Engineering a sea change in ocean wave energy harvesting

C-Power autonomous offshore power systems (AOPS) capture mechanical wave energy and convert it into usable power for a wide range of oceanic applications such as offshore oil and gas exploration and production, offshore carbon sequestration, oceanographic research, aquaculture and homeland defense.

Harvesting ocean energy on the kilowatt scale

Founded in 2005, C-Power has evolved its focus as its expertise in the bourgeoning field of oceanic energy harvesting has grown (Figure 1). While other companies pursue large, megawatt systems, C-Power focuses on remote, kilowatt-scale power for offshore data communications networks, initially through a DARPA project called Wave Energy Buoy Systems (WEBS).

Figure 1:While much attention has been paid to advancements in solar and wind power technology, C-Power is a pioneer in efficiently harnessing ocean wave energy to enable new forms of offshore applications including oil and gas exploration and production, offshore carbon sequestration, oceanographic research, aquaculture and homeland defence.

Through the WEBS project, C-Power discovered a nascent opportunity in the form of localized power generation for underwater vehicles, subsea operating equipment and open-ocean sensors used to collect environmental data. Previously, power for these applications was generated using expensive, cumbersome, non-rechargeable onboard batteries or subsea electric tethers fed from a ship or diesel generator. With the development of AOPS, C-Power opened the door to unimagined new applications by supplying an autonomous, environmentally friendly, ocean-borne power source capable of doubling as a communications conduit.

SeaRAY enhances power efficiency and data communication

The latest AOPS platform, known as the SeaRAY, is key to the near-term focus of C-Power to produce power systems that generate 10W to 1MW from ocean waves. To achieve its goals at the lower end of the power spectrum, C-Power created a SeaRAY AOPS design with a high power-to-weight ratio using power conversion technology from Vicor Corporation.

The small design footprint enhances mobility and commercial viability, making SeaRAY easier to deliver and set up, saving tens of thousands of dollars in daily operating costs.

“We really needed wide-range DC-DC, something that we could control and regulate as we’re converting pulsed ocean wave power into a semi-stable DC bus,” said Joe Prudell, a C-Power senior R&D electrical engineer. “This is extremely challenging. Being able to do that at various power levels using Vicor’s power modules really is an advantage.”

The SeaRAY design also makes autonomous, remote data communications possible by transmitting what happens in the ocean to the cloud in real time. Previously, marine data-gathering systems have been limited in the breadth and frequency of data collection. Using cellular networks and satellite communications to pass data in real-time between the cloud and the SeaRAY allows more and richer data to be collected and delivered more often (Figure 2).

Figure 2: The SeaRAY design makes remote, autonomous data communications possible by sending information from the ocean to the cloud. Using cellular networks and satellite communications to pass data in real-time between the cloud and the SeaRAY AOPS allows more and richer data to be collected and delivered more often.

Harvesting energy from a constantly shifting power source

The key power design challenge for C-Power was to reconcile complex ocean wave energy properties with the demanding power conversion requirements of the SeaRAY. This included an ultra-wide 30:1 input range, which reflects the unpredictable nature of ocean waves. The Vicor Power Systems design team delivered a system capable of converting power with high efficiency and charging energy storage devices. The unit is also capable of accepting external control signals from the C-Power system to match precise power conversion needs in real time.

“The ability to convert a very nasty power profile into a cost-effective, practical solution, and then condition that power and turn it into usable energy for a wide range of mobile and static payloads, is really on the leading edge,” said C-Power CEO Reenst Lesemann. “There’s nobody else that’s been able to do that yet.”

The scalable power design of the SeaRAY uses Vicor BCM fixed-ratio bus converters and PRM regulator modules with complex multistage discrete converters to efficiently convert turbulent, unpredictable wave energy and provide controlled power. This enabled C-Power to increase the SeaRAY design’s conversion efficiency from about 50 percent to a range of 85 to 94 percent.

Figure 3: SeaRAY uses the Vicor BCM fixed-ratio bus converter and PRM regulator modules with complex multistage discrete converters to efficiently convert wave energy and provide controlled power. Using power modules Vicor developed a power delivery network that improved the SeaRAY conversion efficiency from 50% to over 90%.

The use of stable, wide-input Vicor DC-DC converters provided C-Power much-needed control as the SeaRAY converts pulsed ocean wave power into a varying DC bus while still producing a constant current at various power levels. In addition, the power conversion topologies used in Vicor modules help to minimize electromagnetic interference and noise onboard the SeaRAY that could otherwise compromise sensor measurement accuracy.

“There are plenty of companies trying to capture and convert wave energy, but it’s another thing to do something in a small, compact form factor and still satisfy what customers need from an operational and logistics perspective,” Lesemann said. “That’s where we, with Vicor’s assistance, have been able to stick our chins out so much further than everyone else.”