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Renewable Energy

Mandatory portfolio standards have different implications for different technologies.

Fortnightly Magazine - November 2004

result of this transition. According to the American Wind Energy Association, eight to 10 wind generators of a given capacity, installed in carefully matched locations, are required to ensure reliable availability of the capacity of one of the generators 8,760 hours per year. In most cases, with eight to 10 generators available for service, capacity greater than the capacity of a single generator would be available; however, while that additional capacity could be used when available, it could not be relied upon. The number of individual wind generators required could be reduced if the capacity of the individual generators were increased and the installation were accompanied by adequate electric storage capacity.

Wind generation cost would also be severely impacted by the transition to "reliable source" status. The cost of wind energy would no longer be based on the cumulative output of a single wind generator and its cost of ownership, but rather on the reliable output of a group of 8 to 10 wind generators and their associated storage and the cost of those aggregate facilities. Generation output over and above the reliable output of the aggregate facilities will have some reduced value, since it must be backed-up by spinning reserve or must be linked to loads that can be rapidly and reliably removed from the grid when the power output of the wind generator is not available.

Wind generation is probably also the most rapidly variable of the renewable sources. This would tend to complicate the transmission grid reliability management problem, since individual wind generator output can vary quickly and the transmission grid and other generation resources must be able to respond as required to follow the system load. This complication could be relieved to some degree by the availability of adequate storage capacity capable of frequent, deep cycling.

The application of wind generators also has implications for the design of the electric transmission system, which must be capable of adjusting automatically and quickly to the total availability of wind generation and the magnitudes and locations of the power feeds into the grid.

Wind energy systems also are experiencing increasing resistance because of their appearance and the potential harm to certain types of birds that fly into the path of the blades. NIMBY concerns have been raised very recently concerning a proposed offshore wind farm in the Northeast. The requirement for multiple wind turbine installations in selected locations to achieve adequate reliability complicates this issue by increasing both the number of required wind turbines and the number of locations that must be reviewed and approved.

Solar: Not 24-7

Solar electric generation generally is considered to be available a maximum of 6 to 8 hours per day, depending on location and time of year. However, solar energy may not be available for several hours on a given day, or even for several days, depending on weather conditions at the collection location. Thus, solar generation must be accompanied by storage sufficient to meet power demand during the diurnal periods when solar energy is not available, as well as during daily periods when solar