0. B. S. E. E., M. S. Space Technology, LS IEEE
12.4 Wind Hybrid Systems
Frank R. Leslie,
B. S. E. E., M. S. Space Technology, LS IEEE
3/15/2010, Rev. 2.1
(321)

1. In Other News . . .
Wind Turbines in Chicago Tribune 3/14/10
(Source: Chicago Tribune) By Julie Wernau, Chicago Tribune
“Mar. 14--Months have passed since anyone has waved hello to one another in Waterman or Shabbona in rural DeKalb County. Some people claim they've even stopped going to church to avoid having to talk to former friends.
"It's gone. The country way of living is gone," declares Susan Flex, who lives in Waterman with her husband and their nine children.
The animosity stems from the greenest of energy sources: a wind farm. “
Complaints of noise and light flicker
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2. 12.4 Overview: Wind/Solar Hybrid Systems
Erratic energy sources like wind and solar are not dispatchable, that is, available on command of utility dispatchers
Sometimes or often, the wind blows when it is cloudy, or the sun shines when the wind is calm
A system that combines various energy sources is called a “hybrid” system
Diesel generators are often used for “reliable” power, and wind or solar are used to decrease the fuel costs
Studies of a site can indicate the optimal combination of wind, solar, and diesel (or gasoline) to provide power at the lowest overall annual cost
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3. 12.4 About This Presentation
Energy Mixture Availability
Hybrid Mixes
Economics of System Combination
Hybrid System Design
Balance of System (BOS)
Power Control
Power Availability
Hybrid System Examples
12.4 Conclusion
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4. 12.4.1 Energy Source Mixture Availability
Assessment of wind vs. solar for a specific site uses a small representative turbine or anemometer and a PV module
The energy ratio plotted throughout a year indicates the relative energies available, which can then be compared with system cost ($/kWh)
The actual energies available can then be compared with longer-term climate data to estimate annual variations
Life-cycle costs of the two systems must be included to get a comprehensive determination of an optimal system design
One of the systems might be omitted if the energy contribution is less than ~5% of the total
Why bother if $/kWh is too high?
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5. 12.4.1 Energy Source Cost Choices
Hypothetical Cost Line $
100% 0%
Wind $
50%
50% $
33.3%S, 33.3%W, 33.3% F
Solar $ 0%
100% $ $
50%
100% 0%
0%S, 100% F
Fuel
100%W, 0% F
Assess cost of various mixes of energy, enter total costs, sketch contours to seek lowest cost region
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6. Wind/Diesel
Wind/diesel systems work well where sunlight is limited, as above the Arctic Circle or below the Antarctic Circle
Wind turbines have worked well at the South Pole Station, but diesel generators are also hard at work there
Gasoline engines also can be used, but may lack the life of a heavy diesel engine
Diesel fuel costs $2.90; gasoline $2.77 as of 3/15/2010
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7. Wind/Diesel
3/15/2010 diesel prices
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8. Wind/Diesel
crude oil $ vs. production million barrels per day
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9. Solar/Diesel Hybrids
Solar power has a much more stable short term output than wind power; the solar energy is less “volatile” than wind to use an economics term
As the insolation rises in the morning, the diesel engine might be shut down until late afternoon or when clouds reduce solar power for a certain number of minutes
The controller could run the diesel engine only when the battery voltage drops below a very low set point, such as 10.5 volts
The diesel would be stopped when the battery voltage rose to approximately 13.9 volts
A battery-charging procedure minimizes the number of engine starts and ensures full-load engine operation
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10. Diesel Engines
A 9.2 kVA diesel package plant from Genasys Systems in a quieting package (top)
Multiple large diesel sets (bottom)
A small diesel might require 2.5 L/hr at idle and 7.5 L/hr at 14 kW changing somewhat linearly from idle to full load
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11. 12.4.2.4 Propane Engine Generator
Liquefied petroleum gas (LPG) in the United States is primarily propane, but also contains propylene, butane, and butylene
Gasoline-carbureted generators may be converted to propane; often done in pickup trucks in Western US
The Onan (Cummins) generator shown below produces 5.5 kW and costs ~$2970 (~$540/kW)
One gallon/hour of liquid propane will produce ~10kW
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12. Tripartite Systems
A wind/solar/diesel system is only somewhat more complex than the wind/solar type
The system balance between wind and solar is determined as in a conventional system, adjusting the costs of each to match the available energy
If the sun rarely shines, the solar equipment would not be cost-effective
If the wind rarely blows, the wind equipment would not be cost-effective
Each of these sources offsets the need for diesel consumption, yet including some diesel capacity improves the availability and reliability of power
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13. Fuel Consumption
The rate of diesel fuel consumption is critical to the analysis
Diesel fuel costs ~20% more than gasoline
Biodiesel is even more costly
Fuel transportation raises the actual fuel cost and must be included in the total price
The engine speed must be matched to the generator/alternator to optimize efficiency
When the generator runs, it should do so at full load, charging batteries as necessary, then shutting down completely to save fuel
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14. 12.4.3 Economics of Plant Combination
The location is the prime driver of the cost-analysis
When the remoteness and lack of roads makes fuel-hauling or helicopter transport too costly, the wind or solar components must be increased to ensure reliable power
Mountain-top radio repeaters exemplify the inaccessible site, and access may be limited to hiking or horseback (pack trains)
The handset radio has 5W to reach the repeater, the repeater receiver audio is patched to the 50W transmitter on another frequency, and the high power signal reaches other receivers farther away
Matching of the load times to the energy times determines the need for storage capacity
Scottish Moor
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15. 12.4.4 Hybrid Installation Design
Some rules from Manwell, et al.:
Without storage, the load limits what energy may be used or extracted
Load matching for time of day limits output as well
Diesel engines must be sized for highest load to carry the loads in normal operation
The savings is never greater than the fuel savings
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Manwell, et al., 2002

16. 12.4.5 Balance of Systems (BOS)
The balance of system must include the necessary fuel tanks, piping, transportation support, etc.
