need advice

LorenLoren Registered Users Posts: 5
I have 6 panels rated at 255 watts- MPP voltage 30.0, & MPPcurrent 8.50, open circuit voltage 37.2, short circuit current 8.85, and efficiency of 15.8%; The Batteries I have are 4 Interstate L-16HCL 6 volt 420 AH, 250 mins @ 75 a . I am hoping to provide some supplemental power supply for my home and possibly emergency power in case of grid down. what advise would you offer? I'm expecting Pure signe wave inverter of about 5000 watts and a 60 amp MPPT charge controller. [ not sure about 24v battery configuration or 48 v and buy 4 more batteries ] I also have 2 - 12 volt deep cycle marine batteries if they could be a part of this brainstorm. I seem to be confused about the array voltage to choose with these components. What do you advise? I have about 90 ft between batteries and solar panels.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: need advice

    Welcome to the forum.

    My first suggestion is to go with the 24 Volt system. It will be more efficient. A short thread about choosing system Voltage: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    This would give you 420 Amp hours @ 24 Volts, about 2.5 kW hours of power @ 25% DOD. You probably would not need nor want a 5kW inverter. Size it by how much power you need to supply all at once. You'd be surprised at how low this may be. Usually for emergency purposes "one outlet's worth" is enough, and that's 1800 Watts.

    To recharge those batteries you'd want about 1300 Watts of panel. Six 255 Watt panels totaling 1530 Watts should work well, and could produce up to 50 Amps of peak current. The 60 Amp MPPT controller is a good idea. If you were to go up to 48 Volts you'd need even more panel as well. I wouldn't do it for this system.

    Your panels need to be configured as at least three parallel strings of two in series for Vmp 60 but could also be run as two parallel strings of three in series for Vmp 90. Here's a thread about that: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

    Leave the RV/Marine batteries out.
  • LorenLoren Registered Users Posts: 5
    Re: need advice

    Cariboocoot, thanks for the advise. I have been reading some of your other hepful hints to others and have found your information very helpful. I assume I need circuit protection between panels in the 2 strings of 3. What wire size will 3 strings of 2 need between panels and batteries? I would also like to know if the MPPT controller would be a good choice if I added wind to my package?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: need advice
    Loren wrote: »
    Cariboocoot, thanks for the advise. I have been reading some of your other hepful hints to others and have found your information very helpful. I assume I need circuit protection between panels in the 2 strings of 3.

    Actually, no; with only two strings in parallel no fuse/breaker is needed on the panels. With three strings in parallel each string need over-current protection.
    What wire size will 3 strings of 2 need between panels and batteries?

    That's actually two different circuits: panels to charge controller, and charge controller to batteries. They will run at different Voltages and currents and be different lengths. All of those factor in to what size wire is used.

    For example with the panels configured as two strings of three you have Vmp 90 and Imp 17 for the array. Then you need to know the distance from the array to the charge controller. V-drop should be minimal at that Voltage, but you will need minimally 12 AWG to handle the current. That size should accommodate the current for up to 50 feet.

    The wire from the controller to the batteries will be sized for peak charge current and nominal Voltage. In this case 50 Amps and 24 Volts. Usually this wire is kept short as possible. To handle the current it would need to be at least 8 AWG and you'd probably use the maximum that will fit the controller: 6 AWG.
  • LorenLoren Registered Users Posts: 5
    Re: need advice

    Cariboocoot, Thanks this helps alot.
  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    Re: need advice

    You might want to read through:

    http://handybobsolar.wordpress.com/

    A solar blog waited towards RVs. Very good advice in general.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: need advice
    Loren wrote: »
    What wire size will 3 strings of 2 need between panels and batteries?

    You mentioned a 90 ft distance between panels and batteries. Your inverter instructions will tell you what size wire from inverter to battery. Your charge controller instructions will tell you what size wire to use between the controller and the battery.

    With a 24 volt system and your panels configured as three strings with Vmp = 60, if you run a #4 copper cable 90 ft between combiner and controller, you will have a very acceptable voltage drop of 1.9%.

    Think ahead when you lay the cable... any chance you might want to expand the system? Replacing a 90 ft underground cable does NOT have its charms.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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