OFF GRID POWER; various thoughts on...

Started by MountainDon, January 13, 2009, 02:18:39 AM

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Every situation is different... we are very well shaded. There are enough trees that at any given moment there are more shadows than direct sun on any more or less southern exposure. great in summer, not so much in winter. It's especially bad in winter when the low angle of the sun is compunded by the trees on the south facing slope. Because of the slopeand low angle the sun must make its way through more tree tops than in summer. Once again, this is what I see, what I have, others may have different experiences.

If we used the cabin in the winter as much as we use it the rest of the year, I probably would insulate the battery box, add some more mass with solid concrete blocks or something with good mass and hookup a solar air collector from the roof. Maybe a liquid heat collector.

Cold improves battery life/longevity. Warm improves available battery capacity. Trade off.
Just because something has been done and has not failed, doesn't mean it is good design.


Great thread!

I have a battery bank question.  One reason standard car/marine batteries are avoided is due to their tendency to wear out quickly.  Walmart has an Everstart Maxx-29 12V 125ah battery for about $75.  For about $1200, you can get a 24v-1000ah.  While I know batteries of this type tend to wear out in 12 months, these batteries have an 18 month free replacement warranty.  Does the warranty clock reset when a replacement is given?  I'm assuming it's based on the date punched on the battery, but I have never had a battery go bad in the warranty period, so I wouldn't know.

Assuming that when the battery is replaced, the warranty clock does reset, and assuming that one doesn't mind the physical labor to remove/return/replace the batteries, one could keep themselves in a constant supply of new cells.

Again, I haven't ever had to use a battery warranty, so I'm not sure how they work.


I've never had a Walmart battery warranty claim. I have had one other mainstream automotive battery replaced under warranty though. In that case the replacement battery warranty period was counted from the date of the original purchase. The original failed after 18 months, it was a free replacement and I still had up to the three year mark (from original date) for a total free replacement if the battery failed by then, plus the pro rated period out to six years. I think that was fair as I only paid for one battery. And if I was the battery manufacturer/retailer I think that is what I would do.

I sent in a request to Trojan Battery to have the warranty period clarified after a warranty replacement. When/if I get a reply I'll post it.

Similarly, but different... I buy my tires from Discount tire. I buy their tire replacement warranty for the Jeep tires. When I have a claim under the warranty I get a new tire free, but have to buy another warranty to maintain the replacement warranty. Also fair, IMO.

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


It would make sense that it would be from the purchase date, but I do wonder what the walmart policy is.  That said, would it be good for newbie to start with car batteries with a 3 year free replacement warranty?  Learning on a cheaper platform with an insurance blanket so to speak.


Quote from: mgramann on January 19, 2012, 07:24:01 PM
... would it be good for newbie to start with car batteries with a 3 year free replacement warranty?  Learning on a cheaper platform with an insurance blanket so to speak.

My personal opinion is, No. Even a beginner off grid'er can have a successful experience IF they prepare properly.

What's to learn? Keep the battery fluid level up. Don't discharge the batteries too deeply. If anyone has problems with that they should probably hire the maintenance out to a third party.

The planning process begins with an honest up front assessment of the power requirements. That will determine the battery capacity required. Make that estimate for the time of year that would require the most power use; probably winter for most of us. actor in the worst case scenario for PV power production; also probably winter for most of us. Then add at least a quarter of the battery capacity for adding items that you were sure you could do without, but can't. When calculating capacity keep in mind that cold temperatures reduce available battery power. We have charts someplace here.

Most off grid system failures occur for the same reason people have financial failures. They withdraw too much power from the batteries (or checking accounts).  If the PV system owner has to run the generator frequently the system is not designed right. Don't try to start with "this much", thinking you will add "that much" later. That is a guarantee for a failure, in my book, especially with batteries. Do it right and you will then have battery replacement occur pretty much about the expected end of life.

Idle thought from my fertile pesimistic imagination.....  What would happen when you walk into the store with 12 bad automobile batteries and they state the warranty was void because the batteries were not used in a vehicle, or want to see the vehicles so they can test the charging system? I'm not saying they would/could do that, but I wonder what thought process the dealer/store might be going through when somebody shows up with a dozen sick batteries? Maybe that's not a worry.... I worry too much at times.

Anyhow that is my opinionated opinion.  ;D
Just because something has been done and has not failed, doesn't mean it is good design.


Thanks Don.  FWIW I'm a worrier too, and that would be quite a scene getting them replaced :D

I will definitely be chatting with you when I decide to build a system.  I have already used your spreadsheet for some initial estimates-thank you for that.

One last idea I had.  This thread is full of information, but the amount is a bit overwhelming.  I wonder if it would be a good idea to have a thread where members posted a quick overview of their system.  Batterys, inverter, other controllers, and finally what their system runs for them.  They could also comment on any changes they would make, and other contributing factors such as climate.

It would give people who are considering a system a head start, with some real world testing.  To keep the thread "clean" people could PM the member for details if they think the system is similar to what they are after.  As their system evolves, they could edit their posts.

