Really New guy questions....

grpark20
grpark20 Registered Users Posts: 16
Obviously I am brand new to solar and even the solar beginners corner is soem what advanced for me. Hopefully someone can help before I spen any money. I'm looking at putting an off grid system together that can handle my 460 watts 12 volt DC of use. Would it be easier to to use 24 volt panels since they're more readily available and just use a controller that can manage the 12 volt charge from the 24 volt input? What direction do my panels need to face? I'm assuming east or west. I'm located at 08641 so I have no clue. I'ver been reading about true south, lattitude, longitude, etc. I also was reading that if more than 2 panels are used I have to wire them up to a breaker or something like that? My original plan was to run (2) 100 watt 12 volt panels and (1) 85 amp hour battery. Apparently that will not suffice. The load I need to support is a 1.6 amp 12 volt fan that I'd like to run 24/7. I'm now looking at 600 watts and (3) 85 amp hour batteries. This seems like over kill to me for my needs or am I just way off. Also, could I use 24 volt panels to get more wattage to regulate my 12 volt batteries. I'd be looking at using a xantrek controler that has big numbers for input voltage but can regulate 12 volt battery banks. Please offer your opinion before I make a $1000 mistake. Thanks.

George

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Really New guy questions....

    define those loads better for everyone here for we don't know if your load draws 460w for an unknown time span or is that the watt hours per day for your loads?
  • grpark20
    grpark20 Registered Users Posts: 16
    Re: Really New guy questions....
    niel wrote: »
    define those loads better for everyone here for we don't know if your load draws 460w for an unknown time span or is that the watt hours per day for your loads?

    Sorry about that......I would like to power a 1.6 amp 12 volt dc fan for 24 hours a day. By my math from researching it's 1.6 amps x 12 volts x 24 hours giving me 460.8 watts of useage per day. Please let me know if the math/formula is incorrect. I'm trying to absorb as much as I can so please bare with me.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Really New guy questions....

    That is 481 watt*hours per day. Keep the units as you multiply out the equation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Really New guy questions....

    george,
    i do apologize as you did clarify the load in that post and for some reason i thought you were adding that to a load that was already there. the 200w in pv and the single 85ah battery would work, but there's little room for error let alone clouds. i think 170ah in battery will do fine and would be good for up to 2 days, but the pv wattage does need upped some as well.

    here's how i originally figured it.
    200w in pv x 77% efficiency = 154w.
    154w/12v=12.83a.

    85ah battery to 50% dod = 42.5ah useable.

    for rough math 42.5ah/12.83a=3.1hrs bulk charging and would allow for 1.9hrs for absorb charging.

    if cloudy, foggy, or midwinter insolation conditions exist, to name a few negatives, then the pvs will not charge the battery properly.

    with 170ah in battery the minimum charge rate is 5% and that's 8.5a and accounting for the efficiency is 8.5a/.77=11.04a. the 2 100w pvs are within that range, but too close to account for bad conditions. better would be the 10% rate, but i think even around the 8% rate would work. keep in mind we recommend between 5% and 13% for the charge rate. if all you have is 2 100w pvs then you need another and it will need fuses on each pvs' output with 3 or more in parallel. i see you are contemplating what pvs to buy, but before i can recommend something i have to know which xantrex controller you were considering.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Really New guy questions....
    grpark20 wrote: »
    Obviously I am brand new to solar and even the solar beginners corner is soem what advanced for me. Hopefully someone can help before I spen any money. I'm looking at putting an off grid system together that can handle my 460 watts 12 volt DC of use. Would it be easier to to use 24 volt panels since they're more readily available and just use a controller that can manage the 12 volt charge from the 24 volt input? What direction do my panels need to face? I'm assuming east or west. I'm located at 08641 so I have no clue. I'ver been reading about true south, lattitude, longitude, etc. I also was reading that if more than 2 panels are used I have to wire them up to a breaker or something like that? My original plan was to run (2) 100 watt 12 volt panels and (1) 85 amp hour battery. Apparently that will not suffice. The load I need to support is a 1.6 amp 12 volt fan that I'd like to run 24/7. I'm now looking at 600 watts and (3) 85 amp hour batteries. This seems like over kill to me for my needs or am I just way off. Also, could I use 24 volt panels to get more wattage to regulate my 12 volt batteries. I'd be looking at using a xantrek controler that has big numbers for input voltage but can regulate 12 volt battery banks. Please offer your opinion before I make a $1000 mistake. Thanks.

    George
    If you have started buying anything, stop now. You need to understand first, then design, then buy. Designing a cost efficient off-grid system is a non-trivial task even for the knowledgeable and experienced.
  • grpark20
    grpark20 Registered Users Posts: 16
    Re: Really New guy questions....
    niel wrote: »
    george,
    i do apologize as you did clarify the load in that post and for some reason i thought you were adding that to a load that was already there. the 200w in pv and the single 85ah battery would work, but there's little room for error let alone clouds. i think 170ah in battery will do fine and would be good for up to 2 days, but the pv wattage does need upped some as well.

    here's how i originally figured it.
    200w in pv x 77% efficiency = 154w.
    154w/12v=12.83a.

