Apartment EV charging budgets: how to test

What to take away

Nearly every charging budget presented to a board is a single scenario at expected adoption. That scenario is the least likely thing to happen.

Testing means asking what the same project does when the assumptions are wrong, and the useful discovery is usually that low use and high use break different models.

Five scenarios to run before approving

Half the expected adoption. A paid service now spreads fixed costs across fewer sessions. Network fees, payment processing and maintenance do not fall with usage. Does the price still cover them, and if not, who funds the gap?

Triple the expected adoption. A free amenity now has three times the electricity bill, and the guaranteed power per car drops. At what point does the model change, and have residents been told?

Six months of delay. Utility work and permits slip. What does that cost in re-mobilization, price escalation and any funding deadline you were counting on?

A change order of a fifth of the construction cost. Something is found behind a wall or under the paving. Where does that money come from, and who can approve it without another vote?

A major repair in year three. A pedestal is hit, or a run of cables needs replacing. Is there a reserve line for this, or is it an assessment? Cables and readers are consumables, which is why the replacement intervals belong in the reserve study.

If any scenario has no answer, that is the actual finding, and it is better found now.

The exposure most budgets miss

Commercial electricity rates frequently include a demand charge, billed on the highest power draw in a short window rather than on total energy used.

That structure interacts badly with charging. Four cars starting together at 6pm can set a monthly peak that costs more than all the energy those cars consumed. A budget that models electricity as cents per kilowatt hour and stops there can be wrong by a wide margin.

Take a 40 kW peak and an illustrative $15 per kilowatt demand charge: that is $600 for the month, for power the cars drew for a few minutes. Your tariff and the highest interval your meter records set the real figure.

Before approving, ask three things: is this account on a demand rate, what is the charge per kilowatt, and what would a simultaneous start of every port do to it.

Then ask whether managed charging or a time-based rate would reduce it. The Department of Energy's overview of demand response and time-variable pricing programs explains the mechanisms these rates use. That lets you ask your utility a specific question rather than a general one.

Test the funding assumptions too

Every funding line in the budget should be tested for the condition that could void it. Most of those conditions come from utility make-ready programs and charger rebates, not from the equipment.

Utility programs in particular carry requirements that are easy to fail administratively rather than technically, so map the funding deadlines onto the build schedule on a single page. Some jurisdictions publish detailed requirements for commercial charger programs, and the pattern to notice is how many conditions attach to the money rather than to the equipment.

A rebate may require the ports to be networked and reporting data for a set period. It may require them to stay open to the public, or require energization before a fixed date. Miss one condition and the money is gone, even though the chargers work.

After opening: four numbers

Once it is running, you do not need a dashboard. You need four figures, monthly at first, and the commissioning tests that establish a baseline are what make the first month readable at all. The four figures are cost per session against the fee charged, sessions per port, billed peak kW, and the reserve balance.

Three months of those four figures tells you more than any projection did. If fees are under costs, you have a pricing decision. If sessions per port are very low, you overbuilt and should stop at this phase. If peak demand is climbing, managed charging has become worth the money.

Write down the trigger points now

The most useful thing a budget test produces is a set of thresholds agreed in advance.

At what utilization do you add ports. A sample trigger is 70 to 80 percent utilization sustained over a quarter. At what shortfall do you change the price. For example, $500 across a rolling quarter.

At what demand charge do you install load management. When the billed peak pushes the charge past the cost of the control hardware, for example 40 kW at an illustrative $15 per kilowatt. At what point does free charging stop being free.

Deciding those while nobody is affected is straightforward. Deciding them in the meeting where residents are affected is not.

Each threshold maps to a decision. The paid, free and hybrid models are compared line by line in the budget choices, and the funding routes each model depends on are listed in the cost guide.

Common questions