Solar Array Switching

northerner
northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
I'm in the process of installing a second solar array and I have a second midnite Classic charger controller in place, ready to go. This raised the question of putting in the capability to switch the 2 banks so they work as one, and run them through just one of the charger controllers on cloudy days. I happen to have an extra 100 amp DC breaker in place, so it would be very convenient to do. Just wondering if anyone else has bothered to do this, and whether it is worthwhile? You could benefit just a little bit by running everything through one CC when there's not a whole lot coming down the pipe, but then could lose out if the sun ever did happen to come out, particularly if one wasn't around.

It would be ideal if the CC's could work in a stacked fashion, where the inputs are in parallel and the master CC puts the other(s) to sleep, until power input is high enough to switch them on. (ie the master could no longer handle the power input and requires the slave(s) to do some work)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Solar Array Switching

    You'd be wasting effort to do this. The two arrays on one controller aren't going to produce any more power than the two arrays on two controllers. The additional power consumed by the second controller isn't that significant.

    If you have a situation where 'cloudy' happens more often than you like, you can significantly 'over panel' a good controller like the Classic and program it to limit current when the sun does shine so that it doesn't exceed the battery's maximum.

    In one respect Classics do work 'stacked' using the 'Follow Me' protocol so that the master controller tells others what stage to be in.

    A lot of this is predicated on just how much current you're asking the controller to deal with too.

    The basic problem is that when the sun isn't there the power isn't there either, and the output current of the panels drops quite drastically as the light dims.
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #3
    Re: Solar Array Switching
    Cariboocoot wrote: »
    You'd be wasting effort to do this. The two arrays on one controller aren't going to produce any more power than the two arrays on two controllers. The additional power consumed by the second controller isn't that significant.

    If you have a situation where 'cloudy' happens more often than you like, you can significantly 'over panel' a good controller like the Classic and program it to limit current when the sun does shine so that it doesn't exceed the battery's maximum.

    In one respect Classics do work 'stacked' using the 'Follow Me' protocol so that the master controller tells others what stage to be in.

    A lot of this is predicated on just how much current you're asking the controller to deal with too.

    The basic problem is that when the sun isn't there the power isn't there either, and the output current of the panels drops quite drastically as the light dims.

    That's what I was thinking as well, not really worthwhile to bother with. I'm aware of the follow me protocol as well.

    Some inverters can operate that way (ie stacked where there's a master and slave(s)), but I take it they draw more idle power than a charge controller, plus they would be on 24/7.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Solar Array Switching
    northerner wrote: »
    That's what I was thinking as well, not really worthwhile to bother with. I'm aware of the follow me protocol as well.

    Some inverters can operate that way (ie stacked where there's a master and slave(s)), but I take it they draw more idle power than a charge controller, plus they would be on 24/7.

    With stacked inverters (done to get 2X Voltage or 2X Amperage) the master can be on all the time and the slaves in stand-by, so not all inverters will pull full power all the time. And yes they tend to chew up more Watts than a charge controller. Like 20W full-on an 6W stand-by.
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  • H2SO4_guy
    H2SO4_guy Solar Expert Posts: 213 ✭✭✭
    #5
    Re: Solar Array Switching

    I sort of do something like that. Each set of batteries has a dedicated charge controller with RTS and I can switch strings of panels to different charge controllers. Like if I am there and the sun is starting to set, I may put 5k of panels on a Midnite controller to get all of the energy I can as the light conditions fade. It works for me and will harvest just a little more energy. With only a 2 choice option, the Blue Sea switch from the Wind-Sun works great, but when I wanted more switching choices, I split the output of the breaker and fed more breakers to the charge controller busses. I do have to be careful to not run the same panels to multiple charge controllers. Like I said, it works for me and I run lots of stuff not normally run off of batteries, like heat!

    Good luck and let us know how it works out
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Solar Array Switching

    you could run into trouble doing this too as no pv should see the input of more than 1 cc. you are partly correct in wanting to do this switching because a classic's draw is not insignificant. mine draws roughly 10w. it is too much trouble to baby sit the system to gain back the 10w or so by switching things around and you would have to disconnect or shut off the classic being bypassed or these operational losses will still be there. cloudy days are not always consistent and could spike unexpectedly. you could gain back from any losses in a small time period of higher output. no easy answers for cloudy circumstances, but what you propose can have its risks and needs watched. what if you rewired both arrays to one cc and forgot about reversing it for the full day of sunshine the following day? you then lose much more power and strain the operational cc as it will be holding back excess amps.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
    Re: Solar Array Switching
    northerner wrote: »
    Some inverters can operate that way (ie stacked where there's a master and slave(s)), but I take it they draw more idle power than a charge controller, plus they would be on 24/7.

    boB or Robin over at midnite have discussed their plans to build stackable charge controllers (either here or at the midnite forum).
    northerner wrote: »
    That's what I was thinking as well, not really worthwhile to bother with. I'm aware of the follow me protocol as well.
    I agree that its not worthwhile to bother with.

    I have been developing an attitude lately that efficiency of solar production is often not worth bothering about... its just so easy to add another panel. There have been so many discussions of controller efficiency or cable losses.... if you are so worried about 20 watts of power lost in a cable or controller, just buy 20 watts more panel.

    On the other hand, 20 watts is HUGE when its coming out of your battery. I am very concerned with the efficiency of my loads.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #8
    Re: Solar Array Switching
    niel wrote: »
    you could run into trouble doing this too as no pv should see the input of more than 1 cc. you are partly correct in wanting to do this switching because a classic's draw is not insignificant. mine draws roughly 10w. it is too much trouble to baby sit the system to gain back the 10w or so by switching things around and you would have to disconnect or shut off the classic being bypassed or these operational losses will still be there. cloudy days are not always consistent and could spike unexpectedly. you could gain back from any losses in a small time period of higher output. no easy answers for cloudy circumstances, but what you propose can have its risks and needs watched. what if you rewired both arrays to one cc and forgot about reversing it for the full day of sunshine the following day? you then lose much more power and strain the operational cc as it will be holding back excess amps.

    It could also be automated by measuring the solar insolation, and then switching both the banks and the charge controller using relays. But as others mention, it really isn't worthwhile. Eventually I will add even more solar panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Solar Array Switching

    20 watts of "wasted" AC power 24 hours per day in winter becomes:
    • 20 watts * 24 hours per day * 1/0.52 system eff * 1/3 hours = 308 watts of panel
    • 20 watts * 24 hours per day * 1/12 volt battery bank * 1/0.85 inverter eff * 2 days of storage * 1/0.50 max batt discharge = 188 AH of 12 volt battery bank

    Efficiency and losses--The "dark side" of solar.

    It is better these days with $300+ for vs $1,500-$3,000 for 300 watts of solar panels (10-15 years ago)--That part has improved dramatically.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #10
    Re: Solar Array Switching
    BB. wrote: »
    20 watts of "wasted" AC power 24 hours per day in winter becomes:

    I can't argue with your numbers, but the OP was concerned about self consumption of his charge controllers. On overcast days he would like to combine his two arrays into one controller to save on tare losses in one of his two controllers.

    My point was the losses only occur when he is making power... He's not consuming 20 watts for 24 hrs a day.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    #11
    Re: Solar Array Switching

    If the charge controller is in sleep / low-light mode they consume only a couple of watts. If it is charging, it has its full overhead. Only extremely dark stormy clouds would cause charge controllers to go to sleep during the day.

    I would agree with BB - just add some extra panels, provided you have room to mount them and won't be subject to shading due to sub-optimal location.
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