Author Topic: OFF GRID POWER; various thoughts on...  (Read 472911 times)

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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #75 on: February 01, 2009, 11:35:00 AM »
HUP One, or Solar One batteries info...

http://www.hupsolarone.com/benefits.htm

http://thesolar.biz/hup_solar_one_batteries.htm

They warrant their batteries to have 2100 cycles at 80% Depth Of Discharge.: 4000 cycles at 5%, I think.

------------------

sizing tool
http://www.wagonmaker.com/script_calculator.html
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Windpower

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Re: OFF GRID POWER; various thoughts on...
« Reply #76 on: February 01, 2009, 11:45:57 AM »
Thanks Don

I hadn't come across that brand before

now I just need to take out a second mortgage ....... ;D
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #77 on: February 01, 2009, 11:58:19 AM »
$$$   That's one of the big reasons L-16's enjoy great popularity.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #78 on: February 01, 2009, 02:37:29 PM »
Batteries are the heart of off grid power systems. I have loads of notes collected over time. I plan on sorting, condensing and adding to previous posts here.

FIRST… BATTERY ACID is HAZARDOUS. At the very least eye goggles should be worn. Having a bottle of sterile eye wash at hand is also a very good idea. Having it “at hand” so you can grasp it readily when you have your eyes screwed shut because they have acid in them is very important. It does little good if it’s in the shed “someplace”.

Get a plastic bottle and fill it with baking soda and water solution. Keep it by the batteries or with you tool kit. Use it to neutralize accidental splash or spills and to clean normal acid spatter from battery tops. Don't ever wear your favorite blue jeans! You won't know if you ruined them till you wash them next time.



Let's have a look at determining State of Charge on wet cell batteries. That includes standard and low maintenance. The key thing is the ability to remove the cap from the cell and measure specific gravity and/or add water as needed. These are sometimes referred to as Flooded cell batteries.

There are a variety of devices to measure specific gravity. Some use floating colored balls or disks. Do NOT bother with these. Others use a swinging “scale” that “floats” as the electrolyte is sucked into its chamber. Do NOT buy one of those either. Purchase a good old fashioned graduated float style, preferably one with a built in thermometer. NAPA auto parts sell one like that.



http://www.napaonline.com/MasterPages/NOLMaster.aspx?PageId=470&LineCode=BK&PartNumber=7001145&Description=Battery+Tester+%2f+Hand+Held

You want the thermometer as lead-acid batteries are rated at a temperature of 25 degrees Celsius (77 F). Battery capacity, how much power can be pulled from a wet cell battery, falls as the temperature falls. Conversely battery capacity increases as the temperature rises. Battery life is increased at lower temperatures and reduced at elevated temperatures.

Hydrometer readings should not vary more than .05 difference between cells.


A voltmeter may also be used to determine the state of charge. However, the battery must have been sitting with no charge or load having been applied to it for a period of three hours minimum. The reason for this is the battery will hold onto a “surface charge voltage” for some time after being charged. It takes several hours to dissipate. For those in a hurry a load of approx 20 amps for ten minutes will remove the surface charge, more or less and will MTL give a usable reading.


Here’s a chart showing specific gravities for several different States of Charge for wet cell batteries, at temperatures from zero to 120 degrees F. Also included are open circuit voltage readings, based on a 12 VDC battery. Halve the voltage readings for a 6 VDC battery.

The chart uses rounded off figures so in it we refer to the standard temperature as 80 degrees F  (26.7 C)



Lastly, for now, only add water to a charged cell. The electrolyte expands as it goes from less charged to fully charged. The exception to this rule would be if the electrolyte is below the top of the plates; then add just enough to cover the plates.

« Last Edit: February 01, 2009, 05:16:58 PM by MountainDon »
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #79 on: February 01, 2009, 05:16:14 PM »
WHY a MPPT CHARGE CONTROLLER is BEST
(Maximum Power Point Tracking)

Because PV cells and batteries are both not very smart; in fact panels are dumb and batteries plain stupid.

Many PV panels are built to put out a nominal 12 volts. The catch is "nominal". In actual fact, almost all "12 volt" solar panels are designed to put out from 16 to 18 volts. The problem is that a nominal 12 volt battery is pretty close to an actual 12 volts - 10.5 to 12.7 volts, depending on state of charge. Under charge, most batteries want from around 13.2 to 14.4 volts to fully charge - quite a bit different than what most panels are designed to put out.

OK, so let’s use the popular Kyocera 130 watt solar panel as an example. Catch #1 is that it is rated at 130 watts at a particular voltage and current. The Kyocera KC-130 is rated at 7.39 amps at 17.6 volts. (7.39 amps times 17.6 volts = 130 watts).