Local shops may be needed to perform engine overhaul, since the distance to civilization may be great
BOS must include means of transporting fuel to the engine
If a truck is normally used to travel to a location that has fuel, there might not be an extra trip or expense
With dual truck tanks, one might be used just for hauling fuel for the generator
The labor (driver) cost is increased slightly for getting fuel, but increased greatly if the trip would not have been otherwise made
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17. 12.4.5.1 Balance of Systems (Wiring)
An installation in China
Please don’t do this!
Wiring should be neat and well secured to prevent fires!
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18. 12.4.5.2 Balance of Systems (Diesel)
Fueled systems will require tanks, lines, and possibly pumps
In cold weather, diesel oil thickens, and insulation or heating of the lines may be required
Hot water tubes can be run parallel to the fuel lines
Small car engines may use 3 liters per 100 km (78 mpg)
If at 78 mph, that would be 3 L/hr, or to avoid mixed units systems, approximately 3/4 gallon/hour
A typical 500 gallon tank would hold ~500 hours of fuel, so replacement fuel must be obtained faster than that to keep the tank filled so the generator doesn’t stop
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19. Battery Storage
Batteries provide an “inexpensive” form of storage
They are required for wind and solar energy, but diesel (gasoline) generators could run to carry the load
For reliability, some diesel service might expensively be kept online at all times to avoid starting delays
Large battery systems require some maintenance checks but usually last for many years (7-20)
A large Uninterruptible Power Supply (UPS) can carry the load for minutes to hours or longer depending upon the amount of battery ampere-hours that supports it
Adding storage means that the energy available is “leveled” and unnecessary engine starts are avoided
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20. 12.4.5.3.1 Battery Storage (Australia)
This shipping container contains the controller and a very large battery
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21. Power Control
System monitoring by computer allows programming of automated supervisory monitoring and determines actions to take in response
The system functions in software might include
Start an engine
Control battery charging
Control energy load dumping for wind turbine
Change loads to match available power
Engage engine clutch
Report alarms to a distant operator
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22. 12.4.6.1 Power Control for Backup Engine-Generator
The engine-generator starting sequence automatically begins when the line voltage sags (drops) below perhaps 105 volts
A transfer switch changes the load from the wind/solar inverter output to the engine-generator output
The battery is connected to the starter motor and the engine is cranked to start under a solenoid-controlled choke fuel enrichment
As the starter turns over the engine-generator, the speed is sufficient to provide voltage to the load
Once the engine is running, the choke is opened to provide a normal fuel mixture
The entire sequence is so fast that lights on the load side don’t noticeably flicker
When inverter power returns for thirty seconds, the load is switched to the inverter (after a delay) and the engine is stopped
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23. 12.4.6.2 Power Control for Continuous Hybrid System
In a full hybrid system, the engine runs continuously and the wind/solar sources subsidize (add to) the available energy, saving fuel by shutting down the engine whenever possible
The inverter is synchronously matched to the power frequency and voltage, providing more or less power as is available
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24. System Availability
As long as the engine works and the diesel fuel lasts, system availability is high
If the renewable sources are low, the fuel will be used faster (and require replenishment more often)
If the engine fails and there is no storage (battery), the system will only have the varying renewable energy and might not function at all due to voltage variations
Solar energy might carry the load until mid-afternoon, but the wind system would be too variable in many locations
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25. 12.4.8 Example: Alaskan Hybrid Site
Coast Guard Station in Alaska
Wind and solar energy seem to be augmented by five large propane tanks near the base of the turbine
If so, a propane-fueled generator would be used instead of diesel
There is likely a really long fill hose on the supply boat that can connect to the tanks
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26. 12.4.8.1 Example: San Clemente Island, CA
US Navy turbine installation to reduce diesel fuel use by a navigation light
NREL determined that cost of energy (COE) was $0.193/kWh vs. $0.45/kWh baseline with all diesel power
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27. 12.4.8.2 PV Installation in Australia
Diesel generator supplies backup power
See for details
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28. 12.4 Conclusion: Wind Hybrid
Combinations of energy sources will provide more reliable power than any one source alone --- energy diversity
Diesel, propane, or gasoline engine-generators produce power on demand, and can self-start when the power line voltage is dropping
Natural gas can be piped to some areas
When wind or solar energy is available, the fueled generator will shut down, saving its fuel cost
Although overall costs are higher, the power is more reliable
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29. Olin Engineering Complex 4.7 kW Solar PV Roof Array
Questions?
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30. References: Books
Boyle, Godfrey. Renewable Energy, Second Edition. Oxford: Oxford University Press, 2004, ISBN (my preferred text)
Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, , TJ807.9.U6B76, ’4’0973.
Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991
Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., , TJ820.G57, 621.4’5
Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN , TK1541.P , ’2136
Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN
Texter,
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31. References: Websites, etc.
triangle plotting of proportions
RE systems
Lime Village, Alaska by BP
____________________________________________________________________________
Wind Energy elist
Wind energy home powersite elist
rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy map of CONUS Elist for wind energy experimenters
telosnet.com/wind/20th.html
solstice.crest.org/
dataweb.usbr.gov/html/powerplant_selection.html
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32. Notes hybrid
Sorenson p. 851
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