Reference

Off-Grid & Solar Glossary: 80+ Terms in Plain English

A no-jargon dictionary for anyone new to off-grid power, solar, water, and heat. Every term below is explained the way you would explain it to a friend, with no spec-sheet riddles. For the big concepts, each definition points you to a full guide that goes deeper.

Sam Whitaker

By Sam Whitaker · June 2026 · 12 min · How we test

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Power basics

Off-grid: Making and storing your own electricity so you can live without a connection to the utility grid. In practice that means solar panels, a battery, and the gear that ties them together. Full guide.
Watt (W): A measure of how much power something uses or produces right now. A 60W fan draws 60 watts the whole time it runs. Watts are the rate; watt-hours are the total over time.
Watt-hour (Wh): The amount of energy used over time, which is watts multiplied by hours. A 60W fan run for 10 hours uses 600Wh. Battery and power-station capacity is usually given in Wh, so this is the number that decides how long you can run things. See our appliance power chart.
Kilowatt-hour (kWh): Just 1,000 watt-hours. A 1,000Wh battery is the same as 1kWh. It is the unit your home power bill uses, so a 5kWh off-grid bank stores about as much as a small home uses in part of a day.
Amp (A): A measure of how much current is flowing. Wire and fuse sizes are chosen around amps, because too many amps through thin wire makes heat. Watts divided by volts gives you amps.
Amp-hour (Ah): Battery capacity at a given voltage. A 100Ah battery at 12V holds about 1,200Wh. To compare batteries fairly, convert amp-hours to watt-hours by multiplying by the voltage. See the LiFePO4 voltage chart.
Volt (V): The electrical pressure that pushes current through a circuit. Off-grid systems are usually built at 12V, 24V, or 48V. Higher system voltage means lower current for the same power, which means thinner, cheaper wire. Full guide.
AC (alternating current): The kind of power that comes out of a household wall outlet, where the current rapidly reverses direction. Most plug-in appliances expect AC. Off-grid, an inverter makes AC from your battery's DC.
DC (direct current): Power that flows in one steady direction, which is what solar panels and batteries put out. Lights, fans, USB devices, and 12V fridges can run straight off DC, which avoids the small loss an inverter adds.
Load: Anything that draws power: a light, a fridge, a laptop, a pump. Adding up your daily loads in watt-hours is the first real step in sizing a system. Our run-time calculator works backward from a load.
Continuous vs surge (starting) watts: Continuous watts are what a device draws while running. Surge or starting watts are the brief spike some motors and compressors pull at startup, often several times higher. Your inverter and generator have to handle both numbers, not just the running figure.
Phantom (parasitic) load: The small, constant draw from gear that is plugged in but idle, like a TV on standby or a charger left in the socket. Off-grid these tiny drains add up overnight, so a switch or fuse block that fully cuts power saves real battery.
Duty cycle: The share of time a device actually runs versus sits idle. A fridge compressor might only run a third of the hour, so its real daily energy use is far below its nameplate watts multiplied by 24. Always size around the duty cycle, not the peak.
Peak sun hours: A way to describe how much usable sun a location gets in a day, expressed as the number of hours of full-strength sun. A spot with 5 peak sun hours lets a 100W panel make roughly 500Wh on a good day. See peak sun hours by state.
Inverter idle draw: The power an inverter burns just being switched on, before you plug anything in. It can quietly drain a battery overnight, so size the inverter to your real loads and switch it off when nothing needs AC.