So what happens when you hook up this 130 watt panel to your battery through a regular charge controller?

Your panel puts out 7.4 amps. Your battery is sitting at 12 volts under charge: 7.4 amps times 12 volts = 88.8 watts. You lost over 41 watts. That 41 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery. With a very low battery, say 10.5 volts, it's even worse - you could be losing as much as 35% (11 volts x 7.4 amps = 81.4 watts. You lost about 48 watts.

One solution you might think of; why not just make panels so that they put out 14 volts or so to match the battery?

Catch #22a is that the panel is rated at 130 watts at full sunlight at a particular temperature (STC - or standard test conditions). If temperature of the solar panel is high, you don't get 17.4 volts. At the temperatures seen in many hot climate areas, you might get under 16 volts. If you started with a 15 volt panel (like some of the so-called "self regulating" panels), you are in trouble, as you won't have enough voltage to put a charge into the battery. Solar panels have to have enough leeway built in to perform under the worst of conditions. The panel will just sit there looking dumb, and your batteries will get even stupider than usual.


How Maximum Power Point Tracking helps.

This is not tracking like Glenn has his panels tracking the sun. This is digital tracking of the power output of the PV panels and the needs of the batteries, then using high frequency DC to DC converters. They take the DC input from the solar panels, change it to high frequency AC, and convert it back down to a different DC voltage and current to exactly match the panels to the batteries. Digital MPPT controllers are microprocessor controlled. They know when to adjust the output that it is being sent to the battery, and they actually shut down for a few microseconds and "look" at the solar panel and battery and make any needed adjustments.

Assume your battery is low, at 12 volts. A MPPT takes that 17.6 volts at 7.4 amps and converts it down, so that what the battery gets is now 10.8 amps at 12 volts. Now you still have almost 130 watts, and everyone is happy.

Ideally, for 100% power conversion you would get around 11.3 amps at 11.5 volts, but you have to feed the battery a higher voltage to force the amps in. And this is a simplified explanation - in actual fact the output of the MPPT charge controller might vary continually to adjust for getting the maximum amps into the battery.

A MPPT tracks the maximum power point, which is going to be different from the STC (Standard Test Conditions) rating under almost all situations. Under very cold conditions a 120 watt panel is actually capable of putting over 130+ watts because the power output goes up as panel temperature goes down - but if you don't have some way of tracking that power point, you are going to lose it. On the other hand under very hot conditions, the power drops - you lose power as the temperature goes up. That is why you get less gain in summer.

MPPT's are most effective under these conditions:

**Cloudy or hazy days - when the extra power is needed the most.

**Cold weather - solar panels work better at cold temperatures, but without a MPPT you are losing most of that. Cold weather is most likely in winter - the time when sun hours are low and you need the power to recharge batteries the most.

**Low battery charge - the lower the state of charge in your battery, the more current a MPPT puts into them - another time when the extra power is needed the most. You can have both cold weather and low battery at the same time.

**Long wire runs - If you are charging a 12 volt battery, and your panels are 100 feet away, the voltage drop and power loss can be considerable unless you use very large wire. That can be very expensive. But if you have four 12 volt panels wired in series for 48 volts, the power loss is much less, and the controller will convert that high voltage to 12 volts at the battery. That also means that if you have a high voltage panel setup feeding the controller, you can use much smaller wire. That’s my situation, except my cable run is more like 325 feet.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #80 on: February 01, 2009, 05:30:57 PM »
The L16's are 6 volts at 375ah each plus or minus a bit depending on brand and model.  You can series or parallel them for whatever voltage and amps you need.

For a start, running a pretty full house with quite a bit of power probably 2 sets of 4 (or 8 batteries total) for a decent 24 volt system or all 8 in series for a decent 48 volt system will get you going.  That is in lieu of proper figurinng and calculating - Ideally I would like to see 16 of them for a decent 48v system or - 2 groups of 8 batteries paralleled.

I find that a voltmeter can be misleading in that it could show a full voltage, but not the state of the electrolyte like the Hydrometer will.  

The Hydrometer is the most important low cost tool for the state of the individual cells, and in a group of batteries one low cell can cut the capacity of the entire group.  Getting over 31. 2 volts on up toward 32 volts seems to be a critical point of equalization although I have heard as high as 34 volts in several places.  When hitting that point I noted a drop in voltage then increasing acceptance of charge.  That seems to be the point that the low cell starts coming back with the rest and it may take several hours to do it - ideally once a month.  If on a good maintenance schedule , it may not take that long.... I wouldn't know about that.... [waiting]
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #81 on: February 01, 2009, 06:19:48 PM »

I find that a voltmeter can be misleading in that it could show a full voltage, but not the state of the electrolyte like the Hydrometer will.  

