In order to lower the business risk associated with generating power from winds blowing hundreds of meters up in the sky, startup Makani Power needs to accomplish at least one goal: launch, land and fly its kite-like wind turbines via computers. Makani CEO Corwin Hardham tells us the four-year-old company, which has raised at least $15 million from Google.org, plans to use a recently awarded, $3 million grant from the Department of Energy to automate and digitize the process.
While many investors may still consider four-year-old Makani’s technology (like most startups) a risky bet today, Hardham tells us in an interview that he believes “we may see a very strong shift in that very soon.” Putting computers in charge of the high-altitude process is “quite doable,” says Hardham, “It’s just that no one’s done it before.”
Makani’s recent DOE grant came from the highly competitive Advanced Research Projects-Energy, or ARPA-E program, which can allow a company to expand its focus or get started on research that would otherwise take a back seat to work on technology that’s closer to commercialization. Chosen from among more than 5,000 applicants seeking ARPA-E funds this year, Makani’s grant is essentially a vote of confidence from Uncle Sam that kites up in the sky could one day economically produce clean power.
Wind Way Up High
Makani’s Airborne Wind Turbine, or AWT, involves a long tether that conducts electricity (for a utility-scale, 1-megawatt system, the tether would be nearly 600 meters long). In the 10-kilowatt prototype system, one end of the tether is attached to a tower about seven meters above the ground, while the full-scale system would have the tether attached directly to the ground, with a 20-meter tall tower being used only for launch and landing.
At the other end, wings are attached to the tether. Turbines are mounted to the wing, which Hardham said must be able to hover in place like a helicopter or fly at high speeds across the wind at high altitudes (where wind is stronger and more consistent than it is at the level of a typical wind farm). In the process, the system captures wind energy and transmits it to the ground through the tether.
Overall, Makani claims the system can deliver twice as much capacity factor (a measure of productivity) with 20 percent less mass than conventional wind turbines. Conventional turbines don’t typically produce power 100 percent of the time, and according to the trade group the American Wind Energy Association, a wind turbine at a typical location in the Midwestern U.S. will run about 65-90 percent of the time, which means a lower capacity factor. According to Hardham, the Makani system can deliver a capacity factor of 60 percent where a typical turbine would deliver only 30 percent.
Makani also says its design can produce electricity at a lower cost than conventional wind turbines. The system, Hardham explained, performs better in light wind conditions than a conventional turbine, and can therefore generate energy more cost-effectively in many more locations than today’s state-of-the-art systems.
Finally, Makani’s system is especially well-suited for deployment off-shore. A conventional wind turbine at sea needs a very large keel to keep it from tipping over. But with Makani’s design, tension goes right down the cable, and it’s expressed into anchors under water. When it comes to permitting for renewable energy projects, said Hardham, “NIMBY-ism is causing a lot of trouble right now.” Putting the installations “out of sight, out of mind,” with a system like Makani’s could be one way to work around that roadblock.
Automate It, Scale It
The company still needs to demonstrate that the whole thing can operate autonomously. The goal of the ARPA-E project is to demonstrate that the device can launch, generate electricity and land under complete computer control.
According to Hardham, Makani’s “first set of technical challenges” center on control and aerodynamics for the full range of flight modes. The company uses a numerical model of the entire system to predict the kite’s position. Based on expectations set in 2007, said Hardham, the Makani team has been surprised by how accurate this predictive control (under development since 2008) has become. Currently the company is able to predict with meter-level precision where the kite will be seconds into the future, and it’s still working to improve that precision.
In addition to working on the DOE-backed prototype, Makani is also starting to develop components for a 1-megawatt system (without government funds). To meet that megawatt goal, the company is refining the design of its tether, which has a long list of seemingly conflicting demands, including carrying a large structural load, being extremely aerodynamic, being lightweight, having a tiny diameter, and being able to conduct large amounts of electricity.
Despite the DOE grant, and Google’s prior investment, the company is currently looking to raise additional financing to develop the megawatt system. Hardham said Makani has found positive reception among prospective investors so far.
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Image courtesy of Makani Power.