Supplementing off grid system with extra AC

RavemindRavemind Registered Users Posts: 9 ✭✭
Hello All,
I have a 4.5 kW of solar on the roof and 20 kW of battery. Which has been working fine until now.
Recently I've had to add a few more loads that I hadn't planned for. These have brought me to the situation where I'm unable to get my batteries back up to full on a daily basis since my daytime load has gone up and the panels aren't sufficient to charge the batteries while I have such a large daytime draw. I estimate I need to generate about 5000 watts more a day to break even during the short winter hours.

Sure I can just add another 1500 watts of panels an another charge controller, but I don't really see why it would be necessary to have all that extra juice make the round trip through the batteries when this extra usage is only happening during the daytime. It seems like a lot of extra wear and tear on the batteries. I want to only supplement the AC.
I'm using lithium batteries and they don't like to sit at full charge all day with a float charge. I have them set to fill, drain a bit and then fill again. Sometimes the charge controllers decide it's time to top up to late in the day, but the sun is mostly gone. This has been ok since I've got ample battery storage. At lease, until now.

So why can't I use a small grid tie inverter to feed 90% of the energy I use during day light hours? Then my main panels will have ample time to fill the batteries and patiently wait until nightfall.

I've started testing on a small scale to see if this is possible. I bought a cheap grid tie inverter to test with and plugged it in. At first glance it seems to be working. Kill A Watt meter shows the GTi passing power and my Conext Combox and SCP both register a lower AC load on the system. (This really screws up the data logging since I no longer can see how much power I actually used at the end of the day)
Apparently the my Schneider SW4024 outputs power that the GTi thinks is grid. Maybe this a fluke and won't work with other types of grid tie inverters. I don't intend to continue to use the cheapo GTi and I doubt it will last all that long. There are better ones available.

I'm aware of the risk of what happens if the grid tie inverter output surpasses the AC load my house is drawing. That can be avoided a couple of ways. Either keeping the additional AC power low enough or by using a grid tie inverter with a limiter.
I'm not an electrical engineer and there could be other stuff going on I don't know about.

Does anyone know what other problems I may face?


Main property - 4.5 kW panels into 2 x Schneider MPPT60 150v charge controllers | Schneider Conext SW4024 Hybrid inverter | 30 kWh of Lithium Batteries 24V - Water pumping - Grundfos SQflex | 1000w solar panels | Midnite Solar theKid | 48v Lithium battery |

Comments

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    I'm probably just really confused about what you're doing / trying to do.

    You have an off-grid inverter providing AC to a grid tie inverter, rather than supplying loads directly from the off-grid inverter? This is somehow supposed to compensate for a winter shortage of pv?

    If this is the case, what you need is a generator to run for an hour or two to cover the deficit and extra load. With lithiums, you could wait to see what the day brought in with pv, and run the generator to bring the bank up enough to get you through the night.

    My understanding is lithiums don't float at all. They should get to terminal voltage, then stop. With no charging load, 100% of the pv output (less system losses) will be available to power loads. If the batteries are "draining a bit" that would be because loads exceed pv capacity. Adding a GT inverter isn't going to change that.

    You could increase rebulk voltage though, so any deficit gets replaced to the extent possible while the sun is out. If I'm understanding this at all, you're basically using the GT inverter to do what tweaking settings on your off-grid inverter should be doing, and missing the generator to make up for high loads and short days.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    if you have Grid power, why are you paying for the expense of batteries ?

    if you have Li-Ion batteries, DONT charge them to 100%, just charge up to 80% and STOP There. 
    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 ,

  • RavemindRavemind Registered Users Posts: 9 ✭✭
    I can see now my description was to vague and I wasn't technical enough. It made sense in my head.
    What I am wanting to do is not standard. With all the new hardware coming out I'm looking at different ways to use it.

    To clarify:
    Lets forget about problem of not having my batteries full at nightfall. It just confuses the issue. I can fix that the standard way of adding more panels and a charge controller. Or it will fix itself If what I want to do works.

    This is a remote off-grid system. There is no actual grid around around here.
    I have some extra panels lying around and I connected them to the little GTI I purchased on Ebay. It recognized my home power as a grid and started feeding power into it. Shaving about 200 watts off of my 1000 watt AC load according to the Conext SCP. Can I safely feed 800 watts with a better GTI? Is it really reducing my AC load and allowing my main PV to do it's job and fill the batteries? Looks like it.

