Batteries topped off on my 12v bank, how do i get the excces power to a grid tie inverter?

i8work
i8work Registered Users Posts: 4
Hi, Batteries topped off on my 12v bank, how do i get the excces power to a grid tie inverter? is there some component I can buy that can sense that the batteries are full  and direct the Power  to the grid tie inverter?

thanks Andy

Comments

  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Not sure there is a legal 12v to grid tie inverter. I know there use to be and likely still are some 24 volt inverters that will do that. How large an array do you have? Most 12 volt systems have 800watt or smaller array and not worth the bother of contacting the Power company and getting all the inspections to do it...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • i8work
    i8work Registered Users Posts: 4
    Hi, I just 3 250watt panels, but my batteries are topped off by 10am, so I was thinking of getting a grid tie inverter, (no need to inform the power company here in Australia) to put the excess power back in to the grid to help reduce my power bill, but you say it may not work of a 12v bank?
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Check eBay, they have some made in China inverters that will back feed the grid, please be careful though! I would, at a minimum put in a dedicated circuit breaker. I've (we've) heard some poor reviews. Be careful. Not a recommendation, but here's a link;

    http://www.ebay.com.au/itm/1000W-MPPT-Solar-Grid-Tie-Inverter-For-18V-30V-36V-Panel-10-8V-45V-To-230V-/222077816351?var=&hash=item33b4de8e1f:m:m-kxlU995kLx46NZFAG-QEg
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Also you would have to physically switch it....
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • i8work
    i8work Registered Users Posts: 4
    Thanks for that, just one more question, do I have to switch the inverter on  manually when the batteries full or is there some way of automating this?
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    You could automate it, but it would likely take a bit, what charge controller do you have? Do you use you system, or is it mainly a backup? Might just let it back feed 2 out of 3 days if there is no load on it. It's not much in the way of saving's, a 750 watt array might back feed 500 watts an hour. Even if you average 6 hours a day that's 3 Kw's at what ever your electric costs 20 cents? maybe 60 cents a day. doubt those cheapy grid ties are dependable enough for you to get your investment back out of them.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • i8work
    i8work Registered Users Posts: 4
    I have a small load in it, I have four 115ah batteries, I use it to run my Aqua Ponic system, I plan to expend the solar system I have, but just trying to get my head around what is required and some practical experience before I do
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    edited December 2016 #9
    I really think that you would be better served connecting the excess power to feed some kind of opportunistic loads like water heating, or some other load. The road to safely and effectively back feeding the grid with your system, is full of perils and expenses.
    I always have more questions than answers. That's the nature of life.
  • daklein
    daklein Registered Users Posts: 15 ✭✭
    What if:   use a small AC to DC battery charger to keep the bank topped off, when you have excess power to feed to grid, and bank is fully or mostly charged.       And switch the panel DC inputs off of the charge controller, and to the microinverters.
    4.7 kW rooftop grid-tied Enphase M190s (1/21 surviving, have replaced and re-replaced the rest), 21x SolarWorld 225W
    2.6 kW ground mount AC coupled to SMA SI6048 x2 & 1080Ah 48v Exide FLA forklift bank, 10x Talesun 265W (a DC Solar trailer), Enphase m210/M210IG
    3.7 kw  rooftop 12x Astronergy 305W,  9 panels DC coupled w/ Midnite 250-CP CC,  3 panels AC coupled Enphase M210IG
    (sold) 480 W camper system, 2x Panasonic 240W HIT, Midnite Kid CC w/ Whizbang Jr, 2x 6v GC2 FLA 230Ah
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Daklein, as I said in the other post--Connecting the AC output of GT inverters, through an AC transfer switch, to the input of an off grid TSW AC inverter is already supported and easier to configure.

    Another option... Get a central inverter that supports 200-400 volt Vmp-array ("high voltage" array) and use Either a Schneider or Morningstar (or other brand) of 600 VDC input (Vmp-array ~ 200-400 VDC) MPPT solar charge controller. Now you can connect (for example) 10 panels in series (300 Watt Vmp~30 volt) for a 2 wire 300 Volt Vmp array, and a simple two wire transfer switch from GT central inverter to the panel input of a high voltage MPPT solar charge controller.

    This second method can work, but 600 VDC input solar charge controllers are not cheap--This does not seem to be a cost effective solution for most people.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    i8work said:
    Hi, Batteries topped off on my 12v bank, how do i get the excces power to a grid tie inverter? is there some component I can buy that can sense that the batteries are full  and direct the Power  to the grid tie inverter?
    Only inverter I know of that will do that is the old Trace SW2512.  You might be able to find one on Ebay or something.  Failing that there's going to be no good way to do it.  Bad ways include:

    - Boost to a small 24V battery and then use a 24V microinverter with an LVD (so you don't kill the 24V battery)

    - Boost to a large 24V battery with an Outback GTFX inverter

    -Get a Chinese 12V grid tie and then switch your panels from the battery bank to the GT inverter
  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited May 2017 #13
    i8work said:
    Hi, Batteries topped off on my 12v bank, how do i get the excces power to a grid tie inverter? is there some component I can buy that can sense that the batteries are full and direct the Power to the grid tie inverter?

    thanks Andy

    A possible solution?

    At the bottom of this article ...
    http://www.reuk.co.uk/wordpress/electric-circuit/low-voltage-battery-disconnect-circuits/
    is an email address to order an ultra-simple 12 Volt Low Voltage Drop Out device.
    Ask for an adjustable turn-on voltage and an adjustable turn-off voltage.
    When the battery voltage rises above +/- 14.5 volts then the SSR will connect the GTI to the battery.
    When the battery voltage falls below +/- 12.7 volts then the SSR will disconnect the GTI from the battery.

    Use an SSR ( Solid State Relay ) vs Mechanical Relay?
    You need the SSR to function as follows:
    a) ON when battery voltage >  +/- 14.5 volts
    b) OFF when battery voltage <  +/- 12.7 Volts 

    750 watts / 13 volts = 57 Amps !!!

    A possibility ... 
    http://https//www.amazon.com/iMeshbean%C2%AE-Inverter-Accept-10-8v-30-Seller/dp/B009B57L1Q

    Or connect two smaller GTI's, each with its own smaller SSR.
  • mike74820
    mike74820 Registered Users Posts: 44 ✭✭
    mpp solar make what your looking for in their hybrid  charge controllers http://www.mppsolar.com/v3/hybrid-v-series/
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    mike74820 said:
    mpp solar make what your looking for in their hybrid  charge controllers http://www.mppsolar.com/v3/hybrid-v-series/
    Pretty sure they are not 12V.
  • mike74820
    mike74820 Registered Users Posts: 44 ✭✭
    HYBRID V SERIES 1012V is a 12 volt model 
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited May 2017 #17
    Consider putting the relay on the 240VAC side of a GTI to turn it on/off, leaving the input side connected to the panels.   Less amps and less problems with arcing.

    I am available for custom hardware/firmware development

  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    mike74820 said:
    HYBRID V SERIES 1012V is a 12 volt model 
    So it is; I just saw that.  Interesting.