A whopping 77 percent of the approximately 6.9 billion people in the world are mobile subscribers, and both of those numbers are growing. Global demand for wireless solutions and the energy they require -- increasingly expensive, often unstable utility power -- is prompting service providers to explore alternative solutions to their energy needs. Hybrid energy technologies are emerging as an answer, but there are many options available with a host of technical complexities to consider.

In addition to available grid power, hybrid systems are designed to manage multiple active energy sources, including active batteries, generators, fuel cells, and wind and solar technologies, as opposed to standby power devices where power is used only when the primary source fails. These active power devices provide primary power against a defined algorithm, supporting business objectives, where usage is predictable and frequently called upon.

Not only technologies, but logistics, setup, and operation should be considered when exploring what energy source to employ in a hybrid energy site solution. There is no one-size-fits-all solution. Differences in climate, social environments, site objectives, and usage expectations often differ from one site or region to the next, and thus, what works well in one application may be inadequate for another.

Batteries
Over the years, the standard telecom battery has been refined and developed primarily as a standby source of power -- a common-format, front-terminal battery with low cyclic life, low maintenance and low cost. While standby batteries provide excellent return on initial investment (CapEx), the batteries will be exhausted quickly in situations that require high-cycle performance, such as off-grid installations. With that in mind, including operating expense (OpEx) when evaluating batteries is prudent. The primary determinants of total cost of ownership (TCO) become battery life, autonomy, performance, and efficiency with the available energy. The ultimate battery solution should include battery monitoring, which optimizes around these drivers and extends the OpEx investment without sacrificing service or necessitating large fuel consumption increases.

Hydrogen Fuel Cells
Hydrogen fuel cells (HFCs) represent a stable technology for power generation, but this technology is not deployed frequently, so the supply chain for fuel creation is still emerging. Supply chain issues typically are hampered by the availability of hydrogen and hydrogen suppliers, delivery of fuel to remote locations, and local requirements for technicians needed to manage the system and refuel the sub-systems.

A segment of the industry has responded to the challenge of hydrogen delivery by providing reformers, devices that extract hydrogen from a hydrocarbon fuel, such as gasoline, diesel, ethanol, methanol-water, etc. This may mitigate the issues of hydrogen fuel delivery, but it also provides another sub-system to manage and another device that consumes energy and generates emissions at the site. Depending upon the reformer’s fuel needs, it may still require the development of a supply chain, with the associated issues of performance related to response and inventory.

Local acceptance of hydrogen storage may be stigmatized by fuzzy connections to the Hindenburg disaster, but hydrogen is no different than any stored energy, all of which carry some risk. Acceptance may require education of local municipalities and fire departments. There are some arguments for the implementation of HFCs. They divert emission release from the site to the location where fuel is created, and are a low-risk choice in terms of potential theft.

Wind
Wind has been used for centuries as a free, renewable source of energy. Today, small wind turbines, typically less than 10kW, are used to provide energy for telecommunications networks. The question of wind’s viability comes down to both quantity and quality. A site may seem to have enough wind, but it must be “good “wind (i.e., laminar wind, not turbulent). Turbulent air is inconsistent and results in a poor transfer of energy.

The initial consideration is whether the region and locale provides good wind. A region reflects the area and general wind patterns, while the locale refers to the site with performance either limited or enhanced by immediate geography, vegetation, and man-made surroundings. Wind maps, typically available through government agencies, provide substantial information on whether a given region is suitable for a wind turbine (see sidebar).

In investigating a locale, start with the question: “Does the site provide an unobstructed wind path?” If there are substantial topography obstructions or rough terrain in the path of the prevailing winds, the value of a wind solution is substantially reduced. Beyond simple availability, there are 3 additional considerations when evaluating wind as a power source and tools available to help make the decision and ultimately advance good wind solutions.

Consideration A: Obstruction Clearance. The impact of obstructions depends upon many variables, but the following model (See Figure 1.), courtesy of the Department of Energy’s National Renewable Energy Laboratory (NREL), illustrates the substantive effect of obstructions. While acknowledging that obstructions may be unavoidable, a planner should give priority to sites that minimize any obstructions to the dominant incoming winds.

