Off-grid renewable energy systems need the ability to store energy so that it’s available when the sun isn’t shining and the wind isn’t blowing. On a residential scale, lead-acid batteries are usually the storage medium of choice. But batteries are toxic, explosive, and they lose their capacity with time and deep discharge cycles. Inventor Bill Gray thinks that his innovative flywheel design - the VEry Large Kinetic Energy Storage System (Velkess) - will supplant batteries in the renewable energy sector. Gray has applied for a patent on the design.
Image: Kickstarter
One common problem with existing flywheel designs is that they use expensive rigid materials to reduce wobble, vibrations, and other stray mechanical forces. Instead of fighting those stray forces, Velkess uses flexible materials to redirect them. Gray says, “By working cooperatively with these natural rotor dynamics we gain excellent control of the rotor system without having to crush out its irregularities. Because of this we can use much less expensive materials and don't need nearly as much precision as rigid designs.”
Flywheels lose a lot of energy due to air resistance and friction. The Velkess flywheel operates in a vacuum-sealed chamber with magnetic bearings to reduce wind drag and friction. It’s made of inexpensive, recyclable, non-toxic materials, reducing both cost and environmental impact.
Video: Kickstarter
Gray claims that the Velkess will be twice as efficient as batteries at half the cost per kWh, and last three to five times longer. His current prototype stores 0.5 kWh and can deliver up to 2 kW. He hopes to build a 15 kWh unit to develop for the actual market. The stumbling block is creating a magnetic bearing capable of suspending a 750 pound flywheel rotor. Gray states, "The magnets to float 25 lbs are easy to get on the internet and easy to work with by hand. Magnets strong enough to float 750 lbs are a different story. They need to be custom made and are too powerful to safely work by hand."
Velkess flywheels can be connected in parallel to increase storage capacity, making this design a potential player in the grid-level storage market. In addition, flywheels can be used in electric vehicles. Regenerative braking converts mechanical energy (the car’s motion) into electrical energy. Ideally that energy is be used to recharge the car’s batteries, but the energy comes in short high-intensity bursts. Batteries can’t absorb a charge that quickly, but flywheels can. (Supercapacitors can also.) On the flip side, when a car needs a quick burst of energy for acceleration, batteries can’t provide it efficiently. Again, flywheels and supercapacitors are better for this application. That’s not to say that supercaps and flywheels will replace batteries in electric vehicles. Instead, they serve a complementary role. Batteries provide slow-and-steady energy, while flywheels and supercaps give quick bursts when needed.
Are flywheels the future of energy storage? It might be worth taking one for a spin.