I know this information is on the site, but this would put it all in a central location.  An off-grid system applied library so to speak.


I have one of the wally world marine batteries for occasional use.  I don't use a lot of power.  2 years and going strong .  You can get years out of the batteries.  It is a depth of discharge to number of recharges curve.  The better batteries simply handle deeper discharges and more recharge cycles.

The better bet would be a 6v 220 amp battery, which I believe are going for around $100, but I can't seem to find any of these at the discount stores around me.   They last a little longer and it is probably closer to the voltage or string you will be replacing them with. You get more amp hours for the same string.  In your example you would have 8 strings of 2 batteries each.  In every book, magazine, charge controller manual, and retailer I have read they suggested trying not to go over 3 strings, and the less strings the better.  The more strings you go with the more the batteries get unequal charges and it can shorten the life of the whole bank.  That is why they sell 2v - 1700 amp hour batteries.  If it wasn't a serious concern, no one would want to deal with that much lead.  While most books suggest that one string is best for charging they realize that it may be impractical for daily usage. This is because if one cell goes bad you have no battery bank at all, instead of simply operating at 50% or 66% capacity if you have 2-3 strings.  I haven't seen any hard numbers on decreased life expectancy out of a large # of strings though.

Then again Trojan came out with the T-105 RE that I have seen as low as $150 with a 5 year warranty.  The freight shipping is killer though.


In my experience the T105's are excellent

Batteries Plus can get them for you or golf cart places too (that's where I got mine)

I have seen web sites that give free freight to places with loading docks too

to plug Don's favorite good store Thesolarbiz -- my 1800 pounds of Surrettes cost $100 delivery to my door step, he just used a pallet cart and wheeled them into the garage-- pretty cheap, real easy

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


After a previous poster mentioned cycles and discharge depth, I did a quick review but didn't see what I was looking for. I wonder, what is the optimal depth of discharge for maximum life, and, do my lead-acid batteries need to be "exercised" with occasional deeper discharges? My cellphone salesman said I hurt my cp battery by not allowing a discharge before recharching it and to stop the constant charging. I'm sure lead-acid is very different.  I'm about to hook up my 8 Sam's 220A 6V Ever-readys and will be using 2-200W PV's. Depending on optimal DOD, I may spring for 4 more.



Here's a graph from Trojan Battery. This is specifically for their T105RE 6 volt battery, but should be similar for others...

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


Notes from Trojan...

1. Shallow discharges will result in a longer battery life.

2. 50% (or less) discharges are recommended.

3. 80% discharge is the maximum safe discharge.

4. Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.

5. Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice.

6. Do not leave batteries deeply discharged for any length of time.

7. lead acid batteries do not develop a memory and need not be fully discharged before recharging.

8. Batteries should be charged after each period of use.

And a note from me: if the battery is only slightly discharged (maybe 10%) on a regular basis it should receive an equalization charge at shorter intervals. Monthly perhaps?
Just because something has been done and has not failed, doesn't mean it is good design.


Quote from: AdironDoc on January 21, 2012, 12:03:08 PMMy cellphone salesman said I hurt my cp battery by not allowing a discharge before recharching it and to stop the constant charging.

I believe all cell phones use Lithium Ion batteries now. L-ion batteries are a lot like lead acid batteries in that deep discharges hurt them. They have no memory. Their life is based in part on discharge/recharge cycles. They also don't like high temperatures. It is also not good for the L=ion battery to be on charge all the time. In fact if you use a laptop. plugged in mainly, you can remove the battery and keep it warpped in plastic in the fridge and extend its life. Of course if you accidentally pull the power cord everything you were doing could be gone.
Just because something has been done and has not failed, doesn't mean it is good design.


And why not toss inanother battery capacity vs temperature chart for good measure?

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


I have seen some different cost/benefit analysis as to best rate of depth of discharge.  Some say never below 50% and 30% is optimal.  Another I had read supposed there was a standard shelf life and recharge cycle to batteries and it was more cost effective to discharge 50-70% rather than over size your system since after 8 years you will be replacing them anyway.


With the fear of electromagnetic pluses either via solar or weapon delivery.  Would a solar or wind off grid system be really any less susceptible to damage in reality than the norm?  Also would it effect refrigerators, stoves, radios, ovens, my pickup's electronics and OH MY GOD, MY LAP TOP...  Would it make sense to put all the electronics in a cellar maybe less the batteries?  Not being a doomsday prophet but if something would be easily available why not?

Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Dave Sparks

Hey Don!

The number 9 for your Trojan list is the mechanical aspect of a battery. The ones that last really long, like 10 to 20 years, my experience has been that their daily cycles are fairly contant. One might use more energy in the summer, but the pattern over the years is fairly constant. The movement of the internals become "conditioned". This is one of the reasons new people need new batteries so often. The battery is going through so much mechanical stress that is fails.

Alot of other sins for new users are higher on your list failurewise!

Hope all is well ! Spring is coming!
"we go where the power lines don't"


I'm guessing that 4 and 6 are big offenders.

