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Solar panels and air conditioning keep different hours.

Your panels do their best work around midday. Your air conditioner does its hardest work in the late afternoon and evening. Here is one hot day, and how to bring the two closer together.

One hot day

Where the sun is, and where the cooling is.

Solar output and cooling demand across a hot summer dayFrom 6am to 10pm. Rooftop solar output rises in the morning, peaks around 1pm and fades by about 7pm. Cooling demand is low in the morning and peaks in the late afternoon, around 5 to 6pm, after solar has started to fall. The hours from noon to 4pm are shaded as the pre-cool window; 4pm to 9pm is marked as the peak-price window on many utility time-of-use plans. Illustrative, with no values. 6am 9am 12pm 3pm 6pm 9pm Pre-cool Peak price Solar Cooling demand
Illustrative shapes, not measurements. Your own curves depend on the house, the panels, the weather and your utility plan.
A better day

Four steps through the afternoon.

  1. Morning

    Blinds down on the sunny side

    Keep the heat out before it starts; the panels are just waking up.

  2. Noon – 4pm

    Pre-cool on your own power

    Set the thermostat a little cooler while solar is strong, so the house stores the cool.

  3. 4pm – 9pm

    Coast through the peak

    Let the setpoint drift up a little. The cool you stored does the work while electricity is dearest.

  4. Night

    Back to normal

    Once the peak is over, the schedule returns to your usual comfort.

Southern California Edison's time-of-use plans commonly charge the most in the late afternoon and evening. Check your own plan's hours — we set the schedule to match them.

A heat pump on a pad beside a stucco wall in bright midday sun, a clean shadow beneath it
What helps

The equipment matters too.

A smart or programmable thermostat
Set once to your plan's hours, then left alone.
A variable-speed system
Can pre-cool gently rather than blasting and cycling.
Sealed, insulated ducts
So the cool you pay for (or make) reaches the rooms.
Attic ventilation and shade
Less heat coming in means less to take out at 6pm.
A technician showing a homeowner a thermostat schedule on a tablet at a kitchen counter, the screen unreadable
The schedule set together, to your plan.
West-facing windows with light solar shades lowered in a bright living room in the late afternoon
Shade first: the cheapest cooling there is.
Homes

Solar owners

Pre-cooling and schedules set up with your system and your utility plan.

Businesses

Solar on the roof

Rooftop units scheduled around trading hours and the building's own production.

Have solar?

Let's line up your cooling with it.

An assessment of the system, the thermostat and the house.

Request an assessment (530) 394-6533
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