Shading issues

[Ho jo]

I can only get 4 hours 11 to 3 pm of unshaded sun on my panels in June. I park in the shade and use an umbilical cord. A couple times a month I Hook the tt to the truck to dump the tanks, 30 minute round trip. So an isolator wouldn't help much. I use 1000 watts per day and with a 5 day reserve 416 amp hour @12 volt golf cart battery bank. With my limited sun My question is would 2 separate arrays 4 100 watt panels on a 30 amp mppt and 2 260 gt panels on a 40 mppt cause any problems or damage.

[Mike90250]

Look into the price break using several 300w grid tie panels, not 100w 12v panels.

[Ho jo]

Mike I agree that its much cheaper that way. I can get new suniva panels for 38 cents a watt CL. Thing is I already have the 4 12 volt panels. (That cost me 3 times as much). And I have the 40 amp cc. To fix what I have now instead of starting all over. I can buy a 30 amp cc for the 12 volt panels and 2 260 watt panels for $300. Would 920 watts on 70 amps of controllers be to much for my batterys?

[Sunking]

If they are Golf Cart batteries, you can get away with C/6 charge rate. However there is no amount of power that will ever charge your batteries with just 4 hours of direct sun. It takes 4 to 6 hours to go through the Absorb phase after Bulk. Morale to the story is you cannot tolerate any shade on a battery system. There is just not enough daylight in a day to properly charge batteries on solar. That is why a generator is mandatory to top them off once a week.

[Ho jo]

Last summer I saw that 4 hours wasn't enough. I would bulk each morning from the generator and let solar take over never saw float. So charging at c/6 only shortens bulk time. In absorb the batteries will only accept a limited amount of amps and the rest the array could produce for charging is wasted. Sunking absorb takes 4 to 6 hours is it depth of discharge that determines 4 or 6?

[Sunking]

Last summer I saw that 4 hours wasn't enough. I would bulk each morning from the generator and let solar take over never saw float. So charging at c/6 only shortens bulk time. In absorb the batteries will only accept a limited amount of amps and the rest the array could produce for charging is wasted. Sunking absorb takes 4 to 6 hours is it depth of discharge that determines 4 or 6?

Absorption time depends on how fast you charge in bulk. Same for all battery chemistries. If you charge slowly at C/12 for bulk, Absorption phase wil start when the battery reaches roughly 90% SOC, and only takes a few more hours to finish. Charge at a higher rate like C/6, and Absorb phase starts when you reach 70 to 80% SOC and can take several hours up to 6 hours to finish. Once you get to roughly C/10 charge rate, you hit the point of diminishing returns where charging at a higher rate does not shorten total time. Example if you were to completely discharge a battery, charge at 1C is still going to take 14 to 16 hours to fully recharge. You would get roughly the same time at C/10 give or take an hour.

There is one thing you can do. Raise the voltage set points higher. With you very limited sun of 4 hours just makes an impossible job even harder. I wished I could change that but the law of physics cannot be changed. Your application might possible be solved with a Lithium battery as they do not require being full charged, and not as sensitive to Peukert's Law as Pb batteries. The catch is the expense and risk involved. A lithium can be fully charged in 4 hours with a C/3 charge rate.

[Mike90250]

> A lithium can be fully charged in 4 hours with a C/3 charge rate.

And you need a larger PV array to generate the higher charge amps - No free lunch

[Ho jo]

Can't justify the cost of lithium for 12 cents of electricity a day. At 80℅ soc how long would it take at c/10 to fully charge. With generator?

[Ho jo]

Anyone? If from 90% takes 3 or 4 hrs for absorb to finish. Would 10 % charge rate be needed since in absorb it takes less amps as the batteries get closer to full? And im assuming it takes 12 hours bulk and 4 hours for absorb if it takes 16 hours from dead. So 12 hours from 0 to 90 at c/10. 1.33 hrs bulk time from 80 to 90, and 4 hours absorb to 100%. So 5 hours 20 minutes charge time.

[Mike90250]

Anyone? If from 90% takes 3 or 4 hrs for absorb to finish. Would 10 % charge rate be needed since in absorb it takes less amps as the batteries get closer to full? And im assuming it takes 12 hours bulk and 4 hours for absorb if it takes 16 hours from dead. So 12 hours from 0 to 90 at c/10. 1.33 hrs bulk time from 80 to 90, and 4 hours absorb to 100%. So 5 hours 20 minutes charge time.

16 hours is too long. If you have matched your PV power to your battery and your battery to your loads, you should be able to Bulk and Absorb in a day. completing float is tougher with lead acid. with LFP there is no float requirement. Your batteries getting 90% discharged should be a RARE occurrence, not a common one .