The time is right to revisit the issue, Sure Power president and chief executive William Cratty believes. With the spread of e-commerce, even server vendors — which in the past have often allowed themselves a PC-influenced, casual attitude toward reliability — are starting to take near-continuous availability seriously, Cratty noted. But that has created something of a paradox for system managers.

"Vendors like Hewlett-Packard are quoting five-nines availability for their servers," Cratty said, "but then system managers are having to provide power to these systems from uninterruptible supplies that have only four-nines availability. Given the massive cost [incurred when] a credit-card processing center or an e-commerce site goes down even momentarily, there needed to be an improvement in availability for the power systems."

The primary technology for large-scale uninterruptible power today is a complex hybrid system, Cratty said. Typically, a computer center will take high-voltage power from the local utility and condition it through a power converter. The converter is capable of voltage regulation, covering small transients. But for sags or dropouts of longer than a few milliseconds, the system must have a backup supply. Typically, that backup system is a room full of lead-acid batteries.

The batteries, in turn, can only meet the needs of the center for a few minutes. So when the system switches to battery power, it must also start a diesel generator that will switch in to begin driving a generator.

The problem with such an approach, according to Cratty, is that each element in the system beyond the conditioning hardware has its own reliability shortcomings. Lead-acid batteries are notoriously cranky and pose environmental problems. The switching gear, diesel motor and starting equipment and generator all have their own problems as well.

Sure Power's approach, in contrast, does not depend primarily on the ac mains for power. Instead, it uses fuel cells designed by United Technologies subsidiary ONSI Corp. for space applications.

In deep-space use, the fuel cell is fed streams of pure oxygen and hydrogen gases, which react in the presence of an alkaloid electrolyte to generate water, heat and dc. But in a terrestrial computer center, where pure hydrogen would be impractical, Sure Power uses another approach.

Vapor and heat

The company collects the water vapor and some of the waste heat from the fuel cell and then uses that steam to treat a stream of natural gas, Cratty explained. In the presence of 1,500F water vapor, the methane breaks down into carbon dioxide and hydrogen, which can then be sent into the fuel cell.

Oxygen for the cell is supplied in the form of ordinary air. Such use would contaminate and damage a conventional cell, so Sure Power uses a phosphoric acid electrolyte in place of the alkaloid. The cells have an operating life of about seven years when fed air and the processed hydrogen, according to Cratty.

One such cell can supply about 200 kW of continuous power with almost no moving parts and no connection to the public power grid, freeing the power supply from external interruptions. But the fuel cells are by nature constant-current devices, unable to deal with intermittent shorts, motor-start transients and the like.

To provide the stiffness for such transients, Sure Power uses the current from the fuel cells to drive a high-efficiency inverter, which in turn drives a motor-generator set that provides power to the load. For additional stability, the company uses a 16.5-Mjoule flywheel.

The First National of Omaha system is designed for 800-kW output, or about twice the bank's average load. Since the fuel cells operate best at full capacity, the bank sells power back to the local utility when it is not drawing the full 800 kW. In addition, the installation generates sufficient heat to keep the sidewalks clear in the winter around First National's headquarters building.

The systems' cost at a given level of availability is lower than the cost of conventional battery/diesel-generator arrangements, Cratty said. Or, for about the same cost per kWh, the Sure Power system can provide a factor of hundreds or thousands improvement in availability.

But the approach is not immediately applicable to smaller power supplies, Cratty said. "There are other companies looking at fuel-cell approaches from about 1 kW on up," he said. "But cost-effective use of these things in automotive or home applications is probably still 10 to 15 years off."

For the time being, Sure Power will focus on making the power systems in server farms and mainframe clusters as available as the computing hardware.