Published on February 23rd, 2017 | by Tina Casey0
Proof Of Life: US Energy Agency Showcases One-Size-Fits-All Hydrokinetic Device
February 23rd, 2017 by Tina Casey
It looks like the US Department of Energy is still alive and kicking. The agency hasn’t slapped a new press release on its website since January 16, but its blog has sputtered into life again. The latest post, dated February 22, draws attention to the cutting edge ARPA-E Summit taking place in the DC area this week.
ARPA-E is the Energy Department’s funding office for game-changing technologies. The annual summit showcases “transformational energy technologies that could fundamentally change the way we generate, use, and store energy,” so let’s take a look and see what’s cooking.
One Hydrokinetic Energy Device To Rule Them All
The DOE blog highlighted three innovative technologies. The one that caught the eye of CleanTechnica comes under the category of hydrokinetic energy harvesting. That’s when you just use the force of an ambient current to put your device in motion, rather than relying on pressurized water as in conventional hydropower dams.
The implications for squeezing more domestic and local energy out of the US are alluring. Think of all the rivers, streams, canals, water and wastewater systems, and other water infrastructure in the US, and you can see the potentials. Wave and tidal devices also fall into this category.
Some of these devices are already in the demonstration phase in the US.
However, a problem has begun to emerge. Typically, hydrokinetic devices are closely tailored to individual sites.
That means high manufacturing costs, because economies of scale are limited. It also means you have to re-invent the wheel with each installation.
That’s where Brown University comes in. Under the name Leading Edge, researchers at the school have developed a hydrokinetic device that ditches the conventional rotary turbine design in favor of a modular system that is scalable and flexible.
Take It Away, Brown
The name Leading Edge refers to the winglike flaps or foils that distinguish the new design. Here’s the explainer from Brown:
Just as a wind turbine’s motion is driven by the constant flow of air, an oncoming flow of water drives the motion of the hydrofoil which in turns powers a generator that converts it to electricity…rather than a rotation motion commonly seen in wind turbines the foil oscillates in heave (up/down motion) and pitch (rotation about the mid-chord).
That’s just the overview. The design is quite a bit more complicated, because it allows for the pitch of the foil to change at the top and bottom of each stroke, thus eliminating wasted motion:
As the foil moves upward it has a positive angle of attack relative to the freestream flow, and thus a positive lift force, creating positive power. At the top of the stroke, the foil reverses its pitch to a negative angle of attack which provides a downward force on the foil, coupled with a downwards velocity vector also yielding positive power.
Here’s a schematic version of the device:
The result of optimizing the entire set of kinetics is a mechanical efficiency of about 30%, according to Brown.
As described by the Brown team, the long, slender foils can be deployed safely in relatively shallow waters.
That’s a big plus for the emerging trend of local, metro area energy harvesting. Typically, cities import power — lots of it. The US is loaded with coastal and riverside cities, where tidal and river environments could be potential locations for devices designed with relatively shallow water in mind.
The Brown team also notes some additional advantages:
…the foils can be placed close to one another, or even share the same supporting structure, which saves in maintenance and installation costs. The motion of the foils is also slow relative to a large rotary turbines, which means lower relative velocities and less of an environmental footprint on the local marine life.
You can find many more details in Google Patents.
Images (screenshots): via Leading Edge.