    I'd like to accomplish something like this:
    I want to add a pentair 1.5 hp variable speed pool pump that will run almost exclusively during the day. I know direct solar pumps exist but I don't want to go that route. I want the flexibility of pumping into the evenings if needed. I don't know how long the pump will need to run until the pool is finished and people are dirtying it up.
    I want to add to the available power I have during daylight hours. I don't want to store it. I don't need to. I'd prefer if it never gets near the batteries. I also don't want to put to much strain on the SW4024 inverter by having it constantly put out 2000+ watts AC during the day. Being able to add a GTI and a few panels would allow me to scale up or down easily and inexpensively. 

    When my batteries are full, the charge controllers stop. They aren't feeding PV to anything. They are sitting there being wasted until I hit the rebulk voltage. I want to avoid that.
      
    I haven't installed my Conext Charge Controllers yet. I'm using my old Outbacks which aren't ideal for Li-on. Maybe the new charge controller will be different and interface with the Conext Inverter.
    I see there is a Firmware upgrade for my inverter that allows some crazy power sharing options I don't entirely understand. Residential Self-Consumption? One of those references feeding the PV directly into the AC system, but may only in a true grid tie situation.

    I'd like off-grid solar to be more modular and flexible and less of a behemoth that's hard to upgrade after it's installed.

    I don't charge my batteries to 100%. I only use the middle 60%.
    I have a generator, but I hate using it. It's a Honda eu3000. Somehow I got a lemon and it requires tons of maintenance to keep it running. I even have an eu2000 but it's now to small for what we are drawing. I don't mind spending money to upgrade the solar even if a bit of gasoline would be cheaper.

    Thanks!
    Main property - 4.5 kW panels into 2 x Schneider MPPT60 150v charge controllers | Schneider Conext SW4024 Hybrid inverter | 30 kWh of Lithium Batteries 24V - Water pumping - Grundfos SQflex | 1000w solar panels | Midnite Solar theKid | 48v Lithium battery |
  • RavemindRavemind Registered Users Posts: 9 ✭✭
    I haven't really gone into what it is that I'm powering, but it's a lot. More than just a house. Currently it's 2 households and a retreat center. Including 5 refrigerators. 3 yoga studios with stereos and 10 fans. 45 tents with 3 watt led bulbs, 6+ laptop computers and possibly 40 people charging their phones.
    It's the fans that are killing me. We are having the warmest winter I've ever experienced. People should be putting on sweaters, not running 10 fans 6 hours a day. I have plans in the future to break off the two households into their own self contained PV systems. 
    Main property - 4.5 kW panels into 2 x Schneider MPPT60 150v charge controllers | Schneider Conext SW4024 Hybrid inverter | 30 kWh of Lithium Batteries 24V - Water pumping - Grundfos SQflex | 1000w solar panels | Midnite Solar theKid | 48v Lithium battery |
  • RavemindRavemind Registered Users Posts: 9 ✭✭
    Apparently what I want to do, Schneider refers to as AC coupling or DC coupling. My version is a bit of a hybrid of their two methods. I had no idea my inverter was capable of some of this.
    Can I post links here?
    AC Coupling Solutions Guide
    It's nice to know they are looking at power generation and usage in a more flexible way.

    They also talk about why the GTI detects my inverter AC as grid and why other GTI models may not.

    Main property - 4.5 kW panels into 2 x Schneider MPPT60 150v charge controllers | Schneider Conext SW4024 Hybrid inverter | 30 kWh of Lithium Batteries 24V - Water pumping - Grundfos SQflex | 1000w solar panels | Midnite Solar theKid | 48v Lithium battery |
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    Note that big, slow fans can be far more efficient.
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    The added info helps me understand your setup better.

    If the charge controllers are doing nothing, I assume you have float turned off, and a fairly low rebulk voltage. Lithium experts may disagree, but IMHO you may be better off turning float on in your application. That way, any available current current required for loads will go directly from controllers to inverter (it doesn't get stored in the battery to any great extent) instead of cycling from the lower rebulk multiple times per day, and sometimes leaving you short for overnight loads.

    With the GTI hooked up to spare panels, you are actually adding capacity and reducing battery cycling, so I see now what you're trying to do. There are lots of options on newer gear for different situations. Modular and flexible can be nice, but there's also something to be said for simplicity and redundancy. Personally, I would focus on getting the off-grid system right rather than bringing GT into the picture, but I can see why you're looking at it.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    How is the GTI connected? Most of the cheap imported ones simply "plug in" They aren't UL listed and could be a liability in the event of a fire. Insurance companies may void your coverage if this was the cause of a fire.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    I don't know that an unlisted GTI would necessarily even have to be proven to be the proximate cause of the fire.

