Micro-inverter basics

[j3rk]

Can anyone explain the basics of micro-inverters to me?

Here is a hypothetical situation where we live in a fantasy world with no connectivity rules but there is a well-functioning grid:

If I have one 300W panel with one micro-inverter connected to it, and then connect the 3 output wires (North America, 240V) output wires directly to my electric panel, would I be pumping that ~300W of power into my AC lines (and theoretically out to the grid if it's not used locally)?

With big installations I see there are things like energy optimizers and other extra things to make monitoring the output possible. I just want to know the basics of micro-inverters though. Is one inverter and one panel enough to provide useful power? If so, do they scale? e.g. 5 panels + 5 inverters = ~1500W to the grid? (barring efficiency losses of course)

Thanks

 

[SparkyJJO]

Basically yes.

Example: I have two 400W panels connected to a 720W AC output microinverter. It connects directly to the AC grid (of course via a breaker in the main panel). So I have theoretical max continuous output of 720W from that set. I have 10 sets of those, which comes to 7,200W of output available (then plus another ~300W from a single panel and inverter due to a roof vent being in the way of having another 2 panel + microinverter set).

With microinverters, things are simpler, but there is no battery backup that can be connected directly to to them, and they require an active grid connection to operate so they can sync their output to the grid. If the grid goes down, they shut down. So when using microinverters you are still dependent on the grid being up and running. You can then add another inverter with batteries to create your own "micro grid" that will disconnect from the main grid when it goes down, thus providing a "grid" for the microinverters to sync up to (it is called AC Coupling) but it has to support doing so. Not just any inverter can do it without risk of blowing up stuff.

 

[DThames]

This little meter would record (hypothetically) your power production. Just pass one of the hot legs through the transformer core and connect the power wires to 240v.

 

[j3rk]

Cool. Thank you SparkyJJO. I am fully aware that there is no battery backup possibility. Our grid is stable enough that I'm not too worried about that. I have a small 12V system set up to run my home office off-grid, with the option to run an extension cord to the fridge in the case of the grid being down longer than a few hours.

I have a 4kW Tesla system on the roof, which was adequate to run my house+pool over the last year or so. I bought an EV in February and I'm seeing my bills creep up again, so I am trying to find a cost effective way to increase my production to offset the car charging during solar hours. I've got space in the back yard to ground mount about 9-10 panels (it's actually a useless bit of yard between a retaining wall and a privacy wall). It's so far away from anywhere I could safely mount a standard inverter where it'd be protected from weather, I'd incur a decent amount of loss running the DC that far. 240V AC will do much better over the distance and with smaller gauge wire to boot. I'll still need to work out some logistics and permitting issues for actually connecting it in behind my current solar shutoff, but I think in the grand scheme of things, micro-inverters will be a better solution.

 

[ncsolarelectric]

Cool. Thank you SparkyJJO. I am fully aware that there is no battery backup possibility. Our grid is stable enough that I'm not too worried about that. I have a small 12V system set up to run my home office off-grid, with the option to run an extension cord to the fridge in the case of the grid being down longer than a few hours.

I have a 4kW Tesla system on the roof, which was adequate to run my house+pool over the last year or so. I bought an EV in February and I'm seeing my bills creep up again, so I am trying to find a cost effective way to increase my production to offset the car charging during solar hours. I've got space in the back yard to ground mount about 9-10 panels (it's actually a useless bit of yard between a retaining wall and a privacy wall). It's so far away from anywhere I could safely mount a standard inverter where it'd be protected from weather, I'd incur a decent amount of loss running the DC that far. 240V AC will do much better over the distance and with smaller gauge wire to boot. I'll still need to work out some logistics and permitting issues for actually connecting it in behind my current solar shutoff, but I think in the grand scheme of things, micro-inverters will be a better solution.

Microinverters are a great way to expand upon a pre-existing system. They provide the easiest, least expensive means of scaling a grid-tied system. You can continue to add 20A branch circuits to your combiner panel until you reach the limit of your interconnection. However, I do not recommend expanding a grid-tied system without going through all the proper paperwork with the utility and a permit. The NEC has a lot to say about how it's done so as not to exceed the rating of your main service panel.
In answer to your earlier question, yes even 1 panel and 1 microinverter can send power back to the grid if you're not using it, and the utility will see that if you already have a smart meter installed. They can tell if you've expanded your system, so be sure to have your interconnection agreement updated to include the new system. In my home for example, my "always on" load is around 230W. So a 290W microinverter will send power back.
A good monitor is SENSE. Not only does it differentiate between grid and solar sources, it is an AI that can figure out what the loads are in your home and show you what loads are drawing the most power, surges, sags or causing issues. I love my SENSE monitor! It's very slick.

 

[DThames]

Microinverters are a great way to expand upon a pre-existing system. They provide the easiest, least expensive means of scaling a grid-tied system. You can continue to add 20A branch circuits to your combiner panel until you reach the limit of your interconnection. However, I do not recommend expanding a grid-tied system without going through all the proper paperwork with the utility and a permit. The NEC has a lot to say about how it's done so as not to exceed the rating of your main service panel.
In answer to your earlier question, yes even 1 panel and 1 microinverter can send power back to the grid if you're not using it, and the utility will see that if you already have a smart meter installed. They can tell if you've expanded your system, so be sure to have your interconnection agreement updated to include the new system. In my home for example, my "always on" load is around 230W. So a 290W microinverter will send power back.
A good monitor is SENSE. Not only does it differentiate between grid and solar sources, it is an AI that can figure out what the loads are in your home and show you what loads are drawing the most power, surges, sags or causing issues. I love my SENSE monitor! It's very slick.

Yes, Sense monitor is great! I have solar production cloud data from the production equipment but what really gets to my main breaker panel, in and out, the Sense gives a good quick look at what is going on at home.