Dean Kamen calls his private island off the coast of Connecticut North Dumpling Island or the Dumplonian Empire. Now that the Coast Guard has switched the local lighthouse to solar power and has cut the power they were feeding the island via submarine cable, Kamen has decided to take his tiny empire off the grid:
But Kamen is determined to use his North Dumpling empire to show that zero-net energy is not only possible now but that it will be very appealing in the future. He has resolved to live off the renewables on the island: a wind turbine and three monster arrays of solar panels, plus Kamen’s beefed-up version of the Stirling engine. It all adds up to a peak generation capacity of just under 25 kilowatts.To coordinate the different sources, Kamen designed an intelligent system that knows, down to an individual solar panel or light source, how much energy is being produced and consumed on the island and, based on that information, negotiates the relationship between the two in real time. It is this system that he monitors and controls from his basement command center.
Kamen has many strategies to minimize his energy use, but the big breakthrough is the island’s lighting. With the help of his friend Fritz Morgan, chief technology officer at Philips Color Kinetics, in Burlington, Mass., Kamen has replaced every bulb and fixture on his island with light-emitting diodes. That switch cut the power he needed to light his lair by 50 to 70 percent.
Here’s how that peak generation capacity breaks down:
The island’s four arrays of solar panels have a combined peak output of 12.2 kW. A 10-kW wind turbine that looks like a cartoon missile, made by Bergey Windpower Co., perches on a lattice tower 25 meters above the island. The Stirling engine in the basement can contribute another 2 kW if necessary.
The islands high-tech LED lighting would probably cost an ordinary consumer $100,000 — but it doesn’t use much electricity:
An average household dedicates approximately 20 percent of its energy budget to lighting. Here’s how that 20 percent can be manipulated by replacing incandescents with LED lighting. A traditional 60-watt incandescent bulb lasts about 1500 hours and has only a 2.5 percent efficiency because it wastes most of its energy as heat. Its brightness rating is about 16 lumens per watt, which is a measure of how much luminosity your bulb produces for every watt it eats up. A compact fluorescent lightbulb, or CFL, does much better: A 13- to 15-W bulb has about an 11 percent efficiency, emitting around 75 lm/W. The less-wasteful CFL lasts about 10 times as long as an incandescent (a little under two years).On the downside, CFL bulbs contain mercury, which means they must be treated and disposed of as hazardous waste. Now consider LEDs. The best of these can pump out a whopping 150 lm/W (from the ”raw” chips, not the integrated lamp or system) and function at about 22 percent efficiency. With typical use, that’s at least 11 years without changing a bulb.
What happens when the island gets neither sun nor wind?
That’s when Kamen’s Stirling engine kicks in. Kamen’s reimagining of the 193-year old design is about half the size of a refrigerator, and its job is to convert heat energy into work.A Stirling engine contains a sealed cylinder, one end hot, the other cool, with a sliding piston that moves the gas back and forth. On the hot side, the gas expands and exerts pressure on a piston; on the cool side, it contracts. Unlike a gasoline or diesel engine, Kamen’s Stirling is an external combustion device. The fuel that heats the gas inside the engine never touches the engine itself. Unlike spark-ignition or compression-ignition vehicle engines, a Stirling doesn’t require that the fuel be mixed with air in a particular ratio. It can run on pretty much any liquid or gas fuel, including diesel, methane, gasoline, or olive oil. Got cow manure? That’ll work, too. The design is ideal in theory, converting fuel to heat and heat energy into mechanical energy, but one problem remains: The machine generates electricity at an efficiency of only 20 percent. The rest is wasted as heat.
But Kamen says the concept of ”waste heat” changes with context. In winter that heat can be diverted to the house, the clothes drier, and the island’s domestic water supply. ”Think of it as a furnace that’s also making electricity,” Kamen explains. Harness the heat from the Stirling while it generates electricity and you can get an efficiency darn near 100 percent, he says.
His own machine typically produces 1 kilowatt of electricity, enough to power 128 LED lights, each equivalent to a 60-W incandescent. The engine sits in a far corner of the basement. At the moment, it’s inactive because the solar panels are generating a steady, incoming stream of 2 kW.
The Teletrol system runs an iron-fisted dictatorship over all of these processes. If there’s any excess power, the system uses it to feed the vast bank of custom batteries lining an entire wall of the basement, 24 big red plastic containers that resemble gasoline canisters. These batteries weigh 144 kilograms apiece, cost between $1285 and $2000 a pop, and must have their chemistry checked periodically with a hydrometer.They’re also truly and deeply rechargeable. They are lead-acid batteries optimized for what’s called a deep discharge cycle, meaning that their charge can be repeatedly and substantially depleted by 80 or 85 percent. For contrast, most battery chemistries typically tolerate at most 5 to 10 percent depletion on a regular basis. The batteries were made by a company called Surrette Battery Co., headquartered in Springhill, N.S., Canada, and Salem, Mass., which specializes in cells optimized for solar and wind-power charging. Each battery comes with a 10-year warranty.
”Every once in a while, we know we’re going to have to depend on these batteries to run the entire island,” Kamen says. They can power the island for three days continuously in the unlikely case that all sources of energy simultaneously go off-line.
Notice how the waste heat from incandescent bulbs is waste, while the waste heat from his Stirling engine makes it a furnace that’s also making electricity. Hmm…