What I have so far, will it work?

easytimeasytim Solar Expert Posts: 57 ✭✭✭✭
I live in Missouri, I will be using 70 watts for 8 hours straight every night powering
12vdc LED lights. No power loss going from 12vdc to 120vac with an inverter, everything works off 12vdc

I have two 12volt 130 watt solar panels in parallel for a total of 260 watts
max voltage 19.8v each
max current 6.55a each

Morningstar SL Sunlight Controller -20 amp (SL-20)

All I need now is the batteries, I'm going to buy two 6 volt EverReady Golf Cart batteries from Sam's for $71.00 each

Does it look like I'm on the track? Is this a workable plan?


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Comments

  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: What I have so far, will it work?
    easytim wrote: »
    I live in Missouri, I will be using 70 watts for 8 hours straight every night powering
    12vdc LED lights. No power loss going from 12vdc to 120vac with an inverter, everything works off 12vdc

    I have two 12volt 130 watt solar panels in parallel for a total of 260 watts
    max voltage 19.8v each
    max current 6.55a each

    Morningstar SL Sunlight Controller -20 amp (SL-20)

    All I need now is the batteries, I'm going to buy two 6 volt EverReady Golf Cart batteries from Sam's for $71.00 each

    Does it look like I'm on the track? Is this a workable plan?


    .

    Probably not.

    Daily load as a percentage of battery capacity is too high, too much efficiency loss from using that charge controller, no provision for no-sun days.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: What I have so far, will it work?

    You can use the PV Watts program to see how much power you can generate from a set of panels... Pick a city near you, use 1kW (minimum panel size supported); and use a derating factor of 0.77*0.8=0.62 overall system efficiency (solar panel + charge controller + dirty panels + etc. * 80% flooded cell battery efficiency), choose Columbia Mo:
    [FONT=Fixedsys]Results
    
    Month
    Solar Radiation (kWh/m2/day)
    AC Energy (kWh)
    Energy Value ($ at 7.0 ¢/kWh)
    
    1      3.69          73        5.11   
    2      4.73          83        5.81   
    3      5.10          94        6.58   
    4      5.71          99        6.93   
    5      5.58          96        6.72   
    6      6.04          99        6.93   
    7      5.97          99        6.93   
    8      6.03         100        7.00   
    9      5.47          92        6.44   
    10     5.08          92        6.44   
    11     3.56          64        4.48   
    12     3.23          62        4.34 
    =====================================  
    Year   5.02        1053      $73.71  [/FONT]
    

    A 1kW array will 83 kWhrs per month 9 months out of the year or 2.8 kWhrs (2,800 Watt*Hours) per day.

    A 260 watt panel will generate an average minimum of

    2,800 WH * 0.260 = 728 WH per day (9 months of the year)

    December, a 1kW panel will only generate an average of 62 kWhrs per month, or:

    62kWhrs * 1/30 days per month * 0.260 kW of solar panels * 1,000 W/kW = 537 Watt*Hours per day for December

    Your estimated load is:

    70 watts * 8 hours per night = 560 Watt*Hours per night

    So--for 9+ months of the year, your average power collection is probably enough for your needs. For 2 months or so a year, you are using more power than is generated--so either you have to increase the panel size, or reduce your usage.

    And--this gets into a big issue with fixed loads and solar power. You will probably have days (or even a week or more) where you will have bad weather--where the array will generate hardly any useful power (on my home, during a very cloudy/stormy week, my panels will generate less than 10% of their rated output) and you have to plan for what to do...

    Turn off the load, use a back up generator, or utility power for backup.

    And if you automate the load--you have to protect the battery and have it turn off before the battery is discharged below 50% state of charge (for long battery life, and avoid 20% to 0% state of charge--i.e., 80-100% discharge will kill lead acid batteries in a matter of months or weeks).

    It is hard/sort of expensive to automate a system so that it will turn off the loads (or start a genset) to prevent over 50% discharge. Manually, you will have to watch the battery voltage (after a few hours of rest of no load/no charge, or use a hydrometer, or use a Battery Monitor).

    A battery monitor (especially modes with programmable output that can be used to turn off loads if >50% discharged), replacing batteries accidentally killed, backup genset and controls, etc. make solar a pretty expensive solution for daily use systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What I have so far, will it work?

    The "rough" calculation: 70 W * 8 hrs = 560 W/hrs. @ 12 V = 46.6 Amp/hrs times 2 for a max. DOD of 50% = 93 Amp/hrs. So you need a minimum of 100 Amp/hrs of battery, and that will be strained (cheap batteries don't like deep Depth Of Discharged).

    If you get good, direct sun for 5 hours a day where you are the panels would be able to recharge that 100 Amp/hrs. Check the PV Watts program as Bill suggests, and remember that insolation is highly site specific.

    Also remember that 12 V is going to suffer potentially significant voltage drop: longer runs, greater drop. So also look at the wiring calculator: http://forum.solar-electric.com/showthread.php?t=29

    And check out the battery FAQs: http://www.windsun.com/Batteries/Battery_FAQ.htm

    It's always best to ask the questions and get the answers before you spend the money! :D
  • Ralph DayRalph Day Solar Expert Posts: 953 ✭✭✭✭
    Re: What I have so far, will it work?

    It's always best to ask the questions and get the answers before you spend the money! ???

