Plug-In Solar Glossary

AC and DC

Alternating current and direct current

Direct current (DC) flows one way, as from a battery or a solar panel. Alternating current (AC) switches direction 60 times a second and comes from outlets.

Microinverter

A small inverter on or next to each solar panel that converts that panel's direct current (DC) into the alternating current (AC) your home uses.

Plug-in solar

Also called balcony solar or plug-in PV (PIPV)

A small solar system, one to a few panels and a microinverter, that connects to your home through a plug instead of being wired in by an installer.

Portable power station

Also sold as a solar generator

A movable lithium-ion battery with a built-in inverter and AC, USB and DC outlets, charged from the wall, a car or solar panels.

Backfeed

And anti-islanding

Power flowing backwards from a home device into a circuit or the grid. Anti-islanding is what makes an inverter stop exporting when the grid goes down.

GFCI

Ground-fault circuit interrupter

A fast safety device in an outlet, breaker or cord that cuts power when current leaks to ground, for example through a person.

NRTL

Nationally Recognized Testing Laboratory

A private lab that OSHA recognizes as qualified to test products and certify they meet safety standards. UL, CSA Group and Intertek are examples.

UL 2743

Standard for Portable Power Packs

UL's safety standard for portable and movable battery power packs, the category portable power stations fall into, up to 20 kWh of lithium-ion.

UL 3700

Outline of Investigation for Interactive Plug-In PV (PIPV) Equipment and Systems

The first US safety program written for plug-in solar: it sets construction, performance and labeling requirements for plug-in systems and their parts.

Interconnection

And the interconnection agreement

The utility's rules and approval process for connecting a generator, like rooftop solar, to the grid; the interconnection agreement is the contract.

NEC

National Electrical Code, NFPA 70

The US model code for safe electrical wiring, published by the NFPA and updated every three years; states and cities adopt it, often with changes.

Net metering

A deal between solar owners and their utility that pays or credits them for power they send to the grid. Most plug-in solar laws leave it out.

Self-consumption

Using the solar power you generate in your own home, as it's made or from a battery, instead of sending it to the grid. Plug-in solar is built for it.

ENERGY STAR

The US government's voluntary energy-efficiency label. Products that carry it are third-party certified to efficiency specs the government sets.

Payback period

Also called simple payback

How many years it takes for what a solar system saves you to add up to what it cost. Simple payback ignores interest and future price changes.

Standby power

The electricity many electronics and chargers keep drawing while switched off or not in use. The DOE says it could add 5–10% to a monthly bill.

Surge watts

Also called starting or peak watts

The brief burst of power a motor or compressor (a fridge, an AC, a pump) draws when it starts, well above what it uses while running.

Tilt and azimuth

Panel angle and compass direction

Tilt is a panel's angle up from flat (0° flat, 90° upright). Azimuth is the compass direction it faces, measured clockwise from north: 180° is due south.

Watts and watt-hours

W, Wh and kWh

Watts (W) measure power, how fast electricity is used at a moment. Watt-hours (Wh) measure energy, power used over time; 1,000 Wh is a kilowatt-hour (kWh).