By Siân Green
In August 2000, Alaska utility Chugach Electric inaugurated a five-unit, 1 MW fuel cell system at the Anchorage Mail Processing Center, Alaska. The largest commercial fuel cell system in the USA, the power plant has now clocked up around 6000 hours of operation and has saved the mail processing centre from grid disturbances over 30 times.
The 5 x 200 kW fuel cell power plant is thought to be the first of its kind to be part of an electric utility’s distribution grid. The five fuel cells, supplied by International Fuel Cells (IFC) of the USA, are now the main source of power for the US Postal Service facility, and supply excess power to Chugach Electric’s grid.
The five IFC fuel cells are connected in parallel with the utility grid and supply assured power to the US Postal Service mail processing centre in Anchorage, Alaska
Chugach Electric, a cooperative utility serving around 71 000 residential customers in the Anchorage area, already had some experience with fuel cell technology, a factor which helped it in its decision over which technology to choose for the planned on-site power plant. While the capital cost of fuel cell technology makes it prohibitive to most generators, its level of reliability, environmental performance and rapid start-up ability met the needs of the US Postal Service facility.
The Anchorage Mail Processing Center is the main sorting and distribution point for international and domestic mail going into and out of Alaska. It is a 24 hour-a-day, seven day-a-week operation processing on average 1.2 million pieces of mail per day. Parts of its operation are sensitive to disturbances, or transients, in the grid. If a disturbance or outage occurrs, whole parts of its operation can be shut down and jammed sorting machinery has to be cleared of mail. The facility was therefore looking for a highly reliable source of power to protect it from grid transients, and approached Chugach.
The mail processing centre is one of around 12 large load clients that Chugach serves, and the two companies started to look at on-site power technologies that would meet both their needs. Given Chugach’s previous experience with fuel cells, this technology became a promising prospect.
Chugach has participated in two other fuel cell projects in the USA. The first was in conjunction with the National Rural Electric Cooperative Association and involved a fuel cell on a mobile platform that was to operate at two other electric cooperatives before being sent to Chugach to be installed at a customer location. The second involved the State of Alaska Military Affairs Group which wanted to put two fuel cells into the Alaska National Guard facility.
“So we had experience with two fuel cell projects and what we thought would happen with fuel cells over time [would be] to bring the technology into on-site generation at customer locations,” explained Peter Poray, Manager of Energy Services at Chugach. “[But] we thought a couple of things would have to happen first: the price has to drop; and it has to work just as good as recip engines or turbines where you have multiple units operating on a site; and it has to be able to seamlessly switch so that the ‘phones and the computers won’t go out of service when you change between getting your power from the grid and the fuel cells and getting it just from the fuel cells.”
The long-term development of fuel cell technology, and its application in on-site environments was important to Chugach as a study it carried out three years ago indicated that over the next 20 years, it would need to install around 35 MW of on-site capacity at customer locations. It wanted to see if fuel cells were a viable prospect.
According to Chugach, the US Postal Service was also keen to exploit an ‘alternative’ technology. As a federal entity, says Poray, it has a responsibility to respond to certain federal initiatives, such as clean air and environmentally-friendly technologies, and fuel cells fit into this category. “So they were much more interested in fuel cells as a generation source than something that [combusts] a fossil fuel,” said Poray.
Development of the control and site management systems including a switching device and load sharing system, was one of the biggest challenges of the project
The project had three main goals: to make all five fuel cells operate as one; to operate them in an active electric grid using Scada technology so that they operate as if they are just another utility generation resource; and to have high speed switching capability in order to protect the mail processing centre’s business operations.
While these goals meant that numerous technical challenges needed to be overcome, financing had to be in place for the project to go ahead. Fuel cell installations cost around $4500 per installed kW, putting the cost of the Chugach project at around $5m. Funding for the project came from a variety of sources, including the US Postal Service, which paid its electric bill for the next five years up front.
Money or product was also contributed by two national research and development organizations that Chugach is a member of: the Electric Power Research Institute and a research network that is part of the National Rural Electric Cooperative Association. In addition, the US Army Corps of Engineers Construction Engineering Research Laboratory contributed the $1.2m site management system, which includes the switch that allows the fuel cells to isolate themselves from the grid.
In return for their funding, these agencies are receiving data on the operation and performance of the fuel cells to help them in their research into the technology. Chugach collects data on a daily basis and compiles proprietary technical reports detailing information on the plant’s operation.
According to Herb Healy, Manager of Programmes at IFC, the US Postal Service facility in Anchorage has a very dynamic load, peaking at around 800 kW and averaging 450-500 kW. The chosen configuration for the power plant was therefore five 200 kW fuel cells.
Each unit is an IFC PC25, a phosphoric acid fuel cell taking on natural gas fuel at the front end and producing 480 V, three-phase electrical power at its interface. Each fuel cell is essentially a standalone power plant, and is equipped with a fuel processing system. This is an integral part of each unit and consists of a hydrodesulphurizer system that removes hydrogen sulphide (H2S) and other sulphurs present in natural gas.
