adding modules

kenkathykenkathy Registered Users Posts: 9
I have an inadequate solar array to charge my 650 amp hour 48 volt battery bank. I currently have 4 x 110 watt 12 nominal volt evergreen pv's strung in series. I was thinking of either adding 8 to twelve more similar panels using the same blue sky 3048 mppt controller or purchasing 9 more 18 nominal volt panels and stringing them in 3 series of 3 panels and using an additional controller. The cost is very similar due to the larger panels being about the price as the lower voltage panels. The larger voltage 3 panel strings would end up being 80 vmp and the older 4 panel strings were 68.8. The panels sit on the roof housing the batteries and charge controller so distance is not very far. Any input would be appreciated.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: adding modules

    I think you are getting on the right track... For minimum size array (5% to 13% of 20 Hour battery bank rating is rule of thumb for charging the battery bank):

    650 AH * 0.05 * 60 volts = 1,950 watts of solar panels

    Having more of the same panels frequently makes it easier to mix and match the Vmp and Imp of the panels to the requirements of the charge controller.

    In your case, you will probably be purchasing a 60-80 amp solar charge controller (60 amp * 60 volts = 3,600 watts of solar panels maximum--roughly)--So, all of the panels could be moved to a single 60+ amp MPPT charge controller.

    You would only have one charge controller to maintain and the Blue Sky could be kept as a spare or moved somewhere else.

    Regarding the panel musical chairs--you could look at getting one more of the old 110 watt 17.2 volt panels and put it in series with the rest of the "new higher Vmp panels" to bring the string voltage up to ~86 volts--It would then be close enough in string Vmp to that of the new 80 volt string to play together OK (you won't lose much power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mshen11mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: adding modules
    BB. wrote: »
    I think you are getting on the right track... For minimum size array (5% to 13% of 20 Hour battery bank rating is rule of thumb for charging the battery bank):

    650 AH * 0.05 * 60 volts = 1,950 watts of solar panels

    Having more of the same panels frequently makes it easier to mix and match the Vmp and Imp of the panels to the requirements of the charge controller.

    can you elaborate/rephrase that? what is the 60 in the formula? is it the voltage level of the charge controller?
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: adding modules

    The 60 volts is the voltage at which a 48 volt battery bank would be at under maximum current charging conditions (equalization)...

    An MPPT type solar charge controller is the DC equivalent of an AC Transformer--efficiently converter the solar panel power at xx volts and yy amps into aa volts and bb amps at the battery.

    Power = I*V

    Imp*Vmp of solar array = Vbatt-charging * Ibatt-charging

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    I'm running through some permutations to upgrade my current 48 volt system with a 650 amp hour battery bank and my blue sky 3048 mppt controller with a 30 a max output current rating, 1600 watts and 24 a Isc. My mounting surface is 250" x 110 " I've got a buyer for my 4 110 watt panels. I'm now thinking of mounting either 6 kyocera 210 gx modules with 2 strings of three giving me 1260 watts, 16 Imp, 79.8 Vmp or buying 9 kyocera 180 GX giving me 1620 watts, 22 Imp and 70.8 Vmp. The 180's would actually mount allowing me to expand to 12 in the future, whereas the 210's could expand to 9. Any thoughts?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: adding modules

    with that much future power in mind you may wish to still get another controller. these mppt controllers will downconvert and in that process the current is raised nearly in proportion. for example a pv with 24v and 3a output downconverted for 12v may see about 6a. as you know, that blue sky cc is limited to about 30a max output with 24a being a straight forward input at the same voltage level to comply with the nec. your higher voltage inputs will translate to a much higher current than you realize. hope i helped and didn't screw up as i'm tired.
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    First of all, thanks for the input. I'm a solar newbie with very little knowledge. I should have said that my system is being used at my cabin at 10,000 feet which is rarely used for more than 2 days at a time, usually on the weekends. I live in Moab UT. I had a "solar expert" install my system 4 years ago. I paid alot of money for his design and installation expertise. I had a backup generator installed for rare high use, non-sunny times. Since the system was installed I have only seen 1.5 amps of output from the 440 watts of solar panels. After discovering the blue sky controller necessitates separating the pv ground and battery ground the system is now putting out 5.5 amps during a nice day. As you can imagine, I have to use the generator to charge/equalize the batteries. I was hoping to find the best solution to the obvious problem of an undersized solar array. The easiest solution I have come up with is to install 6 of the 210 GX Kyocera panels. I could keep my existing controller which is finally wired correctly and mounting would be simple since I could mount all 6 panels in portrait mode across the roof. My biggest concern is that I make this modification and the battery bank (650 AH) would continue to be undercharged. If necessary, I can mount 12 of the 180 gx panels and buy a new charge controller. It would only cost me $3372 for 6 new 210 panels whereas 12 of the 180's would be 6360 plus 550 for new outback 60.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: adding modules
    kenkathy wrote: »
    First of all, thanks for the input. I'm a solar newbie with very little knowledge. I should have said that my system is being used at my cabin at 10,000 feet which is rarely used for more than 2 days at a time, usually on the weekends. I live in Moab UT. I had a "solar expert" install my system 4 years ago. I paid alot of money for his design and installation expertise. I had a backup generator installed for rare high use, non-sunny times. Since the system was installed I have only seen 1.5 amps of output from the 440 watts of solar panels. After discovering the blue sky controller necessitates separating the pv ground and battery ground the system is now putting out 5.5 amps during a nice day.

