home electricity from the wind

 I know the path to successful home use of wind power is "well beaten",
and I know there are good reason why things are done the way they are,
but I’m trying to understand why some of those good reason exist and
was hoping someone could help explain it to me.

I bought two books on the subject "Windpower Workshop" by Hugh Piggott
and "Wind Power" by Paul Gipe, two very different approaches to the
same subject. Covered well in both books is the math used to covert
wind into electro-mechanical energy, less well covered is converting
the energy the wind turbine produces into home electricity, and this
is where I’m looking for help.

It seems that the "well beaten" path for home built wind-turbine
revolves around Hugh Piggott’s "axial flux" design, producing AC at
some voltage (12/24/48), then rectified to DC to charge a battery and
energy (and cycles) from the battery is then inverted to home
electricity.

What I’m not understanding properly is why the "round robin" with all
the conversions. (AC to DC back to AC) I understand these "axial flux"
type machines produce "wild energy" with the AC voltage, current, and
frequency going up and down with the wind speed, but it seems that
having a DC wind-turbine feed a capacitor that feeds an inverter to
produce home electricity would at the very least save cycles on the
battery, leaving it for back-up only, charging the capacitor in low/no
wind periods.

I though this question has probably been asked and answered one
hundred times before, but I can’t find it though Google Groups?

Any help would be appreciated!
Thanks.

Curbie

  Curbie wrote:


Cost and space are the main culprits. Huge capacitors cost money and
occupy a lot more volume than batteries.

The old fashioned lead acid battery is still the best bet in an isolated =

system for cost/capacity.

$300 per Kw-hr for lead acid.
$12000 per Kw/hr for 'super-capacitors'

http://www.energy.ca.gov/load_management/documents/2008-03-03_workshop/co=
mments/Heinrich%20EPRI%20Overview%20of%20Energy%20Storage%20Benefits%20to=
%20Efficinecy%2003March%2008.ppt

Or, for the 'let's wrap another URL' cursed microsoft crowd,

http://tinyurl.com/dbd6b6


If your grid is dependable, using THAT to store your energy is the
cheapest proposition of all.



mike

 Mike

Thanks for your reply.

I agree with all your points and am sorry for not making myself clear,
I'll try again.

Take the capacitor out of the example circuit:
Turbine > rectifier > inverter. (Using battery only for low/no wind
periods.)

Instead of:
Turbine > rectifier > battery >inverter. Eating battery cycles for
every watt produced. (battery wear & tear)

Curbie

 

If I understand your question you want to know why the rectified power is
not fed directly into the inverter.  With wind power you generally have a
lot of fluctuations in power output.  Sometimes you might be getting a
couple of thousand watts of power and sometimes only a couple of hundred or
less.  If you were to regulate the voltage accurately enough for the
inverter to accept the input without shutting down you would not be able to
power anything reliably.   Every time the wind slowed down your inverter
would probably shut down.  By charging the batteries instead you have a more
or less constant supply of power to feed the inverter.  This is, of course,
dependent upon making sure you use a less or equal amount of power than is
what is being produced.

If you had a wind generator that produced DC directly you would have brushes
and commutators that would require maintenance that the "axial flux" AC
generator would not have.  You can use a DC motor to produce usable power
but you may run into some problems such as finding a motor that produces
enough power at low wind speeds and also there was a discussion about the
position of the brushes in motors as compared to generators and the brush
alignment may need to be modified (this is my understanding anyway).

 Ulysses,

You do understand my question correctly.

Turbine > rectifier > capacitor (condition fluctuations only) >
inverter

For low/no wind periods the battery would feed the capacitor directly.

What about this?


The battery (bank) is by far the single most expensive line item in a
hand built wind system which is the reason for the question.

Thank for the reply

Curbie
On Mon, 23 Feb 2009 08:58:59 -0800, "Ulysses"