectifiers 
  5. EGR 95S / ENRGYEGR Courses (minor website): How to apply wave energy in other areas of harvesting offshore? 

Potential Map of an Undergraduate Degree Path with an Energy Focus [7]

Project Mind Map

This was a way of visualizing our project that shows how we went through project ideas and narrowed our scope as we looked into different methods of a self-sustaining buoy project. We started with our interests of renewable energy, and branched out from there, coming up with our buoy idea. This platform of mind mapping allowed us to shade different topics in different colors, highlighting topics we are currently continuing with in colors and topics we thought of, however have dissipated in grey.  

Project Decomposition

Our project is made up of two main components, a buoy device with 5 subsystems, and a mechanical wave testing device for experimentation purposes. Schematics of these two systems are shown below.  

System Decomposition
Mechanical Wave Device

System Decomposition

Our buoy device is made up of five subsystems. Shown in green in the solar panel system, which is made up of the panels attached to the buoy’s exterior as well as the cabling to connect it with the energy storage system. In red is the ESS or energy storage system, which is made up of the circuitry components and battery that hold the energy created through both energy harvesting elements. The purple component is the onboard sensors, which are to be powered by the buoy in order to conduct offshore water testing. Shown in black is the exterior housing component, which will hold all generator and electrical elements and keep them protected from wave and water damage. And finally there is the wave energy generator subsystem shown in blue, which is made up of all of the elements that are used to harvest and convert the vertical wave motion into usable electrical energy. 

Mechanical Wave Device

The testing mechanism simulates simple wave patterns which causes generator outputs reflecting system operating under an idealized environment. It is going to be made up of two Arduino step motors with a joint connector attached to the wave generator to simulate motion in both the x and y direction, like waves in the ocean. We will be able to control this movement with a frequency input, correlating that input to that of shallow and transitional waves.

Bill of Materials

Bill of Materials for our Prototype

Above is our Bill of Materials used for this project. Besides our purchased items, we also had access to communal materials and testing equipment provided by the MEMS Garage Lab.

Project Breakdown

Below are our key steps to our project, broken into sub-categories based on their strength of difficulty. These steps combined allowed us to come to conclusions on the feasibility of a self-sustaining buoy while applying beginner, intermediate, and advanced level engineering principles along the way. 

Future Work

While we were able to accomplish progress towards many of our initial project goals throughout this semester, there are still many ways for this project idea to improve and grow. Here are some concepts/ideas that we were not able to implement, however feel they should be pursued to determine the full feasibility of a self-sustaining buoy for environmental testing equipment. 

As stated in our initial project decomposition, we wanted to create a device that could mechanically mimic wave patterns based on the projected frequencies of shallow and transitional waves in order to test our full wave energy generator prototype. While this device did not come to fruition during the semester timeline of this project, we still see this component as a valuable system to be built and added to this project. Creating a testing mechanism that mimics periodic wave patterns allows for conclusions to be drawn about the generator, specifically assessing its ability to withstand constant motion input and estimating its peak power output. By visually observing the generator with a wave input, we can see how the mechanical components will interact with each other over a longer period of time as well as at different amplitudes of wave input. In addition, this device will be important for initial testing phases of all the components together in order to relate input wave properties to output power generated.  

In our initial progress goals, we stated how we wanted to incorporate both solar and wave energy into one device. Due to moving this buoy to shallow to transitional waves, we thoughts that wave energy by itself might not be strong enough to completely power the environmental sensors off of the buoy and therefore, we wanted to keep some solar involved as previous large-scale buoys have found success using solar.  

When you look into adding solar to this system, many design constraints will be taken into consideration, especially in regards to the housing of the buoy, as you will need to run tests to determine your total panel wattage you desire and balance that with the total space you have available on your buoy. In addition, solar panels work more efficiently during peak sunlight hours [17] and when sunlight is hitting them at 90° angle [18], so those characteristics should also be considered in the final housing design mounting the panels.  

While we were able to conduct initial testing of the AC motor/generator and record power outputs over three small motors, further testing is needed to see how the wave energy generator affects the final power output. We would want to identify how the different mechanical components change the maximum power output that a specific AC motor could generate as this may cause us to redesign pieces of the generator and/or look for larger motors if the generator is able to push more energy through. This would allow for a larger power output into the Energy Storage System and would be better for the system as a whole, however further testing is needed before any of those design decisions could be improved upon.  

To conduct these experiments, a similar experimental set-up that was used for the initial motor testing would be used. 

With our project using available resources in our Garage Lab for prototyping, our main material source for the mechanical components of the generator were 3D printed PLA. Because of this, we had many tolerance issues between PLA-printed pieces and machined carbon-steel pieces, resulting in our final prototype not being perfectly aligned and not allowing for complete motion between each component. We think that future work should be done with experimenting with different materials for the different mechanical components within the generator, as this would potentially decrease tolerance issues and allow for a stronger overall system. In addition, for components like a flywheel that rely on being heavier in order to create a smoother system, a material like PLA does not have that ability as opposed to carbon steel or similar. While this might present future issues with buoyancy, that can be discussed further once the device reaches a stage of becoming waterproof and ready for water-testing.  

Who We Are?

David Chen


Hi, I’m David. I worked on designing a lot of the components used in this project, such as the gears, clutch, and the flywheel. My passion lies within realms of mechanical design and hydro-electric power generation. Check out my link here if you like to learn more about me.

Mallory Poff


Hello everyone! My renewable energy interest lies in the solar energy sector as well as sustainability as a whole in renewable energy practices. Through this project, I am excited to expand upon my mechanical and prototyping skills as well as work on a project outside of my comfort zone. If you want to learn more about me, click here for my personal page!


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