Figure 1. Obstruction Impact onto Wind Energy
Source: National Renewable Energy Laboratory (NREL) Wind Resource Assessment Handbook
Reference TAT-5-15283-01, Published April 1997

Consideration B: Height. The negative effects of turbulence and aerodynamic drag from the surface are reduced as the height of the installation increases. As a general rule of thumb, higher is substantially better. The effect of drag is called wind shear, and, when factored along with available wind power (determined by wind velocity), it can provide a clear picture of the impact of height. By doubling the height and using the 1/7 power guideline, wind speeds will increase by 10 percent, but the wind energy gain will be 35 percent. Beyond the benefits of reducing drag, the actual gain likely will be greater given the reduction of turbulence seen with height and minimizing the impact of radiative heating-cooling during day-night.

One (1) large turbine typically will outperform 2 small turbines. With that in mind, the investment should be directed to a single turbine, limited of course by local regulations, neighborhood acceptance, and safety considerations.

Consideration C: Safety and Maintenance. Many providers are well-versed in the issues associated with tower planning from height restrictions, lighting, stress and axial loading, wiring in a tower, lightning, grounding, etc., and the steps required to obtain approvals. Acknowledging this, here are some additional considerations that need to be thought out prior to deploying small wind solutions that depend upon the turbine in use:

• What are the procedures to address high wind survivability? Some solutions expect the site to be manned, and provide manual intervention.

• How is a dump load from electrical braking addressed (if one exists)? Many solutions provide electrical braking at high winds to maintain integrity, but how is this additional load diverted?

• How is the turbine maintained? Access to service, access to replacement parts must be a part of the overall plan.

• Will the turbine interfere in normal service operations?

Solar
Solar cells arranged in photovoltaic modules transform the sun’s rays into electricity, and provide a viable energy source in areas where direct sunlight is ample throughout most of the year. In areas such as the American southwest, it is reliable; in the northwest, less so. Internet resources exist to access regional availability of solar energy to help determine the energy available, as illustrated in Figure 2 as an annual summary or, by month and installation format, as seen in Figure 3.

Figure 2. U.S. Solar Availability, Annual Summary, with Fixed Panel Tilt to Latitude
Source: National Renewable Energy Laboratory (NREL), http://www.nrel.gov/gis/solar.html

Figure 3. U.S. Solar Availability, January, with Fixed Panel Tilt to Latitude
Source: National Renewable Energy Laboratory (NREL), http://www.nrel.gov/gis/solar.html

Understanding those basic limitations, solar is an effective technology that will outlast most communications subsystems. However, there are several fundamental considerations that require planning and management:

• Low-Density Energy Source: Solar requires substantial real estate to generate enough energy to be a significant option for most telecom installations. As it is a low-density energy source, consideration to pair solar with other sources should be given, i.e., wind and/or a generator.

• Theft and Security: Solar panels are an attractive target for theft. Steps must be taken to reduce the risk and convenience of theft.

• Obstructions and Landscaping: When sighting a location, no southerly obstructions from the east to the west that can cause shade should be present. The probability of shading can be reduced by placing the array high, as a solar canopy on a roof or above a cabinet. This also will reduce the heat load on the infrastructure below, reducing cooling costs.

• Racking: There are many commercially available racking solutions for open fields and traditional roofs, but many telecom applications do not provide an ideal terrain or the need to place the array above cabinets. As such, the provider may need to define and develop with their partners a custom solution for the local installation (ideally for the region), often requiring a professional engineer signoff for local acceptance addressing conditions such as wind loading.

• Tilt: For fixed-mount solutions, the default answer is to adjust the angle of the array (tilt) to the latitude at the site, which may not address weather conditions or specific objectives driven by electrical rates or neighborhood acceptance.

Generator
Standby generators are a familiar technology to most providers, deploying generators as an active energy device -- not just for backup power. Therefore, generators are another hybrid energy strategy. In this transition to being an active source, the generator run-time will rise and its operational performance and efficiency gain importance in determining TCO and assurance of service availability. Given this new focus, the need to evaluate a generator migrates from a best CapEx answer to the best TCO (CapEx and OpEx) answer, and thus operating performance, maintenance service periods and contracts, performance tracking and alarms, maintenance and monitoring of the starter battery, sizing and storage of fuel become important evaluation criteria in selecting the best solution.

