Reference desk

The labels matter.
Here is what they mean.

Plain-language definitions for planning portable power and checking solar compatibility. These definitions explain the math; the exact product manual still sets the limits.

Power and energy

Watts (W): The rate of power at one moment. A 100W device uses energy twice as quickly as a 50W device.
Watt-hours (Wh): An amount of energy. A theoretical 1,000Wh battery could supply 100W for 10 hours before losses and reserve.
Capacity: The battery’s stored energy, normally shown in Wh. Capacity affects runtime; it does not prove that a high-power appliance can start.
Continuous output: The power an inverter or outlet is designed to supply continuously under its documented conditions.
Surge / starting watts: Short-duration output intended for a motor or compressor start. Its duration and test method differ between manufacturers.
Usable energy: Energy that reaches the device after battery reserve, conversion, standby draw and operating conditions are accounted for.
System efficiency: The share of battery energy that reaches the load after conversion and wiring losses. It varies by output path and operating conditions.
Idle overhead: Power used by the station and active output electronics before the connected device load is counted. It matters most for small loads.
Duty cycle: The percentage of time a cycling device such as a fridge compressor is actually running. It converts running watts into a daily average.
Peak sun hours: A way to express a day’s solar irradiation as equivalent hours at 1,000W per square metre—not the same as hours of daylight.

Electricity and conversion

AC: Alternating current, used by household outlets. A portable power station creates AC through its inverter.
DC: Direct current, used by batteries, solar panels, USB and many 12V devices. A direct DC path can avoid an inverter conversion step.
Inverter: Electronics that convert battery DC into outlet-style AC. It has an output limit and consumes some power itself.
LFP / LiFePO₄: Lithium iron phosphate, a lithium-ion battery chemistry commonly used in current portable power stations.
UPS vs EPS: Both can switch to battery during an outage, but names, transfer times and suitability for sensitive or medical equipment vary. Verify the exact manual and test the load.

Solar terms

Vmp: Voltage at maximum power under the panel’s rated test conditions. This is the array’s normal working-voltage reference.
Voc: Open-circuit voltage when no load is connected. Voc rises as panels get colder and must remain below the controller’s hard maximum.
Imp: Current at maximum power under rated test conditions. Parallel strings add their current.
Isc: Short-circuit current under rated test conditions. It is relevant to cable, fuse and protection design and is not interchangeable with Imp.
Voc temperature coefficient: The percentage change in Voc per degree Celsius. It is normally negative, meaning Voc increases below the 25°C rating condition.
Series wiring: Panels connected end-to-end. Voltages add; current stays approximately that of one matched panel.
Parallel wiring: Matched strings connected side-by-side. Current adds; voltage stays approximately that of one string.
MPPT: Maximum Power Point Tracking: the charge controller adjusts its operating point to harvest power from the panel within its allowed input envelope.
Input voltage window: The voltage range in which the station’s solar controller is documented to operate. Cold Voc must also stay below its absolute maximum.
Current limit: The maximum current an input will accept. Extra available panel current may be clipped on some systems, but must never be assumed safe without the manual.