LiFePO4
Lithium iron phosphate. A lithium-ion chemistry with the highest cycle life (3000–6000 cycles) and the safest thermal profile, making it the standard for off-grid storage.
↑ Back to topOff-grid solar glossary
Plain-language definitions for every acronym, spec and concept you'll meet sizing a LiFePO4 off-grid system. Bookmark this page or deep-link to a specific term.
34 terms
Battery
BMS (Battery Management System)
Electronics inside a lithium battery that protect it from over-charge, over-discharge, over-current, short circuit and (on better units) extreme temperatures. The BMS amp rating dictates the battery's peak inverter load.
↑ Back to topDoD (Depth of Discharge)
How much of a battery's rated capacity you actually use per cycle. LiFePO4 supports 80–100% DoD without lifespan loss, unlike lead-acid which is limited to ~50%.
↑ Back to topCycle life
How many full charge–discharge cycles a battery delivers before its usable capacity drops below 80%. LiFePO4 typically guarantees 3000–6000 cycles; lead-acid 200–500.
↑ Back to topSoC (State of Charge)
The percentage of remaining capacity in a battery, like a fuel gauge. Accurate SoC for LiFePO4 requires coulomb counting because the voltage curve is too flat to read directly.
↑ Back to topAmp-hour (Ah)
A measure of battery capacity: 100Ah at 12V means the battery can deliver 100A for one hour, or 1A for 100 hours. Multiply Ah × V to get watt-hours (Wh).
↑ Back to topWatt-hour (Wh)
Energy unit for sizing systems independently of voltage. A 12V 100Ah and a 24V 50Ah battery both store 1200 Wh. Daily consumption and battery sizing should always use Wh.
↑ Back to topSelf-heating battery
A LiFePO4 battery with a built-in heating film that warms the cells before charging when ambient temperature is below 0°C — preventing the lithium plating that destroys cold-charged cells.
↑ Back to topLow-temperature cut-off
A BMS feature that blocks charging below 0°C (lithium plating risk) and discharging below ~−20°C. Essential for camper, marine and any installation that sees winter.
↑ Back to topSolar
Wp (Watt-peak)
A solar panel's rated output under standard test conditions (1000 W/m², 25°C, AM1.5). Real-world output is typically 70–85% of Wp due to temperature, angle and irradiance losses.
↑ Back to topMPPT (Maximum Power Point Tracker)
A solar charge controller that continuously adjusts panel load to extract the maximum available power, typically 20–30% more than a cheaper PWM controller. Required for high-voltage panel arrays.
↑ Back to topVoc (Open-circuit voltage)
The voltage a solar panel produces with no load connected. Voc rises in cold weather — never exceed your MPPT controller's max input voltage at the coldest expected temperature.
↑ Back to topIsc (Short-circuit current)
Maximum current a panel produces under direct short. Used to size string fuses (typically 1.56 × Isc) and choose MPPT input current rating.
↑ Back to topPeak sun hours
Hours per day equivalent to 1000 W/m² irradiance. A location with 4 peak sun hours produces ~4 × Wp watt-hours per kilowatt-peak per day. Drives all solar yield estimates.
↑ Back to topSeries vs parallel (panels)
Series wiring adds voltage (Voc); parallel adds current (Isc). High-voltage strings minimize cable thickness and let an MPPT operate efficiently. Most off-grid arrays use 2S–4S configurations.
↑ Back to topPVGIS / NASA POWER
Two free databases of historical solar irradiance: PVGIS (European Commission, satellite-derived) and NASA POWER (20-year averages, global coverage). Both feed real yield estimates into the calculator.
↑ Back to topInverter
Pure sine wave inverter
Inverter that produces an AC waveform indistinguishable from grid power. Required for sensitive electronics, motors, induction cookers, CPAP machines and most modern appliances.
↑ Back to topModified sine wave
Cheap stepped-square waveform. Works for resistive loads (incandescent bulbs, simple heaters) but damages sensitive electronics, hums in audio equipment and is unsafe for medical devices. Avoid.
↑ Back to topInverter-charger
Combined unit that inverts battery DC to AC (for loads) and rectifies AC back to DC (to charge from shore power or a generator). Essential for campers and any system with periodic grid hookup.
↑ Back to topSurge / peak rating
Maximum brief power an inverter delivers (typically 2× continuous rating for a few seconds) to start motor loads like fridges, pumps and power tools. Always size around continuous, not surge.
↑ Back to topNo-load draw
Power an inverter consumes just to be on, even with nothing plugged in. Typically 5–25 W. For systems left on 24/7 this becomes the dominant consumer — favour inverters with sleep mode.
↑ Back to topWiring & protection
Voltage drop
Loss of voltage along a cable due to resistance. Off-grid DC systems target less than 3% drop on critical runs (battery–inverter, solar–MPPT) — anything more wastes energy and can prevent inverter startup.
↑ Back to topAWG (American Wire Gauge)
A wire size standard where smaller numbers mean thicker wire. 4 AWG ≈ 21 mm², 1/0 AWG ≈ 53 mm². European catalogues use mm² directly; the calculator shows both.
↑ Back to topClass T / MRBF / ANL fuse
High-DC-rated fuses sized to protect cables, not loads. Class T has the highest interrupt rating (200 kA) and is required directly at the battery terminal of any lithium bank to safely break a short.
↑ Back to topBus bar
A heavy-duty copper bar that consolidates multiple battery, inverter and load connections into single positive and negative terminals. Cleaner than chaining ring terminals on a single battery post.
↑ Back to topShunt / battery monitor
A precision low-resistance resistor inserted in the battery negative line that measures every amp going in and out, allowing accurate SoC calculation by counting coulombs.
↑ Back to topSeries vs parallel (batteries)
Series wiring adds voltage (two 12V → 24V); parallel wiring adds capacity at the same voltage (two 12V 100Ah → 12V 200Ah). Most balanced LiFePO4 banks use parallel; high-voltage systems use series of identical cells.
↑ Back to topSystem sizing
Autonomy days
How many days the battery alone (no solar input) can sustain the load. Typical targets: 1–2 days for sunny climates with daily solar, 3–5 days for winter use or cloudy regions.
↑ Back to topOff-grid
A power system with no connection to the public utility grid. Generation (solar, wind, generator) and storage (battery bank) must cover 100% of demand year-round.
↑ Back to topHybrid system
A grid-connected system with battery backup. The inverter switches to battery (or generator) on grid failure, and can shave peak grid consumption ("self-consumption") during normal operation.
↑ Back to topSystem voltage
The DC voltage of the battery bank: 12V, 24V or 48V. Higher voltage = thinner cables and cheaper inverter at the same power, but requires multiple batteries in series. Rule of thumb: <500 Wh/day → 12V, 500–2000 → 24V, >2000 → 48V.
↑ Back to topDuty cycle
The fraction of time an appliance is actually drawing power. A 100W fridge with 30% duty cycle averages 30W. Always multiply rated wattage by duty cycle when sizing — most consumption errors come from skipping this.
↑ Back to topInrush current
The brief, very high current drawn by motors, compressors and large transformers when first switched on — often 5–10× the running current. The inverter must handle this transient or it will trip.
↑ Back to topParasitic load
Continuous low-level consumption from devices in standby (router, alarm, fridge controller, inverter idle). Often 10–30W round-the-clock — over a day this can equal a high-power appliance running for an hour.
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