The EV Owner's Guide to Smart Charging with a Tesla Powerwall

You bought the Powerwall to ride out outages and shave your peak. You bought the EV because gas was insane and the car is fast. But most people run them as two separate systems that happen to share a meter. The car charges whenever you plug it in, the Powerwall does its own thing, and the utility quietly bills you for the overlap.

That overlap is where the money is. An EV is the single biggest load in your house. A Powerwall is the single biggest tool you have to control loads. Getting them to cooperate is worth more than almost any other change you can make to your energy setup, and the setup takes less time than you'd think.

Charging on sunshine, not on the grid

The whole appeal of pairing solar with an EV is charging straight off your roof. Sun hits the panels, electrons go into the car, you drive on daylight. When it works, your marginal cost per mile drops to roughly zero.

The problem is timing. Most people plug in when they get home, around 6 PM. By then the sun's low or gone, your panels are producing a trickle, and the car pulls 7 to 11 kW from somewhere. If the Powerwall is full it'll discharge into the car. If it's not, you're buying grid power at exactly the worst time of day.

So the real goal isn't "charge with solar." It's "charge when the sun is actually up, or pull from a battery that filled up earlier when the sun was up." A Tesla Wall Connector on a typical Level 2 circuit draws somewhere between 7.7 kW and 11.5 kW depending on your breaker. A single Powerwall holds 13.5 kWh usable, but how fast it can push that out depends on the model: a Powerwall 2 puts out 5 kW continuous, a Powerwall 3 up to 11.5 kW. Either way the tension is the same: one Powerwall can't feed a fast-charging car for long. A Powerwall 2 at 5 kW drains its 13.5 kWh in under three hours; a Powerwall 3 matched against an 11.5 kW charger empties in a little over an hour. Then there's nothing left for the house.

That's why the smart move is usually to charge the car midday, directly off solar, before the battery even gets involved. If you work from home or the car sits in the garage during the day, this is free money. Schedule the car to pull during the production window, say 10 AM to 3 PM, and you're driving on power that would otherwise have been exported to the grid for pennies.

Charging around the peak window

Not everyone can charge midday. If your car's at the office or you're commuting, the car plugs in at night and you're working with time-of-use rates instead of raw sunshine.

This is where knowing your actual rate plan matters. The peak windows and the spread between peak and off-peak vary wildly:

• PG&E EV2-A runs peak from 4 to 9 PM, with the cheapest rates between midnight and 3 PM. PG&E adjusts EV2-A seasonally, so pull the current rate schedule for the exact spread — but the gap between peak and off-peak is consistently steep.
• SCE's residential EV rate (marketed as TOU-D-PRIME, though plan names and off-peak windows have shifted over the years) puts peak at 4 to 9 PM with cheaper overnight hours — confirm the current structure on SCE's rate page before scheduling around it.
• SRP E-27 in Arizona puts on-peak in the afternoon and evening, including Saturdays — summer on-peak commonly runs around 2 PM to 8 PM, with off-peak rates in effect late evening through midday.
• APS time-of-use plans hit hardest from 4 to 7 PM in summer, though on some APS plans the demand charge, not the energy rate, is what really drives your bill.

The rule that falls out of all of these is the same: never charge the car during the 4-to-9 (or 4-to-7) evening block. That window is the most expensive power you'll buy all day. If your car charges then at 9.6 kW for three hours, you've just bought 29 kWh at peak pricing, and on some plans that's the difference between a $40 fill and a $12 one.

So you delay. Tell the car to start at 9 PM, or midnight, or whenever your super off-peak kicks in. The Powerwall covers your house through the peak window on stored solar, and the car waits until power is cheap. Two systems, one schedule.

Where the Tesla app runs out of room

Tesla gives you two scheduling tools, and on the surface they look like enough.

The car has Scheduled Charging and Scheduled Departure. You set a start time, or you tell it when you leave and it back-calculates. Fine for a fixed routine.

The Powerwall has Time-Based Control, which lets the battery favor discharging during your peak hours to avoid buying expensive grid power, and recharging when rates are low. Tesla has a writeup on this — search "Powerwall time-based control" on their support site if the direct link has moved.

Here's the gap. These two systems don't know about each other. The car's charging schedule has no idea what your Powerwall's state of charge is. The Powerwall's Time-Based Control has no idea your car is about to pull 10 kW off the same panel. They each optimize in isolation, and the seams show up fast:

• The car starts charging at its scheduled 9 PM time even though the Powerwall is at 20% and your house still needs to get through the night.
• A cloudy day means your solar never topped off the battery, but the car charges to 80% anyway, draining the Powerwall and forcing a grid buy at 2 AM.
• You set Scheduled Departure for 7 AM, and the car decides to precondition and finish charging at 6 AM, which on a winter morning is inside a secondary peak window on some plans.
• Your rate plan has a demand charge, and the car kicking on at full power sets a new monthly peak that follows you for the next 30 days.

None of these are bugs. The Tesla app is doing exactly what you told it. The trouble is that "charge at 9 PM" is a dumb instruction in a world where the right answer depends on battery level, weather, your rate plan, and what the rest of the house is doing.

Letting the two systems actually talk

This is the problem Grid Getter solves. Instead of two schedules that ignore each other, you write rules that account for the whole picture.

A useful EV rule reads more like a sentence than a timer. Charge the car only when the Powerwall is above 50%, and only outside the 4-to-9 PM peak, and stop pulling if a grid draw would set a new demand peak. That last piece is DemandGuard, which watches your real-time grid import and throttles or pauses big loads before they ratchet up the demand charge that SRP's demand-price plans bill you for.

A few rules that are hard or impossible in the stock app but trivial here:

• Charge the car directly off solar surplus during midday, and only top off from the grid overnight if it didn't reach your target.
• Hold the car's charge until the Powerwall has covered the house through peak, then release it into super off-peak hours.
• Cap the car's draw so it never coincides with the AC compressor in a way that spikes your demand reading.
• Skip overnight grid charging entirely on days the forecast says tomorrow's production will easily cover both the house and the car.

The car still charges, and you leave with a full battery. You just stop buying peak-rate power every time the two schedules collide.

Start with one number

Before you build any rules, go pull up your last bill and find the peak window for your specific rate plan. Not the generic "evenings" your utility markets, the exact hours, like PG&E's 4 to 9 PM or APS's 4 to 7 PM summer block. Then open your Tesla app and check what time Scheduled Charging is set to start.

If those two windows overlap, even by an hour, you're handing money to the utility every single night. Move the car's start time outside the peak first. That one change pays for itself immediately. Then, when you're ready to make the Powerwall and the car genuinely work as one system, start a free Grid Getter account and write the rule that ties them together.