The number that shocks people
With the defaults the site draws 12,000 kWh in a month at 9.5 cents, which is $1,140 of electricity. The demand charge is $3,630. The energy is a quarter of the bill and the peak is nearly three quarters, and the peak lasted fifteen minutes.
Put that another way. Holding 220 kW for one fifteen-minute interval delivers 55 kWh. At the energy rate those 55 kWh are worth $5.23. They also set a $3,630 demand charge, which works out at $66 for every kWh in that interval. Everything odd about a fleet charging bill follows from that arithmetic.
Load factor is the diagnosis
Average draw across the month is 16.7 kW; the peak is 220. That is a load factor of 7.6 percent, which is extremely low and entirely typical of a depot that charges everything in the same two hours. A site whose load runs flat around the clock has a load factor several times that, and barely notices its demand charge.
Low load factor is not a problem in itself. It is a signal that the bill is dominated by a peak, and therefore that the cheapest available saving is spreading rather than reducing. The same 12,000 kWh with a 110 kW peak costs $1,815 less a month and not one kWh was given up.
What staggering actually buys and what it costs
The stagger table pairs the two halves of the trade. Running six ports at once instead of twelve puts the peak at 185 kW rather than 310, but the same energy now needs twice as many hours to deliver. That is fine on a nine hour window with slack in it and impossible on a five hour one, which is why the decision belongs to a scheduling calculation rather than to this one.
The other half is the base load. With 60 kW of site load already there, cutting the chargers to a single port still leaves a 81 kW peak. No amount of charger scheduling gets below the floor the rest of the site sets, and on some depots that floor is most of the peak.
Where this page will mislead you
Three ways, all worth knowing. Ratchets: some tariffs bill this month on the highest peak of the last twelve, so one bad interval last summer is still costing you. Coincidence: the site peak and the charger peak do not happen at the same instant, so adding them overstates the combined figure — interval data is the only way to know by how much. And kVA billing: if your tariff bills apparent power rather than real power, the number on the bill is not the number on this page.
All three are on your own tariff sheet and in your own interval data. Nothing here asserts what any utility does, because the answers differ by utility, by rate class, by season, and they change.
Questions people ask
What is a demand charge?
A charge billed on the highest short interval of power your site drew during the period — commonly fifteen or thirty minutes — rather than on total energy. It is why two sites using identical kWh can get very different bills. With the defaults here, 220 kW held for one quarter of an hour delivers 55 kWh and triggers $3,630, which is $66 per kWh for that interval against 9.5 cents for every other one.
Why is my EV charging bill so much higher than the kWh suggest?
Because the demand charge is being spread over a small amount of energy. With the defaults the blended price is 41.83 cents a kWh against an energy rate of 9.5 — more than four times the number anyone quotes. Load factor is the diagnostic: at 7.6 percent, almost everything on the bill is being bought by the peak.
Does staggering chargers reduce the demand charge?
It reduces the peak, and the demand charge follows the peak. Halving the ports running together roughly halves the charging contribution and doubles the hours needed to move the same energy. Whether those hours fit inside your window is the constraint, and the base load your site draws anyway sets a floor that no charger scheduling gets below.
What is a demand ratchet?
A tariff provision that bills this month on a percentage of the highest peak recorded over some earlier window, often eleven or twelve months. Under one, a single bad interval keeps costing you long after the load that caused it has gone. This page does not model it, because whether you have one, over what period and at what percentage is on your tariff sheet and varies by utility.
Is my demand billed in kW or kVA?
It depends on your tariff and it is printed on the bill. A kVA-billed site pays for apparent power, so a poor power factor raises the charge for the same real load. This page works in kW because that is the more common case, but it will understate a kVA bill and the fix is to read your own tariff rather than assume.