Some pretty famous business ventures began with two guys working out of a garage: Hewlett-Packard, Apple … even the Car Talk radio show, if you want to stretch it a bit. Engineers Alex Hagmüller and Max Ginsburg hope to add their company - AquaHarmonics - to the list. The duo is off to a good start, as they just won the US Department of Energy's 2016 Wave Energy Prize. Of the ninety-two teams that entered the competition, nine made it to the final round. Three walked away with a cash award, with AquaHarmonics taking home the gold. The $1.5M award will allow Hagmüller and Ginsburg to scale up their wave energy harvesting device in hopes of making it a commercially viable source of renewable energy.
The AquaHarmonics wave energy converter is a point absorber that floats on the ocean surface while being tethered to the seafloor. Inside the buoy is a winch that acts as both a motor and a generator.
I asked Alex Hagmüller for more details about their prize-winning device. He was eager to share some information.
TL: What type of technology converts wave motion into electricity?
AH: The device is a point absorber style wave energy device, much like any typical buoy. Inside the buoy is Power Take Off (PTO) that essentially consists of an "over glorified winch". The winch has a motor/generator connected to the shaft, and its line end is connected to the sea floor. When the wave pushes the buoy up, power is extracted. On the fall of the wave, a clever control system activates the generator as a motor and reels up the line, until the next wave occurs.
TL: What is the output power of the small-scale prototype?
AH: The small scale prototype maximum peak output is around 800 watts, though this is in a storm condition, and this is instantaneous not average output.
TL: To what level can it be scaled up?
AH: The device tested is 1/20th scale, and our plan is to work on the design of a 1/4 scale device. The 1/20th scale device is approx. 2.5ft in diameter and at full scale the device would be around a 50-foot diameter. As far as power output at full scale, we are still awaiting all the data from testing, so I cannot speak accurately on that yet.
TL: What price range are you shooting for ($/kW)?
AH: This is a difficult one to pin down for wave energy. For the wave energy prize, a metric was developed called the "ACE" metric. more here:
https://waveenergyprize.wordpress.com/2016/08/18/how-does-the-wave-energy-prize-calculate-ace/
https://waveenergyprize.wordpress.com/tag/representative-structural-thickness/
"The Wave Energy Prize has determined that the ACE value is 1.5 meters per million dollars (1.5m/$1M) in typical deep water locations on the West Coast of the United States. At the final gate, testing at 1/20th scale, WECs must achieve a threshold of 3m/$1M to be eligible to be considered for winning a monetary prize"
Therefore, the state of the art is not given a $/kW value for low technology readiness levels-it wouldn't be accurate. What I can say is that our device per the Wave Energy Prize beat the state of the art by a factor of around 4.9, so 4.9 times cheaper than current state of the art technology based on the scope of the wave energy prize.Our final score was 7.4m capture width per million dollars capital investment.
TL: Are there certain locations that lend themselves well to your product?
AH: West coast conditions have good energy flux/density and would be the best for cost effectiveness, however, they may be not the best places to do initial testing. That is to be determined.
TL: What advantages does your product have over other wave power devices?
AH: Our device is simple and robust, as well as efficient, over current wave energy devices. There are very few moving parts and the control system allows the device to actively input power back into the system at the right time in the waves so that greater power can be extracted over just passively damping the waves. This is what is known as "active control" or "reactive power" in the control world of wave energy devices.
Our device without a control system suffers from the same inefficiencies as any point absorber would if it were just passively damping the waves. This is due to the fact that the natural or resonant frequency of the device is higher than that of the waves that it is operating in. If the device can be tricked into resonance, then greater power can be extracted. Going back to the physics of a simple harmonic oscillator, the knobs you have to work with are mass, spring rate, and damping. Damping does not do much to change the natural frequency of the device, you don't want to make the device excessively heavy so mass is fixed, and therefore spring rate is all you have to tune. We tune this value dependent on the wave state to achieve maximum power output.
The official Wave Energy Prize page has more information about the other teams in the competition. To learn about different kinds of wave energy devices, check out this article.
Images courtesy of AquaHarmonics
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