How does plug-in solar work?

A plug-in solar kit is refreshingly simple compared with a rooftop installation. There are panels, one microinverter per panel or per pair, and a cable that ends in an ordinary plug. No string wiring, no combiner box, no DC disconnect on the wall.

The panels do the obvious thing: they produce direct current at a voltage that varies with temperature and irradiance. On their own that current is not usable by household appliances, which expect alternating current at a stable voltage.

The microinverter is the clever part. It tracks the panel's best operating point, converts direct current to alternating current, and locks its output to the grid's frequency and phase so the two can coexist on the same circuit. It also contains the logic that stops production when the grid disappears.

That is the whole system. Everything else on this page is a consequence of those three parts and the way they are connected.

Energy moves through five stages, and each one has a loss or a limit worth knowing about.

The parts usually arrive as a kit rather than separately: a 1,200 W six-panel example (check current price).

A grid-tied inverter must stop producing when the grid is absent. This is called anti-islanding, and it exists so that a lineworker repairing a downed conductor is not energized from a customer's roof or balcony. It applies to every compliant microinverter, including the plug-in ones.

So the honest description of a plug-in array is: it saves money during the day and produces nothing during an outage. Both statements come from the same design, and no configuration of a grid-tied inverter changes the second one.

Backup requires a battery and a different arrangement, which is why the question "will it keep the lights on" has a separate answer on this site. The guide to adding a battery covers the three architectures that can.

Everything the house does not use at that instant flows out through the meter. What happens next depends entirely on the utility's arrangement, not on the hardware.

With full net metering, exported energy is credited at the retail rate and offsets evening consumption one-for-one. With avoided-cost compensation, the same kWh is bought at a wholesale-like rate, often a third of retail. In some arrangements there is no credit at all, and the export is simply a gift.

That is why daytime self-consumption is the only return the hardware can guarantee. Whatever the credit regime, energy used on site while it is produced is worth the full retail rate, because it never becomes an export in the first place.

The practical consequence is that the same array is worth three different amounts in three different states, and no datasheet can tell you which one you live in. That is a policy question, and it belongs in your utility's interconnection documents rather than in a product listing.

Numbers make the self-use question concrete. A 600 W array at 4.5 sun hours and 80 % efficiency makes about 2,160 Wh on a clear day. A household that is out from nine to five uses perhaps a third of that while the sun is up, so roughly 1,400 Wh is exported and credited at whatever the utility pays for exports, which is often below the retail rate. Point the same array at a battery and that 1,400 Wh waits for the evening, at the cost of the battery. Neither arrangement wins everywhere; the gap between the two rates decides it, and that gap is printed on your bill rather than in a datasheet.

An 800 W array in a 4.5 sun-hour location at 80 % efficiency makes about 2,880 Wh a day. That is an average, not a flat output: production follows the sun, peaking near midday and falling to nothing at dusk.

The evening row is the whole reason storage exists. If the appliances that matter run after dark, a plug-in array without a battery can never serve them, no matter how large the array is. Moving a dishwasher or a washing machine into the middle of the day moves consumption into the rows that have surplus, which is the cheapest optimization available.

For the sizing side of the same question, the panel count calculator turns a daily energy need into a panel count, and the load calculator produces that daily figure in the first place.

Four limits are predictable and each one can be checked before buying.

The balcony row explains why vertical installations underperform their label. A panel rated 400 W produces that figure under test conditions that assume a perpendicular sun; mounted vertically, it sees the sun at an angle for most of the day and at a poor angle in summer. The number on the box is not wrong, it is simply measured under conditions a balcony does not provide.

The shade row is the reason installers talk about strings. A microinverter per panel limits the damage to that panel, while a string inverter lets one shaded panel pull down the whole string. It is the main technical argument for microinverters in small systems.

An off-grid system has a battery, a charge controller and an inverter that can run without the grid, and it is sized so that the worst week of the year still works. A plug-in system has none of those things, and it is sized so that an average day produces something useful.

The difference shows up in three places. An off-grid system can run at night; a plug-in one cannot. An off-grid system can run during an outage; a plug-in one cannot. An off-grid system is sized for the worst week; a plug-in one is sized for the average day, which is why it overproduces in summer and underproduces in winter.

What plug-in shares with off-grid is the physics: panels produce direct current, and something has to convert it. What it does not share is the storage, and the storage is what makes the difference between a bill reducer and a backup supply.

Two columns are worth keeping in mind before reading any product page, because the marketing tends to blur them.

If you want the same panels and the same conversion, plus storage, the packaged version is a station with a solar input. The chain is identical up to the outlet, and then the station holds the energy instead of exporting it. These are the units in our current US list that accept panels directly; the solar input rating is the number that limits the array. For the full comparison, see the portable power station ranking.

For the panel side of the choice, the plug-in panel comparison covers what is actually sold in the US and how the certification claims differ.

That the inverter stores energy. It converts, it does not store. Every watt is used or exported as it is produced.

That a bigger array helps at night. It cannot. Night-time load is a storage question, and storage is a separate purchase.

That the meter spinning backwards equals a credit. The physical direction and the commercial arrangement are different things, and only the second one shows up on a bill.

That plug-in means unregulated. It means small and unfixed, not exempt. Interconnection rules, lease terms and local requirements still apply, and a balcony is not a legal category.

Every figure here is recomputable: daily generation equals array watts times sun hours times efficiency, and self-consumption equals the overlap between production and load. If a value disagrees with a calculator on this site, the calculator is the source of truth, and the changelog records each change.

A kit mounted on a balcony is a different purchase from a rooftop array; the guide on balcony solar kits covers what is actually in the box.

For the comparison most readers actually need, the difference between a grid-tied kit and a battery-in-a-box is set out side by side in plug-in solar versus a power station.