EV charging glossary

• Power and energy
• The utility and the bill
• Hardware and standards
• Software, payments and networks
• Measuring a site
• Money
• Fleets and connectivity
• At home

Power and energy

kW and kWh

kW is power: how fast energy moves. kWh is energy: how much moved. Drivers buy kWh. Demand charges bill kW. Most bad pro formas confuse the two exactly once.

AC and DC

The grid delivers alternating current. Batteries store direct current. Something has to convert one to the other, and where that happens decides how fast a car charges. More in the charging guide.

Level 1

Charging from a standard 120 volt outlet, around 1.4 to 1.9 kW. Fine for a car that sits for days. Not a business.

Level 2

AC charging at 208 or 240 volts, usually 7 to 19 kW. The car's onboard charger does the converting, so the car, not the wall unit, sets the speed.

DC fast charging

The charger converts to DC itself and feeds the battery directly, typically at 50 to 400 kW. Expensive to buy, expensive to power, and the only way to add serious range in a coffee break.

Onboard charger

The converter inside the car used for AC charging. Commonly 7.7 to 11 kW. It is why two cars on the same Level 2 unit can charge at different speeds.

State of charge (SOC)

How full the battery is, as a percentage. Arrival SOC is one of the biggest drivers of session length and revenue.

Taper

The slowdown as a battery fills. Fast charging holds near peak power to roughly half full, then eases off, then drops hard above 80%. Why fleets stop at 80%.

Power sharing

Several dispensers splitting one power cabinet. "Four 150 kW stalls" can mean 600 kW split four ways when the site is busy. Ask before you sign.

The utility and the bill

Demand charge

A monthly charge per kW on your highest short burst of power, usually measured over 15 or 30 minutes. One busy afternoon can set the charge for the whole month. Why it kills quiet sites.

Billed demand

The kW your utility actually bills, which can differ from what you drew because of minimums and ratchets.

Ratchet

A tariff rule that sets your minimum billed demand as a share of your highest peak over the past year. One bad month can follow you for eleven more.

Time of use (TOU)

Energy prices that change by time of day and season. Cheap at night, expensive in the late afternoon, when a lot of charging happens.

EV rate

A tariff designed for charging, often with lower or phased-in demand charges. Always ask your utility whether one exists and whether you qualify.

Make-ready

Everything electrical and civil up to the charger itself: conduit, wire, panels, trenching, pads. Often more than the hardware. Estimate it.

Service upgrade

A bigger connection from the utility, often a new transformer. The utility decides whether you need one, what it costs, and when it happens.

kVA

Apparent power, the rating on transformers and services. For planning, close enough to kW, and the number your utility will ask about.

Interconnection

The utility approval needed before anything that can push power back to the grid, like a battery, is switched on. Budget months, not weeks.

Hardware and standards

EVSE

Electric vehicle supply equipment. The charger. The acronym exists mostly to make RFPs longer.

J1772

The standard Level 2 connector on most non-Tesla vehicles in North America.

CCS1

Combined Charging System. The long-time DC fast connector for non-Tesla vehicles in North America.

NACS and SAE J3400

The connector Tesla designed, standardized as SAE J3400 and becoming the default in North America. New sites usually offer it alongside CCS1.

CHAdeMO

An older DC fast standard, now mostly for legacy vehicles. Few new sites include it.

Power module

The building block inside a DC charger cabinet, commonly 15 to 75 kW each. More modules, more power, more heat, more things to fail.

Software, payments and networks

OCPP

Open Charge Point Protocol. How a charger talks to its back-office software. Insist on it, so you can change software vendors without changing hardware. What it is, and what it isn't.

Back office (CSMS)

The charging software that runs sessions, pricing, monitoring and remote fixes. Also called a charging station management system. How to choose one.

OCPI

Open Charge Point Interface. How networks share chargers and bill each other so drivers can roam.

ISO 15118

The standard for richer communication between the car and the charger. It is what makes Plug and Charge possible.

Plug and Charge

The car identifies itself and pays automatically when plugged in. No app, no card, when it works.

CPO

Charge point operator. The company that runs the chargers and usually owns the relationship with the driver.

eMSP

E-mobility service provider. An app or network that lets drivers start and pay for sessions on chargers it doesn't own.

Site host

Whoever owns or controls the property. Sometimes also the owner of the chargers, sometimes just the landlord.

Pre-authorization hold

A temporary hold a card terminal places before a session. Drivers see it as a charge, and complain accordingly.