    Just having it installed prior to the fire might be a breach of the insurance contract. In that case there would be no insurance contract in force at the time of the fire, making the cause of the fire irrelevant.

    An analogy - I get travel health insurance for a winter trip when I book it. Between now and then, I get a checkup at which the Dr says my blood pressure is up a bit. Probably just a fluke reading, but I'm prescribed a pill just in case, and booked in for a follow up after the trip.

    During the trip, I get hit by a bus and spend a week in hospital. The insurance company denies the claim on the basis I had an unreported change in medical condition which voided coverage. The fact the pill has zero to do with being hit by a bus is irrelevant, because the policy wasn't in force at the time.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    Insurance companies aren't there to help policy holders. Their main objective is to make profits for their share holders. Interesting analogy but entirely credible.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • nickdearing88nickdearing88 Registered Users Posts: 96 ✭✭✭
    edited November 26 #12
    Estragon said:
    The added info helps me understand your setup better.

    If the charge controllers are doing nothing, I assume you have float turned off, and a fairly low rebulk voltage. Lithium experts may disagree, but IMHO you may be better off turning float on in your application. That way, any available current current required for loads will go directly from controllers to inverter (it doesn't get stored in the battery to any great extent) instead of cycling from the lower rebulk multiple times per day, and sometimes leaving you short for overnight loads.

    With the GTI hooked up to spare panels, you are actually adding capacity and reducing battery cycling, so I see now what you're trying to do. There are lots of options on newer gear for different situations. Modular and flexible can be nice, but there's also something to be said for simplicity and redundancy. Personally, I would focus on getting the off-grid system right rather than bringing GT into the picture, but I can see why you're looking at it.
    There's nothing wrong with floating lithium with a good quality charge controller, but it's all about the voltage. My float voltage for LiFePO4 corresponds to about 80% SOC resting voltage (26.4v). If no current is being used, the charge controller simply does not provide current to the batteries. As soon as load kicks in, any available current to maintain that float voltage is passed from the CC.

    I love opportunity loads so I take advantage of them anytime possible. But, if I'm away from home after an absorb cycle is completed (usually to 27.8v) for 15 minutes, the CC usually does not need to provide any current as the voltage slowly drops to the float setting. This can take hours with Li batteries unlike LA that drop almost immediately due to higher self-discharge.

    Edit:
    I would take other's suggestions and avoid the small, likely unlisted GT inverter and focus on opportunity loads and another CC if needed.
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    edited November 26 #13
    Ravemind said:
    Apparently what I want to do, Schneider refers to as AC coupling or DC coupling. My version is a bit of a hybrid of their two methods. I had no idea my inverter was capable of some of this.
    Can I post links here?
    AC Coupling Solutions Guide
    It's nice to know they are looking at power generation and usage in a more flexible way.

    They also talk about why the GTI detects my inverter AC as grid and why other GTI models may not.

    Regarding AC coupling, read page 8 & 10 of the guide, stating lithium batteries cannot be used, just something I noticed, there seems to be no explanation why it's not possible.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • clockmanfranclockmanfran Registered Users Posts: 7 ✭✭
    edited November 26 #14

    AC Coupling Solutions Guide

    Its good to see another manufacturer posting clear information.

    interestingly this manufacturer allows you to limit/set the frequency ramping and suggests 51.3HZ as a max figure, against a base of 50HZ which is good news. As other well known manufacturers allow an increase of 60HZ against a 50HZ base, and at that, as you can guess a fair amount of domestic appliances stop working correctly.

    It seems that the majority of Inverter manufactures are not that keen on AC coupling mixed with DC coupling, and one suggests turning the Frequency ramping off, and buying lots of there expensive control equipment at each power input source.

    However, there is a fair bit of experimentation work going on across a few RE Forums worldwide. As used/second hand GTI's have become widely available, and at very low prices for a MPPT device. So some sort of simple, robust and cost effective universal GTI controller is presently being devised and tested.


     

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (9 years running).  ... 5kW PV on 3 Trackers, (5 years) .... 9kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    @nickdearing88 - I find there's a bit of a lag between starting a load, and the load being powered by pv. Presumably this few second delay is for an mppt sweep to adjust to the demand. The result is a sort of microcycle. Not a big issue for lead acid AFAIK, but not sure if this could be a problem for lithium vs fewer, deeper cycles to a lower rebulk.