    Something wrong there. You should be getting close to 10 amps. 440 watt + 1% per 1000 foot of altitude = 485 watts. At that altitude you should also see some gain from lower panels temps most of the time.
    I could keep my existing controller which is finally wired correctly..

    I am not so sure about that, if you are only getting half power out of the panels.
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    My evergreen cedar 110watt panels have the following specs:
    vmp 17.2
    imp 6.47
    isc 7.22
    voc 21.5
    They are wired in series for 48 nominal volts. It seems that should give me 8 amps at 54 volts in the best case scenario.
    Ken
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    Sorry, I see what you are saying. 480 watts / 48 volts is 10 amps. I'm definitely not seeing those numbers. The measure voc's of all the panels were spot on with specs. Maybe something is wrong with the charge controller.
    Ken
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: adding modules

    Take a look at the Xantrex XW 60 MPPT Charge Controller... They have a "configuration calculator" that allows you to determine the number of panels in series and parallel for proper operation of the controller...

    One of the issues is that solar panels are not really very good batteries--the Vmp varies quite a bit with temperature and load... So when configuring a string--you need to know the minimum and maximum temperatures (air temps) that the panels will be operating in...

    Vmp when the panels are hot and under load (minimum operating voltage to charge xx VDC battery bank). And Voc, the maximum voltage (open circuit) and minimum temperatures that the controller will see on a cold and clear morning.

    Play around a little bit with the tool--and you will get a better idea of how this all plays together.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    I'm still trying to get someone to tell me if I'm throwing good money after bad if I go with 6 x 210 kyocera 210's for my battery bank. I realize that the ideal situation is at least 5% of the amp hour capacity of the battery bank, however, I'm usually not using the system during the week and only use it on weekends. It seems if I'm getting 20 amps/hr out of the new array for 5 hours a day, I could get it recharged in 5 days.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: adding modules

    in my opinion getting more pvs is not throwing good money after bad as you need more to properly charge your battery bank. ideally it should be 5% minimally and would be .05 x 650ah = 32.5a. a 20a charge would be 20a/650ah=3% or the bare minimum we ever recommend for charging without loads routinely on such as yours. adding both the old pvs with these new ones will add together getting it closer to that 5% point and will work better than with just one or the other sets of pvs. if the vmps mismatch then you may wish to consider getting pvs that could add up close to the vmp of the old ones. many may say +/- 10% on the vmp, but i think it would be better for you to try a tighter tolerance especially staying away from the lower end.
  • kenkathykenkathy Registered Users Posts: 9
    Re: adding modules

    So I've decided to install a total of 12 kyocera 180 gx modules to replace my 4 110 w 12 nominal volt modules. I'll wire them in 4 strings of 3. My next question is how to combine the 3 series. They have mc4 connectors and it would be easy to parallel the strings together on the roof with the mc4 combiners bringing a single pos and neg into the outbuilding. I currently have a junction box inside the building which then runs a single 12 awg wire to the combiner box. If I parallel all 4 strings I would end up with 30 amps (adding Imp) and 71 volts (adding Vmp). What is the best way to wire this array?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: adding modules

    there are small jumpers with mc4 connections for that if the modules themselves are separated too far for their own wires to interconnect. look up the module's specs and see the wire lengths and determine if your mounting will not accommodate the wire lengths that come with the pvs.
    http://search.store.yahoo.net/cgi-bin/nsearch?catalog=wind-sun&query=mc4%20jumpers&searchsubmit=Go&vwcatalog=wind-sun&.autodone=http://store.solar-electric.com/hardware---wire.html
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