# how much wind

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how much wind do we need to generate power?

• Solar Expert Posts: 8,861 ✭✭✭✭✭
How much power do you need ?  Generally, you can get that info off your monthly electric bill as KWhrs
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• Super Moderators, Administrators Posts: 30,712 admin
Here is an example of a "home size" Wind Turbine:

https://www.solar-electric.com/lib/wind-sun/Air-spec-sheet.pdf

If you look at the above link, you will find a second chart that shows you need at least 10 mph wind and the turbine will peak at ~20-30 mph. Above ~25-30 mph, most wind turbines will cut back on output or even shut down completely until the wind speed drops.

The above chart, for example, assumes wind at 18 mph for 24 hours per day, 30 days per month:
• ~80 kWH per month = 80,000 WH per month
• 80,000 WH per month * 1/30 days per month * 1/24 hours per day = 111 Watt output from turbine
Note that nobody has constant 18 MPH wind every hour of the day for an entire month (or entire year). 18+ MPH constant wind is a miserable place to live (your plastic lawn furniture is blown around the yard).

To compare with a solar array--In decent location with decent weather, assume a minimum of 3 hours of sun per day (typical sun ranges from ~2 hours per day in places with bad winter weather to near 8 hours per day in best case summer).
• 111 Watt wind turbine output * 24 hours per day = 2,664 WH per day
• 2,664 WH per day * 1/0.77 solar panel+controller deratings * 1/3.0 hours per day sun = 1,153 Watt "equivalent" solar array
• 1,153 Watt solar array / 250 Watt solar panel = 4.6 ~ 5x 250 Watt solar panels
And you can use long term weather/hours of sun tables to "estimate" the typical amount of sun you will get for your location (assuming no shading, not in bottom of valley during winter, etc.):

### San FranciscoAverage Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
(For best year-round performance)

 Jan Feb Mar Apr May Jun 3.77 4.26 5.46 6.07 6.21 6.07 Jul Aug Sep Oct Nov Dec 5.49 5.34 5.40 5.05 4.19 3.69
Using San Francisco Airport (SFO)---Not a particularly sunny location (marine layer), we see that (on average) we get >3.0 hours of sun every month of the year. In summer we see ~2x as much sun (5-6 hours of sun per day).

Here are some examples of a real life, much larger wind turbine (this is ~2.4 kWatt turbine vis the the above ~250 watt peak turbine I used above).

https://forum.solar-electric.com/discussion/5509/skystream-owners-and-actual-production-rates

(I am not sure I trust the numbers from BillF link in the above thread--His numbers do not seem to add up on the summary page vs the daily production numbers:http://loami-windmill.com/winddata.htm).

The old "Jane Skystream" data got hosed again in the archive... A copy I recovered:
It looks like the forum conversion lost Jane's monthly data (only long term, small wind, installation performance numbers I have heard). Very important historical information (In my humble opinion):

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Total 2007 n/a n/a n/a n/a n/a n/a n/a n/a n/a 175 225 0* 400 2008 98* 292 308 246 228 153 92 84 97 164 246 472 2,480 2009 265 348 244 371 182 86 90 84 250 100 194 131* 2,345 2010 101 130

* December, 2007 - Skystream shut down from software problem with cold and would not restart.

* January, 2008 - Skystream down until the 27th. Produce 98kWh in the 5 days remaining in the month.

* December, 2009 - Skystream shut down several times and would not restart on it's own, production very low for wind speeds.

* January, 2010 - Production very low for wind speeds.
* February, 2010 - Production very low for wind speeds.

In the end, as with solar, wind turbine requirements are based on three things; location, location, location.

You need to be in a pretty windy location, the turbine needs to be installed in smooth/clean airflow (laminar airflow), typically on a 60 foot or taller tower, and will need maintenance (typically around once per year, especially after a few years in operation). It needs to be installed away from occupied buildings (turbines throwing blades, dropping nacelles, and tower collapses are common risks, especially if not reliably maintained).

Anyway, fair warning--I am not a fan of small wind systems. I believe for most people, that a solar power system will produce more reliably, less maintenance, and at a lower cost that virtually any "home sized" residential system. Of course, there are some locations (far north, windy hills, etc.) where there are conditions (winter) where wind turbines offer an alternative to generator sets... But there is still the cost of maintenance (servicing a wind turbine on a 60+ foot tall tower).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,309 ✭✭✭✭
60' tall tower? Jeepers.

I studied wind energy a few years ago. Optimal wind speed is 15-30 mph. Major turn off for me since we often get winds well over 30 mph. I was still working on a new roof with 35 mph gusts today. Not the safest endeavor in the world. Just walking up there could be challenging. Now we have 45 mph gusts. My sources said the user needs a minimum of 20'. While 60' would be nice, servicing that would be ridiculous.

People with solar and wind always seem to prefer the solar and by a lot. I wouldn't be opposed to supplementing solar with wind but I certainly would not rely on wind power alone. We notice strong winds but few places are generating 15-30 mph winds for several hours/day.

I often drive by commercial wind generators that were placed in an optimal location. They are absolute bums the vast majority of the time.

Plus wind generators have moving parts which equals maintenance or failure 100% of the time.
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• Super Moderators, Administrators Posts: 30,712 admin
Generally, the turbine needs to be 20 feet above the terrain, trees, buildings, etc.

The turbine needs to be in clean airflow).

Years ago, somebody here suggested to fly a kite on the site. Where the kit flies stable is the minimum blade hight.

There is also the drag if the "Earth". The higher you go, the higher the average wind speed.

Bill

Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset