Solar array sizing

azrc
azrc Solar Expert Posts: 43 ✭
in Solar Beginners Corner #1
Any opinions on running a 48vdc with 2kwp (nameplate) of solar array? I've read that the recommended array sizing for a 48v system using the FM-80 is 3kw. If I get full power from the array, that would be ~40A@48v. I'm only planning on a single string of T105 and isn't the maximum current on these around 20A?

tia
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Solar array sizing

    i'm not sure i'm totally following you here for if you sized the battery bank correctly for your loads you will be overdoing it just a bit with the pvs at 2kw. i also suspect you are viewing the ratings of the controller possibly a bit skewed. the 3kw does not have to be for 48v battery banks and you can input 1kw at 48v if you want to. that 1kw in pvs may be a better match for the batteries, but given losses of charging and the fact pv stc ratings don't always output those ratings you could up it somewhat by dividing by a factor of .77 and a 1300w array would be well suited for the 20a needed to charge the batteries at 48v. now if i recall it would be a bit over 200ah capacity so the charge current at 10% charge rate will also be higher. adding that the batteries can be charged at a 13% rate will give you the ability to go to around 1750w stc in pv if i calculated this right. so what happens with 2kw inputted you might ask? it'll probably do ok as most times it won't be above the 13% rate of charge, but a few % above 13% will most likely be ok with a bit more maintenance involved for faster charging batteries will gas more necessitating more water to be added more often and more cleaning of the posts and battery tops. the batteries will also heat up more so spacing them a bit would be a good idea too.
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  • azrc
    azrc Solar Expert Posts: 43 ✭
    #3
    Re: Solar array sizing

    OK, thanks. That's what I thought. Just wanted to make sure.

    I just don't have the money for the whole system right now and this is only part 1. I plan to start with an MPPT and panels (using some small inverters and old batteries that I have to get by with for now) and later add something like an FX3648 and real batteries.

    In the long run, my primary load will be a small AC unit, about 600w and a refrigerator.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Solar array sizing

    these are large loads and you must find out what the watthour requirement per day you will need to run them to get a better idea of the battery bank size and the pv array size. if one does cut back on the time expected to run these items then a bit of downsizing can be had, but even still it won't be a small system.

    you can find the watthour requirements with meters like a killawatt and they roughly go for just under $30.

    if you are grid tied i might suggest a straight gt system that would boost the efficiency by eliminating the need for the batteries. if your concerns are for power outages then you will still need those batteries.
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