That's the only bad thing about AGM batteries, which I plan on getting into later. They have no available liquid electrolyte. So you need to use volts. The difficult part to me, is having the time for the batteries to sit there with no charge going in, no loads coming out for a long enough time. I've heard three hours is the minimum time. Better is at least 8 to 10 hours. I guess that means shutting down for the night and pulling the PV input breaker/disconnect so the morning sun doesn't start the next charge cycle.  ???

The voltmeter won't find which cell is dead, only narrow down to the battery. But in a multiple cell battery I guess that doesn't matter much.
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Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #82 on: February 01, 2009, 06:28:09 PM »
A good carbon pile load checker could do that but the cost of a good one is up there.  Mike is supposed to get us a good deal on some of the new testers that are electronic pretty soon I think  I may spring for one of them to see how well they work.  Bad thing about the load testers like this is they do pull a lot of current from the battery.
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #83 on: February 01, 2009, 07:45:42 PM »
Sealed cell AGM BATTERIES  (AGM = Absorbed Glass Mats)

I’ve used AGM batteries for years, actually over a decade, in my modified Jeeps. I used them because they are extremely resistant to vibration and shock. As well they are a true maintenance free battery and long lived. I’ve got 5 years of service and most have been still strong at that point. I’ve changed them out of concerns for reliability when off in the boonies. A side benefit for off road use is their sealed nature; no dripping acid if you find yourself dirty side up.  n*

For an off grid power storage battery system AGM batteries have some advantages as well. AGM’s are not gel cell batteries, they are better. The electrolyte in an AGM is not gelled; the electrolyte is still liquid. It is held within a very fine fiber Boron-Silicate glass mat. If the case of an AGM battery is cracked the liquid will still not leak out. The AGM take more abuse than a gel cell. Let it be noted that gel cells do not take kindly to deep discharges or to overcharging. As well gel cells can not be fast charged; they require special chargers. Most good inverter-chargers can be programmed to the required charge rates though.

AGM’s can be mounted sideways or upside down. (Handy for a second battery in the Jeep.) AGM’s are cheaper to ship as there is no Hazmat fee. Nearly all AGM batteries are "recombinant"; that means the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.

The charging voltages are the same as for any standard battery. The internal resistance is extremely low; there is almost no heating of the battery even under heavy charge and discharge currents.

AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. Less to worry about in a three season off grid cabin for example.

AGM’s emit no hydrogen under normal charge rates and under heavy charge rates the hydrogen emissions are so low there is virtually no danger of explosion. They can be safely stored indoors in a non vented enclosure.

Wow, what a super battery!  :D  Is there any downside? Not many; with one being there are not a very large number of choices for 6 volt versions with high capacities for off grid storage systems. As mentioned before the sealed nature means you can not check their charge level with a hydrometer. However, that is more than counterbalanced by their ability to absorb overcharges and to not deteriorate as quickly with high discharges, and being sealed against water loss.

The biggest downside is their cost. An AGM will cost at least 2 to 3 times as much as a conventional wet cell battery of comparable capacity.  :o 

Concorde Sunextender does make a 6 volt 220 amp hour battery, comparable to a golf cart battery, as well as a 305 amp hour battery. The 305 cost about $400+ and the 220 about $275-350. Concorde also has a 2 volt 915 amp hour battery I’ve seen on sale at $200; regular up to $450.

As you can see the advantages do cost. I would use them if the cost was less.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #84 on: February 01, 2009, 07:55:10 PM »
The standard lead acid batteries with the new desulfators we are working on getting set up with may last as long as 15 years they claim. 

I am anxiously awaiting getting the unit from Mike to see what it will do to reclaim the used L16's I have.  That would mean a very substantial savings in battery costs.

That could make them more cost effective than the AGM's I think and no mystery regarding what the cells are up to.
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #85 on: February 01, 2009, 07:57:46 PM »
Are you using those low cost desulphators you mentioned some time back?
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #86 on: February 01, 2009, 08:25:54 PM »
I currently have the low cost one on two of the batteries - I accidently wet one of them washing the batts with the hose so now have only one.  I sealed it with silicone rubber.  Improvement is slow - not much improvement in SG yet but it seems there is some.  I put the desulfator on full time and charger on every other day or so as I get excess power to play with it.

The one we are supposed to get set up as dealers on is around 20 amps of desulfating and charging power built specifically for recovering batteries.  Most battery companies are not interested in selling these desulfator/chargers because they would rather sell batteries.

