Apple Designs a Wind Turbine That Stores Energy
Apple has invented a windmill. This particular design, however, tries to overcome one of the biggest problems with renewable energy: The lights go out when the sun doesn't shine or the wind doesn't blow. Therefore, Apple, which is very interested in wind and solar energy use in its datacenters, is trying to come up with a method to save some of that energy for later.
Here's the overview description:
“The disclosed embodiments provide a system that generates electricity. During operation, the system uses a set of rotating blades to convert rotational energy from a wind turbine into heat in a low-heat-capacity fluid. Next, the system selectively transfers the heat from the low-heat-capacity fluid to a working fluid. Finally, the system uses the transferred heat in the working fluid to generate electricity.”
This, therefore, is essentially a cogeneration wind turbine. When the wind blows and the turbine blades turn, the rotational energy is converted into electricity with the usual electrical generator used by most wind turbine systems. The added idea is to use some of that rotational energy to heat fluids, therefore storing the energy indefinitely. That heat is only converted to electricity when it's needed.
Here's how the system works:
The wind turbine turns a rotor shaft like a normal wind power system. But the rotor shaft is also connected by some combination of “a driveshaft a chain, a belt, and a set of gears” to a second set of blades, which are immersed in a low-heat-capacity fluid—such as an inert gas, nitrogen, ethanol, or mercury. When those blades spin, they heat the fluid, which is contained in an insulated structure to keep it hot.
When the extra electricity is needed, an insulating component is moved, and the heat is transferred through a thermally conductive component, such as a metal surface, a manifold, a conductive rod, or a radiator. An analogy might be opening a valve on an insulated water heater to allow the hot water to flow through a metal radiator, which warms the air in a room. But instead of air, the heat is transferred to a “working fluid” that has a low boiling point. When that fluid boils, the steam rotates another turbine that drives a secondary electric generator.
It's straightforward, if convoluted. The obvious difficulty is whether the wind will blow hard and strong enough to supply sufficient energy to both turn the primary generator and heat the fluid, and whether the fluid will remain hot long enough to keep the electricity flowing until the wind starts up again. Or at least to offset some of the downtime of the idle wind turbine blades.
But it shows that Apple is spending time thinking about how to improve the efficiency of wind generation--and to let others know that it got the idea of using fluid to store energy first.
The patent author is listed as Jean L. Lee, who also recently filed a patent for Apple that describes a computer input device that uses gestures such as tilting, brushing and tapping to control a computer's GUI.
The wind turbine patent, “On-Demand Generation of Electricity From Stored Wind Energy,” was filed on June 23, 2011, and published by the U.S. Patent and Trademark Office on December 27, 2012. It can be seen here.