Operational Issues of Wind Farms P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Issues of Concern during Entire life of Windfarm.......…

Detailed Project Planning Pre-Project Planning Detailed Project Planning Planning of internal Controlling System Financing and Insurance Arrangements Tender Process Master Plan

Detailed Engineering Planning Master Plan Contracting Detailed Engineering Planning Pre-Testing & Training Production & Procurement Installation & Commissioning

Installation & Commissioning Full Operation Operational Services and maintenance Safety Issues Environmental Monitoring

Windfarm Operation Successful operation of a wind farm requires (1) information systems to monitor turbine performance (2) understanding of factors that reduce turbine performance (3) measures to maximize turbine productivity.

Automatic Turbine Operation Automatic turbine operation requires a system for oversight in order to provide operating information to the turbine owner and maintenance personnel. Turbines in wind farms have the capability to communicate with remote oversight systems via phone connections. Remote oversight (SCADA) systems receive data from individual turbines and display it on computer screens for system operators. These data is used to evaluate turbine energy capture and availability. Availability is defined as the percentage of time that a wind turbine is available for power production.

Availability of Wind Turbines The availability of wind turbines with mature designs is typically between 94% and 97%. Reduced availability is caused by: Scheduled and unscheduled maintenance and repair periods, Power system outages, and Control system faults. The inability of control systems to properly follow rapid changes in wind conditions may lead to low availability. Imbalance due to blade icing, or momentary high component temperatures can cause the controller to stop the turbine. The controller usually clears these fault conditions and operation is resumed. Repeated tripping usually causes the controller to take the turbine offline when a technician can determine the cause of anomalous sensor readings.

Daily & Weekly Energy Productions Wind turbine manufacturers provide power curves representing turbine power output as a function of wind speed. A number of factors may reduce the energy capture of a turbine or wind farm from that expected. The reasons are: Reduced availability, Poor aerodynamic performance due to soiled blades and blade ice. Soiled blades have been observed to degrade aerodynamic performance by as much as 10–15%. Lower power due to yaw error, during control actions in response to wind conditions. Interactions between turbines in wind farms.

Losses due to Poor Aerodynamics of Blades Airfoils that are sensitive to dirt accumulation require either frequent cleaning. In these sites blades must use airfoils whose performance is less susceptible to degradation by the accumulation of dirt and insects. Energy capture is also reduced when the wind direction changes. Controllers on some upwind turbine designs might wait until the magnitude of the average yaw error is above a predetermined value before adjusting the turbine orientation. This results in periods of operation at high yaw errors. This results in lower energy capture.

Operation during Turbulent Wind Conditions Turbulent winds can also cause a number of types of trips. In turbulent winds, sudden high yaw errors might cause the system to shut down and restart. In high winds, gusts can cause the turbine to shut down for protection when the mean wind speed is still well within the turbine operating range. These problems may reduce energy capture by as much as 15% of projected values. Operational Service personal should not only be prepared to minimize these problems. Planning should also anticipate them in their financing and planning evaluations

Maintenance and Repair Wind turbine components require regular maintenance. Frequent inspections must be carried to make sure that lubrication oil is clean, seals are functioning. Lean inspections to make sure that components subject to normal wear processes are replaced. Problem conditions identified by oversight systems may require that the turbine be taken out of operation for repairs.

Safety Issues The installed wind turbine needs to provide a safe work environment for operating and maintenance personnel. The turbine also needs to be designed and operated in a manner that it is not a hazard for neighbors. Safety issues include such things as: Protection against contact with high voltage electricity Protection against lightning damage to personnel or the turbine. Protection from the effects of ice build-up on the turbine or the shedding of ice The provision of safe tower-climbing equipment, and lights to warn local night time air traffic of the existence of the wind turbine. Maintenance and repairs may be performed by on-site personnel or turbine maintenance contractors.

Potential Negative Impacts of Windfarms The potential negative impacts of wind energy can be divided into the following categories: Avian/bat interaction with wind turbines; Visual impact of wind turbines; Wind turbine noise; Electromagnetic interference effects of wind turbines; Land-use impact of wind power systems; Other impact considerations. In spite of growing needs, wind energy is still facing resistance from public/authorities due to health and environmental concerns. The governments have published a series of reports regarding noise generation of wind farms. Reflecting increasing public awareness of this potential issue.

