The site must have power. Its equipment is critical to ongoing communications in an area that includes first responders. But the neighbors don’t like the noise of a generator, the State doesn’t like the emissions, and the company has committed to being more environmentally responsible. What do you do?

If you are one of the growing number of outside plant personnel facing these kinds of questions, you get creative. You look at your options. You consider trying something different. There are a number of technologies offered today that make providing clean, hardened power solutions easier than it used to be. Solar, wind, and fuel cell power offer strengths that, when combined, become a strong solution for a number of applications, providing a clean, highly reliable alternative to long-term diesel generator use. These solutions can be used either to harden a grid-connected site or to power an off-grid site. Federal and State funding opportunities lessen the initial cost burden and the solution can actually save money on maintenance costs.

The Options Are Many
In order to discuss the hybrids, it is important to understand each component: solar, wind, and fuel cells. Batteries continue to play an important role as well.

SOLAR
Photovoltaics generate electric power by using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays to convert energy from the sun into electricity. Photovoltaic technologies use both direct and scattered sunlight to create electricity. The solar resource across much of the world is ample for small solar electric systems. However, the amount of power generated by a photovoltaic system at a particular site depends on how much of the sun’s energy reaches it. A map of the United States provided by The National Renewable Energy Laboratory (NREL) shows solar resource areas, color coded by amount of potential power production.1 (See Figure 1.)

Figure 1. The National Renewable Energy Laboratory (NREL) shows solar resource areas, color coded by amount of potential power production.

As a stand-alone system, photovoltaics will not provide continuous power because when the sun does not shine, the system does not produce energy. Therefore, solar must be combined with an energy storage or another energy production technology allowing it to ride through periods of low solar activity. Used with other power sources, solar offers the benefits of renewable energy: clean power with no emissions and no ongoing fueling costs.

WIND
Wind turbines draw upon the force of moving air to generate electricity by rotating propeller-like blades around a rotor. The motion of the rotor turns the drive shaft, which turns an electric generator. Small wind turbines, those rated below 100 kilowatts, can be a viable power source for telecommunications networks in areas where the wind blows consistently and with enough wind speed to provide power for the site, but not overwhelm the equipment. The local meteorological station can be helpful in determining average wind speed for a specific area. In general, hilltops, open plains, the floor of a valley running parallel to the wind, and shorelines facing prevailing winds can be good locations. The U.S. Department of Energy provides a map of the United States showing general areas that can be good for wind.2 (See Figure 2.)

Figure 2. The U.S. Department of Energy provides a map of the United States showing general areas that can be good for wind.

Whether the outage is short-term or long-term, wind alone will not provide continuous power. Used in conjunction with other power sources, it can offer benefits. As long as the wind blows, the site will continue to run without running out of fuel. Like with solar power, wind turbines need to be combined with an energy storage technology or an additional energy production system, allowing them to ride through periods with no wind.

FUEL CELLS
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.

BATTERIES
Even in a clean solution, batteries continue to have an important role. Batteries have been the traditional choice for short duration backup power support, as these devices tend to be relatively inexpensive in terms of an initial cost of capital. Due to their requirements of frequent replacement, particularly in outside plant applications, batteries generally result in a higher lifecycle cost. Batteries provide a bridge between other power sources and a place to store excess energy produced for later use. They are quiet, scalable, and have relatively reliable performance.

In general, there are two reasons to consider a hybrid solution:
1. To harden a critical site, so that it is more reliable in variable conditions.
2. To address an off-grid scenario where communications are critical.

Site Hardening
Many sites normally operate from AC grid power, and are equipped with VRLA batteries to support the site in case of AC power failure. These sites can benefit from a fuel cell connected in parallel with the batteries. For outages that exceed the capacity of the batteries, the fuel cell serves to carry the site load when the batteries drop below a specified voltage, whether due to loss of AC power or in the event of a rectifier failure. The fuel cell minimizes the deep level of discharge on a battery string and allows the site to operate on backup power for much longer than on batteries alone.

The addition of a wind or photovoltaic (PV) sub-system takes advantage of “free” power from the wind/sun. Combining the various backup power technologies allows an operator to quickly recover and provide services to support the truly critical equipment during an outage event. It also allows time to assess damages and implement the longer range reconstruction to restore the entire network.

During daylight hours, the PV/battery system supports the load as shown in Figure 3. When the wind blows, it adds energy to the system. Sizing of the system depends on whether it is sized to cover the entire site load, or also charge the batteries. This solution can provide sufficient backup for most short outages, conserving the fuel cell for longer outages. Once the wind/PV/battery system is depleted, the fuel cell operates to carry the site load. Because it is fueled, the fuel cell delivers power as long as fuel is present, and unlike a battery, additional fuel can be delivered and deployed while the fuel cell is operating, theoretically providing unlimited clean power generating capability.

Figure 3. Combining the various backup power technologies allows an operator to quickly recover and provide services to support the truly critical equipment during an outage event.

Off-Grid
The cost of extending the grid can be daunting. Some estimate it at $1,000,000 per mile or more.3 In many cases, it makes better business sense to employ a hybrid power solution at locations significantly off the main grid highway. (See Figure 4.)

Figure 4. Off-grid power combines the strengths of solar, wind, battery and fuel cell to provide a comprehensive power solution.

Powerful Cases of Hybrid Solutions
Cellcom has operated a hybrid power solution in the north woods of Wisconsin since April of 2008 for one of its off-grid sites. (See Figure 5.) The primary power sources are photovoltaics and wind, with a significant battery string for storage and a fuel cell providing critical backup power. It is a case of creativity finding a way to provide needed reliable cell phone service to a rural customer base.4

Figure 5. Cellcom operates a hybrid power solution at an off-grid site in Wisconsin.

In the deserts of Arizona, another industry has a number of off-grid surveillance sites that are being powered by a hybrid consisting of solar panels and batteries, with fuel cells providing backup power. The fuel cells operate if a period of extended darkness limits the photovoltaic output, or if there is a problem with the solar array in general. The fuel cell systems are supplied with additional fuel storage, increasing the length of time the system is able to operate between site visits. (See Figure 6.)

Figure 6. Hybrid power sites can significantly increase the reliability of a site and the time between maintenance visits.

The goal of the configuration was to maximize the power of the sun in providing energy to the site, while maintaining the battery string at a healthy level of operation so that it had the ability to cover much of the time not powered by the solar array. At issue was reliability of generators, which would occasionally fail to start or would cease to operate shortly after startup, leading to costly, manpower intensive maintenance off normal work hours.

The introduction of the fuel cell solution as a replacement for generators at these sites dropped the maintenance costs significantly, lowered fuel consumption, and eliminated false sensor alarms caused by vibration of the generators, while increasing the reliability of the sites. A side benefit was the ability of the fuel cell data logs to provide information about how the solution as a whole was working, which resulted in adjustments to the solar panels, thus increasing their ability to provide power for longer durations.

Financing Options Help Close the Deal
In order to assist the market, the U.S. Congress passed an expansion and extension to the 2005 fuel cell tax credits to be available for purchases of fuel cells, solar, and wind power beginning January 2009 and going through December 2016. For fuel cells, these credits amount to $3,000 per kilowatt or 30% of the system cost, whichever is less, and entitle the taxpayer to subtract the amount of the credit (dollar-for-dollar) from its total federal tax liability. For solar and wind, this credit is 30% of the cost of the system. As part of the American Recovery and Reinvestment Act (ARRA), a grant option was put into place in order that those companies who do not have a tax liability may be able to participate in the program.5

In addition to the federal program, there are a multitude of State incentive programs in place for solar, wind, and fuel cell solutions. (See the sidebar The State of Backup Power Financing.) (See Figure 7.) Policies continue to be added and changed. A good source for current incentive information is the Database of State Incentives for Renewable Energy website.6

Figure 7. States having specific fuel cell incentive programs are noted in green. Map provided by ReliOn.

Design of a power solution must take into consideration the characteristics of each individual site. Where AC grid power is available, it may be beneficial to harden the site by providing a hybrid power solution in order to cover anticipated extended outages. Where no grid power is available, a hybrid power solution provides clean energy on a continuous basis. Either way, fuel cell/solar/wind hybrids are a viable method for meeting the needs of communications, security, and a multitude of other equipment sites.

Endnotes
1. National Renewable Energy Laboratory (NREL). Facility of the US Department of Energy (DOE) for renewable energy and energy efficiency research, development, and deployment.www.nrel.gov/
2. U.S. Department of Energy (DOE). Governmental department whose mission is to advance energy technology and promote related innovation in the United States. www.energy.gov/
3."Comparing Pipes & Wires: A capital cost analysis of energy transmission via natural gas pipelines and overhead electric wire lines," Bonneville Power Administration and Northwest Gas Association.
4."Cellcom Powers Sites That Are Off the Grid," AGL magazine,February 2009.
5. American Recovery and Reinvestment Act (ARRA) grant option information can be found at www.ustreas.gov/recovery/1603.shtml.
6. Database of State Incentives for Renewable Energy website: www.dsireusa.org/summarytables/finre.cfm. 

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 3 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.

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