Not sure if our use pattern would be classed as constant. Over the summer it is a very constant thing. Then winter comes and it is mainly constant no use; just a daily boot up with the sun with a short bulk charge, then an absorb and the majority of the day in float, interrupted by Sat thru Monday AM a couple times of a month till May when we hit the use it almost every day summer cycle. I guess time will tell. Typical daily use runs about 20%.
Just because something has been done and has not failed, doesn't mean it is good design.


Great info, Don. Thanks for taking the time to dig up the charts and post them. As the cabin shapes up, the power budget is changing. Seems each week another electrical device 'becomes necessary'. I suspect that depth of discharge, while a very important parameter, is dependent on the number of batteries used. It follows that a greater number of batteries will ostensibly lead to a longer battery life. At some point, however, it appears to make sense to use battery funds to add a 200W panel to the two others. That would lead to a lower discharge depth as well. I suspect I'm going to see how this turns out before I can judge the health of the system I've put together.


Quote from: AdironDoc on January 31, 2012, 10:54:38 PM
Seems each week another electrical device 'becomes necessary'.

Been there, done that    ;D   I just hope that I really I knew my wife long enough and well enough to have made the proper adjustments for excess capacity.   ;)   So far it looks so good...  :)

Yes either more batteries as in another series string, or larger capacity batteries, like L16's.

An extra module can help by providing a more rapid recharge. How does an extra module fit in with the limits of the charge controller as to current if placed in parallel, or peak voltage if in series?  An extra module may not help DOD much if the power used is mainly in late afternoon and through the evening as it happens with us. On a normal day we have excess PV capacity and can easily afford to use a small slow cooker (crock pot), even the A/C for a short time on a hot summer afternoon. In winter we help warm the bed with an electric blanket; most days are sunny and we get the power back by afternoon.
Just because something has been done and has not failed, doesn't mean it is good design.


I suspect you're right, Don. I'm suffering "inflation" when it comes to things I need (or would like) to plug in. I'll put timer switches in the bathroom, basement, etc, and motion based in my hallway. Still, that paddle fan you recommended sure seems sweet :D

My controller is a cheap 60V/40A model. It won't handle the voltage of two 27.5V panels in series, but seems likely to handle 3 panels (200W each) in parallel.  I'm assuming approximately 7.5A per panel at full swing into dead batteries. Like you, I expect most of my usage will be in the evenings.


This is the first time I saw off-grid panels at Costco and I thought some here might be interested.  $279.99 delivered for a 100W panel. 

Grape Solar 100W Off-Grid Solar Panels
"The problem with quotes from the internet is that they're not always accurate." -- Abraham Lincoln


Has anyone used the new Outback Radian GS8048 inverter/charger yet?  Is there any downside with the new system compared to the old Outback setup with dual inverter/chargers (for 220V)?


Only know what I have read.

First thought was, cool. It's a more cost effective package than stacking.

Second thought was, uh-oh. There goes the redundancy. If you have 2 old style for 129/240 VAC, if one dies you casn limp along on one. You won't have 240 VAC though. If you have 4 or more stacked for 120/240 VAC with increased wattage capacity and one goes out you can still work but have to watch your loads.

So what is more important? Cost savings or redundancy benefits?  ???
Just because something has been done and has not failed, doesn't mean it is good design.

alex trent

Welding cable...and other power plans.

Any reason not to use this over the "normal" battery to inverter or battery to battery cable. For 4/0, which is what I plan to use for both battery to battery,  battery to inverter, and charger to batteries,the price is 1/2 to 1/3 for the welding cable...and most of all welding cable is readily available here and any other is a real chore to find.

Inverter and charger distance to batteries is 4 feet.

Sure looks OK to me to use it, but just checking.

My system, to start...

4 12 v Marine batteries (120 AH each) in parallel to a 3,000 watt Wagen inverter. Inverter hardwired into house elec. box. Question..the inverter has a volts out read out and I wonder if that is a good (sufficient) way to tell battery discharge. At 12.1 volts, I should be at 50% and using it on the build the reading seem to be in line with what I see with the battery.

Charger..likely an Iota DLS-75.

Recharge is with 2600 watt genset hooked into house and from there to charger. Genset will also provide power to house when charging (or other times) is hooked into box with 8 gauge wire and running off the 240 plug.

Using a simple manual A/B switch to isolate inverter from genset when genset is providing power


Welding cable will work. It won't pass an NEC inspection as it doesn't have the required stamped approvals. But that is not an issue here.

Battery voltage is only a guide to battery state of charge. It's a very handy way to tell pretty much what is going on. The best indicator of battery charge is a hydrometer with a thermometer so the reading can be temperature corrected. Charts for that come with a good hydrometer and there are also some listed here in this topic I think. Of course if you have a sealed battery of some kind you can not use a hydrometer.

Using a hydrometer regularly and recording the reading of each cell can help detect early cell failure or deterioration. When that is found an equalization charge can be done. Unfortunately the Iota chargers don't have that ability. There are some Xantrex that do; not many.  A good inverter / charger combination unit can also have equalization charging built in. I'm not familiar with the inverter you mentioned.

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