Avian/Bat Interaction with Wind Turbines There are approximately 300–400 bird fatalities per MWh due to wind turbines. The species fatalities associated with fossil fuel plants are much higher, approximately 5,200 fatalities per kWh. The implication is that as wind energy displaces progressively more fossil fuel based electricity, the overall effect on avian populations will be positive. There are two primary concerns related to the adverse effects of wind turbines on birds: (1) Effects on bird populations from the deaths caused either directly or indirectly by wind turbines. (2) Violations of the Migratory Bird Treaty Act, and/or the Endangered Species Act.

Birds and Wind Turbines Windfarms can adversely affect birds in the following manners: Bird electrocution and collision mortality; Changes to bird foraging habits; Alteration of migration habits; Reduction of available habitat; Disturbance to breeding, nesting, and foraging. Conversely, windfarms have the following beneficial effects on birds: Protection of land from more dramatic habitat loss; Provision of perch sites for roosting and hunting; Provision and protection of nest sites on towers and ancillary facilities; Protection or expansion of prey base; Protection of birds from indiscriminate harassment.

Quantitative Studies on Bird-windfarm Interactions Bird Utilization Rate (BUR): The number of birds using the area during a given time or time and area. Bird mortality (BM) : The number of observed deaths, per unit search area. Bird Risk (BR) : The likelihood that a bird using the area in question will be killed.

Ecological Optimization of Windfarm Bird risk can be used to compare risk differences for many different variables: Distances from wind facilities; Species, type, and all birds. Seasons; Turbine structure types. It can be used to compare risks between wind resource areas and with other types of facilities such as highways, power lines, and TV and radio transmission towers.

Windfarm Noise & Ecological Issues Although it is still unclear whether wind farm noise has negative health impact, it concerns both the developers and the residents near wind farms. Therefore noise is an important factor in environmental monitoring.

Noise generation in Windfarms Noise generation in wind turbines can be generally traced back to either mechanical noise or aerodynamic noise. Mechanical Noise : Due to operation of turbine’s mechanical components produces noise. Aerodynamic Noise : Generated by wind flow and its interaction with the turbine itself. Noise propagation is affected by several factors: Ground effects Topography, Temperature Atmospheric conditions Aerodynamic effects caused by wake interactions and The geometric configuration between noise sources and receivers.

Quantification of Noise Level The sound pressure level of a noise, L, in units of decibels (dB), is given by: p is the instantaneous sound pressure in Pa.

Noise Modeling ISO-9613-2 standard: Receptors are the locations where the sound level is to be measured or predicted. In wind farm layout design, all residences located within the wind farm terrain, or within a certain jurisdiction-dependent neighborhood. These locations are considered receptors for noise calculation purposes. During design and development, the equivalent continuous downwind Octave-Band Sound Pressure Level (SPL) at each receptor location is calculated for each point source,

Mono Octave Band S P L SPL at each of the eight octave bands with nominal midband frequencies from 63 Hz to 8 kHz, as where Lw is the octave-band sound power emitted by the source, Dc is the directivity correction for sources that are not omnidirectional, A is the octave-band attenuation, and subscript f indicating that this quantity is calculated for each octave band frequency.

The attenuation term (A) Geometrical divergence : Adiv Atmospheric absorption : Aatm Ground effects : Agr Sound barriers : Abar Miscellaneous effects : Amisc Generally the attenuation due to sound barriers and miscellaneous effects are negligible for windfarms.

Effective S P L Several octave-band weightings are available to convert the Individual band SPLs to an effective SPL. For wind farm layout applications, it is customary to use A-weighted SPLs . The equivalent continuous A-weighted downwind SPL at specific location is calculated from summation of contributions of each point sound source at each octave band where ns is the number of point sound sources, j is the index representing one of the eight standard octave-band mid band frequencies, Af(j) : the standard A-weighting coefficients

SPL (A-weighted) as a function of distance from the source

Sound pressure level contour maps generated by OPENWIND WR36 : 30 turbines