Off-Grid Power Glossary

Last updated October 30, 2026

Plain-language definitions of the terms used across the calculators, with a link to the tool or chart that uses each one.

AGM battery: Absorbed glass mat, a sealed lead-acid battery. Usually only about half of its capacity is used. Related tool
Alternator: The generator driven by a vehicle’s engine that charges its battery and can charge a second battery. Related tool
Amp-hour (Ah): A measure of battery charge. Multiply by voltage to get watt-hours. Related tool
Ampacity: The most current a cable can carry safely under given conditions. Related tool
Ampere (A, amp): The unit of electric current. Watts = volts × amps.
Array: A group of solar panels wired together. Related tool
AWG: American wire gauge. A smaller number means a thicker wire. Related tool
Battery management system (BMS): The electronics in a lithium battery that protect it from overcharge, over-discharge, overcurrent and heat.
C-rate: Charge or discharge current relative to capacity. 1C on a 100 Ah battery is 100 amps. Related tool
Charge controller: Regulates solar charging so the battery is not overcharged. Types are MPPT and PWM. Related tool
Continuous rating: The power an inverter or generator can supply steadily, as opposed to its surge rating. Related tool
Cycle life: How many full charge and discharge cycles a battery lasts, at a stated depth of discharge. Related tool
DC-DC charger: Charges a house battery from a vehicle’s electrical system with controlled current and voltage. Related tool
Depth of discharge (DoD): The share of a battery’s capacity that is used. Lead-acid is usually limited to about 50%, lithium to 80 to 100%. Related tool
Duty cycle: The share of time a device actually draws power, such as a refrigerator compressor running a third of the day. Related tool
Energy (Wh, kWh): Power used over time. Watt-hours = watts × hours, and a kilowatt-hour is 1,000 watt-hours. Related tool
Flooded battery: A traditional lead-acid battery with liquid electrolyte that needs ventilation and topping up with water. Related tool
Fuse: A protective device that melts when current is too high. It should protect the cable and sit close to the battery. Related tool
Gel battery: A sealed lead-acid battery with gelled electrolyte. Related tool
Grid-tied: A solar system connected to the utility grid, usually without batteries. Related tool
Inverter: Converts battery DC power to AC power for household appliances. Related tool
Kilowatt-hour (kWh): The unit electricity is billed in: 1,000 watts used for one hour. Related tool
LiFePO4: Lithium iron phosphate, a safe, long-life lithium battery chemistry common in vans, RVs and homes. Related tool
Load: Anything that uses power, or the total power being used. Related tool
MPPT: Maximum power point tracking, a charge controller type that gets more power from panels than PWM. Related tool
Net metering: A utility arrangement that credits you for solar energy sent to the grid. Rules vary by utility and state. Related tool
Off-grid: A power system not connected to the utility grid. Related tool
Parallel: Connecting batteries or panels so the current adds and the voltage stays the same. Related tool
Peak sun hours: Hours per day of full-strength sunlight, equal to the daily kWh per square meter. Related tool
Peukert effect: Lead-acid batteries deliver less total energy when discharged quickly. Related tool
Phantom load: Power drawn by devices that are switched off or on standby. Related tool
Pure sine wave: Inverter output that matches grid power, needed by many electronics and motors. Related tool
PWM: Pulse width modulation, a simple, cheaper charge controller type. Related tool
Round-trip efficiency: The share of energy put into a battery that you get back out. Related tool
Series: Connecting batteries or panels so the voltage adds and the current stays the same. Related tool
Shore power: Electricity supplied at a campsite or dock through a pedestal. Related tool
State of charge (SoC): How full a battery is, as a percentage of its capacity. Related tool
Surge (peak) rating: The higher power an inverter or generator can supply for a moment to start motors. Related tool
Transfer switch: A device that safely connects a generator to a home’s wiring and disconnects the grid. Related tool
Voltage (V): The electrical pressure that pushes current through a circuit. Common DC system voltages are 12, 24 and 48. Related tool
Voltage drop: Voltage lost along a cable because of its resistance. Long, thin cables lose more. Related tool
Watt (W): The unit of power. One watt is one joule per second. Wattage chart
Watt-hour (Wh): The unit of energy used for batteries. Wh = Ah × volts. Related tool

Common questions

What is the difference between watts and watt-hours?

Watts measure power, how fast energy is used right now. Watt-hours measure energy, the amount used over time. A 100 W device running for 10 hours uses 1,000 watt-hours, or 1 kWh.

What is the difference between amps and amp-hours?

Amps measure current, a rate of flow. Amp-hours measure how much charge a battery holds. A 100 Ah battery can supply 10 amps for about 10 hours, ignoring losses.

What does MPPT mean?

Maximum power point tracking. An MPPT charge controller adjusts the panel’s voltage and current to get the most power, and it is usually worth it for larger arrays.

What is depth of discharge?

It is how much of a battery’s capacity you use before recharging. Using less extends a battery’s life, and lithium tolerates deeper discharges than lead-acid.

What is a peak sun hour?

One hour of sunlight at an intensity of 1,000 watts per square meter. It is a way to total a day’s sunlight, not the number of daylight hours.

What is a surge or starting rating?

The brief extra power a motor or compressor needs to start. Inverters and generators list a surge rating higher than their continuous rating to cover it.

Put the terms to work in the solar and battery calculator, the inverter size calculator and the battery runtime calculator. For numbers to start from, see the appliance wattage chart and the 12 V wire gauge chart.