Mike has used their small 2.5 amp one and recovered a big Caterpillar battery - 8D that had been sitting for about 6 years.  I am not sure of the quality of the recovery yet as I don't have hydrometer readings - I keep forgetting to ask him to check.  He just has the one for experimenting now - I have already ordered the bigger one.
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Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #87 on: February 02, 2009, 08:39:33 AM »
On my tracker - as the sun continues to come up, a few minor adjustments in the tracker wake-up trough arm geometry and timing (by moving the center attachment point forward - back - up or down on the angle iron frame) has it waking up around 7:40 with most movement complete around 7:46 - pressure rises on the west side during the rapid movement toward the east so movement slows but it is getting sun to all panels by that time and by 8 AM I am getting about 19 amps at 25 volts. 

I haven't added the rest of the panels to the tracker yet.  6 more 100 watt or so panels to go on there.
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #88 on: February 02, 2009, 11:21:26 AM »
 :o  That's going to be some array!!!


I picked up my top of pole mount from the Uni-Rac warehouse today. Can't wait for the snow to melt.
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Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #89 on: February 02, 2009, 07:51:11 PM »
It is pushing the envelope a bit.  I worked out the maximum expected wind force and think it will take it - but I'm not an engineer.  I do want to truss the bottom and center frames.   I added 3 pipe braces to the top of the post - a 2 inch and 2 one inch pipe ones to the I beam and purlins below. 

I will friction mount the top two so they will blow down decreasing resistance in high wind. d*  I think.... :)  The green house should deflect the wind over it on the front - the mountain should along with turbulence from the trees on the back.  I am going to set my thin film panels up on the green house as a 3' high wind deflecting fence also.  They will be permanent mounted as they take too large an area to track cost effectively - only 40 watts per panel in about the same area as the others. 

I have thought of using the big one as a master and making slaves though. 

Could be a Rube Goldberg, eh?
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Offline JRR

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Re: OFF GRID POWER; various thoughts on...
« Reply #90 on: February 05, 2009, 05:04:18 AM »
Sealed cell AGM BATTERIES  (AGM = Absorbed Glass Mats)

 Concorde also has a 2 volt 915 amp hour battery I’ve seen on sale at $200.


Velly interesting!  I assume each battery is a single cell ... allowing significant single-cell testing at the terminals.  60 batteries in series ... 120 volts ... $12,000 ... and approx 28 kilowatt-hours (at a 50% discharge ... if I did the math correctly).  That's a lot of stored energy for the bucks!

In my neck of the woods, stored energy in a pumped storage (kinda) makes sense ... that battery array would equate to 100k gallons of water dropping 100 ft ... ain't bad!
« Last Edit: February 05, 2009, 05:21:31 AM by JRR »

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #91 on: February 05, 2009, 06:35:01 AM »
  I assume each battery is a single cell ... allowing significant single-cell testing at the terminals. 

Absolutely correct! Big cells.   :)
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Offline Windpower

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Re: OFF GRID POWER; various thoughts on...
« Reply #92 on: February 05, 2009, 01:26:14 PM »






Has anyone got any experieince with these

I can get them locally for about $330

12 V  225 AH @ 20hr

they are actually for floor buffing machines

the the guy at Batteries Plus said he had sold several to solar system users with good luck (but then he is a salesman)


Since I have decided on a 48 V sytem it would cut the number to 8 or 12 for my wind solar system

about  30 % of a HUP or Concorde or Surrette cost

For my off grid system I plan to use
 
  Six AirX (48 V)  These should give about 180 KW-Hr per month  plus 1500 watts of solar panels (haven't got these yet)  but these are looking good cost wise

http://cgi.ebay.com/Pallet-of-SIX-200-Watt-Solar-Panels-NEW-2-60-Per-Watt_W0QQitemZ220356552797QQcmdZViewItemQQptZElectrical_Solar_US?hash=item220356552797&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1309%7C301%3A1%7C293%3A1%7C294%3A50

For the battery bank I am thinking

12 X 225 AH = 2700

50 % charge = 1350 AH

or about 67 KwHrs 

Any Ideas --- this is in south west Wisconsin so only averages about 4.2 hours of effective sunshine according to this site


http://www.wholesalesolar.com/StartHere/OFFGRID/OFFGRIDCalculator.html


I know I should wait until the last minute to buy the batts but I am worried the price is going to skyrocket (along with everything else in hyperinflation) I plan to get this wind/PV system up by fall 2009


I may be in the market for a heavy duty inverter (if the Taiwan unit doesn't work out ) at least 4000 watts to kick the deep well pump over

Outback or  ???
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #93 on: February 05, 2009, 03:22:23 PM »
You have confused me; sometimes that is easy to do  ??? You stated...

