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ECD-Ovonics Tests Solid Storage Technology in Toyota Prius Hybrid

Rochester Hills, MICH. -- Driving the ECD-Ovonics' hydrogen-fueled Toyota Prius hybrid, one thing becomes quite obvious: there is virtually no performance difference from the gasoline version, and that's exactly what ECD-Ovonics is shooting for.

Less obvious is the company's solid hydrogen storage system, which currently yields a nearly 200-mile driving range while taking up no more space than the original Prius gasoline tank. Of course, 200 miles is a far cry from the Prius' 600-plus range, but it's a start. In fact, ECD-Ovonics feels so strongly about the future potential of solid storage that the company recently announced its intention to build a dedicated R&D facility in Akron, Ohio.
ECD-Ovonics 2004 Toyota Prius hybrid can run nearly 200 miles on a single hydrogen fill-up.

The blue-on-white hydrogen hybrid graphics draw attention to mechanical changes underneath: a solid hydrogen storage system, retrofitted turbocharger, gaseous fuel delivery system, plus modified ignition and fuel metering software. But despite all the in-your-face advertising - chosen to focus attention on the vehicle during its participation in an upcoming California Highway event - this vehicle is all about transparency, at least in the eyes of future consumers.

Speaking of his company's goals for solid storage, ECD-Ovonics Chairman and CEO, Bob Stempel, explains that a hydrogen-powered vehicle doesn't need the remarkable range of the gasoline-fueled Prius, it needs just enough range to make it acceptable to the public at large.

"If we can get to a 300-mile range, I think we'll be quite competitive with today's kind of vehicle. If you're used to going about 250 to 300 miles between fill-ups, as long as we can get that for you, I think the customer will understand that," says Stempel.

Efficiency Similar to a Fuel Cell

Addressing the other advantages of a hydrogen-powered hybrid, the former General Motors chairman explains that the vehicle's efficiency is close to that of a fuel cell vehicle. "Surprisingly we were able to match the fuel-cell economy pretty good, because of the hybrid technology and the fact that we're not running the engine all of the time."

The vehicle's retrofitted turbocharger boosts the horsepower of the internal combustion engine (ICE) back up to gasoline levels, with the slight loss in low-end power more than made up for by the hybrid's torquey traction motor. Acceleration with the hydrogen-powered Prius is indistinguishable from the standard gasoline-powered model.

Emissions is also an area where the hydrogen ICE improves on the already ultra clean gasoline hybrid. By employing hydrogen as a fuel, the ECD-Ovonics Prius produces less hydrocarbon, carbon monoxide and carbon dioxide emissions than its gasoline counterpart. In fact, carbon dioxide output - due entirely to the burning of trace amounts of engine lubricants - is reduced to less than 1.5 percent of that produced by the gasoline version.

Of course, the ECD-Ovonic Prius is really a test bed for the company's solid hydrogen storage system, which uses a proprietary mix of powdered metals - nearly a dozen different materials - an internal heat exchanger, a small electric heater (for cold starts), plus an arrangement of internal baffles to keep the metal powder distributed and to avoid any caking within the tank. The baffles are needed not only for improved powder distribution throughout the tank, but also to help transfer heat, mainly because the metal hydride acts more like an insulator.

Jeff Schmidt prepares to fill the hydrogen-powered Prius - the eight-minute filling time is still lengthy.

Dynetek produces the tanks for ECD-Ovonics, using one of their carbon-fiber-wound, aluminum-lined CNG tanks as a starting point. ECD-Ovonics sends their heat exchanger and baffle components to Dynetek for incorporation into the 33-liter tank. "We're experimenting with different types of internal baffles - including an aluminum honeycomb material - to determine position, help the charging time, the density and charging pressures," says Jeff Schmidt, ECD-Ovonics' system engineer working on the project.

Charging pressure for the ECD-Ovonics system is 1500 psi, which allows for complete saturation of the metal hydride powder. The Dynetek tanks are rated at 3600 psi. Once the initial over-pressure is removed, the tank pressure drops relatively quickly to 300-500 psi during vehicle operation, which remains more or less constant until the tank is depleted.

Filling-time Still a Bogey

A filling time of eight minutes (0.4 kg/min) presents a current challenge when compared to the Department of Energy (DOE) target for 2007 of 0.5 kilograms per minute. ECD-Ovonics is shooting for five minutes, which would get them closer to the DOE's minimum, however they want to accomplish it in the most cost-effective manner.

Schmitt explains that the filling time could be reduced by increasing the fill pressure or chilling the cooling water - the ECD-Ovonics system throws off 11,700 BTUs for every kilogram of charge - however either approach would add cost upstream to the delivery system. "We want to keep it cost-effective and consumer-friendly," says Schmidt, explaining that competitive 5000-psi compressed systems yield a faster fill rate, but at additional cost for the 6,000-psi delivery pressure and the potential for high-pressure leaks.

