Upgrading questions...

cizzicizzi Solar Expert Posts: 109 ✭✭✭✭
Allright its been allready a year I've been playing around with solar energy. So I'm thinking of upgrading my system to put more things on my system load. Right now I have a Deka 8GU1 and 2 x 15 W amorphous panels in parallel. I'm thinking of getting:

130W Polycrystaline panel from Kyocera (KC130TM)
180AH Deka Solar 8G4D PV Battery

Current is under 8AH (peak) from the new panel (I checked the datasheet) so my existing charge controller should be fine, (MorningStar Pro-Star 15M).

I plan to add things like a true sine inverter so I can use my sound system on a regular basis and more AC/DC lighting.

What are your thoughts on the new equipment? Keeping in mind I will only use 50% of the 180AH at any given time, which leaves me with 90AH fed with a 130W panel.


  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: Upgrading questions...

    With a 130 watts of solar panel--you are right at the low end of charging your battery...

    130 watt / 17 volt = 7.6 amps or so...

    130 AH * 50% / 7.6 amps = 8.6 hours or, roughly two summer days to recharge from 50% use...

    If this meets your needs--great... If you plan on using and recharging at the same time--your battery may be sitting below ~75% state of charge longer than wanted... May cause your battery to die sooner.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cizzicizzi Solar Expert Posts: 109 ✭✭✭✭
    Re: Upgrading questions...

    so i should get a smaller battery.. what size do you suggest for a 130W panel? to keep the battery level healthy.. 100-150AH range?
  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: Upgrading questions...

    Sort of depends on what you want to do... Roughly, you would want round 5% to 13% of the battery AH capacity as charging current...

    180AH * 5-13% is = 9 amps to 23.4 amps...

    Or *~16 volts (Vmp) = 144 Watts to 374 Watts of solar panels...

    For a deep cycle battery, it would be better to be in the 10%-13% range because you need to have enough current to vigorously "boil" the battery to mix the electrolyte during equalization...

    AGM's don't need (and should not have) equalization, plus AGM's have lower self discharge--so they can work fine nearer to the 5% range. But AGM's can also accept higher charge currents and can work well above the 13%+ charging current range (as always, check the specs. for your batteries).

    Ideally, you probably want to size the solar panels for the amount of power you need to use--And size the battery for 6x daily AH/WH load (3 days of no sun, max 50% discharge for longer cycle life)...

    Without knowing your daily load requirements, what seasons you want to use the system, and such... we are just guessing.

    Using a kill-a-watt meter and this website, you can better size the system to your needs.

    Working backwards, lets say you are in Montreal Canada, 130 watts of panels, fixed mounting at latitude, and using 0.52 as the derating factor (flooded cell batteries, AC inverter).

    From the second link we find that a 1kW (have to use 1kW as this is the minimum value accepted) set of solar panels will generate:
    Solar Radiation
    :Solar Hours per day
    :kWhrs per month
    :$Canadian worth of electricity per month
    1      3.24          55     4.74 
    2      4.02          62     5.34 
    3      4.40          72     6.21 
    4      4.61          67     5.78 
    5      4.77          69     5.95 
    6      5.12          70     6.03 
    7      5.62          78     6.72 
    8      4.76          66     5.69 
    9      4.92          69     5.95 
    10      3.66          55     4.74 
    11      2.01          29     2.50 
    12      2.10          34     2.93 
    Year   4.10          726     $62.58
    If we multiply by 130 Watts/1,000wperkW (I will use Excel):
    :ave Hours of Sun
    :ave kWhrs per month
    :ave kWhrs per day
    1    3.24   7.15   0.238       
    2    4.02   8.06   0.269       
    3    4.40   9.36   0.312       
    4    4.61   8.71   0.290       
    5    4.77   8.97   0.299       
    6    5.12   9.10   0.303       
    7    5.62   10.14   0.338       
    8    4.76   8.58   0.286       
    9    4.92   8.97   0.299       
    10   3.66   7.15   0.238       
    11   2.01   3.77   0.126       
    12   2.10   4.42   0.147  
    Year ave sun=4.10   94.38kWhrs per year

    So--The Fourth column above sows that you can get 200 to 300 Watt*Hours per day for 10 months of the year...

    If you get snow--you can tilt the array to 90 degrees (vertical) and shed snow better during winter.

    So--as you can see, there is not a lot of power from a 130 watt solar panel... So, you have to know your loads well, and, if you use more power than the panels can generate (say during the winter), you will need a back up power source (generator--if off grid).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Upgrading questions...

    you have some options if you get your proposed system. 1> use it less often or to the point you can recharge what's used daily or 2> get another pv like the first one and with 2 pvs it'll charge it up better.
    we really don't know of your loads or time of use, but the pv will charge the battery at a bit over the 4% rate and as bb said it is doable if it has been drained to 50% and you can wait for it to recharge in a few days because that is more than a 20hr rate of charge and 50% makes it >10hrs to recharge a battery at the 50% dod point. not using it to 50%, but rather to 25% dod may also extend the life of the battery and allow that pv to supply your smaller needs. 25% x 180 = 45ah daily. hmmm. that pv won't deliver 25% on a recheck as it can give you about 38ah with 5 full sun hours per day so lightening your loads further would be needed if you need to have it recharged daily unless you can get more pv power. that 38ah equates to roughly 21% dod.
    ps- i could've doctored this to read better and i probably should've, but i'm leaving my train of thought in place.
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