Outside plant communications sites span a number of agencies and markets, but all have the common need for reliable power in order to enable critical equipment to function properly… or at all. In 2007, ReliOn was requested to propose an extended runtime solution to augment the photovoltaic source of primary power at 14 off-grid, remote communications and surveillance sites in the Arizona desert.

APPLICATION OVERVIEW
ReliOn conducted site surveys to assess equipment operating characteristics, actual load requirements, site layout and footprint as well as any code or siting issues that would have to be mitigated. The total maximum potential load was measured for the customer equipment. Total load (potential maximum, excluding battery load) was 250 Watts. Average load (based on load profile, excluding battery load) was 180 Watts.

All of these applications were originally served by extended battery strings of 24 or 48VDC, feeding an AC inverter that would provide AC power to the equipment at the top of the tower. The battery strings were supported by AC propane generators ranging from 6.5kW to 10kW in power capacity. During the winter months, with fewer hours of available sunshine, the generators were called upon to power the site and recharge batteries approximately 50 to 70 hours per month.

Among the issues to be addressed was generator reliability. Occasionally, the generators would fail to start or cease operations shortly after startup. These failures led to costly and manpower-intensive maintenance at night. Another important issue was high fuel consumption, as the generators, despite the relatively low power loads, would consume fuel consistent with their higher power ratings.

ReliOn committed to providing a solution that would increase system availability while reducing overall site operating expenses. This solution involved the installation of the T-1000® fuel cell system with dual fuel cabinets for extended runtime.

ReliOn's approach with these customer sites was to set the fuel cell low-voltage start set point on the lower end of the DC plant operating voltage spectrum. This methodology allowed for the supporting battery string to carry the load through the periods when the naturally renewable source (sun) was not available, yet was likely to return before the batteries hit the low-voltage point.

The float voltage setting on the fuel cell was also set at a relatively low point. The intent was that the fuel cell system would not fully recharge the battery string, but rather would maintain the batteries at a healthy state of charge while serving the critical load. This approach awaits the return of the solar power source to fully recharge the battery string, thereby preventing excessive fuel consumption for the fuel cell solution.

PERFORMANCE SUMMARY
This portion of the case study is focused on the two sites having the most efficient off-grid configurations in the customer's network. These sites demonstrate the true potential savings with the fuel cell option. It is worthy to note that all 14 ReliOn fuel cell systems in the customer network have performed as designed and without unscheduled downtime.

The ReliOn systems at Site A and Site B were turned up in April 2008. To date, from a power perspective, these sites have never failed. The quiet operation and lack of ground vibration from the fuel cells has eliminated any false alarms the customer experienced due to generator vibration. There has been no fuel cell maintenance required since startup in April 2008 vs. just over $19,000 spent on generator repairs and services in 2008.

Although these 2 sites are nearly identical and operate in the same region, Site A required fuel cell runtime beginning in late October 2008, while Site B did not. ReliOn presented this data to customer personnel and was advised by the staff that they had suspected the Site A solar array was not properly aligned with "solar noon" and therefore was not taking full advantage of the available sunlight. The hard data, provided by the fuel cell system, appeared to be a strong motivator to take corrective action and the customer staff shifted the shelter/solar array to align with solar noon. Since this action, the fuel cell has been called upon less often to carry the site, further reducing fuel consumption. The fuel cells at both sites continue to be available to power the site load in situations of extended cloud cover.

The business case for fuel cells is deeper than the concept of clean technology being used at locations where highly reliable power is needed, though those certainly are 2 key benefits. In certain locations, the use of a fuel cell in conjunction with another clean technology, like photovoltaic, can actually save the customer time and money on the OpEx side, as well as providing site data that allows them to further improve efficiencies.

ReliOn's T-1000®, Extended Run, 24 VDC Fuel Cell System
Rated net power: 0 to 1,200 Watts
Runtime: 96kW-hours (384 hours or 16 days for this customer load)
Dimensions: 68.5"w x 35"d x 72"h
Weight: 756lbs without hydrogen fuel tanks installed
Ambient Temperature: -40C to +46C
Noise: 53cBA @ 1 meter during typical operation

WHAT'S A FUEL CELL?
Proton Exchange Membrane (PEM) fuel cells generate electricity through an electrochemical reaction using hydrogen and oxygen. They generate energy without producing harmful emission by-products -- the only by-products are water and heat -- and without combustion, fuel cells are a quiet, highly reliable alternative for backup power. Like with a generator, runtime for a fuel cell is determined by the amount of fuel storage capacity at a site. A benefit to fuel cell usage is that, since the fuel is often hydrogen, it tends to be more readily available than other, more widely used, types of fuel during a longer outage situation. Based on technology available today, sites can be provisioned with fuel for hundreds of hours of runtime. Refueling allows the system to run continuously as long as needed for extended outages.

Most fuel cells for backup power available today range from hundreds of Watts to about 20 kilowatts. For sites with relatively low power loads and outages lasting from hours to days, fuel cells can be the power source of choice.

About the Author
Sandra Saathoff is the Director of Marketing Communication for ReliOn. She has more than 10 years experience with the company in the area of fuel cell power solutions. Prior to this, she worked for three years at Avista Utilities. For more information visit www.relion-inc.com or email ssaathoff@relion-inc.com or email fuel.cells@relion-inc.com.

ReliOn develops and markets modular, proton exchange membrane fuel cell products. Currently, they are marketing a range of stationary fuel cells for emergency and backup power requirements, uninterruptible power supplies, digital power needs, and a variety of off grid power requirements. For more information email ssaathoff@relion-inc.com or visit www.relion-inc.com.

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