bimodal inverter w solar microinverters

[kevincw01]

Hi, I'm starting a plan before engagng an electrician and wanted to get the thoughts of the experienced people here on the design.

My concern is that I know it's not acceptable to island solar microinverters when the grid is down using a generator due to poor sine wave as well as excess solar output dumping into generator. However, with a bimodal inverter, I wonder if it becomes acceptable to use a generator? Do these inverters typically only use the generator to charge the batteries? Or do they also start the generator in the case that the load current exceeds the battery output? Thanks for your input in advance.

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[ButchDeal]

Ok so this is AC coupled bimodal inverter in your drawing.
however either way AC coupled or DC coupled some bimodal inverters can boost a generator output as well as use a generator for extra load. Some however can only use the generator to charge and carry the load.

[Mike90250]

.... I know it's not acceptable to island solar microinverters when the grid is down using a generator due to poor sine wave .....

What exactly has a poor sine wave ? micrinverter or generator ?
Most "real" alternators produce pristine AC since the rotating field HAS to create a sinusoidal waveform. It's when you overload it, slap on a POS AVR and cheap out by using marginal components, you get waveform distortion

SinewaveGeneration.jpg

[Mike90250]

With quality gear, you get quality results. The Schneider XW series (hybrid inverter/charger) has a "Generator Support" feature, where it can, if properly programed, sense the generator being overloaded, and actively sync and assist carrying the load with the inverter until it is no longer required, and will auto-magically return to battery charging.

[kevincw01]

Thanks Mike, the XW+ 5548 looks like a really nice option and it looks like it addresses my generator concern as you describe.

I am now wondering if it will be an issue (for any of these hybrid inverters) to have the AC solar circuit in the critical loads panel? This circuit has the potential to be an AC input once the inverter restablishes sine during a grid down event, if crtical loads are below solar output. Generally I think the inverters are designed for input current coming from grid (ac1), generator (ac2), battery (dc1), or solar charge controller (dc2).

[Mike90250]

Yes, you are now going beyond the design of the hybrid systems. They expect a real Grid. They are instructed as to what your battery and generator are. going beyond that and you are on your own, it's unknown what the results will be.
Remember, there is a lot of energy stored in those benign looking batteries, just like a 5 gallon can of gas looks innocent.

[kevincw01]

Thanks again, and yes I 100% agree wirh your battery comment. I've reached out to magnum, schneider and outback as to the impact of my scenario with their respective products and whether it is recommended. I'll comment back here when I hear back.

I suspect they will not recommend it and then I will need to remove 20x microinverters and purchase a solar charger controller in addition to the hybrid inverter. However, that extra investment (and labor) is enough to make the pricey enphase energy storage modules actually more cost effective.

[kevincw01]

Good news, Outback responded to my question and confirmed that their radian gs8048a-01 supports up to 6kw of direct-grid inverters (4048 supports 3kw). However, right now they don't protect the batteries from overcharging when in this configuration. They have a relay and 12vdc output to trigger a dump load when the batts are at certain batt voltage as a workaround. They expect a 2019 firmware update to fix this issue (via frequency shift to shutoff micros).

[kevincw01]

One more response from magnum. They said essentially the same thing, as long as total solar input doesn't exceed the inverter rating e.g. 4kw for the MS4448PAE, then it's not an issue. Moreover, that inverter already supports the frequency shift method to turn off the microinverters when the batteries are charged.

[Ward L]

This thread is too technical for my complete understanding but I think you are talking about what I want and that is a grid-tied system that will continue to work when the grid goes down. I don't want an off-grid system because of the cost and inefficiency. My current electricity bill is zero or negative, but it is all worthless when the grid goes down. I want a battery system that only uses the battery when the grid is down. Is that anything like you are talking about? Sorry for my limited understanding of this stuff.

[kevincw01]

Hi Ward, yes absolutely and this is my goal as well. Generally, it's much more complicated to achieve than it is to implement residential solar, but I am almost confident enough to contract with an electrician to do it. The last piece for me is battery technology.

[SunEagle]

This thread is too technical for my complete understanding but I think you are talking about what I want and that is a grid-tied system that will continue to work when the grid goes down. I don't want an off-grid system because of the cost and inefficiency. My current electricity bill is zero or negative, but it is all worthless when the grid goes down. I want a battery system that only uses the battery when the grid is down. Is that anything like you are talking about? Sorry for my limited understanding of this stuff.

The problem with any battery is that it will still grow old and die if it is "cycled daily " or just sits there waiting on a grid outage. The cost is still higher then having a reliable stand by generator for long or even short outages.

[jflorey2]

My concern is that I know it's not acceptable to island solar microinverters when the grid is down using a generator due to poor sine wave as well as excess solar output dumping into generator. However, with a bimodal inverter, I wonder if it becomes acceptable to use a generator? Do these inverters typically only use the generator to charge the batteries? Or do they also start the generator in the case that the load current exceeds the battery output?

You are planning an AC coupled system here.

Can I ask why you don't want to do a DC coupled system? If you are already planning on spending the money for a hybrid inverter/battery bank, a DC coupled system is much simpler/cheaper/easier on the batteries/easier to design.

[kevincw01]

Hi Jflorey2, I already have the sunk cost of the prevously installed solar microinverter infrastructure. Originally I was regretting that decision (there are benefits not relevant to this thread), but now, hearing from 2 vendors that they support this config per above, it's not cheaper or simpler for me to change to a DC coupled solar solution unless I'm missing somthing.

[kevincw01]

The problem with any battery is that it will still grow old and die if it is "cycled daily " or just sits there waiting on a grid outage. The cost is still higher then having a reliable stand by generator for long or even short outages.

I have a couple quotes (and googling for average costs confirm) that installing a generator for backup power is not cheaper. At best, it's the same cost as far as I can tell. And ofcourse, generators are not without their own maintenance requirements.