Emergency preparedness, backup power and off-grid gear come with a lot of technical vocabulary. Spec sheets and product pages use these words without explaining them, which makes comparing products harder than it needs to be.
This glossary defines 25 terms you are likely to meet on Predicament Measures and in manufacturer information. The Predicament Measures Editorial Team keeps the definitions short and neutral. If you spot an error, write to editorial@predicamentmeasures.com.
- Alternating current (AC)
- Alternating current is electricity that regularly reverses direction. It is the type supplied by wall outlets in homes in the United States. Most household appliances run on AC.
- Amp-hour (Ah)
- An amp-hour measures how much charge a battery can deliver over time. A battery rated at 100 Ah can, in theory, supply 100 amps for one hour. To estimate energy, multiply amp-hours by the battery’s voltage to get watt-hours.
- Automatic transfer switch
- An automatic transfer switch moves a home’s electrical load from the utility grid to a generator when the grid fails. It switches back when utility power returns. It also keeps generator power from flowing back onto utility lines.
- Backup power
- Backup power is any source of electricity used when the main supply fails. Common sources include generators, batteries and solar systems. The right choice depends on what needs to run and for how long.
- Battery management system (BMS)
- A battery management system is the electronics inside a battery pack that monitor its condition. It typically tracks voltage, current and temperature. It can shut the battery off to protect it from damage.
- Carbon monoxide (CO)
- Carbon monoxide is a colorless, odorless gas produced when fuel burns. Gasoline and propane generators release it in their exhaust. They should only be run outdoors and away from windows, doors and vents.
- Charge controller
- A charge controller regulates the power flowing from solar panels into a battery. It prevents overcharging and helps protect battery life. The two main kinds are PWM and MPPT controllers.
- Deep-cycle battery
- A deep-cycle battery is built to be discharged substantially and recharged many times. This differs from a car starting battery, which delivers short bursts of high current. Deep-cycle batteries are common in solar and off-grid systems.
- Depth of discharge (DoD)
- Depth of discharge is the percentage of a battery’s capacity that has been used. A battery that is half empty has a DoD of 50 percent. Manufacturers often recommend limits on DoD to extend battery life.
- Direct current (DC)
- Direct current is electricity that flows in one direction. Batteries and solar panels produce DC. Many electronics use DC internally, with an adapter converting wall power.
- Generator
- A generator converts mechanical energy, usually from a gasoline, propane or diesel engine, into electricity. Portable models can power selected devices during an outage. Standby models are installed permanently at a building.
- Go bag
- A go bag is a packed kit of essentials kept ready in case you need to leave quickly. Contents vary by household and region. It is sometimes called a bug-out bag.
- Grid-tied system
- A grid-tied system is a solar installation connected to the utility grid. It can send surplus power to the grid. Many grid-tied systems shut down during an outage unless they also include batteries and the right equipment.
- Inverter
- An inverter converts direct current from a battery or solar panel into alternating current. Its rating, in watts, limits how much it can power at once. Inverters are built into most portable power stations.
- Inverter generator
- An inverter generator produces electricity and then conditions it through an inverter. The output is usually cleaner and steadier than a conventional generator. Many models can also adjust engine speed to match the load.
- Kilowatt-hour (kWh)
- A kilowatt-hour equals 1,000 watt-hours. Utilities bill household electricity in kilowatt-hours. Large home batteries are also rated in kWh.
- Lithium iron phosphate (LiFePO4)
- Lithium iron phosphate is a lithium-ion battery chemistry. It is often used in power stations and home storage. Manufacturers commonly rate it for more charge cycles than other lithium chemistries.
- Maximum power point tracking (MPPT)
- Maximum power point tracking is a method used by some solar charge controllers. It adjusts the electrical load to draw the most power the panels can produce at a given moment. It is generally more efficient than the older PWM method.
- Off-grid
- Off-grid describes a home or setup that is not connected to the utility electrical grid. Power typically comes from solar panels, wind, batteries or generators. The term is also used for gear designed for remote use.
- Portable power station
- A portable power station is a battery with an inverter and several outlets in a single case. It can run small appliances and charge devices. It can often be recharged from a wall outlet, a car or solar panels.
- Pure sine wave
- Pure sine wave describes AC power that closely matches the smooth waveform of utility electricity. It suits sensitive electronics and some motors. Modified sine wave inverters produce a rougher waveform.
- Solar panel
- A solar panel converts sunlight into direct current electricity. Its rated output is measured in watts under standard test conditions. Real output depends on sunlight, angle and temperature.
- Surge watts
- Surge watts, also called starting watts, are the brief peak of power a device needs when it starts. Motors and compressors often need more power to start than to keep running. A generator or inverter must be able to handle this surge.
- Uninterruptible power supply (UPS)
- An uninterruptible power supply is a battery unit that switches on instantly when utility power fails. It is typically used to keep computers and network equipment running briefly. Most are designed for minutes of runtime, not hours.
- Watt-hour (Wh)
- A watt-hour is a unit of energy equal to one watt used for one hour. Battery capacity is often given in watt-hours. Dividing capacity by a device’s wattage gives a rough estimate of runtime.