Glossary

Plug-in solar terms, in plain English.

Every word you’ll meet on product pages, safety labels, utility forms, and state bills — grouped by topic and explained without the jargon. Acronyms are spelled out the first time they appear.

Small solar panel sample and planning notebook on a desk

The basics

The handful of words that describe what plug-in solar is.

Plug-in solar: A small solar system you connect to your home with a plug instead of wiring it permanently into the roof. While the sun shines, it lowers the electricity you buy from the utility.
Balcony solar: The same thing as plug-in solar — a common nickname, because a balcony railing is a popular place to mount it. Patios, fences, walls, and yards work too.
Plug-and-play solar: Another name for plug-in solar, emphasizing that it's meant to be easy to set up. It does not mean you can plug it into just any outlet without checking the rules.
Solar panel (photovoltaic panel): The part that turns sunlight into electricity. 'Photovoltaic' (or PV) simply means 'turns light into electricity.' We mostly just call it a solar panel.
Inverter: The small box that converts the panels' electricity into the type your home's outlets use, and keeps it in step with your home's power.
Microinverter: A small inverter that handles just one or two panels, rather than one big inverter for the whole system.
Complete-system certification: Testing and approval of the whole plug-in kit as one finished product — not just its individual parts. This is what you want to see before buying.
Component certification: Testing of a single part, like an inverter or panel. It's a good sign, but on its own it does not mean the full system is certified for plugging into your home.

Electricity words

The units and terms that show up on spec sheets and your bill.

Watt (W): A measure of how much power something uses or makes right now. A 400 W panel can make up to about 400 watts in strong sun — not all day.
Kilowatt (kW): 1,000 watts. Solar system sizes are often written in kilowatts.
Kilowatt-hour (kWh): The unit of electricity on your bill — power used over time. Running a 1,000-watt appliance for one hour uses one kWh.
Direct current (DC): Electricity that flows steadily in one direction, like from a battery. It's what solar panels produce before the inverter converts it.
Alternating current (AC): Electricity that rapidly switches direction, which is what your home's outlets and appliances use. The inverter converts the panels' DC into AC.
Nameplate rating: The rated output printed on a device, like '400 W' on a panel. Real-world output is usually lower, because conditions rarely match the ideal test all day.

How the power moves

What happens once your panels start feeding electricity into your home.

Backfeed: Electricity flowing backward — from your plug-in system into your home's wiring — instead of the usual direction, out to your devices. It's the defining feature of plug-in solar.
Bidirectional current: Electricity that can flow in either direction through a plug, outlet, or safety device. Plug-in solar needs parts rated for this.
Branch circuit: The wiring that runs from a breaker to a group of outlets. Plug-in solar is unusual because it sends power into this circuit rather than only drawing from it.
Load: Anything using electricity — a fridge, a router, a light, an air conditioner.
Self-consumption: Using your solar electricity in your own home the moment it's produced. For plug-in solar, this is where most of your savings come from.
Export: Solar electricity that your home doesn't use right away and that flows out toward the grid. It's often worth little or nothing unless your utility pays for it.
Zero-export: A system feature that prevents any electricity from flowing out to the grid, keeping all production inside your home.
Curtailment: When a system deliberately holds back solar output — for example because your home can't use it, a battery is full, or export isn't allowed.

Safety and protection

The features and devices that keep a plug-in system safe.

Anti-islanding: A required safety behavior: the system stops sending out power the instant the grid goes down, so it can't shock utility workers on lines they believe are dead.
Islanding: The dangerous situation anti-islanding prevents — where a local power source keeps part of the grid energized after the utility's supply is gone.
Ground-fault circuit interrupter (GFCI): A protective device (common in kitchens and bathrooms) that quickly cuts power if it senses electricity leaking where it shouldn't, reducing shock risk.
Circuit breaker: A safety switch in your electrical panel that shuts off a circuit when it carries more current than it's rated for.
Overcurrent protection: Breakers and fuses that protect your wiring from carrying more electricity than it can safely handle.
Touch-safe: Designed so you can't accidentally touch live electrical parts during normal use.
Backup mode (outage mode): A special, separately certified feature on some products that can power a few devices during an outage without feeding the grid. Ordinary kits don't have it.

