Adding plug and play wall socket kit to off grid system?

desertsundesertsun Registered Users Posts: 7 ✭✭
I've been looking at these plug and play solar kits as an alternative to upgrading our current off grid solar array.
Can someone tell me if this would work for an off grid system and if so, would the extra power feed into our Magnum MS448PAE inverter and charge the batteries? My current charge controller can handle another 1.5kw of panels. This kit would probably still be worth it if it only offset some of the house power usage and didn't feed into the inverter. I just don't really understand how this kit would work off grid and if it would be safe. I'd really appreciate some input if anyone has used a kit like this before. Thanks.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    The system above is a 240 VAC output system (they show plugging into a 120 VAC outlet--Which is incorrect).

    Your Magnum is a 120/240 VAC inverter.

    So, those two components should wire and play together fine (make sure you use 240 VAC connections).

    Magnum does have some information on connecting to a GT inverter:

    https://www.solar-electric.com/maenms4444wa.html (general information)
    https://www.solar-electric.com/lib/wind-sun/Magnum-MS-PAE-Manual.pdf (manual)
    2.3.1 Pre-AC Wiring Requirements CAUTION: Before installing any AC wiring, review the safety information and cautionary markings at the beginning of this manual and the following guidelines. • Always use properly rated circuit-breakers. If using an electrical sub-panel, circuit breakers can only be moved from the main electrical panel to the sub-panel if the breakers are also listed to be installed in the sub-panel. • AC wiring must be no less than #10 AWG (5.3 mm2) gauge copper wire and be approved for residential wiring per the NEC (THHN as an example). • DO NOT connect the inverter’s output to an external AC power source unless used in an AC coupled application*. Otherwise, severe damage to the inverter may occur; and this damage is easily detected and is not covered under warranty. * This inverter has the ability to be used in an AC coupled application, which allows the inverter’s output to be connected to a grid-tie inverter’s output. The grid-tie inverter’s output is synchronized to the inverter’s output so that the two AC outputs can be connected together without damaging either inverter. • The wire sizes recommended in this manual are based on the ampacities given in Table 310.16 (in conduit) or Table 310.17 (in free air) of the NEC, ANSI/NFPA 70, for 167°F (75°C) copper wire based on an ambient temperature of 86°F (30°C).

    5.1 What is an AC Coupled System Many homeowners utilize renewable energy (e.g., PV, wind, etc.) by installing high effi ciency, battery-less, grid-tie inverter systems to offset their power consumption from the utility grid. However, during a utility power outage, the grid-tie inverter normally stops operating. This can cause considerable frustration as the homeowner realizes that the critical loads in the home (e.g., refrigerator, lights, water pump, etc.) are no longer powered, and all the energy produced by the renewable energy source is being wasted while the utility power is out. In an AC coupled system, since all the energy sources and loads are connected directly to the AC side, an option would be to install a bi-directional battery-based inverter, such as the MS-PAE Series. The MS-PAE Series would allow the existing battery-less, grid-tie inverter to continue operating during a power outage; thereby, continuing to utilize the renewable energy to power the home’s critical loads—all from the AC side. However, in an AC coupled system—during a utility power outage—the utility grid is not available to export any excess power that is generated. This means there may be more power produced than the critical loads can consume, causing this excess current to be pushed back through the output of the inverter into the battery bank. Since this is not the normal path for the inverter to control incoming current, it is unable to regulate the battery voltage, providing the possibility that the battery voltage will rise and cause damage to your batteries. However, the MS-PAE Series inverter includes a “frequency shift” feature that can be used to regulate the battery voltage by changing its output frequency. 5.2 Frequency Shift Feature The frequency shift feature—when enabled—causes the output frequency of the MS-PAE Series inverter (≥Version 6.0) to change based on the inverter’s battery voltage. If the battery voltage begins rising, the output frequency starts decreasing; as the battery voltage returns to its correct voltage level, the frequency increases. In an AC coupled system, the MS-PAE Series inverter is optimized to work with Magnum Energy’s MicroGT5001 grid-tie inverter to regulate the battery voltage. During a utility power interruption, if the battery voltage begins to rise above the custom-absorb voltage level, the output frequency of the MS-PAE Series will start shifting down. The MicroGT500 grid-tie inverter responds by decreasing its output current to avoid overcharging the battery. As the battery voltage falls, the MS-PAE Series frequency starts shifting back up allowing the MicroGT500 inverter to gradually provide more current so that the battery can return to its custom-absorb voltage level. The response time and whether the frequency continues to shift down or start shifting back up depends on how fast the battery voltage rises or returns to the custom-absorb voltage level. Note1: If you are using a grid-tie inverter other than the MicroGT500, you may need to use an additional primary battery management system to ensure the batteries are not overcharged. This may require you to install a diversion controller and a load capable of absorbing the majority of the expected surplus energy. Options include: 1) a DC diversion controller and DC resistance loads; 2) AC diversion using AC resistance loads driven by DC controlled relays; or, 3) Sensata’s AC Load Diversion controller (ACLD-40).

    http://www.northernep.com/en/index.php?c=msg&id=230& (line diagram)

    I have not studied this in detail... More or less, the Magnum signals the GT Inverter to reduce output power by shifting the 60 Hz +/- xHz.

