By Tom Decker, Jonathan Goebel, M.SAME, Bjorn Oberg, and Holly Kuzmitski

The Department of Defense defines operational energy as the energy required for training, moving, and sustaining military forces and weapons platforms for military operations, and includes energy used by tactical power systems, generators, and many weapons platforms. In FY2017, the U.S. military consumed over 85-million-barrels of fuel to power ships, aircraft, combat vehicles, and contingency bases at a cost of nearly $8.2 billion.

To achieve successful outcomes in a multi-domain environment, extending the operational reach of the U.S. Army’s forward formations is of paramount importance. Improving infrastructure and logistical efficiency by more effectively utilizing energy accomplishes these goals.

Toward this end, after a deployable metering and monitoring system study found that most tactical generators in contingency environments are typically loaded to only 30 percent of their rated capacity, the U.S. Army Engineer Research & Development Center’s Construction Engineering Research Laboratory (ERDC-CERL) saw an opportunity to deliver a solution. The resulting technology, the Hybrid Power System (HPS), works with program of record, legacy, and commercial generators to optimize energy consumption efficiency.

The Hybrid Power System can receive power from solar photovoltaic panels, increasing the cost savings in contingency environments. U.S. Army Photos


First developed in 2014 as the Hybrid Power Trailer (HPT), the HPS technology has been continuously modified until its current iteration. The system resides on a towable high mobility multipurpose wheeled vehicle and consists of control electronics, energy storage, and a ruggedized inverter, which converts direct current into alternating current and vice versa. When a generator is combined with the system, it operates at maximum capacity each time it is switched on, storing excess energy in lithium-ion batteries. Once energy storage is full, the HPS turns the generator off, and power is provided from the batteries.

If a program of record generator malfunctions in some way, it can easily be changed out with another. If there is a problem with the system itself, it can be disconnected, with the generator still having the capacity to operate. The HPS can also utilize up to 3-kW of solar input from photovoltaic panels, consequently providing 20 percent of a 15-kW load requirement in this manner. The HPS can receive power from a 15-, 30-, or 60-kW generator and output either U.S. power or NATO power, 230–400-V alternating current at 50-Hz.


The HPS will likely deliver the greatest benefits in three distinct situations.

The first would be when the only generator available is overrated for the peak and average load calculations. This happens frequently on the battlefield, due to the immediate need for power and space limitations. This was the case at a demonstration conducted at the Contingency Basing Integration & Technology Evaluation Center at Fort Leonard Wood, Mo. The replacement of the oversized 60-kW generator with the HPT resulted in a fuel consumption savings of 64-gal/day.

The second situation is where there are isolated power requirements, such as a radar at the end of a runway. In this instance, equipment is often powered by an oversized generator or must be powered even when not in use. If a system requires a 5-kW load, the HPS connected to a 15-kW generator would run for eight hours to provide the required load and store the remaining energy. The system then turns the generator off for eight hours. In the alternative scenario, running a 15-kW generator at 5-kW non-stop would average 24-gal/day. The HPS, therefore, could reduce the average fuel usage by 12-gal/day, or approximately 50 percent. Using solar panels, further savings could be achieved.

The third situation is when tactical generators have to be sized according to peak loads; however, some peaks are exponentially higher than their average loads, which creates the need for an oversized generator. In another documented study, when a facility had a temporary power requirement that peaked over 15-kW, there was a need for a 30-kW generator that consumed 64-gal/day of fuel. Both the HPT and HPS have a large inverter, combined with energy storage, that allows the system to handle peaks and still store energy when under the 15-kW rating of the generator. The switch to the HPT resulted in an average fuel use of 11-gal a day, resulting in a 53-gal/day savings.

Using the HPS will also likely prevent “wet stacking.” This condition occurs when a generator runs at less than 50 percent capacity. It significantly shortens the equipment’s life expectancy, leading to unplanned power outages that could place the mission and lives in jeopardy.


Designed to integrate into current warfighter formations, the HPS can be introduced unobtrusively without significant investment in additional user training. The Army relies on nonmilitary occupational specialty specific generator operators and a 40-hour licensing process. Since the HPS has an interface similar to the generator, a user with this training background would only need an additional three-hour block of instruction to be sufficiently prepared.

Currently, the project team has developed three HPS prototypes, two of which will be delivered for Combatant Command operational evaluations. This is the first time the system has been delivered anywhere for use.

The first prototype has been delivered to the U.S. Indo-Pacific Command’s 130th Engineer Brigade in Hawaii for use in partnership with ERDC-CERL. The second unit will be delivered to the U.S. Africa Command area of responsibility for one of its operational exercises during FY2020. The third HPS will stay in the United States for demonstrations.

If the combat developers receive enough positive feedback, the information could drive hard requirements for large-scale production in the future.


Optimizing generator fuel consumption is a benefit at the tactical, operational, and strategic levels. Less time dedicated to fuel resupply operations and generator maintenance means more time can be spent fighting.

Research is now further investigating systems to work with the Army’s gap of 100- to 800-kW systems, developing standards for the military transport of lithium-ion, and standardizing large-format batteries for tactical energy storage. These efforts will extend the operational reach of forward formations and improve logistical efficiency.

Tom Decker is Operational Energy Program Manager, Jonathan Goebel is Mechanical Engineer, M.SAME, Bjorn Oberg is Mechanical Engineer, and Holly Kuzmitski is Public Affairs, ERDC-CERL. They can be reached at;;; and

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