The Charge Sheet

EV charging glossary

54 terms that come up when you plan, finance or run a charging site, in plain English. If a vendor uses a word that isn't here, ask them what it means. If they can't say it simply, that is also an answer.

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.
Back office (CSMS)
The charging software that runs sessions, pricing, monitoring and remote fixes. Also called a charging station management system.
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.