Far from being regarded as a restriction on wind development, the inclusion of specific rules for wind energy in America's national grid code is cause for celebration in wind industry circles. "We saw increasing discussions about reliability," says Mike Jacobs of the American Wind Energy Association (AWEA). In response, the association worked with a group of experts to develop a set of performance specifications that the new grid rules closely follow.
"We wanted wind to address as many concerns about reliability and broaden the market for wind. Anytime there's a question, there's hesitation. We were trying to broaden the market by reducing objections.... This really is part of a wider acceptance of wind by the utility world."
Jacobs says the new rules, issued by the US Federal Energy Regulatory Commission (FERC) in May, are likely to add to the cost of equipment initially. But they will provide a uniform set of requirements known to all equipment vendors, thus reducing costs in the long run. "The technical specifications for performance will allow manufacturers to plan turbine design with greater certainty," he says.
Michael Skelly of Zilkha Renewable Energy says that increased cost is acceptable. "It will increase costs," says Skelly. "But since the rules are the same for all players in the industry, it should not affect us unduly." As for how the new technological requirements might affect the wind turbine supply situation, Skelly says: "I think it's fair to say 2006 will be a turbine-constrained year all around."
The rules for wind are contained in FERC's Order 2003-A and are intended to deal with concerns expressed by wind turbine manufacturers and developers who have sought standardised interconnection requirements, the order states. It adds that the need to meet widely varying standards across the US contributes to increased manufacturing costs and serves as a barrier to development.
The order, which applies only to projects of 20 MW or more, contains several key provisions. It demands that during a voltage sag on the network down to 15% of what it should be, wind turbines ride-through the fault and stay connected for 625 milliseconds. "The low voltage ride-through standard is the same as the anticipated standard for interconnection for Europe," says Jacobs. Grid codes in at least some European countries, however, are demanding a higher standard.
The North American Electric Reliability Council (NERC), too, is proposing a higher standard, demanding that even at zero voltage, wind turbines stay connected for 167 milliseconds. FERC has granted a rehearing on the issue and given NERC and AWEA until September 14 to resolve the issue. A subsidiary of NERC, the Western Electric Coordinating Council, has already adopted the 625 millisecond standard.
There are no specific requirements for reactive power during recovery from a grid fault. Rather, the wind plant is required to return to status before the fault. If a plant was providing reactive power to the grid, it would return to that status. Wind stations of 20 MW and more must meet the same technical criteria for provision of reactive power as conventional large generating facilities. They must generate reactive power so that the power factor lies in a range of 0.95 leading to 0.95 lagging, meaning that power plant must provide or draw reactive power by up to 30% of the active power. The order does not apply to individual wind turbines.
While projects are required to be equipped with supervisory control and data acquisition equipment (SCADA), demands for real-time communications and data exchanges between the wind power producer and the grid operator are not specified in the grid code, which leaves them to be governed by contracts or market rules adopted outside FERC's regulatory domain.
Requirements for wind turbines to ride through momentary grid faults and meet demands for reactive power apply only to wind power interconnection agreements signed on or after January 1, 2006. Unlike in Europe, the US code does not stipulate that wind plant provide frequency control services. Neither does it make reference to constraining wind power output, in contrast to demands being made by transmission system operators on the European mainland.
Important for business planning and getting into the interconnection queue, the order allows developers to study the feasibility of interconnection designs without costly detailed studies. Developers can provide simplified electrical models when initially applying to connect with the grid, and can take up to six months before completing electric specifications and choosing turbine models -- both of which are required for a full interconnection study. It allows the developer to receive base case grid data from the transmission provider without providing load flow parameter data. Previously, FERC required that a project's initial study include such things as precise siting and turbine types -- variables that typically are not detailed until later in a project.