Small Wind Site Assessment

Learner Guide

Produced by the Institute for Sustainable Futures; UTS in partnership with the Alternative Technology Association and TAFE NSW - Northern Sydney Institute

Supported by the NSW Government as part of the
Energy Efficiency Training Program — visit savepower.nsw.gov.au

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Topic: Estimating energy output from a wind turbine, Parts 1 and 2

Duration: 90 mins

Pre-reading: n/a

Objectives:

  1. Participants become familiar with two methods available to estimate (predict) the energy yield from a wind turbine
  2. Using a spreadsheet program such as MS Excel and inputting data manually
  3. Using a wind energy calculator software tool, inputting estimated variables manually

Instructions:

If time allows, ideally each participant will undertake these exercises individually to clearly demonstrate competency.

If partnering participants for time constraint reasons, it is suggested to ensure that each team includes at least one participant who is comfortable using Excel for data entry and basic mathematical functions. It is suggested to encourage the less confident or experienced Excel user of each teams to enter data, values and formulas to ensure they get the benefit of the exercise.

A.  Using a spreadsheet program such as MS Excel to estimate energy output from a wind turbine.

Using a spreadsheet tool such as MS Excel:

1.  Teacher to present in tabular form a Weibull derived (for example based on a K-value of 2.0) wind speed frequency distribution this is indicative of a ‘typical’ wind resource. 26 lines of data should be presented

  1. a percentage figure ranging from 0 to 100, or a factor from 0 to 1
  2. in speed bins of 1m/s, ranging from 0 to 25 m/s.

2.  Teacher to present in tabular form an appropriately verified power curve for a small wind turbine over a corresponding range of wind speeds. A 1kW wind turbine is recommended for this exercise.

3.  Guide participants to enter the above data into an Excel spreadsheet to allow calculation of the annual energy yield in three columns with appropriate headings (eg ‘wind speed’, ‘Frequency’ and ‘Turbine power’).

Ensure all participants/teams have accurately entered data before proceeding.

4.  Guide participants for convert frequency values to hours/year for each speed bin, under a new column. (There are 8,760 hours in a year)

5.  Guide participants to determine the gross energy yield for each speed bin, by multiplying the corresponding turbine power value with the hours/year at that speed.

Ensure all participants/teams have made the above calculations before proceeding, and understand the resultant data (Watt-hours or kilowatt-hours?)

6.  Guide participants to estimate the gross energy output by summing the data created in 5. Above

7.  Guide participants to derate values arrived at above to account for

  1. turbulence
  2. availability
  3. air density (as a product of elevation and mean temeperature)
  4. and so on (these topics are covered elsewhere in the course, so this should be a recap)

Compare results and discuss.

8.  (Optional) Ask participants to calculate the mean, median and modal wind speed values, and discuss the results (these topics are covered elsewhere in the course, so this should be a recap)

B.  Using a wind energy calculator software tool to estimate energy output from a wind turbine.

Using as tool such as WindCad or 7th Wind:

1.  Guide participants to determine and enter values (use similar/equivalent values to those used in A. where relevant) for

  1. reference wind speed (identified through 8. above),
  2. at a nominal hub height
  3. site altitude
  4. weibull K values
  5. wind sheer
  6. turbulence and other deratings
  7. other required inputs

Compare the results. Ensure all participants/teams have accurately entered valid values before proceeding.

2.  Guide participants to select different turbine types (or source and enter different power curves if required, this will depend on the features of the tool)

3.  Encourage participants to play around with all of the different values and consider the effect these changes have on the predicted energy output.

Discuss the results.

Discussion

Suggested discussion points:

What do we learn from A? And from B?

Which do you prefer?

What are the limitations of each?

What does A allow us to do that B does not, and vice versa?

What is the likely effect of underestimating or overestimating different values?

How are tools like this useful for wind site assessment?

When would you use them?

How would these be useful when educating customers?

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