For clarification, the "Vestas availability" you talk about is not specific 
to Vestas nor is it based on any Vestas contractual availability.   This 
availability is a multi- industry standard for simple "series component" 
availability.   There is no credit for maintenance or repair time time which 
is why a 3-5% loss is considered acceptable for long term performance.   The 
3-5% loss includes maintenance.   An availability metric that shows the 
turbine as available during repairs would be very objectionable to future 
owners.    Pausing the turbine during maintenance may be acceptable if the 
long term goal is set accordingly.   For example, if the turbine is always 
paused during maintenance then the long term system goal should be close to 
the 99.5% goal for grid availability.




Hollis Kimbrough
05/15/2002 07:40 AM
To: Mark Fisher/EWC/Enron@Enron, Mark V Walker/EWC/Enron@ENRON, Jeff 
Duff/EWC/Enron@ENRON
cc:  

Subject: Calculating "Vestas Availability"

Guys,

In an earlier e-mail Ben made the statement:  "Have you been able to 
determine what these numbers would look like using Vestas' definition of 
availability:  Hours of Wind Turbine in Operation mode X 100 / Hours of Grid 
in Operation Mode." 

We now need to develop a methodology to calculate the Vestas definition using 
VisuPro data.  I think this boils down to:

Vestas Avail = (SOT+WOT+EST+RT+MT)/(ST-LOT)

Where:

SOT = System Okay Time
EST = External Stop Time
WOT = Weather Out Time
LOT = Line Out Time
DT = Down Time
RT = Repair Time
MT = Maintenance Time

ST = SOT+EST+WOT+LOT+DT+RT+MT

This calculation is based on an operating assumption that the current day 
machines are placed into "pause" mode during maintenance and repair time.  As 
a result the availability counters will continue to increment even when the 
turbine is being serviced.  

Let's get together and discuss,
Hollis