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Wind turbine economics

post #1 of 9
Thread Starter 
Wind Turbines - How to Calculate Cost Per Killowatt Hour
 
First point İ would like to make - İ like wind turbines! İ believe they are a good thing! But - liking a Chevy will not turn it into a Ferrari!  
 
İ just finished reading a blog about a wind turbine where the writer gives the manufactırer a great review and notes that by having this turbine you won't have to use power generated by the filthy fossil fuels that utilities like to use. İf you follow the recommendations of the writer you will probably end up with an expensive lawn ornament and still be using the same fossil fuel generated power as always.
 
İf you look at most wind turbine sales literature they tell you that , 'No problem - with 25 mph winds you will make a zillion kWh per year'.  They are highly optimistic about the output.

All this does you no good at all in trying to determine if a wind turbine is a good investment or not  - or if it is even the most practical place to put your money if you are simply trying to reduce your carbon footprint.
 
Some writers are little more than shills for the suppliers. İn some cases their green colored glasses are blinding them and in others possibly their ethics are possibly not all that great. This goes for many things and not just wind turbines.
 
You can find the average wind speed for your area in many places on the net - 
 
On one site İ found historical wind speeds for some 279 locations throughout the US. İn 186 locations annual average wind speed was below 10 mph, 
in 88 cases annual averages were in the 10 to 15 mph speed range,
4 in the 15 to 20 mph range, 
1 lone entry at 35.1 mph.
There will be places where there are higher winds but they are not normally where people live - ridge tops, mountain tops etc.
 
Commercial wind farms ALWAYS consider what is called 'capacity factor'. The turbine is not always available, winds not blowing adequately or whatever. Commercially a factor of between 10 and 35% is typically used meaning you take your locations average wind speed, look at the turbines power curve to determine the annual production and multiply that number by the capacity factor.

There are more scientific and accurate means of determining average wind speeds for a turbine but most cases never get that far. 
 
There is no standard method of rating a turbine so the manufacturers make up their own which naturally happen to make their unit look good. Most units are rated at 25 to 30 mph wind speeds which is meaningless for probably 98% of the population! The output at 10 to 12 mph is of much more interest.
 
There is 12.5% the power available to generate electricity from in a 16 mph wind speed as compared to a 32 mph wind speed. The power available in wind is calculated using Betz' law - a formula worked out nearly 100 years back. There are no exceptions - regardless of what suppliers may claim. 

Shrouds and other attachments are utilized to claim some magic enhancement for turbine output but until today none have been successful. 
 
Most locations are lucky to have an annual average wind speed of 10 to 12 mph.
 
Compare as proposed by a typical manufacturer (fairy tale) 12,000 watt output would be from a manufacturers power curve:
 
a) 30 mph wind speeds = 12,000 watts per hour * 8760 hours per year * 35% capacity factor / 1000 / 12 months = 3066 kWh per month
 
b) 30 mph wind speeds = 12,000 watts per hour * 8760 hours per year * 10% capacity factor / 1000 / 12 months = 876 kWh per month
 
To a more likely scenario - again the 1,000 watts is from the manufacturers power curve:
 
c) 10 mph wind speeds = 1,000 watts per hour * 8760 hours per year * 35% capacity factor / 1000 / 12 months = 256 kWh per month
 
d) 10 mph wind speeds = 1,000 watts per hour * 8760 hours per year * 10% capacity factor / 1000 / 12 months = 73 kWh per month
 
 
İn calculating returns at a 15 cent power cost:
 
a) fairy tale:  3066 kWh per month * .15 =  460 USD per month or 5520 USD per year
b) fairy tale:  876 kWh per month * .15 = 132 USD per month or 1577 USD per year
 
c) more likely: 256 kWh per month * .15 = 38 USD per month or 460 USD per year
d) more likely: 73 kWh per month * .15 = 11 USD per month or 131 USD per year - the owner would most likely save between 131 and 460 USD/year
 
With the 'more likely' production the unit is an expensive lawn ornament that will never pay for itself!  
 
Some turbines claim to start generating at 2 to 3 mph wind speeds - OK great but as there is very little (as in none) power available in 2 to 3 mph winds who cares.
 
İn the case of many people (many locations through out the world) one is better off to invest in a wind farm company than to own their own turbine. 
 
post #2 of 9
Russ,
This is a good report. We have a mountain cabin in a very windy area, so looked into Wind turbines. It is my experience that your information is spot on. In 99% of the instances, it just isn't there yet.  Another issue is wind direction change. Depending on topography, a small amount of turbulance can destroy a turbine. Vertical axis turbines handle this better, but their production in no better.
post #3 of 9
Thread Starter 
Good points whirnot!

Siting is an immense problem for residential wind turbines. A few more points about siting and other considerations:

a) A turbine should be at least 30 feet above any obstruction within 300 feet to have reasonably laminar air flow
b) Buildings are not a good location for a turbine despite claims by various manufacturers and bloggers.
c) A turbine must be maintained - any reputable manufacturer will state this clearly. This means either lowering the unit to the ground or using a crane/lift truck for access.
d) İf a flying object strikes the tower during a storm with strong winds chances are good it will come down. Not good to have a turbine too close to the house (or neighbor's house).
e) The turbine must have direct air flow into it. One concept has the turbine installed horizontally in the roof ridge of the house. There would be a small amount of power generation some small proportion of the time - unless you can figure out how to rotate the house.
f) Generally, heavier is considered better. An old Jakes or Bergey turbine will be be quite heavy and some of the new companies will have lightweight units. As a rule of thumb - the heavier the better (like the Jakes or Bergey).
g) Automatic turnoffs:
     1) New Patents or New Design - ain't nothin new in the industry - Betz' law is still 100% on and no one has figured out a way around it. Betz calculated the amount of power available in the wind and how much of that power can be extracted using a turbine.
     2) Time in business - the longer the better - hopefully they will still be there when you need them
     3) Shrouded turbines - just turn around and run - these have been tried and tried and tried and and and
     4) Silent - ain't no such thing according to the real experts - some do make more noise than others
     5) Multi-level marketing - forget it! You want to buy from a dealer who will be there in years to come not from a salesman in an frayed suit!
     6) Does not kill bats or birds - modern turbines rotate fairly slowly. Birds and bats are not totally stupid and they face far greater dangers such as cars and cats
     7) DIY - Build your own out of old coke cans and an electric shaver for 49.99. There are a few people who have the capability and interest to build one but 99.9% of us don't belong in that class.
     8) Fancy web site - often used to distract you from other shortcomings.
     9) Roof top mounted - probably the worst place possible to site a turbine. Best case you get little power and nothing goes too wrong. Worst case your whole house vibrates. İn any case there will be turbulent air flow.

Just in case the reader hasn't noticed İ get irritated at people who write puff stories for manufacturers and build up expectations with unreal data and calculations.

As regards economics off grid is another story altogether with some of the same considerations but other factors enter in as well. 
post #4 of 9
Thread Starter 
NREL is to have a wind turbine certification program operational - didn't see when though.

İt would be similar to the SRCC program for solar thermal panels & systems - that is a great program.

When buying a car you don't have any idea of all the certifications that the supplier must meet but you know that it was done. İt needs to be the same for solar PV, solar thermal, wind etc. There will be production figures that you know have been obtained under similar conditions. At present the manufacturer uses whatever numbers they think make their particular unit look best.

http://wind.nrel.gov/cert_stds/Certification/certification/index.html#The NWTC's Role 
post #5 of 9
Thread Starter 
Site selection is all important with a wind turbine! For example İ live in an area which is well known for wind surfing and within just a few kilometers there is a commercial wind farm. However - İ live on the sheltered side of the bay and wind would never pay off. My Davis weather station usually indicates wind speeds of 2 or 3 meters per second - about 50% of what is needed to become economical. İf you double the wind speed the available power in the wind goes up by 8 times - so not much there for me!

The following URL (from solacity) provides good information on turbine siting: http://www.solacity.com/SiteSelection.htm
post #6 of 9
Wonderful article. Except that the data make no sense. I talked to my neighbors, but even teenagers were not convinced.

You base your calculations on "average wind speed". However, the wind has quite more complex time behavior. Looking into a slightly more advanced data, which list speed average AND peak gusts (PGU), you may find out that gusts of wind usually are about 10X of the mean. Which means that most of the time you likely have winds that are well below the listed yearly average. Which also means that the turbune must fold down in one or another way when wind approaches the limit of its mechanical constuction.

More, given strong nonlinear energy output versus wind speed, the mean data are even more misleading. More, you forgot to include "sound pollution" from turbines even if they are not roof-mounted. And you forgot to include "light pollution", the psycologically unnatural and disturbing interuption of sunlight. Even more, you forgot to mention the cost of energy accumulators, due to high intermittency of winds. And a likely cost of insurance. And repairs.

In short, you probbaly need to revise your conclusion from wind energy being based on "build up expectations with unreal data and calculations" to "being totally uneconomical and unrealistic". Which would make it a very wonderful article for a green website.
post #7 of 9
Thread Starter 
Short summary of previous posts:

Residential wind turbines are generally not economically viable. Few locations have adequate wind. Even fewer have adequate wind at less than say 50 meters up. Turbines on roof tops are rarely successful.

Sound can be a problem with some models and in some locations - more so for the high speed smaller turbines.

The light pollution thing is generally a fruitcake thing. No science behind it that İ have ever seen.

Commercial wind turbines - many are being installed by companies that plan to make money on them. Must not be all bad.

With the net being a forum for all to post, there are some wacky ideas that get repeated and become quasi truth after so many repetitions. Many items are attacked from both extremes with little to back up their positions except the chatter on another blog. 

To the best of my knowledge, green sites are not required to only post crazy ideas. There is no reason they can not be practical and that is what we are trying for.
post #8 of 9
Hello Russ, your research is very great.
now I also intend to build my homemade wind turbines, I find a formula "Annual Output (KWH/year) = 0.01328 (d^2) (v^3)",
d is the blade diameter in feet squared.
v is wind velocity cubed in mph (average wind speed per year).
I do not know how does this formular really work? can you give me some advice, thank you very much!
post #9 of 9
Thread Starter 
Hi lichong712 - again welcome to the huddle!

Look for an article Apples and Oranges on www.homepower.com - most of their documents are available with subscription but a few like the one İ mentioned are free downloads - they explain better than İ.

The basic formula behind all wind is the Betz' law - it states how much power there is available in wind and how much of that you can capture. Anytime someone exceeds those limits you can be sure they are crooks.

One thing İ find greatly irritating is that the great green google loads pages to do with solar or wind with links from every shyster out there. There is no such thing as free power for most people - unlike what those sites claim.

When one of the shysters gets too bad a name on the market they just change the name and start again. 

One major thing with wind is location which includes elevation. Poor location and guaranteed nothing will happen.
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