What Is a Demand Charge — and Why Does EV Charging Make It Worse?
Most businesses don’t know demand charges exist until they install EV chargers. Then the utility bill arrives.
A demand charge is what your utility bills you for the highest single rate at which your facility drew power during any 15-minute window in a billing period — not for how much total energy you used. It appears as a dollar-per-kilowatt ($/kW) charge and can represent 30–70% of a commercial electric bill. EV chargers trigger demand spikes by drawing large amounts of power quickly, often doubling or tripling this charge.
How Demand Charges Work
Your electric bill has two fundamentally different components that most people never separate. The first is the energy charge — how much electricity you consumed in total, measured in kilowatt-hours (kWh). The second is the demand charge — the peak rate at which you consumed that electricity, measured in kilowatts (kW).
Here’s the crucial distinction: you could use a very small amount of total energy and still owe a large demand charge if that energy was consumed in one concentrated spike.
The 15-minute window
Utilities measure your power draw in 15-minute intervals throughout the billing month. Your demand charge is set by whichever single interval was highest — even if that peak lasted only 15 minutes out of 43,200 minutes in a month. That one interval determines what you pay for the entire period.
Why utilities charge this way
Utilities must build and maintain enough infrastructure — transformers, lines, substations — to handle every customer’s peak load simultaneously. That infrastructure costs money whether it’s being used or not. Demand charges recover those costs from the customers whose peaks drive the need for it. From the utility’s perspective, your peak demand is your footprint on the grid.
Think of energy as how much water flows through a pipe over a month. Demand is the widest the pipe ever opened. The utility builds pipe to handle your widest opening — and bills you for that capacity whether you use it or not.
Demand ratchets: when one bad month costs you for a year
Many utility tariffs include a demand ratchet clause: a provision that bills you based on a percentage — often 80–90% — of your highest demand over the past 11 or 12 months, even in months where your actual peak was lower. If EV charger installation pushes your demand to 300 kW in August, a ratchet clause may bill you as though your demand is at least 240 kW every month through next summer — regardless of what actually happens on the meter.
Why EV Chargers Create Demand Spikes
EV chargers are demand-charge machines. Here’s why.
A Level 2 charger draws 7–11 kW. Modest on its own. But a fleet of 10 Level 2 ports, all activated by employees arriving at roughly the same time, can simultaneously draw 70–110 kW — a spike that may not exist anywhere else in your facility’s load profile.
A DC fast charger draws 50–150 kW at full power, immediately, for the entire session. Two DC fast chargers charging at the same time create a 100–300 kW spike that is often larger than the entire building load that preceded charger installation.
The coincidence factor problem
Not every charger peaks at exactly the same moment — but enough of them do to matter. This probability is called the coincidence factor. Level 2 chargers have a coincidence factor of roughly 0.65 (moderate risk of simultaneous peaks). DC fast chargers run at 0.90 or higher because they draw full power immediately and hold it. The more DC fast chargers on a site, the closer you get to a worst-case demand spike every time multiple vehicles plug in.
The compounding summer problem
Summer makes it worse. Many utilities charge 15–20% more for demand in summer months when grid load is highest. On some tariffs, summer demand rates are nearly double the winter rate. At the same time, HVAC load peaks in summer — so EV charging demand spikes coincide with building cooling peaks. The combined effect produces the highest demand charge of the year precisely when rates are highest.
A dealership that installs 8 chargers — 6 Level 2 and 2 DC fast — without load management can realistically see $2,000–$6,000 added to its monthly utility bill from demand charges alone. Annually, that’s $24,000–$72,000 in costs that were never in the pro forma.
What Demand Charges Actually Cost
Here is a worked example, followed by real numbers from EVready-managed sites.
That is $48,000 per year in demand charges added by chargers that the OEM required. And that is before accounting for summer rate premiums or ratchet clauses.
From real EVready-managed sites
Mixed charger deployment, mid-Atlantic utility territory
Higher-volume deployment, DC fast charging included
Actual results vary by site, load profile, charger mix, and utility tariff. Data from two EVready-managed dealership sites over 30-day billing periods.
How to Control Demand Charges From EV Charging
The answer is load management: software that communicates with your chargers in real time and staggers when they draw full power, preventing simultaneous peaks without meaningfully delaying charging sessions.
EVready’s Energy Guardian monitors your facility’s power draw against your utility tariff structure and actively manages charger output to keep demand below expensive thresholds. It works with chargers already on site — ChargePoint, Blink, EV Connect, and other major networks — without hardware replacement.
What load management actually does
- Monitors all charger ports and building load in real time
- Detects when simultaneous charging would create an expensive peak
- Throttles individual charger output slightly to prevent the peak from forming
- Restores full charging speed once the risk window passes
- Logs every intervention so you can see exactly how much was saved
What load management does not do
- Does not require replacing existing chargers
- Does not meaningfully delay most charging sessions (vehicles rarely need maximum speed for a full session)
- Does not require utility approval or special metering
On EVready-managed sites, Energy Guardian recovers 35–55% of added demand charges annually. For a site adding $4,000/month in demand charges, that is $16,800–$26,400 per year returned to the bottom line — from chargers that are still running.