On the other hand, cycle life of the solid storage system is not a concern, according to Schmidt. "We've cycled canisters over 500 cycles and have no degradation of the powder, or very minimal at most, so the capacity of the tank would not be changed," he states.

The two solid storage tanks are mounted in place of the Prius' gasoline fuel tank below the rear seat area. They sit in exactly the same position as two similar-sized Quantum-made 5,000-psi gaseous tanks, which were used during earlier testing. To date, the solid storage Prius has achieved 198.6 miles on a single charge of 3.3 kilograms of hydrogen, far outstripping the approximately 80-mile range from compressed hydrogen storage.

Twin 33-liter Dynetek storage tanks each house a proprietary heat exchanger, baffle system and metal hydride powder; the red hoses transfer water to the heat exchangers.

Pursuing Increased Storage Capacity

Results have been good, but the ECD-Ovonics wants more. When asked if added efficiencies in the internal heat exchanger and baffling could allow for smaller components and increased metal hydride volume, Stempel says that the internals will not change any time soon. All improvements will come from advances in the metal hydride powder.

"What we're working on is to improve the hydride's ability to hold hydrogen," said Stempel. "We don't want to make the tank(s) bigger - we want to try and hold the mass - but we want to get some more hydrogen in there."

Stempel's concern for not increasing the system's mass is quite valid. The weight of an ECD-Ovonics' solid storage system is roughly 2.5 times that of a similar capacity 5000-psi storage system, however on a volumetric basis the compressed system requires 2.5 times more space to hold the same amount of hydrogen. At this point, improvements in the metal hydride alloy is key to the company's success.

ECD-Ovonics asserts that its metal hydride powder will perform better than other solid storage mediums, such as chemical hydrides like sodium alanate. According to ECD-Ovonic's Dr. Ben Chao, titanium-doped sodium alanate has several issue that are not a concern with his company's system. "Soduim alanate storage suffers poor cycle stability because of the titanium segregation from the matrix," says Chao, adding that there are also material compatibility issues between that kind of chemical hydride and the storage tank liner.

"The volumetric density of sodium alanate is worse than the Ovonic metal hydride alloys," explains Chao. "Typically, Ovonic metal hydride alloy has a density of 6.4 grams per cubic, while sodium alanate is 1.25 grams per cubic centimeter." According to Chao, a lower density material normally infers a lower volumetric density at the system level, translating to a more bulky storage system, which is a major problem for a vehicle-based storage system.

"Sodium alanate needs more than 120 degrees Celsius to start the desorption of hydrogen," adds Chao, saying that the typical operating temperature of an ICE or fuel cell would not be sufficient to release hydrogen from a sodium alanate system, yet is enough for the ECD-Ovonics system to function.

Greater Safety Margin

From a safety standpoint, ECD-Ovonics believes that 10,000 psi is too much pressure for automotive applications and that solid storage is the safer route. "We're the only company that has compliance with the Department of Transportation," says Stempel. "We can ship a charged cylinder anywhere in the United States and one of the reasons is that hydrogen is happier in the powder than it is outside."

ECD-Ovonics Chariman and CEO, Bob Stempel, believes solid storage is the best and safest route for automotive hydrogen storage.

In fact, according to Stempel, there are some competitive hydrides that are so good at holding hydrogen, they don't want to give it up. "It has to be a two-way system," he reminds, "the invention here is to develop an alloy of the various elements that will not only retain the hydrogen, but when I want to back, it will let me have it."

ECD-Ovonics' expanded work in the area of solid storage has necessitated a move away from their current location, which is why the company wants to establish a solid storage R&D facility in Akron, Ohio.

"What we're doing down in Akron, as a first step, is a facility where we can test bigger tanks and high-volume tanks," said Stempel, adding "Zoning was very favorable, which is an issue here (in Michigan)."

"We can do the small cylinder testing (in Rochester Hills), but because of regulations, we can't go any bigger. Akron has a former industrial facility down there that they can zone for hydrogen - and they're willing to do that - plus good electric power and a good water supply. It's a great way to start the program down there," Stempel adds.

As for other solid storage opportunities, ECD-Ovonics is canvassing the globe. "We have a project with India," says Stempel. "Scooters are used by everybody for transportation right on up to the middle class. The problem is they're smokey and pollute like hell. They are very interested in running on hydrogen, because essentially the tailpipe is clean; there are virtually no emissions." What we have is one of (our) canisters under the seat."

The smaller EDC-Ovonics tanks used for scooters and uninterruptible power supplies (UPS) do not employ an internal heat exchanger, but rely on heat from the ICE or fuel cell to desorb the hydrogen. According to Chao, "Waste heat from the fuel cell air exhaust to the portable canister surface is sufficient to ensure the performance for UPS applications. Waste (heat) from the engine exhaust is utilized for the scooter application."

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