    It was on this point I was thinking lithium experts might disagree.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,872 admin
    Single Phase 50/60 Hz inverters (typically) pull DC power from the battery bus with a "sine squared" wave from (100 or 120 HZ for 50/60 Hz AC).

    That means that when you supply a steady DC current to the battery bank/hybrid inverter, part of the cycle the inverter is drawing zero amps, and another part of the cycle it is drawing ~2x the DC bus average current. Since big DC capacitors are expensive, most inverters simply use the battery bank as the "capacitor".

    With Lead Acid batteries, you "float them" at a high enough voltage that the battery is never "micro discharged" when the sun is shining (i.e, the ~13.6 volts float never drops down below ~12.8 volts during the 2x current draw). If you held the voltage at (for example 13 volts), part of the cycle the battery is discharging and part of the cycle the battery is charging or "micro cycling".

    With typical Li Ion chemistries, you charge them to (for example) 3.8 to 4.2 volts per cell (depends on chemistry, maximum charge to 80-90% instead of 100% for longer cell life). You generally do not "float" LI cells at higher voltages as this over charges them and can cause short life (or other problems).

    I am guessing, but the micro cycling of an AC inverter does "wear" the LI cells. And if you "float" (as done with Lead Acid), you over charge the cells and kill them that way.

    -Bill "guessing" B.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nickdearing88nickdearing88 Registered Users Posts: 96 ✭✭✭
    Estragon said:
    @nickdearing88 - I find there's a bit of a lag between starting a load, and the load being powered by pv. Presumably this few second delay is for an mppt sweep to adjust to the demand. The result is a sort of microcycle. Not a big issue for lead acid AFAIK, but not sure if this could be a problem for lithium vs fewer, deeper cycles to a lower rebulk.

    It was on this point I was thinking lithium experts might disagree.
    Of course it depends on the chemistry (and float voltage) but you can find the sweet spot. Most Li chemistries are excellent at micro-cycling -- see electric vehicles with regen braking. When I turned in my leased Nissan Leaf -- it had about 30,000 miles in three years. The Leaf battery expert at the dealership said my batteries tested an average of 90% original capacity. They perform cell-level testing and reconditioning before selling the Leaf as a certified pre-owned vehicle.

    Also, the voltage curve is so flat with lithium, even a large load kicking in affects DC buss voltage much less than with LA. Trust me, when some of you guys start playing with Lithium, you'll see what I mean. Just my $0.02; my lithium experience continues to be very positive.
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • BB.BB. Super Moderators Posts: 26,872 admin
    Just to be clear... A car battery cycling with regenerative braking is still only 10's- 100's of times per day.

    An AC inverter "micro cycles" 120x per second (assuming 60 Hz) for many hours on end. (see post #16 above).

    Not saying that lithium is good or bad specifically for floating applications with Hybrid AC inverters--It is just something that may be an issue from what (little) I know of these systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    Kind of off-topic... I forgot to turn off the power bar I use for the assorted chargers one night recently, which had my phone charging on. The inverter went into search mode overnight.

    The next morning, the phone was dead. Normally an LED lights up, and a charge status icon appears on the screen if off, or a haptic feedback if on. My theory is the search pulse was enough to buzz the haptic feedback, but not enough current draw to turn the inverter on. Doing that every ~8secs took the battery down to some setpoint at which the phone flips a bit to prevent further use or charging. Fortunately, the bit was apparently flipped in memory persistent during power-off, but not when battery removed. It charged normally after putting the battery back in.

    Back on topic, LA batteries have a DOD vs cycle life curve. The tiny DOD involved is pretty insignificant on the curve. As I understand it, lithium doesn't care about DOD if kept in the happy range, but does have a rated cycle life. At 120x/sec, those cycles would get chewed up pretty fast. It seems to me a/c microcycling would happen at any stage of charging, not just at float, wouldn't it?

    If so, you'd think lithium banks would be failing much faster than they seem to be in our applications.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,872 admin
    Some (many newer phones?) are able to feed power out the usb port.

    Perhaps the ac power glitches turned on the power output mode?

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    I didn't know that. My phone is a Samsung note 3, getting a bit long of tooth but not ancient.

    What would a person do with power output mode of a phone?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    On the other hand, 120hz microcycles are only about 2 millionths of the batteries capacity.  I doubt that counts as a "cycle".
  • nickdearing88nickdearing88 Registered Users Posts: 96 ✭✭✭
    I know it's getting off-topic (and feel free to move if desired Moderator Bill) but I'd like to know more about this inverter "micro-cycle" power draw. I didn't know that, but I'm also on a steep learning curve about the details of AC power. And the explanation makes sense.