Solar

Photovoltaic (PV): The technology that turns sunlight directly into DC electricity. A solar panel is a PV panel. The word just means light-to-voltage, so you will see it on spec sheets and in product names.
Monocrystalline: A solar cell cut from a single silicon crystal, which gives the best efficiency and the smallest panel for the watts. Most quality off-grid panels today are monocrystalline. Full guide.
Polycrystalline: An older, cheaper solar cell made from many silicon fragments. It is slightly less efficient than monocrystalline, so panels are a bit bigger for the same watts. Less common now that mono prices have fallen.
Rigid vs flexible panel: Rigid panels have a glass face and aluminum frame and last longest, ideal for roofs and ground racks. Flexible panels are thin and light and can curve to a van roof, but they run hotter and usually do not last as long.
Portable (folding) panel: A panel that folds like a suitcase so you can set it in the sun and pack it away. It pairs naturally with a power station and is the easiest way to add solar without mounting anything. See solar panels.
Bifacial: A panel that also captures light reflected onto its back side, adding a few percent of output when mounted over a bright surface like snow or light gravel. The gain is real but modest and depends heavily on the mounting.
Vmp / Voc: Two voltage ratings on a panel. Vmp is the voltage at its best working point, the figure your charge controller actually sees. Voc is the higher open-circuit voltage with nothing connected, and it is the number you must stay under when wiring panels in series.
Imp / Isc: Two current ratings on a panel. Imp is the current at the panel's best working point. Isc is the slightly higher short-circuit current, used to size fuses and confirm your charge controller can handle the array.
MC4 connector: The standard weatherproof plug on almost every modern solar panel. Matching MC4 connectors snap together to wire panels in series or parallel, and MC4 branch connectors let you combine panels into one run to the controller.
Array: Two or more solar panels wired together as one unit. How you connect them, in series or parallel, sets the array's combined voltage and current, which has to match what your charge controller can accept.
Series vs parallel (panels): Wiring panels in series adds their voltages and keeps current the same, good for MPPT controllers and long wire runs. Wiring in parallel adds their currents and keeps voltage the same. Series strings can underperform badly in partial shade. Full guide.
Tilt angle: The angle a panel is set at relative to flat ground. Tilting a panel toward the sun, roughly to your latitude, noticeably boosts winter output compared with lying flat. Flat-mounted van and RV panels trade some output for simplicity.
Derating (loss factor): The gap between a panel's lab rating and what it makes in the real world, after heat, dust, wiring loss, and controller losses. A common rule is to expect about 75 to 80 percent of the nameplate watts, so always size with a buffer.
Shading: Shadow falling on even part of a panel, which can drop its output far more than the shaded area suggests, especially in a series string. Keep panels clear of vents, branches, and antennas, and plan layout around the worst time of day.

Batteries

LiFePO4 (LFP): Lithium iron phosphate, the battery chemistry most off-grid builds use now. It lasts thousands of cycles, is very safe against fire, weighs about half what lead-acid does, and lets you use nearly all its capacity. Full guide.
Lithium-ion: The broader family that includes the cells in phones and laptops. Off-grid usually means the LiFePO4 type specifically, which is far more resistant to overheating than the high-energy lithium-ion used in consumer electronics.
Lead-acid (flooded / AGM / gel): The old standby battery chemistry. Flooded types need watering and venting, while AGM and gel are sealed and maintenance-free. All are cheap up front but heavy, short-lived, and you can only safely use about half their capacity. LiFePO4 vs lead-acid.
Depth of discharge (DoD): How far down you drain a battery, as a percent. Pulling a battery to 20 percent left means an 80 percent DoD. LiFePO4 happily handles deep discharges, while lead-acid lasts far longer if you rarely go past half.
State of charge (SoC): How full a battery is right now, as a percent, like a fuel gauge. With LiFePO4 the voltage barely changes across the middle of the range, so a shunt-based monitor reads SoC far more accurately than voltage alone. See the voltage chart.
Cycle life: How many charge-and-discharge cycles a battery is rated for before it fades to a set fraction of its original capacity. LiFePO4 is commonly rated for several thousand cycles, which is the main reason its higher up-front cost pays off.
C-rate: How fast a battery is charged or discharged relative to its capacity. A 100Ah battery at 0.5C is charging or discharging at 50A. Staying within the maker's C-rate limits protects the cells and the built-in BMS.
BMS (battery management system): The electronics inside a modern lithium battery that protect it from overcharge, over-discharge, short circuits, and charging while frozen. A good BMS is what makes a LiFePO4 battery safe and forgiving, so it is not a feature to skip.
Self-heating battery: A LiFePO4 battery with a built-in warming pad that lets it charge safely below freezing, where a standard lithium battery must refuse the charge. Worth the extra cost for cold-climate vans and unheated cabins.
Server-rack battery: A tall 48V LiFePO4 module that slots into a rack, common in cabin and whole-home systems. It gives you a lot of storage for the money and connects with a single set of cables, which beats wiring up many 12V batteries.
Bank (battery bank): Two or more batteries wired together to act as one larger battery. Wiring in parallel adds capacity at the same voltage; wiring in series raises the voltage. Use matching batteries, ideally from the same batch, in a bank.
Capacity fade: The slow loss of usable capacity as a battery ages and cycles. It is normal and gradual. Cycle-life ratings are usually quoted to the point where a battery has faded to 80 percent of its original capacity, not to total failure.

