Plain-language definitions for the terms that come up most in plug-in solar — from UL 3700 to anti-islanding to Balkonkraftwerk. No jargon left unexplained.

Anti-Islanding

A mandatory safety feature in all grid-connected solar inverters. When the utility grid goes down, the inverter detects the outage and immediately disconnects the solar system from the grid — typically within 0.1 seconds. This prevents the solar system from “islanding” (continuing to generate power on an otherwise dead line), which would endanger utility workers repairing the line. Anti-islanding is required under both US standard UL 3700 and the German/EU standard VDE-AR-N 4105. It is not optional, and no UL-certified plug-in solar system can be purchased without it.

Balkonkraftwerk

German for “balcony power plant.” The common term in German-speaking countries for a small plug-in solar system mounted on an apartment balcony. Germany is the world leader in this technology: over 1.3 million systems were registered as of mid-2026, with roughly 375,000 new systems added in the past year alone. The German market is roughly five years ahead of the US in adoption, providing a model for what legislative normalization can achieve.

DC (Direct Current)

The type of electricity that solar panels produce. Electrons flow in one direction. This is the raw output of photovoltaic cells — but household appliances and the grid use AC (alternating current). A microinverter or inverter converts DC to AC.

AC (Alternating Current)

The type of electricity used by your home’s wiring and all standard appliances. The grid runs on AC. Plug-in solar systems convert DC solar output to AC before it enters your home’s circuit.

Interconnection Agreement

A formal contract between a property owner and their utility that governs how a solar system connects to the grid. Traditional rooftop solar requires an interconnection agreement — a process that can take weeks or months and sometimes costs fees. Plug-in solar legislation specifically exempts small systems from interconnection agreement requirements, treating them like any other household appliance.

IP65

An international weatherproofing rating under the IEC 60529 standard. IP65 means the device is dust-tight and protected against water jets from any direction. UL 3700 requires IP65 minimum weatherproofing for plug-in solar components. Most quality microinverters are rated IP67 (submersion-proof) or higher. Avoid any plug-in solar component without a documented IP rating.

kWh (Kilowatt-Hour)

The unit your electricity bill uses. One kWh is the energy produced by a 1,000-watt device running for one hour — or a 100-watt device running for 10 hours. A single 400W panel produces roughly 1.5–1.8 kWh per day in average US conditions. Multiply that by your electricity rate (in $/kWh) to get your daily savings.

Microinverter

A small inverter mounted on or built into the plug-in solar panel that converts DC output directly to AC. Unlike string inverters (used in large rooftop systems), microinverters work panel-by-panel, meaning partial shading on one panel doesn’t affect output from others. All plug-in solar systems use microinverters. Well-known microinverter brands in the plug-in solar market include APsystems, Hoymiles, and Deye. Microinverters include the anti-islanding circuit and typically have 10–25 year warranties.

MPPT (Maximum Power Point Tracking)

An algorithm in the inverter that continuously adjusts the electrical load to extract the maximum possible power from the solar panel given current conditions (temperature, light level, cloud cover). MPPT is standard in all modern plug-in solar microinverters. Without it, a system would operate less efficiently as conditions change throughout the day.

Net Metering

A billing arrangement where the utility credits you for excess electricity your solar system sends back to the grid. Important clarification: plug-in solar systems in the US do not typically qualify for net metering — they’re too small to have a bidirectional meter installed, and their legal framing as “appliances” specifically excludes them from grid credit programs. Your savings from plug-in solar come from offsetting consumption in real time, not from selling power back. Electricity you generate while you’re not home typically flows to the grid without credit.

Peak Sun Hours

The number of hours per day during which solar irradiance averages 1,000 watts per square meter — essentially, the daily equivalent of full midday sun. Used to estimate solar panel output: a 400W panel in a location with 4.5 peak sun hours produces roughly 4.5 × 0.4 = 1.8 kWh/day (before losses). The Southwest US averages 5–6.5 peak sun hours; the Northeast, 3.5–4.5; the Pacific Northwest, 2.5–4.

UL 3700

The US safety standard written specifically for plug-in (bipolar) photovoltaic systems, published by Underwriters Laboratories. It launched in early 2026 and requires: automatic anti-islanding shutdown, overload and short-circuit protection, IP65 weatherproofing or higher, reverse-arc prevention in the plug connector, and clear labeling of system capacity. As of mid-2026, no products have yet completed certification under UL 3700 — it’s a newer, narrower standard than UL 1741, the established certification for grid-connected inverters that current plug-in solar kits actually carry. UL 1741 covers the same core safety ground (anti-islanding, overload protection, automatic disconnect) and is what to look for when buying today; UL 3700 is the one to watch for as the market matures. Verify any certification claim on UL’s public database (database.ul.com).

VDE-AR-N 4105

The German/EU technical standard for small generating plants connected to low-voltage grids. The European equivalent of UL 3700. German plug-in solar systems (Balkonkraftwerke) must comply with this standard. A 2023 amendment simplified registration requirements, allowing systems up to 800W to register via an online portal rather than requiring utility approval. Many European-manufactured microinverters carry both VDE-AR-N 4105 and UL 3700 certification.

Watt vs. Watt-Hour (Wh) vs. Kilowatt-Hour (kWh)

The most common source of confusion in solar discussions. A watt is a unit of power — how fast energy flows (like miles per hour). A watt-hour is energy — power over time (like miles driven). A kilowatt-hour is 1,000 watt-hours. Panel ratings (e.g., “400W”) are peak power output. Actual energy produced depends on how many hours the panel operates near that peak — which is why “peak sun hours” matter.

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