Idle fee

A per-minute fee once charging ends and the car stays plugged in. The polite way to free up a stall.

Measuring a site

Session

One charge, from plug-in to unplug. This site counts a session when it delivered at least half a kWh.

Utilization

The share of time a port is in use, or sessions per port per day. This site uses both. A ceiling check, not a goal.

Sessions per port per day

The number that decides whether a public site pays. See what real sites do.

Uptime

The share of time a charger reports itself available. A charger can be "up" and still fail every driver who tries it.

Session success rate

The share of attempts that actually delivered energy. The reliability number drivers experience.

Dwell time

How long the car is parked. Match charger speed to dwell time and most design questions answer themselves.

AADT

Annual average daily traffic. Vehicles passing a point on an average day. State DOTs publish it, and the forecast can look it up.

Capture rate

The share of passing EVs that stop to charge. The least certain number in any forecast.

Money

Pro forma

A projection of what a site costs, earns and returns over time. Build one.

NPV and IRR

Net present value is what the project is worth today after paying back the capital at your required return. IRR is the return at which NPV is zero.

Payback

How many years of operating profit it takes to earn back the build cost. Simple, popular, and blind to everything after year one of profit.

Debt service coverage (DSCR)

Cash flow available for debt divided by debt payments. Lenders generally want 1.25x or better. Check yours.

SBA 7(a) and 504

The two main SBA loan programs. 7(a) is one loan from one bank. A 504 splits the borrowed amount between a bank and a certified development company.

Federal credits: 30C and 48E

Tax credits for charging equipment and for energy storage respectively. Eligibility and timing rules change, so read the incentives section before you count on either.

FEOC

Foreign entity of concern. Sourcing rules that can reduce or zero a federal credit if key components come from restricted suppliers. More in the batteries guide.

NEVI

The federal formula program funding highway fast charging through the states, generally covering up to 80% of project cost.

Fleets and connectivity

Charge window

The hours a fleet vehicle is available to charge. Everything in fleet planning starts here.

Porter

The person who moves vehicles on and off chargers at a depot. Often the real bottleneck.

RSRP, RSRQ and SINR

Cellular signal measures: strength, quality under load, and signal over noise. Grade a site with them.

Multi-carrier SIM

A SIM that can fail over between carriers. Cheap insurance for a charger that has to stay online.

At home

NEMA 14-50

The 240-volt, 50-amp outlet an electric range uses, and the one most plug-in home chargers want. It can carry 40 amps of charging, not 50, because a car is a continuous load. Buy the industrial-grade receptacle; the $12 one melts. Plug in or hardwire.

Hardwired charger

A wall box wired straight to its circuit, no plug. The only way to get 48 amps or more at home, and one less connection to loosen and heat up. Harder to take with you when you move.

Load calculation

The math that says whether your panel can take a charger. It adds up what the house could draw at once and compares it with the service. The NEC gives two ways: nameplate loads, or a year of your actual peak demand from the utility. Run it for your house.

Load management

A device that watches the house’s draw and slows the charger when the dryer and the oven are both on, so the service never overloads. Code lets you size the charger to the managed limit, which is often far cheaper than a service upgrade.

Scheduled charging

Telling the car or the charger to start at a set time, so it fills during off-peak hours. It costs nothing and is most of the savings on a time-of-use plan. Time of use, and the 4pm trap.

eGallon

What it costs to drive an EV as far as a gallon of gas would take a similar car. A fair way to compare the two at the pump sign. Compare for your car and your rate.

Surge (locked-rotor current)

The kick a motor needs for a split second to start. An air conditioner can pull five or six times its running power. A battery with plenty of kWh can still fail to start one if its surge rating is too low. Why it catches people out.

Transfer switch

Disconnects the house from the grid before backup power flows, so you aren’t feeding a line a utility crew is working on. Required for any home backup: battery, generator or car.

Bidirectional charging

Power flowing both ways between the car and what it’s plugged into. The umbrella over V2L, V2H and V2G. The car and the charger both have to support it.

V2L (vehicle to load)

Outlets on the car, or an adapter in the charge port, that you plug things into. Usually 1.5 to 3.6 kW, up to 9.6 kW on some trucks. No house wiring involved.

V2H (vehicle to home)

The car backs up the house through its panel, with hardware that disconnects from the grid first. From the house’s point of view, a very large battery. Few cars can do it today. Which cars, and the catch.

V2G (vehicle to grid)

The car sends power back to the utility, usually during grid emergencies and usually for a payment. In the US, still almost entirely pilot programs.