Inverters & charging

Pure sine vs modified sine: Two inverter output qualities. Pure sine wave matches the smooth power of the grid and runs everything cleanly. Modified sine is cheaper but its choppy output can buzz, overheat motors, or upset sensitive electronics. Buy pure sine for an off-grid home. Full guide.
Inverter/charger: A single unit that both inverts battery DC into household AC and charges the battery when shore power or a generator is connected. It is the heart of many cabin and van systems because it handles the switchover automatically.
Surge rating: The brief peak power an inverter can deliver above its continuous rating, to start motors and compressors. A pump or fridge can spike well above its running watts at startup, so the inverter surge number has to cover that jump.
MPPT (maximum power point tracking): The smart type of charge controller. It constantly finds the panel's best operating point and converts excess voltage into extra charging current, harvesting more usable power than the older PWM type, especially in cold or cloudy weather. Full guide.
PWM (pulse width modulation): The simpler, cheaper charge controller. It works by switching the panel connection on and off rapidly, but it wastes any panel voltage above the battery voltage, so it suits only small, matched 12V systems. MPPT vs PWM.
Charge controller: The part that sits between the solar panels and the battery and regulates the charge so the battery never gets overcharged. It comes in PWM and MPPT types, and it is not optional, since panels alone would damage a battery. Full guide.
DC-DC charger: A device that charges your battery from a vehicle alternator while you drive, stepping the voltage up or down so the battery charges correctly and the alternator is not overloaded. Many models also take solar input as a built-in MPPT controller.
Bulk / absorption / float: The three stages a charger moves through. Bulk pours in current fast while the battery is low, absorption holds a steady voltage to top it off, and float trickles just enough to hold it full without overcharging.
Shore power: An outside AC source you plug into, such as a campground pedestal or a home outlet, which runs your loads and charges the battery through the inverter/charger. The name comes from boats tying up to dockside power.

Wiring & safety

AWG (gauge): American Wire Gauge, the standard for wire thickness, where a smaller number means thicker wire. Off-grid battery and inverter cables must be thick enough for the current, so always size from a chart. See the DC wire gauge chart.
Voltage drop: The voltage lost as current pushes through wire, worse with thin wire and long runs. Too much drop wastes power and can keep a battery from fully charging, so keep runs short and wire sized generously. The wire size calculator handles the math.
Ampacity: The maximum current a given wire can safely carry without overheating. Every cable in a build must have an ampacity above the current it will see, and its fuse must protect it, which is the core rule of safe DC wiring.
Bus bar: A solid metal bar with several studs that acts as a shared connection point for many wires, keeping a battery's main positive and negative tidy. It replaces a messy stack of ring terminals piled on a single battery post.
Shunt: A precise low-value resistor placed in the main negative cable so a battery monitor can measure exactly how much current flows in and out. It is what lets a monitor report a true state of charge rather than a rough voltage guess. See battery monitors.
Fuse vs breaker: Both protect wiring from too much current. A fuse is a one-time link that melts and must be replaced, while a breaker trips and can be reset by hand and doubles as a switch. Either one is required, never skipped, near the battery.
Ground / bonding: Connecting metal parts and the system's negative to a common reference so a fault trips protection instead of energizing a chassis. Vehicle and home systems have specific grounding rules, so follow the equipment manuals and local code.
Battery monitor: A gauge that tracks energy in and out through a shunt and shows a true state of charge, often over Bluetooth. It removes the guesswork of reading battery voltage, which is the single most useful add-on for living off a battery. Full guide.
Kill A Watt meter: A plug-in meter that measures exactly how many watts and watt-hours an appliance actually uses. Metering your real loads before you size a system beats guessing from labels, and it quickly finds phantom drains. See appliance power use.

Water

Potable: Water that is safe to drink. The whole job of an off-grid water setup is turning a raw source, like rain or a well, into potable water through filtering and, where needed, disinfection.
Gravity filter: A countertop filter with two stacked chambers, where water drips through filter elements under its own weight with no power or plumbing. It is the simplest way to make safe drinking water off-grid. Full guide.
Micron rating: The size of particle a filter blocks, measured in microns. A smaller number filters finer. Removing bacteria needs roughly a 0.2 micron filter, while sediment filters are much coarser. The rating tells you what the filter actually stops.
Absolute vs nominal micron: Two ways to state a micron rating. Absolute means the filter blocks essentially everything at that size, the figure to trust for safety. Nominal means it catches most particles at that size, which is fine for sediment but not for guaranteeing clean drinking water.
Hollow fiber: A filter made of many tiny straw-like tubes with walls full of microscopic pores that strain out bacteria and protozoa. It is common in lightweight personal and gravity filters, and it must never freeze, which cracks the fibers.
Carbon block: A filter of compressed activated carbon that absorbs chlorine, many chemicals, and bad tastes and odors. It is often paired with a finer element, since carbon improves taste and removes contaminants but is not by itself a reliable bacteria barrier.
First-flush diverter: A simple device on a rainwater system that throws away the first dirty surge off a roof, which carries the most dust, leaves, and droppings, before clean water flows into the tank. It noticeably improves stored rainwater quality.
Rainwater harvesting: Collecting roof runoff into barrels or tanks for later use. With a first-flush diverter and proper filtering it can supply drinking water; without treatment it still covers washing, flushing, and the garden.

