Page 296 - Alternative Energy Systems in Building Design

270 WIND ENERGY TECHNOLOGIES

POWER-PRODUCTION INTERMITTENCY LIMITS

In general, electricity generated from wind power is quite intermittent, and power output
differs from hour to hour and day to day and from one season to another. Since grid-
connected power production and consumption must remain in balance and be stable at
all times, this presents a substantial technical challenge for wind farm operators.
To stabilize wind power production, wind electrical technologies resort to a number
of energy-management strategies, including incremental operating reserves, energy
demand management, load shedding, and storage solutions.
In the event of low levels of wind power production, commonly referred to as pen-
etration (which may result from wind fluctuations or the partial failure of generating
capacity), wind farms are required to provide a certain amount of reserve power-
production capacity that can be used to regulate and stabilize the variability of wind
generation. One such energy-management strategy is referred to as pumped storage,
which is wind energy developed during high-wind periods that is stored and then
released when needed. Energy storage is accomplished by pumping water uphill into
reservoirs during peak power-production periods and making use of the stored poten-
tial energy of the water during peak demand periods. In some instances, in the absence
of water-storage reservoirs, solar wind farms supplement additional stabilizing power
by means of natural gas–fired electric generators.
In California and Texas, for example, during hot days in the summer, there is low
wind speed at exactly the time when there is high electric demand. In contrast, in
England during winter, the demand for electricity is higher than in summer, and so are
the wind speeds. Since during most days of the year peak solar power tends to occur
during the daytime in the absence of wind, it cannot be used as a complementary
power production to wind.

PENETRATION

Wind energy penetration refers to the percentage of energy produced by wind turbines
when compared with the total available wind kinetic energy potential. Factors affecting
the penetration ratio are capacity for energy storage, cost of power production, and
energy management.
In the event of equipment failure, all grid-connected wind energy farms, for power
regulation purposes, are required to have a guaranteed energy storage capacity that
will allow for consistent power transmission. Depending on the location and specifics
of a wind farm, energy storage capacity may be as much as 20–25 percent of the over-
all power-generation capacity. This adds significant technical and economic chal-
lenges for operators.

WIND POWER FORECASTING
Owing to the intermittent nature of wind energy, in order to regulate power-plant pro-
duction, operators are required to predict short-term hourly or daily plant output. As a
result, as with all other grid-connected electricity sources, wind energy also must be