Inverter, Battery & Solar Glossary: Terms Explained

The words on a spec sheet, in plain language. Each entry links to the guide that goes further.

Jump to: Electrical basics · Inverters and UPS · Batteries · Solar · Installation and safety

Alternating current (AC) reverses direction many times a second and is what comes from the mains socket, at 50 or 60 cycles per second. Direct current (DC) flows one way and is what batteries and solar panels supply. An inverter turns DC into AC; a charger turns AC into DC.

Volt (V)

The electrical "pressure" that pushes current. Household mains is about 230 V in most of the world and 120 V in North America. Home battery banks are usually 12, 24 or 48 V.

Amp (A)

The rate at which current flows. For the same power, lower voltage means higher current, which is why battery cables are much thicker than house wiring. See the battery cable size calculator.

Watt (W)

Real power: volts × amps. Appliances are rated in watts, and inverters should be compared in watts, not VA.

Watt-hour (Wh) and kilowatt-hour (kWh)

Energy: watts × hours. A 100 W fan for 3 hours uses 300 Wh. 1000 Wh is 1 kWh, the "unit" on an electricity bill. Battery and power station capacity is best compared in watt-hours.

Amp-hour (Ah)

Battery capacity as current × hours at the battery's voltage. It only means something alongside the voltage: 12 V × 150 Ah = 1800 Wh, while 48 V × 50 Ah = 2400 Wh. See how many appliances an inverter can support.

VA (volt-ampere) and kVA

Apparent power, which is always at least as large as real power in watts. Inverters are often sold by VA because it is the bigger number. A typical home inverter delivers about 0.8 W per VA, so 1000 VA ≈ 800 W.

Power factor

The ratio of real power (W) to apparent power (VA), between 0 and 1. Motors and some electronics have a power factor below 1, meaning they draw more current than their watts suggest.

Duty cycle

The share of time an appliance actually draws power. A fridge compressor might run 40% of the time, so its average draw is well below its rated watts.

Inverters and UPS

Inverter

A device that turns battery DC into mains-style AC. In everyday use "inverter" and "UPS" often mean the same home backup unit, which also contains a charger.

UPS (uninterruptible power supply)

A backup unit that switches loads to battery automatically when mains fails. Computer UPS units are small and short-running; home "UPS" inverters run fans and lights for hours from large batteries.

Hybrid inverter

An inverter that also contains a solar charge controller, and can run the house from solar, battery and grid together. See UPS vs generator vs solar.

Portable power station

A battery, inverter, mains charger and solar controller in one portable case. See power station vs home UPS.

Continuous rating

The power an inverter can supply indefinitely without overheating. Your running load should stay comfortably below it.

Surge (peak) rating

The higher power an inverter can supply for a moment, typically seconds or less. It must cover motors starting, which can draw several times their running watts.

Pure sine wave

AC output with the same smooth waveform as the mains. It runs fans, fridges, motors and electronics as designed.

Modified sine wave

A cheaper stepped approximation of AC. It makes fans buzz and run hot, and can upset some electronics. See modified sine wave and computers or TVs.

Switchover (transfer) time

How long a UPS takes to switch loads to battery when mains fails, usually in milliseconds. Home inverters are around 10–20 ms; online UPS units have no gap at all.

Standby (idle) consumption

The power an inverter uses just being switched on, with no load. Over a long night it can use a noticeable share of the battery. See why a battery drains overnight.

AVR (automatic voltage regulation)

A feature that corrects low or high mains voltage without switching to battery, saving battery for real outages.

Batteries

Lead-acid (flooded or tubular)

The traditional inverter battery. Cheap and robust but heavy, with about half its capacity usable, and it needs distilled water top-ups. See refilling battery water.

AGM and gel

Sealed lead-acid batteries that need no water. They cost more than flooded batteries and usually have a shorter cycle life in daily use.

LiFePO4 (lithium iron phosphate, LFP)

A lithium chemistry used in home batteries and most power stations. Long cycle life, 80–90% usable capacity, fast charging and good heat tolerance. See lithium vs lead-acid.

