Making progress

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elesaver
elesaver Solar Expert Posts: 185 ✭✭
in Solar Beginners Corner #1
Congratulations to all the responders to my questions and comments. I am making progress in the understanding of this whole process. It's a miracle! :D After reading many of the threads with the information provided, it's all beginning to come together.

So, with my understanding growing, I am going to continue to work at building a system. One of the biggest hurdles, it would seem to me, is that "we" (beginners) have a difficult time in creating a trial system due to the problem with batteries needing to be equal in age and Ah when put into service as well as other things, too, not the least of which is the cost. Mistakes can cost big money.

Would you think this idea would work? To produce 1.5 kW per day, I would get an MPPT controller...at least 30 amps and maybe even spring for a 60 amp knowing that would be an integral part of the ultimate system plus 1 or 2 mono panels above 230 Watts, depending on price and run them on a 24V system. These panels could also be put into the final system.

If I had 8 ea 6V 228 aH batteries (2 strings of 4 batteries each), they could be kept charged by the 2 panels with 2 days of storage considered.

Now, here's the tricky part. The battery bank. My garage or barn is too hot. The only place that I can think of that would have some relief is under the deck, close to the house foundation where there is almost 100% shade. I do not know the ambient temperature on a hot August day (in NC) but it gets hot here. Cold is not supposed to affect batteries but we've had a spate of single degree temperatures every once in a while during a cold winter. The forum points to 6V batteries but there are lots of them with many choices of aH. It would seem the gel battery would be better since it does not have to be maintained but buying 8 batteries is quite an investment. Going under the deck frequently would get old fast.

So, if you would, validate (or annihilate) the calculations and perhaps offer some battery options. I had read a woman's posts earlier and she seemed to really know her stuff. As a woman, I, too, am trying to become proficient. Your willingness to help is appreciated. I love learning about this stuff.
1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: Making progress

    One thing that hits hard is the use of expensive and unforgiving of mistakes gel batteries in a new/learning system.
    Flooded batteries are in general far more forgiving of mistakes, are a lot cheaper and last longer. You just have to keep an eye on them. Gel batteries you don't have to add water, nor can you. You also cannot check their SG, so you can't check their state of charge.
    Re the heat: What is the ground like in your area? Does it tend to be wet, or might it be possible to dig a small and well drained "root cellar" and keep the batteries there, where the temps are cooler and more steady?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Making progress
    elesaver wrote: »
    Would you think this idea would work? To produce 1.5 kW per day, I would get an MPPT controller...at least 30 amps and maybe even spring for a 60 amp knowing that would be an integral part of the ultimate system plus 1 or 2 mono panels above 230 Watts, depending on price and run them on a 24V system. These panels could also be put into the final system.

    If I had 8 ea 6V 228 aH batteries (2 strings of 4 batteries each), they could be kept charged by the 2 panels with 2 days of storage considered.

    Well let's see.
    1.5 kW hours per day on a 24 Volt system requires about 74 Amp hours. At 25% DOD that would be a 296 Amp hour 24 Volt battery bank, which there's no such thing as. Nor is there a 228 Amp hour battery that I know of. But you could use two parallel strings of 220 Amp hour 6 Volt batteries to get 440 Amp hours. But you probably don't need that much. You are right about the age/capacity problem when it comes to adding batteries, but well-cared for ones within a year can be doubled up without any major performance sacrifice. If I were you I'd start with one set of GC2's @ 220 Amp hours. You may find it's sufficient for what you need with the fudge factors of Voltage range and direct-from-panel power added in.

    A couple of 230 Watt panels would keep that much charged too: 460 Watts * 0.77 / 24 = 15 amps peak current. That's about 6.8% peak charge rate, or a bit above bare minimum. It would not do for a larger bank. It would be better to have >685 Watts for this.
    Now, here's the tricky part. The battery bank. My garage or barn is too hot. The only place that I can think of that would have some relief is under the deck, close to the house foundation where there is almost 100% shade. I do not know the ambient temperature on a hot August day (in NC) but it gets hot here. Cold is not supposed to affect batteries but we've had a spate of single degree temperatures every once in a while during a cold winter. The forum points to 6V batteries but there are lots of them with many choices of aH. It would seem the gel battery would be better since it does not have to be maintained but buying 8 batteries is quite an investment. Going under the deck frequently would get old fast.

    Hot is not good. Especially not for batteries. In the shade on the North side, buried below grade, anything but locked up in a hot garage. Cold does affect batteries, but if they are charged they will not freeze; merely slow down. Gel batteries are not a good choice for RE: they are very picky about Voltage and current and can all-too-easily be destroyed.
    So, if you would, validate (or annihilate) the calculations and perhaps offer some battery options. I had read a woman's posts earlier and she seemed to really know her stuff. As a woman, I, too, am trying to become proficient. Your willingness to help is appreciated. I love learning about this stuff.

    You are doing well so far. Nearly right first time out. For example you've got the most important lesson down pat: mistakes are expensive so ask and plan first before you buy anything! :D
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
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    Re: Making progress
    elesaver wrote: »
    It would seem the gel battery would be better since it does not have to be maintained but buying 8 batteries is quite an investment.

    Wayne and Cariboocoot already mentioned this in regular font. It needs to be mentioned in bold: Do not get gel batteries for a RE system.


    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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