    The GT inverter you are looking at may be 100% at 60 Hz +/- 1 Hz, and 0% (shutdown) at >+/- 1 Hz...

    If the GT Inverter does not respond "correctly" (per Magnum's assumptions), you would need to look at adding a diversion load and controller to the battery bank... I.e., if battery charging voltage gets too high, the loads are turned on to "dump excess charging current".

    Another option would be a simple relay (or silicon relay) to turn off the GT to Magnum AC connection when Vbatt>Charging setpoint (probably better--You do not need a large dump controller and load bank--Simply "kill" the AC feed instead).

    There are other issues (like the solar GT inverters should have their own circuit breaker to the AC subpanel). If you (for example) put 2x300 Watt panels+GT inverters on a shared 240 VAC circuit, you would have on a sunny day upwards of 15 amps from AC branch breakers+2.5 amps @ 240 VAC from the GT inverter--And you could have "too much" AC current in an "overload condition"). The more solar+GT inverters you add, the more "over current" is available if this was a shared 240 VAC circuit in the first place.

    I don't see any big issues, assuming you have the "over charge protection" requirements worked out (i.e., dump load, AC disconnect, or verify that +/- xHz output of the Magnum will "trip" the GT inverter to off).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • desertsundesertsun Registered Users Posts: 7 ✭✭
    BB. said:

    Another option would be a simple relay (or silicon relay) to turn off the GT to Magnum AC connection when Vbatt>Charging setpoint (probably better--You do not need a large dump controller and load bank--Simply "kill" the AC feed instead).

    There are other issues (like the solar GT inverters should have their own circuit breaker to the AC subpanel). If you (for example) put 2x300 Watt panels+GT inverters on a shared 240 VAC circuit, you would have on a sunny day upwards of 15 amps from AC branch breakers+2.5 amps @ 240 VAC from the GT inverter--And you could have "too much" AC current in an "overload condition"). The more solar+GT inverters you add, the more "over current" is available if this was a shared 240 VAC circuit in the first place.

    I don't see any big issues, assuming you have the "over charge protection" requirements worked out (i.e., dump load, AC disconnect, or verify that +/- xHz output of the Magnum will "trip" the GT inverter to off).
    Thank you for your response. 
    I think I am understanding everything you said correctly but please let me know if I'm misunderstanding something.

    We have a 240 volt plug outside that was for a previous air conditioning unit that is not being used. This plug has it's own circuit breaker in the panel box. So, I assume this would be a great place for plugging the kit into.

    My Magnum inverter has a controller where we have limits set to it for maximum amps, voltage, & charge time. So, if the Magnum sends the signal to the GT to shut off but it does not... would the Magnum instead just slow down the power coming in from our 3kw array to accommodate the GT's power? Also, would the power coming from the GT not first be used by the running appliances and then the excess sent to the Magnum? I'm not sure how that works.
    We also have a Midnite solar classic 150 charge controller that should limit our batteries from overcharging. With all of this, would I still need a relay?

    While not ideal, we could also turn the breaker off during the times of the year when we are not using much power (heating or cooling) and just have it on when we know we need the extra power (no chance of overcharge).
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Yes, your unused A/C 240 VAC circuit will be fine. One thing to watch for. Most of these small GT inverters are designed for 15 Amp or 20 Amp maximum circuit breakers (typically 14 or 12 AWG wire minimum). If your A/C breaker was (for example 30 amps), you should replace it with a smaller breaker per the GT inverter's manual.

    The typical off grid TSW inverter like the Magnum (and others) do not have the capability of directly regulating battery bus voltage and charging current when fed by GT Inverters... The off grid inverter just takes any "extra current" 240 VAC circuit (say GT inverters output 2 amps, your AC load is 1 amp, then 1 amp is fed "backwards" through the OG inverter to charge the battery bank--run other possible DC loads). The only possible "backup" is (for example, if the battery bus exceeds 61 VDC) is for the OG inverter to shutdown (battery bus voltage error).

    GT inverters (in general) simply take 100% of whatever energy the solar panel/array can generate and "push it" out to the 240 VAC bus. They do not have any ability to regulate output current (wattage)--Just 100% of the array input.

    There are GT inverters that can be "throttled" based on the AC line frequency. The "typical" method to regulate the Battery state of charge is the Magnum inverter varies the 60 Hz +/- a couple of Hz (I do not know the details)... The farther from the 60 Hz, this signals the GT inverter to output less energy (from 100% to 0%). This frequency dithering is the basis for Sunny Island (SMA) "micro grid" systems.

    However, not all GT Inverters can do this (I think this is more common with newer inverters--May even be a requirement for "new" GT inverters to allow utilities to remotely control their networks).

    So, a backup method is to have the OG inverter go from +/- 0 Hz offset to +/- 2 Hz (for example) frequency offset. This will knock the GT inverter offline and stop any charging current from going to the battery bank (because all GT Inverter must qualify the AC voltage and frequency and will shut down until the line voltage/frequency is restored). Once the frequency goes back to 0 Hz offset, the GT inverter will wait 5 minutes and then restart (GT inverter needs frequency and voltage qualifications for 5 minutes before restarting per utility requirements).

    For OG inverters that cannot do the +/- Hz offsets, then the backup is the GT inverter AC shutdown relay and voltage controller, or battery dump controller/load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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