Battery ideas for longer life and better use of solar array

H2SO4_guy
H2SO4_guy Solar Expert Posts: 213 ✭✭✭
in Advanced Solar Electric Technical Forum #1
The challenge with one large battery pack is that the last 10% of charge takes a long time. If your solar panel array size is pretty large, it only uses a bit of it for the last 10% or so. What if you ran 2 or more battery packs. There could be 2 charge controllers. One for bulk charging and another set for much lower amperage for finishing charge. When you start making power you could you could bulk charge the most discharged pack and with the second charge controller you could top off a different pack that would need less amperage to finish the charge cycle. There would need to be a way to switch which charge controller would go to which pack and hopefully automate the process.

Real numbers:

3 year old VRLA batteries 48 volts @ 400 AH @ the 10 hour rate price to pick up $672. These work at over 90% efficiency too. If you have 2 of these you are into all of the batteries for $1344 pickup price. Not too bad for 800 AH @ 48 volts @ the 10 hr rate. Divide these up into 2 400 AH packs and use multiple charge controllers. The challenge is the switching part so you don’t have to change connectors. Automating this would be even better.

Anyone have any ideas on the subject?

We are looking at an off grid house, but the battery pack is only 24 volt. (12 2 volt Surrettes, 5 years old. Couldn’t see the model number as it is printed on the side, not the top and didn’t want to unhook one and pull it out to read the model number) We already have a flooded GNB 3 years old 48 volt pack (500 AH @ 48 VDC @ 8 Hr rate) that could be reconfigured to 24 volts. Since there is already a 4024 there, why change anything, other than adding another battery pack, just have only one connected to SW-4024 at a time. I could put the inverter to a combiner area fed by 2 disconnects from the battery packs, so the only time they would both feed the inverter is the brief couple of seconds that they were on while the packs were being changed. One would be added for a second and the other would be disconnected from the inverter. Taken off of the buss and that way the inverter is not without power so you won’t lose power in the house.

Skip in Kansas City
12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
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Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: Battery ideas for longer life and better use of solar array

    If I'm reading you correctly, wouldn't you be using the same PV array for the final absorb charge? Wouldn't you be using those panels in an inefficient mode anyway in that case?

    It seems to me that unless you have a use for the excess panel capacity once you have reached absorb charge you are searching for a solution in search of a problem.

    One way to counter act the issue would be to design you bulk charging in the morning for example (aiming your panels accordingly), and then using you big loads in the afternoon. If for example your panels could put out say 40 amps, but in absorb the batteries only can use 10 amps, you could run 30 amps of "free load".

    We pump all our water this way, as well as charging and using most of our computer and modem time. The trick is to try to balance the loads to the supply as best you can. We have lived with a system that has been way to small for years. By using power at the right time we were able to live quite well. It will be curious to see how it works when I complete the upgrade this spring to a double sized Pv system. (the load are already creeping up!)
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  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    #3
    Re: Battery ideas for longer life and better use of solar array

    Icarus is right, KIS is the way to go, Ive recently upgraded to 2.4 kw of solar and on a sunny day in January Im hitting float by 3 oclock yes Im spilling power but with a massive 2100 ah (1500kg) 24 volt battery bank . We try and use the power by using the washing machine, ironing (well somebody does) but hey some days it just goes to waste, but getting 2 hours of absorb charge regulary is good for the bateries.

    We spend so much effort reducing our loads so that our system can provide the energy we need to keep that hydro carbon munching generator quiet that if we achieve the holy grail of more power that we need thats why we buy charge controllers , complicating the issue with two battery banks and complicated switch gear will only lead to tears, the sun doesnt shine everyday and although I need only 4 hours of the stuff a day and have a realistic 2/3 day battery capacity I still intend to add another 1600 w of solar taking my solar sunshine get to float requirement to about 2 hours a day . I live in Sunny Spain but you still get peeved when the clouds come out and force you to fire up Gerald the Grumpy Generator who gobbles Gas. KIS ;)
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #4
    Re: Battery ideas for longer life and better use of solar array
    ...Gerald the Grumpy Generator who gobbles Gas.
    ROTFLMAO!! I suppose its nickname could be "G5". ;)
    Jim / crewzer
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