Posted by Curbie on February 27, 2009, 3:02 am
daestrom,
Thanks for your efforts in explaining this, I really appreciate it!
I agree with your assessment on:
>You do get more life if you use a smaller DOD. But you would need a bigger
>battery to store the same amount of energy and only operate to 50% DOD. (to
>reduce typical DOD from 70% to 50% you need 70/50 = 1.4 times larger
>battery). So it may not be worth it compared to just replacing the smaller
>battery slightly sooner.
You probably guessed that this is the reason behind the question you
answered, without DOD to cycle information I can't calculate total
(life time) amp-hours, which in turn I need for any meaningful cost
annalist. I have a spreadsheet (a column of which is posted somewhere
in this thread) which I need to update for cost annalist using your
numbers and revisiting the manufactures spec sheets for DOD cycles.
I didn't keep all of their spec sheets and from the ones I did, only
Northern Energy publishes cycles for DOD for its "Solar One". I should
be able to reverse the equations (for the others) to find DOD based on
their published cycles & amp-hours. I'll e-mail it to you when I'm
finished updating, if you want it, it's the least I can't do for all
your help. But that'll be in a few days at least, I haven't even
started the updated due to trying to win the "Moron of the Month"
award for tower forces. I compiled everything in that thread into one
place, re-read it, took two steps back, and started from scratch. I'll
"get it" eventually, I always do, just takes more time than others
slow (or through) and tenacious has done pretty well for me so far.
Thanks again for all your help, I owe you a couple so don't hesitate
to ask.
Curbie
wrote:
>Discharge to 50% and recharge, that is 0.5 cycles. Discharge to 20% and
>recharge, that is 0.2 cycles. Discharge to 70% and that is 0.7 cycles. (so
>far we've 'used' 1.4 cycles of battery life).
>The 'trick' is that just how many cycles you can get out of a battery is a
>function of what you do for average DOD. Say a battery is quoted as '1000
>cycles at 50% DOD' That means you can discharge it to 50% and recharge it
>2000 times (0.5 cycles per charge/discharge). But that same battery may
>also be rated as '900 cycles at 70% DOD'. So you could discharge it to 70%
>and recharge it 1286 times. While these two numbers *seem* quite a bit
>apart (2000 vs 1286), they aren't really. If a cycle is 500 amp-hours, in
>one you got 250 amp-hours * 2000 times for 500,000 amp-hours of storage life
>and in the other you got 350 amp-hours * 1286 = 450,000 amp-hours total
>storage life.
>You do get more life if you use a smaller DOD. But you would need a bigger
>battery to store the same amount of energy and only operate to 50% DOD. (to
>reduce typical DOD from 70% to 50% you need 70/50 = 1.4 times larger
>battery). So it may not be worth it compared to just replacing the smaller
>battery slightly sooner.
>Of course, probably each time you use it you won't discharge it to exactly
>the same DOD, so you have to make a bit of a guesstimate of your average
>DOD.
>And if you *don't* get them fully recharged right away, that shortens their
>life. So it may often be prudent to charge with a gas generator if the wind
>isn't available for a day or two.
>daestrom
Posted by harry on February 23, 2009, 9:05 pm
> 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 Im 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 Im looking for help.
> It seems that the "well beaten" path for home built wind-turbine
> revolves around Hugh Piggotts "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 Im 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 cant find it though Google Groups?
> Any help would be appreciated!
> Thanks.
> Curbie
There is no such thing as a "DC machine/motor/generator". They are all
AC. Some are fitted with a mechanical rectifier (called a commutator)
so enabling them to work in a DC system.
To be efficient, there needs to be as few conversions (AC/DC &
voltage) as possible.
So your power is generated as AC. This needs to be converted to the
voltage you need and finally to DC if that's what you require.
That said there are numerous practical problems.
Stablising the voltage and frequency being the worst.
The simplest way forward is to steal automobile technology, ie to lift
the whole system from a motor car [alternator, regulator (if not
incorporated) and battery]
The battery stablises the system ie prevents wild swings in voltage
due to wind gusts. Also the "flywheel effect" of your wind rotor
smooths out gusts. Obviously the heavier it is the better from this
point of veiw. (Though heavy rotors have an adverse effect in light
conditions)
If you want AC you will need to buy an inverter.
There is an innate problem with electronic inverters & that is it's
really difficult to design one that makes a sinusiodal wave. (Square
and sawtooth waves are really hated by all electrical appliances) This
means they are expensive.
Even more expensive is an inverter that ups the voltage and more $
again is one that synchonises to the mains for the purpose of running
in parallel.
Which brings the subject of "asynchronous generators" This is just an
induction motor that is first parallelled up to the mains supply &
then driven a bit faster. It wont work without the mains supply being
there. This is the the simplest way to do it. It's possible your
local power company might not like such devices. (But then they'd need
to find out)
You need to be very sure the thing is running super synchronous (ie
generating)and not sub synchronous (ie as a motor) There needs to be
a gizmo to shut down if there is not enough wind to prevent this and
also if there's too much wind which could bugger up your motor/
generator. there's lots of stuff on the internet about asynchronous
generators. And quite a bit of BS too.
Posted by Curly on February 24, 2009, 4:18 pm
> 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.
Forget the batteries.
The problem of storing power from home wind has been solved for a long
time but it requires hilly land, two ponds, a pump and a water-powered
generator. One pond downhill, the other as high up the hell as you can.
Pump the water uphill ding generation and generate power hen you let it
flow down to the lower pond.
Posted by Curbie on February 24, 2009, 4:45 pm
On Tue, 24 Feb 2009 16:18:15 +0000 (UTC), Curly@surmudgeon.tv wrote:
>> 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.
>Forget the batteries.
>The problem of storing power from home wind has been solved for a long
>time but it requires hilly land, two ponds, a pump and a water-powered
>generator. One pond downhill, the other as high up the hell as you can.
>Pump the water uphill ding generation and generate power hen you let it
>flow down to the lower pond.
Love the idea of Hydro Batteries but terrain is a problem where I’m
planning to move.
Even studied the idea of building underground vertical cisterns, still
trying to make it cost effective.
Reservoir Length 18 Feet
Reservoir Width 18 Feet
Reservoir Height 8 Feet
Backup Time 48 Hours
Head 50 Feet
Reservoir 19390 Gallons
Flow 6.7329 GPM
PSI 21.65 PSI
Factor 10
Watts 3366 Watts
Outside Diameter 7 Inches
Inside Diameter 12 Inches
Inside Radius 6 Inches
Inside Surface Area 21 Ft.^2
Volume 67858 In.^3
Cross Sectional Area 113 In.^2
1 Horsepower (HP) 746 Watts
1 Watt (w) 0.001340483 HP
1 Foot Head (H) 0.433 PSI
1 PSI (PSI) 2.309468822 Feet
1 Cubic Feet per Second (CFS) 449 GPM
1 Gallon Per Mintute (GPM) 0.002227171 CFS
1 Cubic Foot of Water 7.481 Gallons
1 Gallon of Water 0.133671969 Ft.^3
Good suggestion can't make it cost effective, yet.
Thanks.
Curbie
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>battery to store the same amount of energy and only operate to 50% DOD. (to
>reduce typical DOD from 70% to 50% you need 70/50 = 1.4 times larger
>battery). So it may not be worth it compared to just replacing the smaller
>battery slightly sooner.