A pit full of cow dung may not come to mind when thinking about electricity, but to Dean Kamen, engineer, entrepreneur and famed inventor of the Segway, it does.
Kamen is working in concert with Think Global to develop a Stirling engine for the Think City car, which relies on heat for fuel. Kamen has been developing on the nearly 200-year-old Stirling technology as a method for generating electricity, charging batteries and powering these cars.
“We ran for 24 weeks around the clock in Bangladesh,” says Kamen, who has taken his Stirling engine to the developing world where there is little or no infrastructure. “We electrified two villages on nothing but a pit full of cow dung evolving methane gas that we were capturing to keep the hot end of this engine hot.”
The Stirling engine is different from a typical engine in that no fuel goes into the engine. It uses a process of cycling hot and cold air through two chambers which in turn drive pistons and generate a charge. Since the only energy required to drive the engine is heat, it can come from virtually any source.
Compared to a combustion engine, the Stirling engine lacks horsepower and a high energy density and it isn’t cost efficient. The engine is, however, very power efficient especially considering it can charge using wasted heat from other appliances or spatial environments. Also, the engine isn’t what directly drives the car, it’s the electric motor. “Your entire performance envelope in terms of acceleration and all that is determined by the batteries, the motor control and the motor,” says Kamen.
The advantage of the Stirling engine in use with the Think City car is that it can recharge itself while not in use. “You put it in these cars and let it trickle charge the battery all day long,” says Kamen. “You’re not depending on it for peak power.”
Kamen’s design of the Stirling engine, which uses helium as its principle gas, has incorporated some major innovations. It is virtually sealed with nothing penetrating the engine, it doesn’t have a drive shaft and, with the exception of the bearings that sit on the generator, the rest have all been removed, “which is a really big deal,” says Kamen. The heat and energy lost to the friction of the bearings accounted for too much of the net power output that it made more sense to remove them. “We are finding ways to run a hermetically sealed isolation chamber inside the engines so what few bearings we have will run completely immersed in pressurized oil,” says Kamen, “so we should get an extraordinarily long life.”
The Think City car incorporated with Kamen’s Stirling engine is still in development but, according to Kamen, “we’d like to have in the next couple of months a couple of running machines out doing concept demonstrations.”
Another of Kamen’s projects, which directly relates to his work with the Stirling engine, is a remotely operated energy management and control system called Teletrol, which can “help people have control with power consumption and energy conservation in their homes,” he says.
Kamen’s vision of Teletrol when used with a Stirling engine, like the one to be available in the Think City car, is that power can be created by the Sterling engine using excess heat from the house. That electricity generated can then be used by the house’s appliances before drawing expensive power from the grid.
“So you put the Teletrol system in the house and you put the car in the house, it doesn’t matter where it sits anymore; you plug the two together and the system takes over,” says Kamen. “It looks at what’s going on, on the grid, it looks what’s going on in the load demand of the house, it looks at what’s going on in the load capacity in needs of the car and it can run power from anyplace to anyplace else.”
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