By Maj. Nathan Thomsen, P.E., M.SAME, USAF, Lt. Col. Andrew Hoisington, Ph.D., P.E., M.SAME, USAF, and Maj. Steven Schuldt, Ph.D., P.E., M.SAME, USAF

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Remote locations, such as military forward operating bases (FOBs), are disconnected from traditional power grids, forcing them to rely on diesel generators. These generators require a constant supply of fuel and result in increased operating costs, noise pollution, environmental impacts, and challenging fuel logistics.

In 2009, the Government Accountability Office (GAO) recognized the massive cost of fuel use at forward deployed locations, placing the minimum fully burdened cost of fuel at $15/gal when logistics concerns are included. The fuel logistics issue creates a potential threat to FOB energy resiliency—if fuel convoys are cut off, attacked, or depleted, base electrical power to mission essential operations is lost. Additionally, fuel convoys require security protection, which places personnel in harm’s way. A study from the Army Environmental Policy Institute showed that in dangerous environments such as Afghanistan, there was one casualty for every 24 fuel convoys.

RESEARCH EFFORTS

The Air Force Research Laboratory (AFRL) has examined several experimental renewable technologies for FOBs in recent years that could lessen dependence on diesel generators. From 2008 to 2012, AFRL experimented with tent shelter designs that integrated flexible solar panel shades, enhanced insulation, and redesigned HVAC systems for a 35 to 65 percent reduction in peak energy requirements. In 2010, Lockheed Martin received a contract with the Air Force  to provide experimental solar microgrids. The project concluded with the testing of the Integrated Smart BEAR Power System at Holloman AFB, N.M., consisting of 75-kW of solar photovoltaic power and 25-kW of wind power, but no energy storage. The system demonstrated that solar power was feasible and could be set up by Air Force engineers with minimal training. More recently, the National Renewable Energy Laboratory collaborated with AFRL to create a 30-kW CUBE microgrid convertor that is capable of integrating renewable energy sources into existing high-voltage AC grids used at contingency locations.

Advancements like these are important steps to developing a practical renewable power grid for FOBs and other remote or isolated locations, including assets in the desert, on islands, or even in space. However, a complete solar power replacement for prime-power generators has yet to be implemented or designed. The scale of previous designs was small, only fulfilling the requirements of localized generators or individual shelters. To power a complete FOB, multiple large, prime-power diesel generators of 800-kW or larger are necessary.

RAPIDLY IMPROVING OPTION

Generators present a problem to the Department of Defense’s ambitions for energy sustainability. According to the DOD Strategic Sustainability Performance Plan for 2016, the military seeks to assure continued availability of energy through reduction of fossil fuel use.

Rapidly improving renewable technologies such as solar cells have expanded the potential power generation options for isolated sites. Solar photovoltaic arrays produce electrical power from sunlight, which is abundant, free, and available during daylight hours over nearly the entire globe. The distinct advantage of these arrays over generators is that they produce power nearly 365 days a year with no fuel resupply requirements, no noise, no air pollution, and minimal maintenance over their lifespan. However, solar arrays only produce power during daylight and are dependent upon the weather. Therefore, energy storage solutions such as batteries are required to supply electricity at night. Energy storage technology is rapidly improving with new developments reducing cost while increasing capacity. The advances in photovoltaics and energy storage technologies are making potential renewable replacements for generators better and more cost-effective than ever before.

While other renewable energy power sources are available, Air Force Research Laboratory analysis has shown the technology may be the best candidate for alternative energy generation in the deployed environment compared to other solutions such as wind turbines, for example.

LARGE-SCALE MODELING

Recent research at the Air Force Institute of Technology (AFIT) in collaboration with the Air Force Civil Engineer Center examined a case study for the replacement of a single 800-kW generator with a solar-based renewable energy system. Marjah, Afghanistan, in Helmand Province was selected as the location for this hypothetical examination. The goal of the study was to examine, optimize, and determine the feasibility of replacing a large prime-power generator with a solar photovoltaic array and battery storage system.

Renewable energy systems require the consideration of both the power generation capacity (solar array size) and the energy storage (battery size). Industry has developed practical standalone battery systems to replace existing generators and multiple modeling and optimization methods are available. However, military engineers need to account for logistics and land requirements in addition to cost in optimizing these systems. Therefore, properties to optimize for military FOBs should include weight, volume, and land area required. In the optimization process, tradeoff decisions are made between these variables, depending on the key factors for defense applications.

The research at AFIT demonstrates an optimization model based on the military priorities and generates a design solution to minimize initial cost and logistics while maintaining 99 percent reliability. The model utilized MATLAB software and one year of solar data to examine all potential solar photovoltaic array sizes and battery storage capacities to determine the optimal configuration that would match the continuous output of an 800-kW generator. Following GAO guidance, $17.74/gal was used as the estimated fully burdened cost of the fuel.

Results of the model demonstrate a high initial cost and logistics burden for the renewable system (30-times the cost, 27-times the weight, and 50-times the volume compared with current generators). However, these factors are rapidly offset by the ongoing high costs and logistics of diesel fuel. In less than two years of operation, the total cost for the renewable system would be less than diesel generators. Furthermore, in only 120 days the weight of fuel transport would overcome the initial weight burden of the renewable system. Replacing a single diesel generator with this type of renewable system would result in a savings of over 500,000-gal of fuel annually and eliminate the need for 100 fuel tanker deliveries.

A SUSTAINABLE FUTURE

The Air Force research demonstrates that renewable energy systems may be viable candidates for contingency bases and are reasonable from economic and logistic perspectives in relatively short timespans when compared with typical FOB lifetimes. During deployments of only a few months or less, generators are lighter and cheaper to operate; however, for the majority of FOBs and remote operating locations, photovoltaic and energy storage systems provide significant operation and economic advantages.

For the practical implementation of a renewable system at an expeditionary base, during the first 30 days of a beddown an FOB might use existing generators, with photovoltaic and energy storage following soon after. Once the complete renewable system is operational, the generators could remain as backup, further increasing resiliency. A sustainable FOB based on this system would possess enhanced resiliency and could operate indefinitely without the need for fuel resupply—working toward military goals to assure supply and improve energy resiliency.

These sustainable FOBs could be very desirable in many locations where fuel sources are scarce, but the need for power is critical.


Maj. Nathan Thomsen, P.E., M.SAME, USAF, is Master’s Student, Lt. Col. Andrew Hoisington, Ph.D., P.E., M.SAME, USAF, is Assistant Professor and Engineering Management Curriculum Chair, and Maj. Steven Schuldt, Ph.D., P.E., M.SAME, USAF, is Assistant Professor and Engineering Management Program Director, Air Force Institute of Technology. They can be reached at nathan.thomsen@ afit.edu; andrew.hoisington@afit.edu; and steven.schuldt@afit.edu.

[This article first published in the March-April 2020 issue of The Military Engineer.]