In this guide
Short answer: the microinverter turns the panels' DC power into 120-volt AC your home can use, squeezes the most out of the panels, caps the output (which is what state wattage limits measure) and shuts off in outages. Choose one that's certified (UL 1741 at minimum, UL 3700 where required), rated for your state's cap and sized to your daytime use.
What it does
- Converts DC to AC, matched to the grid's voltage and frequency.
- Tracks the maximum power point (MPPT): it constantly adjusts how hard it draws from the panel as sun and temperature change.
- Limits AC output to its rating, for example 400 W or 800 W. State laws measure this AC number, not the panels' watts.
- Disconnects in outages (anti-islanding) and reconnects when the grid is stable. See power outages.
- Reports production to an app over Wi-Fi or Bluetooth on most models.
Reading the spec sheet
| Spec | What it means | What to look for |
|---|---|---|
| Max continuous AC output | What it can push into the outlet | Within your state cap; usually 400–800 W |
| Nominal AC voltage | Grid it's built for | 120 V (US). Not 230 V |
| Number of inputs (MPPTs) | Panels it can manage separately | 2 for an 800 W, two-panel kit |
| Max DC input per input | Panel size it accepts | Equal to or above your panel's watts |
| MPPT voltage range | Panel voltages it can use | Covers your panel's Vmp in heat and cold |
| Peak efficiency | Losses in conversion | About 95–97% |
| Certifications | Legal and safety basis | UL 1741 / IEEE 1547; UL 3700 for the plug-in system |
| Warranty | Expected life | 10–15 years or more |
Panels bigger than the inverter?
It's common to pair, say, two 450 W panels with an 800 W inverter. On bright days the inverter "clips" the peak, but on cloudy days, in winter and on vertical railings, where panels rarely reach their rating, the bigger panels add output. A ratio of up to about 1.2 to 1.3 panel watts per inverter watt is a reasonable rule, as long as each input's DC limits are respected. Your state cap applies to the AC side. See which kit size you need.
Certification is the deciding factor
Most state laws require certification by UL or an equivalent lab; Vermont requires UL 3700, and New Jersey requires it above 400 W. A grid-tied microinverter listed only to UL 1741 may be fine in Utah or Maryland but not in Vermont. Products announced for UL 3700 so far include the Hoymiles HiFlow Pro and the APsystems EZ1 plug-in version. Details in UL 3700 explained and the kit guide.
Don't buy a European balcony inverter (230 V) for a US home, and don't buy one without a listing you can check in the lab's directory.
Microinverter vs a battery unit
All-in-one units such as EcoFlow's STREAM Ultra put the inverter, a battery and the solar inputs in one box. They cost more but let you shift power to the evening. Compare in plug-in solar with a battery.
Frequently asked questions
What does a microinverter do in a plug-in solar kit?
It converts the panels' direct current (DC) into alternating current (AC) synchronized with your home's 120-volt supply, finds the panels' best operating point, limits output to its rated AC power and shuts off within moments if the grid goes down.
What size microinverter do I need?
Match the AC output to your state's cap and your daytime use: about 400 W for one panel, 800 W for two. The panels can be somewhat larger than the inverter rating; the inverter caps the output.
Can I use any microinverter for plug-in solar?
No. It must be certified for grid-tied use (UL 1741 at minimum) and, in states like Vermont and New Jersey, as part of a UL 3700 plug-in system. It must also have a 120-volt US plug output, not a European 230-volt one.
Single or dual-input microinverter?
A dual-input unit takes two panels and treats each separately, so shade on one doesn't drag down the other. It's the usual choice for an 800 W two-panel kit.
Update log
- Guide published.
Sources and official texts