Solar and battery glossary

Plain-language definitions of the terms used on this site’s datasheet pages and calculators.

Amp-hour (Ah)

A battery’s charge capacity. Multiply by the battery’s voltage to get energy: 100 Ah at 51.2 V is 5.12 kWh.

Battery energy (kWh)

How much energy a battery stores. A 5 kWh battery can in principle supply 5,000 W for one hour or 500 W for ten hours, before losses.

Cold-weather Voc

A solar panel’s open-circuit voltage rises as it gets colder. String sizing uses the higher, cold-weather figure so the string never exceeds the inverter’s limit.

Continuous output

The power an inverter can supply for as long as needed, as opposed to the higher surge figure it can supply for seconds or minutes.

Depth of discharge (DoD)

The share of a battery’s energy you actually use. Makers often quote cycle life at a stated DoD, such as 80%.

Hybrid inverter

An inverter that works with solar, a battery and the grid together, and can keep the house running when the grid goes down.

Idle consumption

The power an inverter uses just by being on, with nothing connected. It drains the battery around the clock, so it belongs in any runtime calculation.

Inverter

The device that turns the DC power from panels and batteries into the AC power household appliances use.

LFP (LiFePO4)

Lithium iron phosphate, the battery chemistry used in EG4’s batteries.

MPPT

Maximum power point tracking: the circuit that adjusts the load on a solar array so it delivers as much power as the conditions allow. Each MPPT accepts a limited voltage and current.

Nominal voltage

The standard label for a battery’s voltage. EG4 describes its 48 V-class batteries as 51.2 V nominal.

Off-grid inverter

An inverter designed to run a house without a grid connection, using solar and batteries (and often a generator).

Parallel units

Connecting several identical inverters or batteries together to add capacity. Each datasheet states how many it supports.

Split-phase

The North American arrangement that supplies both 120 V and 240 V from one service. Many EG4 inverters list 120/240 V split-phase output.

String

Solar panels wired in series. Their voltages add up, which is why string length is limited by the inverter’s maximum PV voltage.

Surge (peak power)

The short-term power an inverter can supply above its continuous rating, for example to start a motor. The datasheet states how long it can last.

Vmp

The voltage a panel delivers at its maximum power point. It must stay inside the inverter’s MPPT voltage window.

Voc

Open-circuit voltage: the highest voltage a panel produces, with nothing connected. It sets the hard limit on string length.

Watt (W) and watt-hour (Wh)

A watt measures power at a moment; a watt-hour measures energy over time. A 100 W bulb running for ten hours uses 1,000 Wh, or 1 kWh.

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