Confused about types of inverters I should choose

harrisonpatm said:

My current plan is to use an interlock kit to lockout my home's (small, 100amp) panel from the grid and feed my house from battery/solar via an inverter. So I'm trying to select an inverter type to use, and I'm getting a bit confused at some of the options available, hoping someone could clarify for me.

I realize that if I use an interlock to feed power into my house, the whole house will be powered by either inverter, or grid, but not both. Why am I seeing some big inverters that have both AC input and AC output? I would guess that these are grid-tied inverters, obviously, but I'm wondering if there's a way to use one of these grid tied inverters, without actually every using the grid, only in emergencies.

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AC input does not mean hybrid or grid-tie. Hybrid + Grid-tie is traditionally interactive (both directions) with the grid - e.g. in particular you can push excess power back to the power company. This hybrid/grid-tie back feed to the grid requires a different level of permits, permissions, contracts, etc. Hybrid is often thought of as grid-tie with a battery and straight Grid-tie is no battery needed.

I boils down to this question: Do you want to feed excess power back to the grid?
- If no, then you're after off-grid models (MPP or GrowWatt or dumb inverters like AIMS) or hybrid (battery) that can operate in off-grid mode (like Sol-Ark)
- If yes, then the available equipment is in a different relm. Some, like MPP Solar have both off-grid and hybrid/grid-tie models but it can be confusing.

For context, I'm off-grid, have no experience with hybrid or grid-tie.


Off-grid AC input....
Many off-grid AIOs like MPP 3048LV (3000w / 48v) will have 1) AC input, 2) Solar input, 3) battery input and 4) AC output. The unit can manage the 3 inputs to provide a steady AC output. I use an MPP in my camp trailer with DIY 48v battery. The batteries provide the AC output when driving or boondocking but when I hook to grid at a campground or sun hits the panels it will use the incoming energy to power the loads and any extra is used to charge the batteries. When the sun goes down OR I disconnect from the grid, it seamlessly continues to run on the battery until the battery dies because these units have built-in ATS & UPS as core to their design.

A 'dumb' off-grid unit like my AIMS 12,000w inverter has AC input and to let me charge the battery but is dicey on how it splits charging the battery and providing AC output at the same time. You have to read the fine print more carefully for dump inverters.

Another key question is do you need 240v/120v vs 120v vs 240. 240v/120v is US split-phase and Europe is 3-phase 240v. In both US you can do 120v only and in Europe you can power a lot with 240v single phase only. The smaller wattage units are 120v only and some like GrowWatt are 240v only. For phases (US 240v/120v or European 3-phase) AIOs such as MPP Solar require you buy 2 or 3 of them that synchronize their outputs. Also you need to buy in >=5000w-6000w range or higher to get 240v capability.

harrisonpatm said:

In theory, it'd be nice to have grid backup. If I get 5 cloudy days in a row and I haven't expanded my battery to compensate, then it'd be nice to be able top pull some power from the grid. One reason I originally decided to learn about and install solar on my own is that in my area, if you get grid tied solar installed, you need permission from both the city and the utility company, and I am against that on principal. So I see these inverters that have the option to charge your battery from mains, but if those are only available for grid-tied setups, then I'll have to pass and just go with a totally off grid setup, and size my solar and battery to compensate.

Apologies if this is a totally obvious question, I'm just confused by these charge-verters and how they can be off-grid while also charging from grid. If at all.

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I use my inverters (AIMS and SGP) in dumb mode so......

I have ATSs (instead of manual interlocks) to automatically switch between grid power and off-grid inverter power. Since I use cheaper 50a @ 240v ATSs, I have several so I can do accommodate the range of 200a@240v worth of circuits in my home. One is at the main panel in combination with an MTS.


And I use dedicated ones at the big amp locations like this one at the heat-pump outdoor compressor. I have another at the cooktop (and oven) area.


Between 4 of them I can do 200a@240v/120v worth of circuits. In you're case you could cover 100a@240v/120v with only 2 of them. They also make 120v ATSs - you don't have to do 240v/120v.

By default, an ATS passes thru grid. When the solar power turns on, the ATS will automatically switch from grid to solar power. When the solar power runs out (low battery) the inverter shuts-off and the ATS reverts to grid automatically. The caveat is I have to use UPSs for sensitive (computers, Tivo, ...).

One cool thing about default ATS I have to do is turn off the inverter and the house automatically defaults to grid. So I can work on the solar system and my wife isn't bothered and I don't have to do anything manual. Just turn off the solar system, work on it, and enable it when finished and the home circuits are powered one way or the other automatically.

AC input does not mean hybrid or grid-tie. Hybrid + Grid-tie is traditionally interactive (both directions) with the grid - e.g. in particular you can push excess power back to the power company. This hybrid/grid-tie back feed to the grid requires a different level of permits, permissions, contracts, etc. Hybrid is often thought of as grid-tie with a battery and straight Grid-tie is no battery needed.I boils down to this question:- If no, then you're after off-grid models (MPP or GrowWatt or dumb inverters like AIMS) or hybrid (battery) that can operate in off-grid mode (like Sol-Ark)- If yes, then the available equipment is in a different relm. Some, like MPP Solar have both off-grid and hybrid/grid-tie models but it can be confusing.For context, I'm off-grid, have no experience with hybrid or grid-tie.Many off-grid AIOs like MPP 3048LV (3000w / 48v) will have 1) AC input, 2) Solar input, 3) battery input and 4) AC output. The unit can manage the 3 inputs to provide a steady AC output. I use an MPP in my camp trailer with DIY 48v battery. The batteries provide the AC output when driving or boondocking but when I hook to grid at a campground or sun hits the panels it will use the incoming energy to power the loads and any extra is used to charge the batteries. When the sun goes down OR I disconnect from the grid,until the battery dies because these units have built-in ATS & UPS as core to their design.A 'dumb' off-grid unit like my AIMS 12,000w inverter has AC input and to let me charge the battery but is dicey on how it splits charging the battery and providing AC output at the same time. You have to read the fine print more carefully for dump inverters.Another key question is240v/120v is US split-phase and Europe is 3-phase 240v. In both US you can do 120v only and in Europe you can power a lot with 240v single phase only. The smaller wattage units are 120v only and some like GrowWatt are 240v only. For phases (US 240v/120v or European 3-phase) AIOs such as MPP Solar require you buy 2 or 3 of them that synchronize their outputs. Also you need to buy in >=5000w-6000w range or higher to get 240v capability.I use my inverters (AIMS and SGP) in dumb mode so......I have ATSs (instead of manual interlocks) to automatically switch between grid power and off-grid inverter power. Since I use cheaper 50a @ 240v ATSs, I have several so I can do accommodate the range of 200a@240v worth of circuits in my home. One is at the main panel in combination with an MTS.And I use dedicated ones at the big amp locations like this one at the heat-pump outdoor compressor. I have another at the cooktop (and oven) area.Between 4 of them I can do 200a@240v/120v worth of circuits. In you're case you could cover 100a@240v/120v with only 2 of them. They also make 120v ATSs - you don't have to do 240v/120v.By default, an ATS passes thru grid. When the solar power turns on, the ATS will automatically switch from grid to solar power. When the solar power runs out (low battery) the inverter shuts-off and the ATS reverts to grid automatically. The caveat is I have to use UPSs for sensitive (computers, Tivo, ...).One cool thing about default ATS I have to do is turn off the inverter and the house automatically defaults to grid. So I can work on the solar system and my wife isn't bothered and I don't have to do anything manual. Just turn off the solar system, work on it, and enable it when finished and the home circuits are powered one way or the other automatically.

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