Quote from: rick91351 on September 24, 2014, 10:06:05 AM
Strange post and it is not even a full moon........  Another group I follow went in the toilet this week.  Attacked by four or five most likely one that is trying to bust it up....  Doing a great job of it.....

You Administrators do a remarkable job with this group.  We have had our issues but pretty dog gone good info at the grass roots level. 

And John also for selecting therm !   Where has Glen gone or has he found a full time job?

It's been a long time since I posted anything new to this topic.

Today I want to mention something new in the battery world. Lithium ferrous phosphate batteries, or LFP, also known as LifePO4 batteries. Note there are other lithium based battery technologies out there. LifePO4 are the safest... no bursting into flames like those on the Boeing Dreamliner. 

They have great promise. They do not sulfate when left in a partial state of charge for example. They can also be severely damaged with improper charging or discharging. There is a whole lot of partially correct information out there. I've been looking at LFP for a few months and it has been a confusing time. I found one of the better, if not the very best, articles on this battery technology on another forum.

If interested in new stuff like batteries go have a read over here...   That's page one.

Thanks Don, my GCB's are getting old (and abused) but sill holding out after 4 years of heavy use and I'm thinking next year I'll get a new battery bank (and double the capacity).

On a side note I finally sorted my charge controllers 'state of charge' light issue.  Somehow 'd missed one dip switch and got it sorted today

Now I just need to survive another winter but I'm in pretty good shape I think.

I've been giving a lot of thought to my problem of trying to find some A-205-fa3 solar panels which appears to be pretty much impossible these days.  You see I have three of these panels and could really use 4 or 5 of them but finding an 11.15IMP panel these days is nearly impossible (if not impossible) so I've been thinking that instead of going out and buying ANOTHER charge controller and 1000 watts of panels (or less) I might just bite the bullet and buy enough panels to get to around 1000 watts and under 150vmp and swapping out the panels.

Then I'd still have the current 615 watts of panels for another year when I can justify spending another $600+ on a controller for them and either using on another cabin or adding to my system to increase it's charging capacity.

Today's prices are pretty low and it looks like I can add 900-1000 watts of panels for under $1k which would get my charging up to what I need in the short term (since my 615 watts isn't really enough for my current needs (no pun intended)).

THoughts?  IDeas?

I could use a few of those fa3 class panels as well, as we want to build a small 12V solar generator. Any idea why they are so hard to come by lately?   My guess is that the panel industry is mainly producing for the rooftop grid-ties, and 12 volt is not used much now in those installations.  Not much demand?

I think it's a combination of:  Most people want higher wattage and higher voltage panels now so supply and demand is dictating the industry (i.e. you see a lot of 300+ watt panels in 24-48v now and few 12v.

Most systems you see being built today are 48v systems so all the professional shops are selling panels to suit.


In a way it's almost like the computer industry a decade or two ago with panels constantly increasing their capacity.  You see few 200 watt panels (if any) but tons of 300 and higher...heck I think I saw some in the 390watt range recently!

I'd love a few of those frankly but the voltage was too high for my controller (max 150v)

The cost per watt is usually much higher on the so-called 12 volt panels. Unless one only needs a couple of panels I believe it is better to buy the larger wattage, higher voltage panels. Especially is the plan includes an MPPT controller anyhow.


Our GC-s's have been in service now for 64 months. For the most part they still perform very well. Two cells lag behind the others a little (lower sp gr) but the occasional equalization brings them back to being very close. I hope they go another couple years.  At that time the LFP's (lithium ferrous phosphate) might be lower priced than today. There are some nice advantages but LFP also bring their own quirks along.  Little, if any, room for overcharge / discharge errors. And the biggest bugaboo I see right now, other than initial $$ outlay, is cold weather. They do perform better than FLA in discharge mode, but they should never be charged below freezing. In many situations that will not be a factor, but in our case where the batteries will sit in an unheated space for weeks in winter, that is an issue.

...............link to story

linky

Grrrr....

After much debate, research, more debate and a call from SolarWorld I think I've gone about this wrong. 