12 x 225 = 2700 amp-hr    and you also stated you were going to use a 48 volt system.

That 2700 amp-hr is true if those 12 volt batteries were all connected in parallel in a 12 volt system. That would be 2700 amp-hrs rated at 12 volts, not 48 volts.

With four 12 volt batteries in series to supply the 48 volt basis for the system, one string of four would have a capacity of 225 amp-hrs. Two series strings in parallel would have a capacity of 450 amp-hrs and a battery bank of three series strings in parallel would be equal to 675 amp-hrs. All at 48 volts.

I guess it depends on whether or not you are taking 48 volts as the system basis into account when calculating loads and reserves.


Regarding those J185H-AC batteries, I'm not familiar with them. How do those prices work out compared to L-16's. They are rated as deep cycle. It would be interesting to know if the plates are the same thickness as in an L-16 or if they are thinner like the T-105's. That could make a difference to their life.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline JRR

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Re: OFF GRID POWER; various thoughts on...
« Reply #94 on: February 05, 2009, 04:25:14 PM »






For the battery bank I am thinking

12 X 225 AH = 2700  the math is correct, its the absense of terms that get us in trouble: 12v x 225 AH = 2700watt-hr.

50 % charge = 1350 AH  50% discharge = 1350 watt-hr, or 1.35 kw-hr.

or about 67 KwHrs  ??


1.35 kw-hr for $330 is close to, but not quite as good a purchase as .915 kw-hr for $200.  (This assumes "everything else" is equal.)

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #95 on: February 05, 2009, 04:28:05 PM »
Before buying those J185H-AC batteries I'd really want to know about the plate thickness. Going by the weight I would believe that one of those 12 volt batteries is about as good as two 6 volt T-105 GC batteries in series. The T-105 weighs in at 62 lbs. each. The J185H-AC weighs in at 128 lbs. Both are rated at 225 amp-hrs.

Info taken from Trojan's website
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #96 on: February 05, 2009, 05:14:43 PM »
Windpower, does your system have to be inspected and up to NEC code??

...from the website link to the PV panels "SUN MODULES ARE NOT UL CERTIFIED"

Good price otherwise



Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #97 on: February 05, 2009, 05:24:59 PM »
The formula is    (amp-hours * voltage) / 1000 = kilowatthours

 225 amphours x 12 volts = 2700 / 1000 = 2.7 KwH per battery
50% of 2.7 = 1.35 KwH per battery

1.35 KwH x 12 batteries = 16.2 KwH

Windpower references a 67 KwH figure... 

I still think he believes that battery array is more powerful than it really is, by a factor of approximately 4.

67 / 16.2 = 4.13

 ???   ???
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Windpower

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Re: OFF GRID POWER; various thoughts on...
« Reply #98 on: February 05, 2009, 05:54:17 PM »
Thanks Don for catching the math error

I thought that seemed too high for  KwHr(that will teach me to do the arithmetic in my head  NOT)

duh

 d*

 :-[

let's try this again

 4 batteries in series times 3 parallel equals 675 AH at 48 V

 675 AH X 50 %  = 330 (Recommended useful discharge capacity)

330 AH X 48 V = (about) 16 Kw Hrs


anyway, now that we're on the same page (planet ?) mathematically


What do you think Don, enough battery capacity at 16 KW Hr

I think we will, on average, use up about 6 to 10 KW Hr per day between business and shop use

I forgot to mention we do have a  diesel back up generator running on biodiesel (just in case)

The nice thing about the farm is that it is quite windy and the wind usually is there when it is not sunny


but my gut feel here is that I need more battery capacity ---maybe 32 KW Hr


whoa    the mind boggles -- that seems like a big battery bank


This is a great forum

Thanks guys

Often, our ignorance is not as great as our reluctance to act on what we know.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #99 on: February 05, 2009, 06:16:14 PM »
What do the power company bills / records indicate your use to be. Ours has about 4 years worth available online.  We run 14 to 28 per day depending on time of year. (summer A/C)

Big battery banks are sometimes needed and that's where those big 2 volt cells come in handy. And they come in expensive.  :(

You could also add one string if it proved necessary. Is most of your use going to be during daytime or nightime?

How about grid tie, using the grid as the "battery"?

Depending on the local power company it can work advantageously. Of course I'm seeing that from a NM point of view where the power company (has to) pays us more (13 cents) than what the user pays them for purchased power (9 to 10 cents).
Just because something has been done and has not failed, doesn’t mean it is good design.

 

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