system upgrade

I currently have 8 75w Siemens (Shell Solar, SolarWorld), Sb50, 4024, 8 Surrette t-12-250 batteries (1000ahr, 24kW storage), bogart trimetric, and a 8.5 rmy Kohler generator. Except for the sb50, this is all 1999 hardware. I'm in the northeast and temps get down to -30.

I am adding 8 Suntech 170w and an mx60.

I am planning to upgrade batteries for two reasons, 1) I need more capacity and 2) I think my batteries are about dead.

I just tested my batteries and all cells were about 1.1-1.15 with a common car battery bulb tester. I used the generator and charged the batteries before testing and the meter read 25v. I also noticed that the fluid in a few cells had a dark coloration.

Any idea what caused the dark coloration?

Given the panel setup, what is the largest battery bank that I can use?

I guess I'm figuring

75w panels are 4.43a/16.9v and wired in strings of two; so 4.43*8/2 =17.72 amps
170w panesl are 4.83a/35.2v ; so 4.83*8=38.64amps

so as a total, the panels produce 56.36 amps at 24v configuration

which if I understand it correctly, means the battery bank size should be 563-1127.2 a-hr folowing the 5-10% rule.

Is that correct?

I'm also trying to estimate how much I would like to use and I come up with ~500a-h/day. I think I may have this way overestimated due to some of the wattages and usage times.

So far, I'm looking at this scenario:

Lights 502w-h/day
Television 250w x 2hrs/day= 500wh/day
Stereo 200w x 2hrs/day= 400wh/day
vacuum 1200w x 1 hr/day= 1200wh/day
water pump 800 x 0.5hrs/day = 400wh/day
septic pump 800 x 0.5hrs/day = 400wh/day
washer 600 x 1 hrs/day = 600wh/day
dryer 400 x 1 hrs/day = 400wh/day
coffee maker 700w x 0.25 hrs/day = 175wh/day
computer 100 w x 1 hr/day = 100wh/day
telephone 50w x .5 hr/day = 25 wh/day
power tools 1000w x 1 hr/wk = 140wh/day
subtotal 4842wh/day
dehumidifier 12hrs/day 700KWH/y =
6742 wh/day

so 6742/24= 281 a-h/day

then if I factor in efficiencies, etc I think I am looking at 281 a-h/day *1/0.5 *1.2 = 674 a-h/d

I'd really like to be able to survive 2 weeks of no sun , but that means a 9441 a-h battery bank. So two weeks is probably way out of the question.

What does a typical home use? I must be hugely overestimating my usage.


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system upgrade

    your proposed pv system will be (8x75w=600w)+(8x170w=1360w)=1960w stc. realistically let's take it to 90% of that for 1764w as it may be closer to that for the ptc ratings. do note i usually do things from the current prospective, but the voltage is a constant 24v so it's the same thing in this case.
    for the min battery requirement for your electrical needs you come up with about 1150ah which at 24v is 27,600w of storage. now 1764w/27600wh=6.39% and that is an acceptable charge rate. given your 1764w amount/5%=35,280wh in batteries maximumly. this is 35,280wh/24v=1,470ah maximumly for the 5% charge rate. the larger ah capacity of your bank, of course it will take longer the time to reach full charge. you will get a bit more current from the mppt of the mx60, but i ran this straight up for you, as in not banking on it and typically this would be around 10% on average. you do of course know that any cloudy periods or even sunny winter days will not give a large return on the power you will produce so you may need more than that extra 10% kick from the mppt as another pv expansion may be in order if you can't cut back on your power usage levels. cross that bridge when you get to it though.
    as to the dark coloration in some of your cells i would suspect it has something to do with extreme sulphation as i saw the same thing with a few of my older batteries that went bad.
  • System2System2 Posts: 6,290 admin
    Re: system upgrade

    "this is 35,280wh/24v=1,470ah maximumly for the 5% charge rate."

    Thanks for the reply.

    I'm still working on my usage numbers. I'm still showing about 220a-h/day. I'm also thinking of switching from propane refridgerator to an electric energy star model. Electric fridges advertise ~450KWH/y which equates to about 1240WH/day or 71A-h/day.

    Does anybody here have practical experience using an electric fridge like a kenmore? Is stated electrical usage correct?

    The way I see it if I need about 300ah/day then my maximal battery bank only gives me about 2 days of storage.
  • BB.BB. Super Moderators, Administrators Posts: 33,085 admin
    Re: system upgrade

    My 1 year old Maytag Freezer has been running at less than the Energy Star Tag Rating--(freezer is in a, somewhat, insulated shed in the back yard and stays nicely around 70F or a bit cooler.

    In another thread here on why zero degrees F for a freezer, in looking between SunFrost's specs. and the Energy Star specs., it appears that, for SunFrost, their "90F ambient" ratings gave the same kWhr usage as the Energy Tag Rating--so, I would guess if your room is cooler than 90 degrees F, you should see total kWhr usage at slightly less than the Energy Tag. (SunFrost also rates their freezers as 0 to 23F range--quite a bit warmer than the Zero F or less that most folks should be using for long term food storage--that may account for the difference between the Energy Tag ratings and SunFrost's 70F ambient)

    Go to the SunDanzer Web site and you can probably guess from their curves about how room temperatures affect energy usage. (PDF Link)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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