The business case is straightforward: load management software pays for itself in months, not years, on any site with meaningful DC fast charging or more than 8 Level 2 ports.
Demand Charge Questions, Answered
These are the questions facility managers, dealership operators, and fleet directors ask us most. The answers are complete — not summaries.
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A demand charge is a fee on your commercial electricity bill based on the highest rate of power your facility draws during any single 15-minute interval in a billing period — not on how much total energy you use. Utilities use it to recover the cost of infrastructure they must build to handle your peak load. Demand charges typically appear as a dollar-per-kilowatt ($/kW) line item and can represent 30–70% of a commercial electric bill.
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Your utility measures your power draw in 15-minute intervals throughout the billing period. The single highest interval — even if it lasted only 15 minutes — sets your demand charge for the entire month. The formula is: Peak kW × demand rate ($/kW) = demand charge. A facility that peaks at 200 kW with an $18/kW demand rate owes $3,600 in demand charges that month, regardless of how much or how little energy they used the rest of the time.
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EV chargers draw large amounts of power quickly, especially DC fast chargers. When multiple chargers activate simultaneously, they create a sharp spike in your facility’s peak demand. That spike — even if it lasts only 15 minutes — resets your demand charge for the entire billing period. A single event of four DC fast chargers charging simultaneously can add 150–200 kW to your peak demand, translating to $2,100–$4,400 in additional monthly demand charges at typical commercial rates.
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An energy charge bills you for the total amount of electricity you consume, measured in kilowatt-hours (kWh). A demand charge bills you for the highest rate at which you consumed electricity during any 15-minute window, measured in kilowatts (kW). You can use very little total energy and still owe a large demand charge if you had one brief, intense spike. Think of energy as how much water flowed through a pipe over a month; demand is the widest the pipe ever opened.
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No. Demand charges typically apply to commercial and industrial customers on certain rate schedules, not to residential accounts. Whether you pay them depends on your utility, your rate tariff, and the size of your electrical service. Most businesses with 50 kW or more of peak demand are on tariffs that include demand charges. When you install EV chargers — especially DC fast chargers — your peak demand often grows enough to trigger a higher-cost tariff tier or significantly increase your existing demand charge.
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A coincidence factor describes the probability that multiple EV chargers will reach their peak power draw at exactly the same time. Level 2 chargers have a coincidence factor of about 0.65 — most don’t peak simultaneously. DC fast chargers run closer to 0.90 because they draw full power immediately. The higher the coincidence factor, the larger the demand spike, and the more important load management becomes to prevent it.
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A demand ratchet is a utility tariff clause that bills you based on a percentage of your highest demand over the past 11–12 months, rather than just the current month’s peak. If your highest demand was 300 kW in August, a ratchet clause might bill you as if your demand is at least 240 kW (80% of 300 kW) every month through next summer — even in months where your actual peak was much lower. This makes a single bad peak extremely expensive over time, which is why preventing peaks with load management pays dividends for 12 months.
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Yes. Load management software communicates with your existing chargers to stagger when they draw full power, preventing simultaneous peaks without meaningfully slowing down charging sessions. EVready’s Energy Guardian works with ChargePoint, Blink, EV Connect, and other major networks — no hardware replacement required. On managed sites, Energy Guardian has reduced peak demand from EV charging by 30–90%, recovering thousands of dollars per month in demand charges.
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Yes, significantly. A Level 2 charger draws 7–11 kW and charges gradually — its peak impact is moderate. A DC fast charger draws 50–150 kW immediately at full power for the entire session, creating a much sharper demand spike. Sites with DC fast chargers are at substantially higher risk of large demand charges, and the payback period for load management software is correspondingly shorter — often less than six months.
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Yes. Many utilities set higher demand charge rates in summer months when grid load peaks due to air conditioning. Summer demand charges can run 15–20% higher than the annual average, and in some utility territories they are nearly double the winter rate. EV charging sites face a compounding problem in summer: charger demand peaks coincide with HVAC peaks, creating the highest combined demand of the year at the moment rates are highest. Load management strategy must account for seasonal rate variation.
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Look at your current electric bill for a line item labeled “demand charge,” “peak demand,” or “kW charge” with a dollar-per-kW rate. If you see it, you are already paying demand charges. If you do not see it, you may still be on a tariff that will add demand charges once your peak exceeds a threshold — which EV charger installation commonly triggers. EVready reviews your utility tariff as part of every site assessment to identify demand charge exposure before installation, not after.
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Yes. EVready’s free EV Demand Charge Impact Estimator lets you enter your number of ports and charger type and calculates your estimated monthly demand charge exposure alongside what Energy Guardian would likely recover. It uses conservative industry-standard coincidence factors and shows a before/after comparison. For a precise figure tied to your actual utility tariff and location, schedule a strategy call — EVready reviews your tariff as part of every site assessment.
Find out what demand charges will cost your site — before they arrive.
A 30-minute strategy call gets you a utility tariff review, a demand charge projection, and a clear picture of what load management would recover. No obligation.