WINDMILLS - How many watts per hour does a windmill ACTUALLY produce?

Question

I am confused about the energy output a windmill has. How much overall watts per day can you receive from a 3000 watt waindmill? From what I understand, a windmill will only produce lets say 3000 watts when wind speed is 28 mph. If that is the case, how many watts will it produce when the wind speed is 7 mph which is the average wind speed in most places? So how many watts per hour per day would you receive from this? Considering a 3000 watt wind mill costs $6,000 would it really only produce 1kW every hour on average cause that isnt much? And if that is correct or close to it, if 1kWh is produced 24 hours a day, and it is used for 12 hours a day, will the other 12kW be stored in a battery for later use? Thanks a lot for your answers!

Answer 1

To be absolutely correct, the windmill produces no electrical energy. It's simply the driver used to turn a set of coils in a magentic field, thereby producing electric current and voltage.

The limitation on the output is dependent on a couple of things:
- the efficiency of the electrical machine (usually located inside the nacelle, behind the blades)
- the allowable variability in blade pitch (to make the most out of changing wind speeds)
- the mechanical efficiency of the gear unit (typically, the blades turn MUCH slower than the electrical machine, to try and keep the size of the machine within reasonable bounds).
- the actual 'wind speeds' in the area
- the ability of the windmill to pivot (to accomodate for changing wind direction).

Using a wind generator does not automatically mean there is a 'battery' or other energy storage system attached. In fact, most do not. This is because wind energy is used to supplement the energy generation from other sources ... which means the connection to the grid is already present.

If the blade has no provision for variable pitch, the power produced is approximately equivalent to the cube of the speed ... thus if the generator produces 3000 kW at 28 mph, it will produce 47 W at 7 mph (3000 x 7/28 x 7/28 x 7/28 = 47).

If the wind gets too high, there has to be a brake on the propellor shaft to stop rotation (to pervent damage to the internals); at very low wind speeds, the device does not generate enough energy to overcome its internal friction and other losses. This means the 'active range' is fairly narrow - something like 7 to 20 miles per hour. Using variable pitch blades can help somewhat ... but only by extending the top end to perhaps 30 mph.

As to how much the wind generator can produce per hour? Typically, the generator is rated at a given kW output. This means the generator can produce this much power indefinitely, provided the conditions are suitable to do so. In a year, it will produce that many kilowatts times the number of hours in operation (typically assumed to be about 50 percent of the time).

Answer 2

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RE:
WINDMILLS - How many watts per hour does a windmill ACTUALLY produce?
I am confused about the energy output a windmill has. How much overall watts per day can you receive from a 3000 watt waindmill? From what I understand, a windmill will only produce lets say 3000 watts when wind speed is 28 mph. If that is the case, how many watts will it produce when the wind...

Answer 3

First, lets assume that the 3000 watt windmill operates continuously for 24/7 all year long. 3000 watts = 3 kW so it could potenttially produce 72kWH per day, or 26,280 kwH per year. At $0.08/kW, that could save you $175 a month or $2102 a year. That would be great if you needed that much power and could get that type of return (less than 3 years). Everyone should install one if these results could be acheived for $6,000. However, that would be the maximum, theoritical amount saved by this unit and the real savings would be much less. Most newer, typical homes, 1500-3000 sq ft, would not require that much electricty each month, and even if they did, there would be times in the day where they required more than 3kWh and times at night where they would require less than 3kWH.

The way to look at this would be to find out the ratings for the windmill based on wind speed and compare that to an average wind speed distribution for your area. My best guess would be that for most places, instead of receiving 72kWH per day, you would probably receive 15-30 kWH per day with this size unit. One benefit that you asked about concerning the over-production that could occur during your low-load period is that most utilities will allow you to connect your system such that the excess energy will subtract from your overall bill, so that the excess energy created will not be wasted, nor will you have to go to the trouble of storing it. It will simply subtract from your electrical usage for that month. The old electro-mechanical meters would actually spin in reverse, thereby removing the kWH from the meter. New solid-state meters can be set-up to also subtract reverse power flow. Other utilities might require a second meter for accumulating the excess power generated and then pay you based on that. Most times that rate will be called an avoided cost of production rate and will be less than the retail rate. In effect, that compensates the utility for having the system in place to serve your entire load at all times, even though your net usage may only be half of what your neighbor's is. Check with your local utility and they can inform you of what they need to connect your system.

I would be surprised if you could get it bought, installed, and add the necessary equipment to your electrical system for $6,000. You have to purchase and install some means of disconnecting your windmill from the utility side for protection during outages, otherwise, a dangerous situation could occur if you are producing power when the utility workers think the lines are de-energized. Also, your system would then try to reverse power everything connected around you and that could overload your system.

So, finally, lets assume a $6,000 initial cost and a daily savings of 30kWH. At $0.08/kWH, you would save approx. 30kWH * 30 *0.08 = $72/month. Dividing $6000/72 would give you approx. 84 months or 7 years to payback, without considering additional maintenance/upkeep costs.

Well, I have rambled on long enough. Hopefully some of what I've said makes sense to you. Here is a link to James Dulley's website where he addresses some issues concerning residential windmills. Good Luck.

http://www.dulley.com/docs/f485.htm

Answer 4

windmills watts hour windmill produce

Answer 5

look around and if you do not see any windmills/turbines = zero watts
next find the nearest working wind turbine and ask for the actual output
in kwh/year and divide that by 9,000 = watts
kiss