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Wind power (view source)

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[[File:wind-turbine1.jpg|thumb|A wind turbine]]
[[File:Wind Turbines to the south of Stowford Cross - geograph.org.uk - 410831.jpg|thumb|Wind turbines]]
[[Category:Energy sources]]
 
Wind power is a possible option for renewable [[energy]].
Wind power is a possible option for renewable [[energy]].


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<small>A lot of people incorrectly call wind turbines "windmills". But in fact windmills are a much older technology, which use the wind to mill grains ''mechanically'' (no electricity involved).</small>
<small>A lot of people incorrectly call wind turbines "windmills". But in fact windmills are a much older technology, which use the wind to mill grains ''mechanically'' (no electricity involved).</small>


==Intermittency==
==Considerations==
{|class="wikitable"
|[[#Intermittency]]
|Needs [[energy storage]]
|-
|[[#Geography]]
|Restrictive
|-
|[[#Rare earth magnets]]
|Possible problem {{rn}}
|-
|[[#Cement]]
|Not a significant problem
|-
|[[#EROI]]
|Manageable
|-
|[[#Land use]]
|Manageable
|-
|[[#Noise]]
|{{rn}}
|-
|[[#Recyclability]]
|{{rn}}
|}


Wind power is even more intermittent than [[solar]]. There can be weeks where the wind blows strong{{x|although if it blows ''too'' strong, power also can't be generated - more on this later}}, and weeks where it barely blows at all.
===Intermittency===


Having multiple wind farms might ''somewhat'' reduce the intermittency. But in practice, this doesn't seem to help much.<ref>David JC McKay, Sustainable energy - without the hot air [Online], Available: http://www.inference.phy.cam.ac.uk/withouthotair/c26/page_187.shtml</ref>
Wind power is even more intermittent than [[solar]]. There can be weeks where the wind blows strongly{{x|although if it blows ''too'' strongly, power also can't be generated - more on this later}}, and weeks where it barely blows at all.


===Energy storage===
{{minor|Having multiple wind farms might ''somewhat'' reduce the intermittency. But in practice, this doesn't seem to help much.<ref>David JC McKay, Sustainable energy - without the hot air [Online], Available: http://www.inference.phy.cam.ac.uk/withouthotair/c26/page_187.shtml</ref>}}


Scaling up [[energy storage]] is already a challenge, even for solar which only needs about a day's worth of energy storage in general. Wind might need several weeks worth.
Scaling up [[energy storage]] is already a challenge, even for solar which only needs about a day's worth of energy storage in general. Wind might need several weeks worth.


Maybe wind power could be stored via [[hydrogen]], which doesn't have a ''fixed capacity'' the way batteries do. {{x|A battery can only store a fixed amount of energy at any given time. But hydrogen could be produced and stockpiled if necessary (as long as [[hydrogen gas/safety|safety]] concerns are addressed). Hydrogen production units (electrolyzers) still have a fixed ''power'' rating: There's a limit to how much hydrogen can be produced ''per unit of time''.}} [[wind/hydrogen|This has its own challenges.]]
Maybe wind energy could be stored via [[hydrogen]], which doesn't have a ''fixed capacity'' the way batteries do. {{x|A battery can only store a fixed amount of energy at any given time. But hydrogen could be produced and stockpiled if necessary (as long as [[hydrogen gas/safety|safety]] concerns are addressed). Hydrogen production units (electrolyzers) still have a fixed ''power'' rating: There's a limit to how much hydrogen can be produced ''per unit of time''.}} [[wind/hydrogen|This has its own challenges.]]


==Suitable wind speeds==
<tab name="(suitable wind speeds)" collapsed>
Most wind turbines can only generate power when wind speeds are between '''3.5 m/s''' and '''25 m/s'''.
Most wind turbines can only generate power when wind speeds are between '''3.5 m/s''' and '''25 m/s'''.
<ref>DASH, Meteorologically Defined Limits to Reduction in the Variability of Outputs from a Coupled Wind Farm System in the Central US [Online], Available: http://dash.harvard.edu/bitstream/handle/1/10981611/Meteorologically%20defined%20limits%20to%20reduction%20in%20the%20variability%20of%20outputs%20from%20a%20coupled%20wind%20farm%20system%20in%20the%20Central%20US_1.pdf?sequence=6</ref>
<ref>DASH, Meteorologically Defined Limits to Reduction in the Variability of Outputs from a Coupled Wind Farm System in the Central US [Online], Available: http://dash.harvard.edu/bitstream/handle/1/10981611/Meteorologically%20defined%20limits%20to%20reduction%20in%20the%20variability%20of%20outputs%20from%20a%20coupled%20wind%20farm%20system%20in%20the%20Central%20US_1.pdf?sequence=6</ref>
{{x|Power is proportional to the cube of the wind speed.}} When the wind speed is ''too high'', the wind turbine has to switch itself off completely{{x|maybe with the right innovations, it could just dissipate ''excess'' power instead of shutting off completely? If so, we should write a page about it.}} to prevent damage.
{{x|Power is proportional to the cube of the wind speed.}} When the wind speed is ''too high'', the wind turbine has to switch itself off completely{{x|maybe with the right innovations, it could just dissipate ''excess'' power instead of shutting off completely? If so, we should write a page about it.}} to prevent damage.
</tab>
<!-- TALK:
the above tab should probably be moved elsewhere.
-->
===Geography===
The best places for wind turbines [[wind/geography|aren't usually near where people live]]. In most cases, the distance is far enough that power lines wouldn't even be viable. {{qn}}
This might not be an issue if [[wind/hydrogen]] (as described above) is the main solution. Instead of power lines, the wind turbines would generate [[hydrogen gas]] which would be [[hydrogen gas/shipping|transported]] and used for [[energy]] elsewhere.
We'd need to estimate the full [[EROI]] of such a system, to make sure it's [[Term:viable|viable]].
===Rare earth magnets===
To build a wind turbine{{x|specifically, the ''dynamo'' component which converts spinning motion into electricity}}requires either ''strong magnets'' (made with rare earth metals{{qn}}) or a complex gearbox (which requires maintenance{{qn| - labor}}and isn't suited for offshore wind).
This page needs more research to determine which rare metals are needed, in what quantities, and whether there would be enough global [[mineral reserves]] to scale up wind power enough to replace fossil fuels or not.
===Cement===
The footing of a wind turbine requires a lot of concrete - a potential concern because cement production releases CO<sub>2</sub>. However, it turns out that the amount of CO<sub>2</sub> is '''not''' very significant:
<tab name="(see maths)">
{{dp
|<nowiki>concrete.density</nowiki>
|<nowiki>2400 kg/m^3</nowiki>
|<nowiki></nowiki>
|<nowiki>Dorf, Richard. Engineering Handbook. New York: CRC Press, 1996. "The density of normal concrete is 2400 kg/m^3 and the density of lightweight concrete is 1750 kg/m^3"</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
McGraw-Hill Encyclopedia of Science and Technology. "Volume generally assumed for the density of hardened concrete is 150 lb/ft^3. (2400 kg/m^3)"</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Read more: https://hypertextbook.com/facts/1999/KatrinaJones.shtml</nowiki>
}}
{{dp
|<nowiki>wind.rq_concrete</nowiki>
|<nowiki>125 m^3 concrete.density / MW</nowiki>
|<nowiki>Concrete needed to build a wind turbine</nowiki>
|<nowiki>Concrete mass, per megawatt of capacity (peak power), not per megawatt of the average output.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
SUSTAINABLE CONCRETE FOR WIND TURBINE FOUNDATIONS www.bnl.gov › isd › documents </nowiki><br /><nowiki>
"Turbines in the 1 to 2 MW range typically use 130 to 240 m3 of concrete for the foundation"</nowiki>
}}
{{dp
|<nowiki>concrete.cement_by_mass</nowiki>
|<nowiki>15%</nowiki>
|<nowiki>How much of concrete is cement</nowiki>
|<nowiki>The rest is rocks & sand (aggregate material) and water. I don't think the rebar is counted here.</nowiki>
}}
{{dp
|<nowiki>cement.ghg_by_mass</nowiki>
|<nowiki>0.81 tonnes per ton</nowiki>
|<nowiki>CO2 emissions of cement</nowiki>
|<nowiki></nowiki>
}}
{{dp
|<nowiki>wind.capacity_factor</nowiki>
|<nowiki>35%</nowiki>
|<nowiki>Wind power: ratio: average output / peak power capacity</nowiki>
|<nowiki>"The capacity factor of a wind turbine is its average power output divided by its maximum power capability. On land, capacity factors range from 0.26 to 0.52. The average 2019 capacity factor for projects built between 2014 and 2018 was 41%. In the U.S., the fleetwide average capacity factor was 35%."</nowiki><br /><nowiki>
https://css.umich.edu/factsheets/wind-energy-factsheet</nowiki>
}}
{{dp
|<nowiki>gasoline.ghg_by_energy</nowiki>
|<nowiki>71.30 kg / million btu</nowiki>
|<nowiki>CO2 emissions of burning gasoline</nowiki>
|<nowiki>https://www.eia.gov/environment/emissions/co2_vol_mass.php</nowiki>
}}
{{calc
|<nowiki>wind.rq_concrete * concrete.cement_by_mass * cement.ghg_by_mass / wind.capacity_factor</nowiki>
|<nowiki>days gasoline.ghg_by_energy</nowiki>
}}
</tab>
Compared to burning gasoline{{x|for the same amount of energy per unit of time}}, a wind turbine's cement footprint "pays itself off" in just under 20 days.
<small>This is pretty reasonable considering that a wind turbine's lifespan is about 20 ''years''.<ref>United States Environmental Protection Agency (EPA) - [https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100IL8K.TXT Renewable Energy Fact Sheet: Wind Turbines - epa nepis]</ref></small>
===EROI===
[[Energy return on investment]]: About 19.
In other words: wind turbines, over their entire lifespan, produce about 19 times as much energy as it takes to make them.<ref>Hall, C., et al. (2013) EROI of different fuels and the implications for society. Energy Policy (64), 141-152.</ref> There would still need to be some [[fossil fuels]] invested into wind power to "get the ball rolling".
Maybe there are some other wind turbine designs that have a better EROI. {{rn}}
===Land use===
Per unit of energy, wind needs far more [[land]] than solar{{x|in terms of the spacing between the wind turbines; not in terms of the footing size of the turbines}}. However, wind turbines can coexist with crop land, without interfering with [[crop yields]]. Crop land alone could meet global energy demands.{{qn| on a separate page}}
There should be no need to destroy natural habitats to build wind farms.
===Noise===
{{empty}}
===Recyclability===
{{empty}}


==References==
==References==
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<!-- TODO:
<!-- TALK:
sections to add:
sections to add maybe:
* viability: how much land is suited, how it can coexist with agriculture, how much energy can be captured per unit of land, capacity factors, etc
* designs: wind turbine types, with their pros and cons and pictures
* designs: wind turbine types, with their pros and cons and pictures
* something about rare-earth magnets{{qn}}
-->
-->
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