I can get away with 740AH of capacity on my battery bank, though it would be a bit small but with an average of 4.7hrs of sunlight at my location (the engineer at SolarWorld gave me that from a 40yr database he has) I would need 3.9hrs of charging (after bulk) to get the 740AH bank back to 100% after use.  He's telling me to do that I need 6 280watt panels and another MPPT controller and this would leave my generator for only when it was absolutely needed.  He's telling me that I never fully charged the GCB's on solar because my 605watt array just wasn't enough to do it and eventually they just wore out (sulfated etc).  This would mean a $5000 build to add the 6 280watt panels, 8 batteries and an outback MPPT controller not to mention racking, wiring etc.

So what went from a $2500 +/- battery bank purchase has gone to double that to try to get enough solar to charge the bank enough that it will last a long time.  He also told me that he's seen well maintained GCB's run 8 to 10 years (interesting).

So, what to do???

I might be able to swing the $5k but it will be a serious downer since I hadn't planned on it at all and don't really want to finance anything.  Let's hope the biz has done well enough that I'll get a bonus big enough to cover that much cost.

I've been messing with the calculator a lot lately and plan to run these through it to see what it tells me but man I really didn't want to have to buy 6 new solar panels let alone a controller at the same time I bought the batteries.

If I input a fairly abusive power usage at the cabin I can use about 140AH in a day (TV, Internet, Fridge, Lights etc based on winter use not summer use) so by setting my autonomy to 1 day I'll need 8 L16's at 370AH ea for a 740AH 24vdc bank.  I set it to 1 as the only time I'd actually be in that position is in the 4 months of low sun usage and during that time I'll mostly NOT use even half of the 140AH (more often than not I'll only use that 3 to 4 days out of every 2 to 3 weeks).  So 740AH should be find since I do have a genny to back things up when the sun decides not to show up or I abuse the power.  I just have to set the genny to run at a higher voltage to ensure the system doesn't drop below 20% DoD.

Next, if I put in 4.7hrs of ave sun (thank you SolarWorld) and I put in the 280watt panels (9.07Imp) it shows 4 of them not the 6 he calculated though I think his calculation was based on having to recharge the 740AH completed (maybe?).  This does not include the 3 205 watt panels (11.07Imp) I already have so perhaps 3 of the 280 watt panels coupled with my 3 205's and I might be just fine.  After all that will give me ~1445watts of solar charging which is more than double what I have now.  I'm no expert but my 605watts maintained my GCB's pretty well when I wasn't abusing the system.

Price drops down to $3150 which s a lot easier to swallow.

So knowing what I've written here what are your thoughts?

The plot thickens!  I used altestore's calculator to 'build' a system using my PV spreadsheet calculator to see what the difference was.  Using 3380 watt hours per day, 24v system 2 days autonomy, 40F min temp it shows a 843AH battery bank then using 4.7hrs of ave sun I would need 935watts of charging and recommended 4 280watt panels for 1120watts.

This makes me think that going with 740AH and 1400+ watts of solar I should be good to go really.

QuoteNote: All calculations assume only a 50% discharge to your batteries to optimize battery life.

I'm seeing this a lot.

Question:  To recover 140AH in a battery bank am I right in assuming:

1. That if I am charging with 11 amps at 54 volts and the MPPT controller reduces the volts to 30v that I'm then going to be charging at ~20amps?
2.  If I am charging with 20amps from the MPPT controller I'd need 7 hours to charge 140AH?
3.  If the above is correct to recover 140AH in 4 hours of sunlight I'd need 35amps of charging?
4.  If the above is correct then by adding 4 300 watt panels with 8amps the MPPT controller would convert the 152volts (4 panels at 36v ea in series) to 30v and 40amps and would charge the 140AH in 3.5 hours?

Finally with the above can I assume that the 20amps from the first set of panels (3 205 watt 11.3imp panels in series) plus the second set of panels (300 watts 36v 8imp in series) 40amps the two working together would charge at 60amp and complete the charge in just over 2hrs?

What I am trying to do is determine exactly what I need to charge up my 740AH battery bank (when I get it and install it) with solar and 3 to 5 hours of sun (ave is 4.7 hrs).