According to Healy, the fuel cells are designed to operate at 99.999 per cent reliability, equating to one outage of one minute every three years – a factor of high importance to both Chugach and the US Postal Service. “This means very high power availability to the load, which is what assured power is all about,” said Healy.
The five fuel cells connect to a common fuel cell bus, which is tied directly to the mail facility load bus and also to the grid. In this way, the fuel cells provide power to the facility, and any excess power generated is supplied to the grid. Connection to the grid is via a fast, solid state switch which allows the power plant to be isolated from the grid in the event of a grid disturbance.
In addition to supplying power to the mail processing facility and the grid, the fuel cells also supply the mail processing centre with heat. Hot water from the fuel cells is used as boiler makeup feedwater to supplement the existing space heating system, and is also used directly for space heating in a previously unheated warehouse. The use of the fuel cells as cogeneration units brings the thermal efficiency of the overall power plant to 85 per cent.
The power plant is equipped with several ‘layers’ of control systems that allow Chugach to control and monitor the fuel cells remotely. There is a PLC-based site management control system that interfaces directly via telephone lines between the five units and Chugach’s main dispatch centre, allowing Chugach to raise and lower output, power factor and so on. In addition, each individual fuel cell can be controlled separately, and there is a local Scada system so that the the five units can be controlled on site as a single entity.
A rapid switch
Implementing the control systems was perhaps the greatest challenge that the developers of the Chugach power plant faced. It was important that the plant could be controlled by Chugach from its main dispatch centre like any other generating resource, that it could supply the US Postal Service facility with reliable power, and that it could switch rapidly between grid parallel operation and grid isolated operation.
This set a number of precedents for IFC and its partners: “This is a first time capability in terms of paralleling multiple fuel cells onto a common load, it is a first time in terms of providing a group of fuel cells in combination with a static switch, and to be able to provide switching between grid parallel and grid independent operation,” said Healy. “It is a first time for us – and it may be a first time anywhere – that a distributed generation resource has been tied to a utility’s local dispatch centre using its own Scada system to control that distributed resource.”
An essential part of the plant’s site management system is the switch that allows the plant to be isolated from Chugach’s grid in a matter of milliseconds. According to Chugach, technology with this capability did not exist, and had to be developed specifically for this project. “We knew that if we couldn’t make it exist then there really wouldn’t be much of a role for fuel cells in our customer locations,” said Poray.
Steve Gilbert, Manager of Energy Projects Development, Operations and Maintenance at Chugach, also highlighted the importance of the switch to the project: “[The Postal Service] needed a highly reliable on-site generation source with the ability to run in parallel with the grid and at the same time separate from the grid should [a grid anomaly] occur, to ensure that there were no business interruptions related to energy delivery. So the switching capability becomes extremely important and very valuable as part of the overall inclusion of fuel cell technology.”
The switching device is therefore key to the project and also makes it unique. The switch permits the fuel cells to operate in parallel with the grid whenever the grid is present and within standard protocol limits of operation, i.e., operating correctly. In the event of either a grid outage or a grid disturbance, the switch immediately opens and takes the grid out of the loop. The fuel cells will continue to supply power to the facility load, independent of whether the grid is there or not there.
The capability of the switch is to open and isolate the grid in less than 4 milliseconds, which is less than one quarter of a cycle. With that speed, the momentary load disturbance that occurs when taking the grid out of the loop is well within the power quality limits established by computer and equipment manufacturers, thus protecting the postal facility’s operations. “[The fuel cells] are able to continuously provide power to the load well within any power qualities that have been established by solid state control and communications equipment,” said Healy.
IFC has delivered over 200 PC25 fuel cell units to projects around the world
Another technical challenge was the development of a load sharing device. In previous projects it has supplied, IFC’s fuel cells have been attached to their own individual dedicated loads. In the case of the Chugach project, when the grid is taken out of the loop and the fuel cells go into grid independent operation, they share equally the load of the postal facility. The load sharing device is a system that communicates with each of the on-board fuel cell control devices to keep the fuel cells synchronized. It also has to work with the switch device and its controls so that frequency and voltage transients are recognised and that the switching process takes place correctly.
According to Chugach, the fuel cell power plant is operated like any other of its power plants from its main control dispatch centre. It is run as a baseload unit, constantly supplying power to the mail facility and exporting power to the distribution grid. The fuel cells were started up in March 2000, and since then have generated 6000 MWh.
The site management system installation was completed in June 2000, and since the plant’s official inauguration in August, the switch has reacted to 32 grid disturbances to isolate the plant and assure power to the US Postal Service.
Overall, Chugach believes that there is potential for fuel cells to become a major technology solution for the on-site power market, but will examine future on-site projects on a case-by-case basis. Poray explains: “We have now dealt with the issue of multiple units operating at a customer site, load sharing, being able to go between grid parallel and grid independent operation, and now we need to make sure that we can find where it’s going to be cost-feasible to do this without grants and research money. Obviously [fuel cells] are expensive but they have many advantages.”