Heat & cooling

BTU: British Thermal Unit, the standard measure of heating and cooling output. A bigger BTU number means more heat or more cooling. Heaters, air conditioners, and propane appliances are all rated in BTU, so it lets you compare them and size to your space.
Catalytic heater: A flameless propane heater that creates heat through a chemical reaction on a pad rather than an open flame. It is quiet and efficient, but like any combustion heater it uses oxygen and needs ventilation and a carbon monoxide alarm.
Diesel (air) heater: A small heater that burns a little diesel to warm air, drawing combustion air from outside and venting exhaust out, so only clean hot air enters the cabin. It sips fuel and almost no battery, which makes it a favorite for winter vans.
Carbon monoxide (CO): A colorless, odorless, deadly gas produced by any fuel-burning appliance. Every off-grid space with a propane, diesel, or wood heater needs a working CO alarm and proper ventilation. This is a safety item you never leave out.
Thermoelectric vs compressor cooler: Two kinds of 12V cooler. Thermoelectric coolers are cheap but only chill a bit below the outside temperature and draw power constantly. Compressor coolers are true fridges that reach freezer temperatures and, thanks to their duty cycle, often use less daily energy.
SEER: A rating of how efficiently an air conditioner cools over a season, where a higher number means more cooling per watt. It matters off-grid because a more efficient unit pulls less from your battery to deliver the same comfort.

Comms & misc

GMRS: The General Mobile Radio Service, a set of higher-power two-way radio channels for family and group use that needs only a simple paid license, with no test. It reaches much farther than basic walkie-talkies, which makes it popular for property and convoy use. See comms gear.
Ham (amateur) radio: Licensed two-way radio with the widest range and capability, including talking across regions and even worldwide. It requires passing a test, but it is the most resilient way to communicate when cell and internet are down.
NOAA weather radio: A receiver that picks up the government's continuous weather broadcasts and emergency alerts. Many off-grid radios and lanterns include it, and it is a cheap, no-subscription way to get storm warnings without cell service.
Starlink: Satellite internet that works in remote places with no cable or cell coverage, using a small dish that points itself at the sky. It draws real power, so off-grid users plan its consumption into the battery budget. See comms gear.
Bug-out: Leaving home quickly for a safer place during an emergency. A bug-out bag holds the gear to get you through the first days, and bug-out power usually means a portable power station and a folding panel you can grab and go.
EDC: Everyday carry, the small kit of tools you keep on you all the time, such as a knife, flashlight, and lighter. The idea is that the most useful gear is whatever you actually have when something goes wrong.
Inreach / satellite messenger: A pocket device that sends text messages and an SOS over satellites where there is no cell signal. It is the standard backcountry safety tool, letting you check in or call for help far from any tower.

How to use this glossary

You do not need to memorize any of this. Skim it once so the words stop looking scary, then come back when a product page or spec sheet throws a term at you. The two ideas worth getting straight early are the watt versus watt-hour difference and how the five system parts connect, since almost everything else builds on those.

When you are ready to put the words to work, start with how off-grid solar works, then size your setup with the sizing guide and the solar calculator. The appliance power chart and the peak sun hours table fill in the real numbers.

Frequently Asked Questions

What does Wh mean?

Wh stands for watt-hours, the amount of energy used or stored over time. It is watts multiplied by hours, so a 60W fan run for 10 hours uses 600Wh. Battery and power-station capacity is given in watt-hours, which is why it is the number that decides how long you can run your gear.

What is the difference between watts and watt-hours?

Watts measure power right now, the rate at which something uses energy. Watt-hours measure the total energy over time. A 100W load running for 5 hours uses 500Wh. Think of watts as speed and watt-hours as distance traveled.

What does DoD mean for a battery?

DoD is depth of discharge, how far down you drain a battery as a percent. Draining to 20 percent left is an 80 percent DoD. LiFePO4 batteries handle deep discharges well, while lead-acid lasts far longer if you rarely go past about half.

What does MPPT stand for?

MPPT means maximum power point tracking, the smart type of solar charge controller. It finds the panel's best operating point and converts extra voltage into more charging current, so it harvests noticeably more power than the older PWM type, especially in cold or cloudy weather.

What does it mean to be off-grid?

Off-grid means making and storing your own electricity instead of buying it from the utility. A typical setup is solar panels that charge a battery, a charge controller to protect the battery, and an inverter to make household AC power.