the arrow pointing at me says,"I'm with stupid"

[Charles B]

Hello. At what average speed would a turbine have to continually operate in order to power a household's average daily electricity usage? Is there a formula I could use to figure this out?

 

Thank you.

 

Charles B

"Stupid"

[Cap'n Refsmmat]

You'd need to know the size of the wind turbine for one. You could look up a few statistics on different wind turbines, and figure out a decent formula from there.

[Charles B]

I'm probably not using the correct words... hence "stupid". It's not a wind powered generator. Let's say I have an endless but not constant amount of force... not wind though. Enough to create movement of some kind. How can I figure out if this force can create enough movement to be worth harnessing? Can I just use the wind turbine formulas?

 

Thank you.

 

Charles B

[cessna7686]

I'm not a turbine expert but I think you have to be a bit more specific. There are a lot of different factors that would affect the performance of the turbine: turbine surface area, size of the generator the turbine is connected to, and the gear ratios you are using (if you are using gears). The more information you can provide the better an answer you will get.

[Pleiades]

I think the problem is with your understanding of the mechanics involved, knowing the speed alone doesn’t tell you anything about how much power you can extract from some sort of movement.

 

Read this page in detail; look up any words you don’t understand: http://www.howstuffworks.com/fpte.htm/printable

 

For a more detailed explanation about power and torque, read this in detail, again, looking up any words you don’t fully understand: http://www.epi-eng.com/BAS-PwrTrq.htm

 

In short, you need to know the torque and the speed to find the power of the rotating shaft.

 

HP = Torque x RPM ÷ 5252

 

Where Torque is measured in pound feet.

[chilehed]

I'm probably not using the correct words... hence "stupid". It's not a wind powered generator. Let's say I have an endless but not constant amount of force... not wind though. Enough to create movement of some kind. How can I figure out if this force can create enough movement to be worth harnessing? Can I just use the wind turbine formulas?

 

Thank you.

 

Charles B

Power = Force x Velocity. You know the force, you know the velocity it's acting at, that gives you the power. Use an appropriate conversion factor to express it in watts, and don't forget to account for inefficiencies in the process of turning it into useful work.

 

And it's not a stupid question.

 

This is cool: I was wondering once how much power the Saturn V rockets produced. As I recall they generated 5,000,000 lbf of thrust and first-stage separation occured at around 3,000 mph, which calculated to about 90 BILLION horsepower!!

[Norman Albers]

Depending upon the mode of heating, mostly, a house in the US uses roughly a steady kilowatt or two, saying monthly consumption is, maybe a thousand kilowatt-hours. Figuring out load is part of the issue, especially vis-a-vis power availability. Storage is dealt with if, as most places here, you can feed back to the grid.

[Prime-Evil]

Hello. At what average speed would a turbine have to continually operate in order to power a household's average daily electricity usage? Is there a formula I could use to figure this out?

 

Thank you.

 

Charles B

"Stupid"

Hey Charles. Maybe we are related. We seem to share the same last name.

 

Let's say you have an average monthly bill of $100/month and your cost is 10 cents per Kwh. Your average power use would be:

 

$100 / ( 24h/d x 30.4d x $0.10/Kwh ) = 1.37 Kw.

 

If you had a water turbine or a deseil generator running 24/7 driving a 90% efficient generator and you had additional losses on 50% of your power used averaging 90% for inverter losses to DC, 90% for charging losses to the battery, 80% on discharge losses from the battery, and you ran all your stuff off the battery as DC, then your water turbine would have to generate:

 

1.37Kw x 0.5/0.9 + 1.37kw x 0.5/(0.90x0.90x0.90x0.80) = 1.94 Kw

More likely you would have 6 Kw running 8 hours a day.

 

If you had a wind turbine, and you had enough batteries that your charging and discharging efficiencies were similar, but 100% of your power came off the batteries, and you had a wind regime and wind turbine performance curve such that you had a Capacity Factor of 0.30, then you would need a wind generator this big:

 

1.37kw / (0.90x0.90x0.90x0.80x0.30) = 7.83 Kw

 

If you get all you power from the wind you would need an aweful lot of batteries, and sometimes they would be full and you would have to dump power. For this reason it is usually best to have a combination of wind turbine, generator, and perhaps a few solar panels also. Cost of all this offgrid stuff works out to perhaps $0.50/Kw life cycle, so to keep your energy costs within reason you really want to knock down your usage to the equivalent of perhaps only $40/month on grid.

 

That would imply a combination of something as follows:

Average Power: 550watts

25% Gas Generator = 1.6 Kw running 3 hours/day

50% Wind Turbine = 1.5 Kw running at 0.30 Capacity Factor

25% Solar Power = 800 watts perhaps at 0.25 Capacity Factor

Perhaps 6000 Amp-hours of batteries.

 

At times you would still likely have to dump power from the wind however, to a large hot water tank for example, so perhaps a 3 Kw Wind Turbine would be better so that you generate 500-1500w more regularly and dump the rest on the rare windy days when generation exceeds demand and storage capacity.

[Norman Albers]

Awesomely analytic! I've heard that most places in the USA you can feed back to the grid at least the amount you are sized for. This is a serious problem to developing largescale windfarms; they need to be near grid mains.

[Prime-Evil]

I think wind power can also be distributed, and I think the grid will become more decentralized also. Wind power will also need to be near pipelines for hydrogen produced from surplus power on windy days. Farms will use land for growing food, but also be net exporters of wind generated electricity and hydrogen. They will probably use their own methane, but run tractors primarily on hydrogen, filling up directly at the Wind Tower. Wind Turbines will typically be a 3.0 MW wind turbine on a 80-120m Tower, with one every square kilometer or 100 hectares, 200 acres.