Consideration should be given that the generator is not just another energy source, but is paired with the battery for efficiency and to provide extended autonomy. As the battery capacity is sized for active use, the fuel capacity must be sized as an active energy source with consideration for access and restrictions (such as seasonal road conditions). A generator is a high-density energy device, and thus, with batteries, can provide a low CapEx solution that may be deployed in a small footprint in off-grid locations.

Another consideration is emissions acceptability, including acoustics and air pollution. With respect to air pollution, the type and availability of fuel (for example, diesel versus propane) needs to be measured against emissions and generator efficiency (i.e., the cost to operate at the expected loads).

Grid
The grid is a great source, if it is available and when it is stable. This makes the grid a virtual infinite source of energy with a low real-estate impact. When connecting renewable sources to a stable grid, the purpose will drive the best fit solution:

• Feed-In-Tariff (FIT). Using renewable energy to put energy back into the grid and be paid for it.

• Reduce grid reliance, also known as peak-shaving, reduces energy consumed from the grid with the probable focus at peak time-of-use charges.

• Grid as a backup device. The grid replaces the generator as a backup device and is used to deliver standby (or recharge) energy when requested.

The grid, when available, can be used as a high-density (and usually cost-efficient) energy source, but its role depends upon the objectives of the provider.

Conclusion
With the introduction of multiple energy sources, the complexity of design and management has risen. This multiplicity drives the need to refine objectives for deployment and operation, and involves the introduction of new technologies and procedures, from those engaged in the management of the technology to those who manage the real estate and landscaping.

But, it is not necessary to develop individual solutions for each site. With consideration for the region, working with local authorities and planners, common integrated network solutions can be created, deployed and effectively managed as traditional solutions. Expect no less.

 David Wilson is Director, Application Engineering, Emerson Network Power’s Energy Systems business. He has more than 27 years of experience in Systems-Solution Design, including OSP enclosures and broadband solutions. For more information, email EnergySystems@Emerson.com or visit www.EmersonNetworkPower.com/EnergySystems.

A Windy Rule
Want to rule the wind? Know the rules:

• If the average wind speed is below 11.4 mph at 98' (Class 1, <160W/m2, <5.1m/s) the locale is probably not a good candidate for wind power.

• If the average wind speed is between 11.4 and 13.2 mph at 98' (Class 2, 160-240W/m2, 5.1-5.9m/s), it may be worth investigating the locale.

• If the average wind speed is above 13.2 mph at 98' (Class 3 or greater, >240W/m2, >5.9m/s), there is good probability that good wind is available at the locale.
 

Weibull What?
Wind Energy often is expressed in the form of a Wind Rose and reference to a Weibull Distribution. (See Figure 4.) Weibull is similar to the bell curve, a probabilistic distribution used to describe events, quality, school grades, etc., but a bell curve is a symmetrical shape. Weibull is more complex in that it is an asymmetrical distribution that can approximate distribution of wind speed (energy) at a site, and thus be used to simulate and model the amount of energy a turbine can collect at a site.

Figure 4. Weibull Distribution with a Mean Wind Speed of 7 m/s.

The standard (default) Weibull model used to describe the wind is the Raleigh Distribution, which is a defined shape parameter (Gamma or K) of 2, with the Mean Wind Speed anchoring its position on the X-Axis (Wind Speed). As illustrated by the plot in Figure 4, the actual distribution will shift by definition-assumption of K. As power is a function of wind velocity to the third power, the assigned value for K will have significant impact on the expected energy that will be delivered. As the value K is reduced for any given Mean Wind Speed, the available wind power is significantly reduced.

There are many studies that validate the strengths and weaknesses of using a Weibull Distribution to predict energy delivered. These studies have shown the actual best-fit K extends beyond the illustrated range above of 1.5 to 2.5. Nevertheless, Weibull is a valid tool to provide a fair comparative analysis of solutions and provide an estimate of energy available without extensive site surveys. Acknowledging the many compromises when locating a telecom site, a provider may be better suited to predict expected energy delivered with a more conservative wind distribution profile of K=1.5.

What’s your take on this subject? Leave a comment and get the conversation going.