I also want to make sure I understand what my generator needs to be set to to ensure a complete charge after a day or two without much solar.  The inverter has a 50amp charger so I'm under the belief that if set at 100% of charger capacity it would take 2.8hrs to recover the 140AH of usage.

I'm using 140AH as it's the most I'd use in a day based on current calculations.

Any response appreciated.

QuoteCurrent Boost
Under most conditions, TrakStar TM MPPT technology will "boost" the solar charge current. For
example, a system may have 36 Amps of solar current flowing into the TS-MPPT and 44 Amps
of charge current flowing out to the battery. The TriStar MPPT 150V does not create current!
Rest assured that the power into the TriStar MPPT 150V is the same as the power out of the
TriStar MPPT 150V. Since power is the product of voltage and current (Volts x Amps), the follow-
ing is true*:
(1) Power Into the TriStar MPPT 150V = Power Out of the TriStar MPPT 150V
(2) Volts In x Amps In = Volts Out x Amps Out
* assuming 100% efficiency. Losses in wiring and conversion exist

That is from the Morningstar site on MPPT controllers so a quick calculation suggests the following:

3 panels of 205 watts @ 11.27Imp @ 18.2v in series will give 615 watts @ 11.27Imp @ 54.6v and when converted by the controller to 29.4v to charge a 24v bank will give 20.9Imp and 615watts (power in equals power out) if I understand the above correctly.

Quote from: OlJarhead on January 20, 2015, 11:18:20 AM
Question:  To recover 140AH in a battery bank am I right in assuming:
1.     2.    3.

In a theoretical, 100% efficient world, Yes. Here on earth with the equipment and materials we have, No.
(a) Batteries will not charge at a constant rate from start to finish. As they become closer to full the amp rate will taper off.
(b)There will be some charging loss due to battery inefficiency as well as some loss as charge controllers are also not 100% efficient. As well, the greater the difference between the incoming PV voltage and the outgoing charge to battery voltage, the less efficient the CC is.
(c) The closer you can get the amps into battery current to be C/10 of the AH capacity the better off it will be. If too high amps then more energy is wasted in making heat which in turn will cause electrolyte loss to a greater degree. Too low an amp input and the time for a charge gets to be longer than the sun will be up.

Potential issue with scenario 4. The Voc voltage is too high for the commonplace 150 volt MPPT charge controllers. Midnite does have models with 200 and 250 volt limits that would be suitable.

Regarding the two strings of PV; old and new.  Pardon me if I missed it but is the plan to use two charge controllers, one for each string, or to route all the PV through the one charge controller?   Knowing the Vmp, Imp and Voc ratings of the two different panels would help in figuring how well they will play together.

The info from Morningstar is fine as far as it goes, but they do state in the last line that the example is for 100% efficiency.  So the power out is = to the power in less the internal losses. I can always feel the loss with our CC's as they are almost always warmer to the touch than the surrounding materials.

My plan is to add a second string of panels (4x310watts) and a second controller (Outback Flexmax 80).  If the Flexmax 80 can only take up to 145vdc input then I can make the array a series parallel system with two panels in series parallel to two more panels in series giving me ~72vdc input.  Which will be fine with 10awg cables from 50 feet away.

QuoteWatts    310   
Cells    72   
Panel Vmp    35.80   
Panel Imp    8.68   
Panel Voc    45.42   
Panel Isc    8.99

That's the new panels I'm looking at but frankly it will depend on who has stock etc when it comes time to buy.

What is 'c/10'?  Capacity of battery bank divided by 10?  If so I'd need to add 6 of the 310watt panels instead which would give me about 60Amps of solar charging on that array which, when added to the 20amps on the old array minus varius efficiency factors should work out nicely if I understand you correctly.

Another thing I've been contemplating:  740AH of battery cap would mean I'd have to run my generator 3 hrs every day if there is no sun at all and I use 140AH of electricity in the cabin.  Thus on full usage I'd run as much as 90hrs in a month on the genny using approx 45 gallons of propane.

On the other hand if I had 1110AH battery cap and allowed it to run for 1.5 days without sun/gen I'd have to run my generator for a total of 4 3/4 hrs for a total of 95hrs per month using 47.5 gallons of propane.

