By Michael Doud, Brian Davenport and Scott Wilshire
In 2002, the Watervliet Arsenal in upstate New York served as the host site for ten 5 kW Plug Power fuel cell power systems providing electricity to power a telecommunications facility, a research and development laboratory and base housing. Table 1 provides system specifications.
While the systems remained operational for almost 94 percent of the time during the year, exceeding the contract availability limit of 90 percent, the program faced a series of unexpected obstacles. The challenge to overcome each obstacle to shed considerable light on future projects for fuel cell use at military bases, industrial/commercial buildings and residences. The systems produced more than 214,000 kWh of electricity to support arsenal operations over the one-year life of the project during 2002, reducing the arsenal’s energy bill for the year by nearly $6,000, as well as reducing their reliance on the grid. The program monitored each fuel cell for electrical efficiency and total availability, and posted monthly data on the Internet for anyone to view.
Because fuel cell systems use an electrochemical process to generate electricity rather than combustion, they have an extremely clean exhaust consisting of mainly air and water vapor. They produce no particulate matter and only trace amounts of nitrogen and sulfur oxides (see Table 2 for emission details). The fuel cells installed at the Arsenal were quiet and ideal for all its applications, particularly for the systems installed near homes on the base.
Like any first time project, unforeseen issues caused delays that required solving, such as low water-pressure, water treatment to correct hardness, and gas lines difficult to locate.
The location of the sites — which included an elevated concrete pad, a gravel bed behind substation transformers and a grassy area — made it impractical to move the fuel cell systems with a standard fork truck. The installers chose to utilize a small crane to lift the systems into place. This required the engineering and manufacture of lifting fixtures. The new lifting procedure served to broaden the installation options for Plug Power.
The fuel cell systems installed at the arsenal were equipped with a grid-parallel package designed to interconnect with the grid by means of tying into a circuit breaker in the electrical service panel of the adjacent building. Because of the age of the facilities selected, upgrades to the building’s electrical service were required to meet current electrical codes.
Four fuel cell systems operated more than 32,000 combined hours producing more than 79,000 kWh to provide all the electricity needed by four single family residences at the Watervliet Arsenal. Photo Courtesy of Plug Power.
The systems installed at the arsenal required a supply of potable water, which is purified in a de-ionization process. Potable water provided to each of the three facilities presented two challenges. In a typical residential application, the system’s water filters are designed to last one year. The hardness of the arsenal’s water required changing the deionization filters twice a month. Plug Power installed cartridges that extended the life of the filters by six months. Secondly, normal operating conditions require a minimum water pressure of 40 psi to completely process potable water into deionized water. Backflow preventors installed at each facility significantly reduced the water pressure from the building’s supply. Booster pumps, similar to the kind found on residential wells, were installed. In the end the water-pressure problem was solved but it required unanticipated installation costs.
At the telecommunications facility, voltage levels of the electrical system fluctuated from +/- 5 to 10 volts rms. These fluctuations exceeded inverter anti-islanding set points. Subsequently, the inverters would detect these fluctuations, classify them as loss of grid or grid fault, and disconnect themselves from the grid. After waiting a required five minutes, the inverters would again detect the grid (if voltage returned to within specifications) and reconnect, entering into their power export sequence. The facility’s fluctuations caused the fuel cell systems’ inverters to cycle on and off of the grid, a condition that prevents the units from exporting power to the grid. This situation was solved by re-tapping the electrical transformer serving the building to provide a more stable voltage that met the operating requirements of the inverter.
The project demonstrated that a variety of PEM fuel cell applications could be successfully integrated into DoD facilities. The experience gained from this installation has led to better installation and operational documentation, and reduced effort for future such installations. The DoD, the Army Corps of Engineers and Plug Power expect to continue future work to continually seek more innovative methods to provide a clean, efficient alternative to traditional energy generation.
How It Works
The PEM fuel cell systems used in the Watervliet Arsenal project operate at relatively low temperatures (under 200 F/93 C), have high power density, and can vary their output to meet a base-load power demand up to 5kW.
The fuel cell systems installed at the Arsenal use a reforming process to turn natural gas into a hydrogen-rich mixture. The gas is then introduced into a fuel cell stack where the membranes split the hydrogen gas molecules into protons and electrons. The protons pass through the membranes to react with oxygen in the air (forming water). The electrons, which cannot pass through the membrane, are collected and provide a source of DC electricity. The DC electricity is sent to an inverter where it is converted into AC power.
Michael Doud, Brian Davenport and Scott Wilshire work at Plug Power, Inc., Latham, N.Y., the fuel cell partner in the Watervliet Arsenal project.