    I wonder if there is difference in this behavior between inverters such as high/low frequency, different brand/technologies, and inverter capacity. I know my Samlex SA is considered high-frequency and doesn't include a large transformer. I wonder if "low frequency" inverters like a Magnum or Schneider work in the same way.

    From what I understand the high-frequency inverters boost the DC voltage, then convert to an AC sine wave and low-frequency inverters convert the power to AC first (at DC voltage), then use the transformer to step-up to the correct voltage. 
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • clockmanfranclockmanfran Registered Users Posts: 7 ✭✭
    edited November 27 #24

    Yes, the lithium battery question is interesting, and something that I have not really got involved in at a practical level regards micro cycle's.

    With the LF, (our own built/design of large torroid), PSW 6kW -15kW OzInverter, we run the 8010 (HN1518HT1536) chip at 23.4kHz. 

    EG8010 is a digital pure sine wave inverter ASIC (Application Specific Integrated Circuit) with complete function of built-in dead time control. It applies to DC-DC-AC two stage power converter system or DC-AC single stage low power frequency transformer system for boosting. EG8010 can achieve 50/60Hz pure sine wave with high accuracy, low harmonic and distortion by external 12MHz crystal oscillator. EG8010 is a CMOS IC that integrates SPWM sinusoid generator, dead time control circuit, range divider,soft start circuit, circuit protection.

    We use reasonable caps to smooth things out a bit with the OzInverter, but I suspect that the BMS for the Lithium would have difficulty detecting the micro cycles going back through the H BRIDGE of the Inverter. and therefore give a poor record of actual real world charging.


     

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (9 years running).  ... 5kW PV on 3 Trackers, (5 years) .... 9kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • bill von novakbill von novak Solar Expert Posts: 711 ✭✭✭✭
    Ravemind said:

    I have some extra panels lying around and I connected them to the little GTI I purchased on Ebay. It recognized my home power as a grid and started feeding power into it. Shaving about 200 watts off of my 1000 watt AC load according to the Conext SCP. Can I safely feed 800 watts with a better GTI? Is it really reducing my AC load and allowing my main PV to do it's job and fill the batteries? Looks like it.
    The time you will have an issue is when batteries are full and loads are low.  The question then is what will trip due to overvoltage sooner - the main inverter or the grid tie inverter?  If grid tie, all is well - but if it's the main inverter you'll lose power. 

    When my batteries are full, the charge controllers stop. They aren't feeding PV to anything. They are sitting there being wasted until I hit the rebulk voltage. I want to avoid that.

    You can do that without a grid tie inverter.  When your batteries are fully charged, your power is going from the panels to the inverter.  You are still using that power.  Whether or not it goes through your main inverter or a grid tie inverter doesn't matter.

    I have a generator, but I hate using it. It's a Honda eu3000. Somehow I got a lemon and it requires tons of maintenance to keep it running. I even have an eu2000 but it's now to small for what we are drawing.

    I believe the SW4024 has a generator support mode; that allows you to use any size of generator.


  • RavemindRavemind Registered Users Posts: 9 ✭✭
    mcgivor said:
    Ravemind said:
    Apparently what I want to do, Schneider refers to as AC coupling or DC coupling. My version is a bit of a hybrid of their two methods. I had no idea my inverter was capable of some of this.
    Can I post links here?
    AC Coupling Solutions Guide
    It's nice to know they are looking at power generation and usage in a more flexible way.

    They also talk about why the GTI detects my inverter AC as grid and why other GTI models may not.

    Regarding AC coupling, read page 8 & 10 of the guide, stating lithium batteries cannot be used, just something I noticed, there seems to be no explanation why it's not possible.
    The reason they say this form of AC coupling can't be used for Lithium is because it just dumps all the extra AC into the batteries and doesn't know when to stop unless you jerry rig a contactor to disconnect the GTI's when the batteries are full.

    I'm going to add another charge controller and 2000 watts of panels. If I need more after that I will add a 1000 watts with a GTI to help with the daytime load. I'll look for a GTI with a power limiter.
    Main property - 4.5 kW panels into 2 x Schneider MPPT60 150v charge controllers | Schneider Conext SW4024 Hybrid inverter | 30 kWh of Lithium Batteries 24V - Water pumping - Grundfos SQflex | 1000w solar panels | Midnite Solar theKid | 48v Lithium battery |
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