My point? and these are rough calcs only, but with only 50amps of max charging capacity and a max timer of 5 hrs on the auto gen start I can run the genny daily for 3 hrs to give me 150amps of charging roughly vs running it every 1.5 days for nearly 5 hours to get the 220amps I'd need if I used 140ah in 24hrs.  In other words, I'd have to actually run the gen longer despite not needing it as often.

Seems to me without a much bigger charger on the inverter I'm better off having a smaller bank with lots of solar and limiting use on cloudy days.  Make sense?

QuoteWhat is 'c/10'?  Capacity of battery bank divided by 10?

Yes; with the result being the number of amps that would be near to ideal for charging the batteries, nless the battery manufacturer recommends something different. You can usually charge at that rate and be safe and as quick as possible w/o overheating.



??  If the present charge controller could handle the watts from the new PV array how about buying a Midnite Solar Kid for the old set? The Kid can handle 150 volts maximum, 30 amps output to batteries and with a 24 volt battery up to around 850 watts of panels. Actually Midnite states up to around 1000 watts of panels for a 24 volt system would be a good match. That is because for most of the day the panels will not be producing the rated watt output. So for a short time (noonish) a good CC can handle the excess wattage. It does mean the output would be limited to the max rating; 30 amps on The Kid.    Just food for thought as it is <$300 (NAWS).  We have one now; since lightning strike.


Regarding the panel watts and C/10 thing... Systems can also work / live, with having a lesser output from the PV. Ours, for example. But that is because we have more battery than we really need. I overdid the battery capacity. Right now if I was re-doing the batteries I would have either 8 GC-2 or maybe 4  L-16.  But one disadvantage to the L16's for us, would be that tall case batteries should really have a higher amp charge to guarantee better mixing of the electrolyte from gassing. 

QuoteIf the Flexmax 80 can only take up to 145vdc input then I can make the array a series parallel system with two panels in series parallel to two more panels in series giving me ~72vdc input.  Which will be fine with 10awg cables from 50 feet away.

Yes, that would be about a 3& maximum voltage drop at 72 volts and 18 amps. That's workable.

Never been really happy with the MorningStar MPPT controller or their support so I'd rather relegate it to 2nd fiddle

I'm currently running 12 GCB's but as mentioned in my cabin thread pretty much smoked them this winter   Oopsie.  SO I'm working working working the PV Calc tool to come up with something I can live with and am fairly certain 740AH of L16's is going to do the trick.  Of course, from the above you're suggesting I have 74Amps of charging but I think I can do well with the 60Amps, after all I have both the autogen start and don't spend as much time up there in the winter anymore so likely will get a lot more sun then not.  In the summer I can see good charging from early in the morning (7-9 is a trickle but it comes on hard before 10am and runs very very strong past 3pm...usually I use less power than is floating by the sun until the night starts to come on.

I just thought I'd toss the lower cost option of the Kid in there.      I do like the Outback equipment. I especially like it when one of their inverter/chargers is a part of the system as it can all be tied together with a Mate.  But if there is no other OB equipment in the system there is also the choice of the Midnite Classic.  Both MN and OB are better than MS. FWIW, the MN software is a little more aggressive than the OB. I notice that the MN wakes up earlier than the OB ever did. Not that it produces much power at 8 AM, but it is on the job early. Also FWIW, the OB founders/engineers are the folks who started and now run MN.

Interesting, looks kinda like the OB too.  The FlexMax 80 is a couple hundred less than the MN Classic by looking at MN's site but that might just be retail.

Quote from: rio on June 05, 2015, 04:07:51 AM
Off-grid throws away 30% or more of your solar power in charging/discharging losses as shown to the right. Further, battery systems throw away another 50% of your annual incoming solar power because the battery can't save the excess power in summer for use in the winter when you need it .

Point being?  In many of the cases here 'off-grid' means we're too far from any grid to even consider grid tie systems...we're off the grid in more ways than just a cable

Quote from: OlJarhead on June 05, 2015, 12:09:55 PM
Point being?  In many of the cases here 'off-grid' means we're too far from any grid to even consider grid tie systems...we're off the grid in more ways than just a cable

Some of us are even off the map. Hope you are doing well and hey Don! I have been lurking incognito!  Friday!!!