Renewable Electricity Technology



Wind & Hydro Power Technology

Mid Term Exam

Spring 2007

Name: ________________________________________

Please, clearly and neatly show all work and circle your final answer (extra paper for your preliminary work is included at the end of the test, and there is also an appendix at the end of the test with required formulae. Please neatly show your calculations on this test paper and circle your answers)

Circle true or false

1) True or False Most PV charge controllers can be used on hydro and wind systems.

2) True or False Wind generators for electricity production usually have many blades on their rotor.

3) True or False Assuming one has a good site, wind produced electricity generally cost less than PV produced electricity.

4) True or False When the wind speed doubles for a given location, say from 5 to 10 mph, the potential power in the wind increases by 800%.

5) True or False Wind speed normally increases with elevation

6) True or False A wind generator should be at least 30' above anything within 300' to 500'.

7) True or False Air density decreases with increasing temperature and increasing altitude.

8) True or False Wind speeds may double as the flow accelerates up the gradual slope of a long ridge, but the increase in wind speed mainly occurs in the top third of the slope.

9) True or False Wind speed data is often reported at about 30'

10) True or False The average of the cube of many different wind speeds will always be less than the cube of the average

11) True or False It is generally better to place a wind turbine downwind from obstacles

12) True or False Wind energy currently produces less than 1% of US energy

13) True or False Germany in the world’s leading adopter of wind technology

14) Identify 3 major or primary variables affecting the amount of power that can be extracted from the wind

15) What would be the power density (P/A) when the wind speed was 15 mph and the site was at sea level and 59 F? (Provide proper units)

16) Using the appropriate formula provided in the appendix indicate what the wind velocity would be at 100' when it is 10 mph @ 30', with a surface exponent of 1/5 or .20.

17) What would be the Average Annual Power Density (P/A), which could be used to estimate the AEO of a wind generator, if the annual average wind velocity was 12 mph and the site was at sea level and 59 F? (assume cube factor for Rayleigh frequency distribution)

18) Estimate the power (watts) available to a wind generator having a rotor diameter of 10 feet in a 12 mph wind at sea level & 59 F?

19, 20) Using the “Swept Area Method” estimate the quantity of wind energy one could expect to produce in a year with a Bergey XL.1 at sea level & 59 F on a 100’ tower when the hub average wind speed or average wind speed at 100’ is 7 m/s. The XL.1 has a rotor diameter of 8.2’. Assume that the “cube factor” or “energy pattern factor” is 1.9 and efficiency is 20%.

21,22) Estimate the annual energy output (AEO) in KWH of a Bergey XL.1 at sea level & 59 F on a 90' tower on Howards Knob where the annual average wind speed is 6 m/s @ 30'. Use power curves and Rayleigh distributions. Assume a surface roughness of exponent of .25.

Bergey XL.1

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|Wind speed bin m/s |Bergey XL.1 power (KW) | |Rayleigh frequency |Hours per year |Bergey XL.1 KWH/yr | |

| | | |distribution for annual |8760 | | |

| | | |average wind speed @ 90' | | | |

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Total KWH on Howards Knob from Bergey XL.1 @ 90':

23) What would be the power density of a 12 mph wind at 5,000’ and 10 F?

24) Using the AEO manufacturers performance curve (in appendix) for the Whisper 100 estimate the output in KWH produced on average in a month time when the average wind speed is 12 mph at the hub height.

25) What are the three major types of towers used for small wind systems and what type is generally the least expensive?

26) What would be the approximate cost per KWH for a wind system that costs $3500 and produces 3,626 KWH/year?

27) What is generally the maximum efficiency of a small wind system?

28) What does rated wind speed mean when used to describe a wind generator?

29) Identify 2 major categories of wind generators.

30) How many amps would a 1KW - 24 volt Bergey XL.1 wind generator produce at its rated wind speed?

31) Identify two commonly used methods of overspeed control for wind turbines in high winds.

32) What does the author of our wind book believe to be the best way to evaluate the output and cost of a wind turbine?

33) What are the 2 leading adopter states in the US for wind energy?

34) What is a nacelle?

35) What is the swept area of a wind turbine with a 14’ diameter rotor?

36) What is a typical capacity factor for a modern utility scale wind turbine and what does this mean?

37) What would be the simple payback of a Bergey XL.1 that has an installed cost of $3500 and produces 3,000 KWH per year that is worth $.10/kwh and there is a 35% tax credit in effect?

38) Identify two ways noise has been reduced in modern turbines?

39) What major incentive currently exists in the US for utility scale wind turbines and what does it provide?

40) Describe what a Weibull distribution of wind speeds describes ?

41) Describe what a wind turbine’s power curve is?

42) What are two major categories of vertical axis wind turbines ?

43) What is the horizontal movement of a wind turbine called which allows it to track the wind?

44) Describe the wind power classification system used throughout the world today.

45) Identify three commonly used instruments used to measure wind resources?

46) What is a qualitative measure used to assess the wind potential of a site?

47) What wind resource information can help one learn the prevailing wind direction?

48) What are two advantages of offshore wind projects?

49) What two countries are the leading adopters of offshore wind technology?

50) What does the tip/speed ratio describe and what would you expect it to be for a modern wind turbine?

Appendix

S/So = (H/Ho)(

1 m/s = 2.24 mph

1 mph = .446 m/s

A = (( r2)

P/A = ½ air density x S3

Average Annual P/A = ½ air density x v3 x 1.9

P = P/A x A

P/Po = (H/Ho)3(

AEO = AV P/A x A x % efficiency x 8760 h/yr or 720 h/mo.

P = V x I

V = I x R

Standard air Density = 1.225 kg/m3

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