Where do you divert your excess power to?

benthere
benthere Solar Expert Posts: 113 ✭✭✭
in Off Grid Solar & Battery Systems #1
From my reading, I see that the Xantrex C60 has a diversion feature whereby excess DC power can be sent to a water or space heater. Presumably other models are similar.

It seems to me that the output to the diversion device is variable in both voltage (predictable) and amperage. What kind of devices do well with that type of power? What types don't? Stuff with controllers, relays, and motors, right? Does that leave anything besides resistance heaters?

I think I also understand that the XW and Outback inverters are designed to "sell" AC power back to the grid which I see as about the same thing for an inverter.

What clever places have you sold or diverted your excess power to in an off-grid application?

Is there any reason a person should or shouldn't do this? What if the dump device fails or is not on? No problem for PV, right? Potential problem for wind generator, as it then has no brake, right?

Thanks.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Where do you divert your excess power to?

    The major drawback to a dump based charge controller is that, as you say, your load is probably larger than your array/wind generator. So, you end up discharging the battery, controller "turns off", battery recharges, and controller turns back on...

    Lots of "little" cycles probably are not best for the life of the battery and not an optimum battery charging algorithm either.

    If you have grid power--than Grid Tied Inverter where you feed back to the grid is the way to go.

    There was one post here where somebody (IIRC) had a boat, and their desalination unit was the dump load.

    -Bill

    PS: For wind turbines--if you follow the NEC (US National Electric Code) and the turbine requires a dump load--then you should install two--one as a backup if the first where to fail. Protects both the batteries and the turbine from dangerous failures (turbine self-destruct or battery overheat/melt down).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • benthere
    benthere Solar Expert Posts: 113 ✭✭✭
    #3
    Re: Where do you divert your excess power to?

    My application will be off grid.

    I expected the charge controller to be capable of only sending the unneeded input rather than taking the batteries down.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #4
    Re: Where do you divert your excess power to?
    benthere wrote: »
    My application will be off grid.

    I expected the charge controller to be capable of only sending the unneeded input rather than taking the batteries down.

    If the PWM switching frequency is high enough, the little ONs and OFFs will filter out to cause the battery voltage to be relatively constant... Instead of being ON for seconds, bringing the battery voltage obviously down, and then OFF for seconds, letting it charge back up again.. That certainly would not be good for the battery.

    This is why these types of controllers (C40, Morningstar, etc) work OK. They switch faster than the time constants of the batteries and capacitors storing and releasing energy in the circuit.

    boB
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #5
    Re: Where do you divert your excess power to?

    Benthere,
    From my reading, I see that the Xantrex C60 has a diversion feature whereby excess DC power can be sent to a water or space heater. Presumably other models are similar.
    Many controllers can be used as charge controller, a diversion controller, or as a load controllers. However, they can typically only operate in one of the three modes at any one time. Morningstar’s user manual for their TriStar controller covers this topic quite nicely. See: http://www.morningstarcorp.com/en/support/library/TS.IOM.Operators_Manual.03.EN.pdf

    One exception is the OutBack FLEXmax controller, which can be simultaneously operated as a solar charge controller and as a diversion controller using the AUX feature's "Diversion SSR" mode. Please see this link for additional information: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865
    It seems to me that the output to the diversion device is variable in both voltage (predictable) and amperage. What kind of devices do well with that type of power? What types don't? Stuff with controllers, relays, and motors, right? Does that leave anything besides resistance heaters?

    What clever places have you sold or diverted your excess power to in an off-grid application?
    Resistance heaters (water and/or air heating) are the typical “dumb” load for diversion applications. OutBack charge controllers’ AUX feature includes a “Float” mode that can activate a load as long as the charger can meet the battery float target voltage. A pump or a fan might be a useful load.

    See page 34 in the User Manual: http://www.outbackpower.com/pdf/manuals/flexmax.pdf
    I think I also understand that the XW and Outback inverters are designed to "sell" AC power back to the grid which I see as about the same thing for an inverter.
    Grid tie inverters are designed to sell excess power back to the grid. However, both companies (and others) offer products that are intended for off-grid applications and cover a broad range of power specs and types (some are just inverters, others are inverters with built-in battery chargers that use 120 VAC from the grid or a generator to recharge the batteries).

    You may find this off-grid application brochure to use useful: http://www.outbackpower.com/pdf/brochures/Off_Grid_Power_Solutions.pdf
    Is there any reason a person should or shouldn't do this? What if the dump device fails or is not on? No problem for PV, right? Potential problem for wind generator, as it then has no brake, right?