    85ah battery to 50% dod = 42.5ah useable.

    for rough math 42.5ah/12.83a=3.1hrs bulk charging and would allow for 1.9hrs for absorb charging.

    if cloudy, foggy, or midwinter insolation conditions exist, to name a few negatives, then the pvs will not charge the battery properly.

    with 170ah in battery the minimum charge rate is 5% and that's 8.5a and accounting for the efficiency is 8.5a/.77=11.04a. the 2 100w pvs are within that range, but too close to account for bad conditions. better would be the 10% rate, but i think even around the 8% rate would work. keep in mind we recommend between 5% and 13% for the charge rate. if all you have is 2 100w pvs then you need another and it will need fuses on each pvs' output with 3 or more in parallel. i see you are contemplating what pvs to buy, but before i can recommend something i have to know which xantrex controller you were considering.

    I was looking at buying the xantrex C40 controller. I've been doing more research and I'm now leaning towards getting (2) 145watt 12 volt DM Solar panels rated at 145 watts each. Might help compensate.... Still curious is 24 volt panels would be more power for my application if using the Xantrex C40 controller.
  • grpark20
    grpark20 Registered Users Posts: 16
    Re: Really New guy questions....
    ggunn wrote: »
    If you have started buying anything, stop now. You need to understand first, then design, then buy. Designing a cost efficient off-grid system is a non-trivial task even for the knowledgeable and experienced.

    Believe me.....I haven't boght anything yet. I'm a firm believer of if I have any doubt at doing a project that cost serious money and feel iffy. I just pay the man in the begining versus me having to pay the man twice. And Murphy (Murphy's law) is always riding shotgun with me. As soon as I get setup for solar we'll have a 200 day blackout......
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Really New guy questions....
    grpark20 wrote: »
    I was looking at buying the xantrex C40 controller. I've been doing more research and I'm now leaning towards getting (2) 145watt 12 volt DM Solar panels rated at 145 watts each. Might help compensate.... Still curious is 24 volt panels would be more power for my application if using the Xantrex C40 controller.

    It depends...

    If you have "24 volt panels" (basically anything with Vmp>~20 volts), a PWM (Cxx family) controller will not give you more power into a 12 volt battery bank. More or less, the estimated losses when compared to a "reference" system would be:

    Eff=Vmp-ideal/Vmp-array
    Eff=17.5 volts / 35 volt Vmp (for true 24 volt panel = 0.5 = 50% efficiency (compared with "ideal" Vmp-array of ~17.5 volts)

    If you have the choice between "true" 24 VDC panels (Vmp ~35-38 volts or so) on a 24 volt battery bank--Charge controllers are rated by their output current. So with Power=Volts*Current, if you have 2x the voltage with the same maximum current, a C40 can run 2x larger wattage panel into a 24 volt battery bank (vs 12 volt battery bank).

    In the end, many times the less expensive solar panels (>>100 watt panels and less than $2 per watt) tend to have Vmp-panel>>~17.5 volts (and usually not in the ~35-38 volt Vmp range) -- So usually a person is "forced" to use a much more expensive MPPT type charge controller which can efficiently "down convert" from high voltage/low current from the array to low voltage/high current for the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Really New guy questions....
    grpark20 wrote: »
    I was looking at buying the xantrex C40 controller. I've been doing more research and I'm now leaning towards getting (2) 145watt 12 volt DM Solar panels rated at 145 watts each. Might help compensate.... Still curious is 24 volt panels would be more power for my application if using the Xantrex C40 controller.

    The C40 is a PWM type controller. It can not down-convert the higher Voltage panels for use on a 12 Volt system. The 'extra' power would just be lost.

    Two 145 Watt panels will be about 8 Amps maximum each. They will also be "12 Volt" panels with a Vmp around 17 to 18. You only need a 20 Amp PWM type charge controller to handle that. Something like this: http://www.solar-electric.com/ss-20l.html You would wire the panels in parallel; no fuses/breakers required on the panels for just two in parallel.

    Also note that much panel is only good for batteries of roughly 180 Amp hours @ 12 Volt. It would just barely make the minimum for a couple of 220 Amp hour 6 Volt golf cart batteries (in series). On a good day you could get about 600 Watt hours AC from those panels.
  • grpark20
    grpark20 Registered Users Posts: 16
    Re: Really New guy questions....

    The only reason I was thinking of going with the Xantrex controller is because the quality seems to be very good and it will give me lots of future options in case my system decides to grow. I think I'm sold on the DM solar 145 watt panels unless any one has a negative experience. As far as batteries. I'm considering (2) 6-volt golf cart batteries rated at 200+ amp hours and wiring them up in a series. I think I'm finally getting somewhere. Thanks all for the help so far.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Really New guy questions....
    grpark20 wrote: »
    I think I'm sold on the DM solar 145 watt panels unless any one has a negative experience.

    I have no negative experience. BUT... I believe they are not UL listed. Are you planning to install them on or near an insured structure? If so, your insurance company may deny claims. If you are subject to any building codes, the panels will be a violation.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • grpark20
    grpark20 Registered Users Posts: 16
    Re: Really New guy questions....
    vtmaps wrote: »
    I have no negative experience. BUT... I believe they are not UL listed. Are you planning to install them on or near an insured structure? If so, your insurance company may deny claims. If you are subject to any building codes, the panels will be a violation.

    --vtMaps

    I plan on installing them on top of a 7x14 enclosed trailer. If any issues should arrise, I feel rpetty good that my isurance company will be good with the coverage. I haven't ever had a claim and put insurance on everything I own with a VIN #...
  • Logan5
    Logan5 Solar Expert Posts: 32
    Re: Really New guy questions....

    Consider a PWM motor speed controller. some have a reverse switch, this way you can modulate your air flow to your needs and greatly reduce your amps draw.