    Marc, are you single? How's a guy supposed to fill up a workshop with that attitude?;)

    RALPH
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What I have so far, will it work?

    No, Ralph; I've been married about 65 million years now. Got tons of stuff, despite losing things and having things stolen et cetera.

    The trick is: don't ask your wife the questions!:p
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: What I have so far, will it work?
    No, Ralph; I've been married about 65 million years now. Got tons of stuff, despite losing things and having things stolen et cetera.

    The trick is: don't ask your wife the questions!:p

    Nah, the trick is to explain how you can use those new toys to do wonderful things for her.

    Back on topic, 100AH being charged by 13A is certainly within reason, though at C/8 it might be a little high. There are inexpensive small capacity MPPT charge controllers on the market that would raise the output of the 260 watts of panels from 189 watts (6.55A x 2 x 14.4V = 189) to something closer to 260 watts (let's not forget he spec'd a PWM controller, not a MPPT one). Assuming 95% conversion, MPPT should deliver 17A at peak, which is C/6 -- almost certainly too high. Based on that, I'd go with something closer to 150AH in batteries. That would help with low sun days because instead of 13A @ 14.4V minus losses for the sun being low in the sky, it's 17A @ 14.4V minus winter losses.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What I have so far, will it work?
    tallgirl wrote: »
    Nah, the trick is to explain how you can use those new toys to do wonderful things for her.

    Back on topic, 100AH being charged by 13A is certainly within reason, though at C/8 it might be a little high. There are inexpensive small capacity MPPT charge controllers on the market that would raise the output of the 260 watts of panels from 189 watts (6.55A x 2 x 14.4V = 189) to something closer to 260 watts (let's not forget he spec'd a PWM controller, not a MPPT one). Assuming 95% conversion, MPPT should deliver 17A at peak, which is C/6 -- almost certainly too high. Based on that, I'd go with something closer to 150AH in batteries. That would help with low sun days because instead of 13A @ 14.4V minus losses for the sun being low in the sky, it's 17A @ 14.4V minus winter losses.

    wonderful things for her? i can see it now, honey, i got you 100w of pv power for your birthday and come my birthday she'll give me the homemade electric chair to use it with.:roll: as to toys, i can't address that properly without having to ban myself, but she don't need them.:p

    the 13% charge rate is perfectly fine and mppt might give about another amp or so with occasional higher excursions which agms would easily handle and most flas too with just a bit of higher maintenance.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What I have so far, will it work?
    niel wrote: »
    wonderful things for her? i can see it now, honey, i got you 100w of pv power for your birthday and come my birthday she'll give me the homemade electric chair to use it with.:roll: as to toys, i can't address that properly without having to ban myself, but she don't need them.:p

    the 13% charge rate is perfectly fine and mppt might give about another amp or so with occasional higher excursions which agms would easily handle and most flas too with just a bit of higher maintenance.

    Well actually my wife would love more PV power and bigger storage batteries. She also likes larger tires for the truck. Anything that helps us spend more time at the cabin she's in favour of.

    As for the OP, I think we're on track here with a viable solution.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: What I have so far, will it work?
    niel wrote: »
    wonderful things for her? i can see it now, honey, i got you 100w of pv power for your birthday and come my birthday she'll give me the homemade electric chair to use it with.:roll: as to toys, i can't address that properly without having to ban myself, but she don't need them.:p

    the 13% charge rate is perfectly fine and mppt might give about another amp or so with occasional higher excursions which agms would easily handle and most flas too with just a bit of higher maintenance.

    Are the Sam's GC batteries (EverReady) VRLA or FLAs?

    And while C/6 is probably okay for people with experience, I'm thinking training wheels for beginners.

    And yes, women do welcome more electricity. It's not "solar panels" it's "more electricity for the things you enjoy." She'll think you're about as romantic as guys who buy their wives a new iron or dishwasher, but at least you're not buying a bass boat she'll never use.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What I have so far, will it work?

    My wife would rather use a bass boat than an iron or dishwasher. So would I.

    Pretty sure the Sam's batteries are FLA.

    We don't have Sam's in BC. Barely have Wal-mart.
    But we do have a "carbon tax"! :grr
  • Ralph DayRalph Day Solar Expert Posts: 953 ✭✭✭✭
    Re: What I have so far, will it work?

    Marc,
    In BC you have the only carbon tax in Canada. The Smilie you required would be the one with the halo...middle column, second row:-). It's what everyone here would like to support, I'm sure:roll:

    Ralph
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What I have so far, will it work?
    Ralph Day wrote: »
    Marc,
    In BC you have the only carbon tax in Canada. The Smilie you required would be the one with the halo...middle column, second row:-). It's what everyone here would like to support, I'm sure:roll:

    Ralph

    You mean if the tax was actually dedicated to doing something "green" instead of just going into the general fund. This tax is supposed to be "revenue neutral" but they completely ignore the cost of administering it. We also have environmental levies on just about everything already. Yet it's nearly impossible to recycle some of the stuff: six hours on one Saturday a year to take your old electronics in, et cetera. A very confused, inconsistent, and over-all ineffective plan.

    This is getting way too political. My apologies to everyone.

    It's a sunny day and my defective batteries are undergoing an intensive equalization process. Maybe that will help. :blush:
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