NMC (nickel manganese cobalt)

A lighter lithium chemistry with fewer cycles and less heat tolerance than LiFePO4. See LiFePO4 vs NMC.

BMS (battery management system)

The electronics inside a lithium battery that protect it from overcharge, over-discharge, overcurrent and extreme temperatures, and keep its cells balanced.

Depth of discharge (DoD)

How much of a battery's capacity is used before recharging. Lead-acid lives much longer at 50% DoD than at 80%; LiFePO4 handles 80–90% routinely.

State of charge (SoC)

How full a battery is, as a percentage. The opposite of depth of discharge.

Cycle life

How many full charge-discharge cycles a battery lasts before its capacity falls to a set level, usually 80%, at a stated depth of discharge.

C-rate

Charge or discharge current relative to capacity. For a 100 Ah battery, 1C is 100 A and 0.1C (C/10) is 10 A. Lead-acid prefers low rates; LiFePO4 tolerates higher ones.

Peukert effect

A lead-acid battery delivers less of its rated capacity when discharged quickly. A battery rated over 20 hours gives noticeably less when emptied in two. The backup time calculator allows for it.

Bulk, absorption and float

The three stages of charging lead-acid: full current up to about 80%, then a tapering current while voltage is held, then a low voltage that keeps it topped up. See how long charging takes.

Sulphation

Hard lead sulphate crystals that form on lead-acid plates when a battery is left partly charged, permanently reducing capacity. Common where outages leave no time to recharge fully. See load shedding backup.

Low-voltage cutoff

The battery voltage at which an inverter stops drawing power, to protect the battery. On a heavy load, voltage sags and the cutoff can arrive early.

Solar

Peak sun hours

The equivalent hours per day of full-strength sunshine (1000 W per square metre) a location receives on average. 1 kW of panels gives roughly 1 kWh per peak sun hour before losses.

MPPT (maximum power point tracking)

A charge controller that continually adjusts to draw the most power from the panels and can use panel voltages well above the battery's. More efficient than PWM, especially in the cold or with higher-voltage panels.

PWM controller

A simpler, cheaper charge controller that connects the panels to the battery in pulses. It wastes the difference when panel voltage is much higher than battery voltage.

Voc (open-circuit voltage)

A panel's voltage with nothing connected, the highest it produces. It rises in cold weather and must stay below the controller's maximum input voltage. See charging a power station from solar.

Series and parallel

Series wiring adds voltages at the same current; parallel adds currents at the same voltage. The same applies to batteries and to solar panels.

Performance ratio

The share of panel rating that reaches your sockets after heat, dust, wiring and inverter losses, typically 75–85%.

Tilt angle

The angle of a panel above flat ground. The best fixed angle depends mainly on latitude; see the solar tilt angle calculator.

Net metering

A tariff arrangement where exported solar energy is credited against energy you import, sometimes at a lower rate. It shortens solar payback; see the solar payback calculator.

Installation and safety

DC fuse or breaker

Protection on the battery's positive lead, rated for DC, that disconnects the battery if a cable shorts. Every battery-inverter connection needs one. See installation mistakes.

Voltage drop

Voltage lost along a cable because of its resistance. Too much makes fans run slow and inverters cut out early; it is fixed with thicker or shorter cable.

Transfer switch and interlock

Devices fitted by an electrician that let a generator or battery system power house circuits while keeping them disconnected from the grid.

Backfeeding

Sending power from a generator or battery into house wiring through a socket, with the house still connected to the grid. It can electrocute utility workers and start fires, and is illegal in many places.

Carbon monoxide (CO)

A poisonous, odourless gas from engines and anything burning fuel. Generators must run outdoors, well away from the house, and homes using fuel-burning equipment need CO alarms.

Thermal runaway

A self-sustaining chain reaction in which a failing lithium cell heats up and spreads the failure to its neighbours. LiFePO4 is much more resistant to it than other lithium chemistries.