    My application will be off grid.
    Right; it’s typically not a problem for PV. The NEC requires a backup controller for diversion applications.
    I expected the charge controller to be capable of only sending the unneeded input rather than taking the batteries down.
    That’s the typical configuration. Diversion and Float loads are also called “opportunity” loads, and they’re only connected when there’s “excess power” available.

    HTH,
    Jim / crewzer
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: Where do you divert your excess power to?

    As I have alluded to on another thread,, I am going to try to power the 120vac element of my propane fridge from the load control side of the controller.

    T
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: Where do you divert your excess power to?

    1) Phaser banks

    2) Shields

    3) Photon torpedos

    4) uphill water tank, for emgerency use, like the Big Creek hydro electric project
    http://www.sierrapacktrip.com/bigcreek.htm
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: Where do you divert your excess power to?

    How 'bout an uphill laser photon torpedo tank shield?

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Where do you divert your excess power to?

    HEY!

    Don't make us go all "moderator" on your behinds!

    -Bill :p
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #10
    Re: Where do you divert your excess power to?

    I have a fan and water pump setup as a DIY geothermal cooling. This cools two room during the summer.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Where do you divert your excess power to?

    I've been thinking about this for some time. If the day ever comes that I get enough panels on the roof to off-set my wife's ever-increasing energy demands ...:p
    The Outback MX60 has an 'auxiliary' function that can trigger a small relay under a number of different programmable circumstances. So my questions for those who divert excess power is: how exactly are you doing it? Sending the PV voltage off? Cutting in a load on the battery side? Or tripping an AC switch to the inverter? That and what criteria do you use to divert? Float voltage seems the obvious choice.

    We need to practice up our wiring diagram drawing abilities for more lucid posts!:p
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #12
    Re: Where do you divert your excess power to?

    Cariboocoot,

    You may find this related post to be of interest: http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865

    :cool:

    Enjoy!
    Jim / crewzer
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Where do you divert your excess power to?

    Crewzer;

    That is really valuable! I'm always glad when someone else does all the preliminary work and I can benefit from their experience. Even if it does give me more ideas. :D

    'Coot
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  • SolarJohn
    SolarJohn Solar Expert Posts: 202 ✭✭
    #14
    Re: Where do you divert your excess power to?
    Cariboocoot wrote: »
    I've been thinking about this for some time. If the day ever comes that I get enough panels on the roof to off-set my wife's ever-increasing energy demands ...:p
    The Outback MX60 has an 'auxiliary' function that can trigger a small relay under a number of different programmable circumstances. So my questions for those who divert excess power is: how exactly are you doing it? Sending the PV voltage off? Cutting in a load on the battery side? Or tripping an AC switch to the inverter? That and what criteria do you use to divert? Float voltage seems the obvious choice.

    We need to practice up our wiring diagram drawing abilities for more lucid posts!:p

    I use my Morningstar Relay Driver, which is actually a Voltage Controlled Switch. When connected to a suitable relay, it is programmed to connect another load ONLY AFTER my primary battery bank is fully charged. The disconnect voltage is much lower than the connect voltage, eliminating the possibility of rapid on and off cycles.

    My primary goal is to see that a secondary battery bank remains fully charged.

    John


    John
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  • System2
    System2 Posts: 6,290 admin
    #15
    Re: Where do you divert your excess power to?
    icarus wrote: »
    As I have alluded to on another thread,, I am going to try to power the 120vac element of my propane fridge from the load control side of the controller.

    T
    Did you get this (excess power- diversion switch to refrigerator 120vac heater element, supplement to propane (I assume)) to happen and if so how. I have a combo mppt diversion controller 3024 duo by bluesky and 3-210w panels on order. after ordering I found out how little good the "dump" power actually is... I'm still confused after my last convo with bluesky as how to best use this.
    I hope you got this to work and would love to hear how you're going to do it.
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  • System2
    System2 Posts: 6,290 admin
    #16
    Re: Where do you divert your excess power to?
    boB wrote: »
    If the PWM switching frequency is high enough, the little ONs and OFFs will filter out to cause the battery voltage to be relatively constant... Instead of being ON for seconds, bringing the battery voltage obviously down, and then OFF for seconds, letting it charge back up again.. That certainly would not be good for the battery.

    This is why these types of controllers (C40, Morningstar, etc) work OK. They switch faster than the time constants of the batteries and capacitors storing and releasing energy in the circuit.

    boB
    What would make for acceptable cycling? It seems a supplemental resistive device (heater element) that augments (propane/syngas) refrigeration could work well. This is what I'm hoping to do with mine... in process...
    Would love input. Want the right dc heating element for my currently ac only dometic rm2810 refer. Or do I use the built in ac heater element with an inverter? How exactly this done (relays and such) with the bluesky 3024duo .. am still wrapping my head around this.
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