Standards and certification

The rulebooks and testing marks worth recognizing.

UL 3700: The U.S. safety standard written specifically for plug-in solar systems. A kit certified to it has been tested as a whole product for the risks of plugging solar into a home.
UL 1741: A safety standard for inverters and related equipment. Useful, but it covers a component — it is not a substitute for certifying the complete plug-in system.
IEEE 1547: A technical standard for how small power sources connect to the grid safely, including how they behave when the grid misbehaves.
National Electrical Code (NEC): The main U.S. electrical safety rulebook that electricians and inspectors follow. Local governments adopt and sometimes tweak it.
Nationally Recognized Testing Laboratory (NRTL): An independent lab — like UL, Intertek, or CSA — that the federal workplace-safety agency (OSHA) authorizes to certify that products meet safety standards.
Listed / certified equipment: Equipment an independent lab has tested and approved for a specific use. 'Listed for plug-in solar use' is stronger than a vague 'meets UL standards.'
Authority having jurisdiction (AHJ): The local official — often a building or electrical inspector — who interprets and enforces the codes where you live.

Setting it up

Terms about mounting the panels and giving them good sun.

Azimuth: The compass direction your panels face. In common solar tools, due south is 180 degrees. South-facing panels usually produce the most in the U.S.
Tilt: The angle of a panel from flat. A panel hung vertically on a railing is about 90 degrees; a tilted patio rack might be 25 to 35 degrees.
Shading: Loss of sunlight from trees, buildings, railings, or a balcony above. Even partial shade can cut output more than you'd expect.
Soiling: Dirt, dust, pollen, salt, or bird droppings on the glass that block sunlight and reduce output until cleaned.
Weatherproof / IP rating: How well equipment resists dust and water. An 'IP' rating with two digits describes that protection — but always within the limits the maker states.
Railing load capacity: How much weight and force your railing can safely hold. A certified panel doesn't prove your particular railing is strong enough — that's a separate check.
Wind load: The force wind puts on your panels and mount. Balcony and rail mounts especially need to resist being pushed or lifted by gusts.

Savings and the calculator

The words behind any savings or payback estimate.

Performance ratio: A single 'real-world discount' that accounts for everyday losses — heat, the inverter, wiring, dust, and imperfect angles — versus a panel's ideal rating.
Equivalent sun hours: A simple way to express a day's sunlight as hours of full-strength sun. Four sun hours is a common national planning figure.
Self-consumed or credited energy: The share of your solar output that actually lowers your bill — either used in your home or paid for by your utility. Exported energy with no credit doesn't count.
Retail rate: The price you pay per kilowatt-hour for electricity from the grid. A higher rate means each unit of solar you use saves you more.
Export credit: What your utility pays, if anything, for surplus electricity you send back. Many plug-in solar rules offer little or none.
Simple payback: How long your savings take to add up to what you paid: cost divided by yearly savings. It ignores rising prices, slow panel wear, and replacements.
Degradation: The slow decline in a panel's output as it ages — typically well under 1% a year.

Rules and policy

The legal terms you'll meet in state trackers and bills.

Interconnection: The utility's process for connecting a power source to the grid. Plug-in solar laws often replace it with a simple notice — or waive it entirely for small kits.
Enacted law: A bill that has completed every step to become law. It may still have a future start date.
Effective date: The date a law actually starts to apply. A law can be signed months before it takes effect.
Introduced bill: A proposed law that's been filed but not yet passed. It might pass, change, or fail — so it isn't permission to install.
Net metering: A billing setup that credits you for exported solar, often near the retail price. Many plug-in solar programs do not include full net metering.
Tariff: Your utility's official price list and service rules. It sets your rate and any fixed monthly charges.
Homeowners association (HOA): A neighborhood or building association whose rules can limit exterior attachments — sometimes affecting where or whether you can mount panels.
Right-to-solar law: A law that limits how much a landlord, HOA, or local rule can restrict solar. The specifics vary a lot by state.