The Pentagon Aggressively Deploys Multiple Renewable Energy Systems

April 30, 2003

Photo of Pentagon's newsly installed 70-kilowatt photovoltaic array.

(left to right) Bob Billak, Energy Manager, Pentagon, and Dr. Get Moy, P.E., Director of Utilities and Energy Use, Office of the Deputy Under Secretary of Defense for Installations and Environment, in front of the Pentagon's newly installed 70-kilowatt photovoltaic array.

The Pentagon Reservation Solar and Hydro Energy Farm has expanded its renewable energy capacity. With the recent installation of a 70-kilowatt photovoltaic (PV) array, the 3rd phase of the Pentagon's PV deployment is in place. The Pentagon's newest PV installation, located at the Pentagon Heating and Refrigeration Plant (HRP) is producing more than 106,690 kilowatthours annually.

The 70-kilowatt PV system features ultra-high efficiency, 315-watt PV modules from RWE Solar/ASE Americas of Billerica, Massachusetts. The panels are 5 percent more efficient than the 300-watt PV modules deployed in earlier phases of the project. A total of 276 modules have been installed in 23 rows of 12 modules per row. Tilt-angle modules were chosen to minimize row-to-row separation, allowing greater power density to be achieved at the site. The DC capacity of the array is 87 kilowatts.

The system's multiple distributed small inverters will be used to provide protection against loss of power due to a single inverter fault. A total of 46 SMA1800 inverters with 6 modules have been installed. The inverters will be mounted on wall sections to be constructed at the north end of the array field. This wall of inverters allows convenient viewing of the status of each subsystem and simplifies system troubleshooting and maintenance in the future. Pentagon Energy Manager Bob Billak said, "The Department of Defense continues to step out decisively as a leader utilizing renewable resources at DOD facilities. Our goal for the Pentagon Reservation Solar and Hydro Energy Farm is to increase the PV capacity of the facility to more than 120 kilowatts."

The Pentagon has also completed a 76-kilowatt solar-thermal system consisting of 1,080 Thermomax Vacuum Tubes on the Pentagon's mechanical roofs. The unique design of the system integrates solar arrays directly into the facility's existing domestic hot water recirculating system. The Pentagon's new solar-thermal system provides domestic hot water using evacuated tube collector technology to supplement the Pentagon's existing domestic hot water recirculation loops during daytime hours.

Another recent Pentagon installation is a solar thermal tile system, manufactured by American Solar, which uses high-temperature metal absorbers to drive an air conditioning system activated by solar heat. The technology uses centuries old slate and tile roofing techniques to install translucent tiles over corrugated metal solar absorbers. Solar energy passing through the tiles heats absorber plates. Air moved through the system and across the painted absorbers becomes heated to as much as 190 degrees Fahrenheit.

A fourth system in development, an intake/outfall energy recovery turbine system, utilizes discharge water from the Pentagon's HRP to generate electricity. The system, which is expected to be completed by December 2003, takes advantage of the HRP's outfall discharge rate of more than 30,000 gallons of water per minute. This structure will concentrate discharge water flow through two parallel turbines into a second set of parallel turbines. A 60-inch valve will regulate discharge flow for the turbines and the turbines will use a gearbox to drive generators that produce power at 4,160 volts.

The system's total available horsepower at a flow rate of 30,000 gallons per minute will be 288 horsepower. The net anticipated power generated, with an equipment efficiency of 70 percent, is 204 kilowatts resulting in an annual cost savings of $98,290 and life-cycle savings to the DOD of more than $4.1 million.

For more information, please contact Bob Billak of the Pentagon at 703-695-7909 or