Solar for air conditioning

Cooling load tracks sunshine. The hotter and clearer the afternoon, the more the AC runs and the more the panels produce, so a solar home’s net draw from the grid on a July afternoon can be close to zero while the neighbors are pulling several kilowatts. Over a season, Colorado’s cooling load falls mostly in June through September, which are also the four highest-production months on any Front Range array.

The same is true for evaporative coolers, which draw far less — a few hundred watts for the blower and pump — and for whole-house fans. Those are easy loads. The place solar strains is the modern trend toward larger, tighter homes with central AC set to 72°F from noon to midnight; that is a load an array can cover by day and net-metering credits can cover by night, but the on-peak pricing in between deserves attention.

A conventional central air conditioner is a single-speed compressor sized for the worst hour of the year, drawing 3–5 kW whenever it runs. Newer variable-speed central units modulate down and run longer at lower draw, which suits solar well. Ductless mini-splits are smaller still, often 0.5–1.5 kW per zone, and cooling only the rooms in use rather than the whole house. Many older Denver and Boulder homes with no ducts have gone to mini-splits for exactly that reason.

Every mini-split and most modern central units are heat pumps: the same equipment runs in reverse to heat in winter. Cold-climate models hold their efficiency well below zero and are steadily replacing gas furnaces along the Front Range. If you are replacing a furnace and an AC unit, a heat pump does both jobs, and the solar sizing conversation becomes a whole-year electrification conversation; the switching-to-heat-pump page and the electrification calculator cover that in detail.

Since November 2025, Xcel’s residential time-of-use plan charges about 2.7 times the off-peak rate on weekdays from 5 to 9 pm, with higher summer pricing on top. Colorado afternoons peak in temperature around 3–5 pm and homes shed heat slowly, so the compressor often runs hardest between 5 and 8 pm — precisely when a west- or south-facing array is producing a fraction of its midday output and an east-facing array is producing almost nothing.

The first fix is free: pre-cool. Set the thermostat two or three degrees lower from 1 to 5 pm while the panels are producing, then let it drift up during on-peak. A well-insulated house coasts for hours. Ceiling fans and closing west-facing blinds extend the coast. For many households, that plus net-metering credits handles the evening without hardware.

The second fix is a battery. A Tesla Powerwall 3, Enphase IQ Battery, or SigenStor charged from the array by mid-afternoon runs the AC and the rest of the house from 5 to 9 pm, so nothing is bought at on-peak rates. One 13.5 kWh unit carries a 3–5 kW compressor cycling through a four-hour evening with capacity left for everything else. That battery also keeps the house cool during a summer outage, which on the Front Range increasingly coincides with wildfire safety shutoffs and thunderstorm season. The peak-shift calculator shows how much of your evening load one battery would cover.

A central AC in a typical Front Range home uses roughly 1,500–3,000 kWh over a cooling season; a large house set cold can use more, a mini-split serving a few rooms less. At Colorado’s roughly 1,300–1,600 kWh per installed kilowatt per year, cooling adds about 1–2.5 kW to a system, or roughly 4–8 panels at 400–440 W. Because that production arrives in the same months it is used, the AC is the load least dependent on carryover credits — good news in co-op and municipal territory where annual true-ups can devalue surplus.

We size to your last 12 months of usage, which already includes the AC if you have it. If you are adding AC to a home that has never had it, we add the estimated seasonal load and size accordingly. And if your utility is Colorado Springs Utilities, note that its net-metering terms have changed; the springs-net-metering calculator reflects how surplus is valued there.

We start from annual kWh and the roof, not from the AC’s nameplate. A 4-ton unit’s 5 kW draw does not mean you need 5 kW of panels; it means that on the hottest hour the house draws 5 kW, which the array supplies directly when the sun is up and net metering supplies when it is not. Under C.R.S. 40-2-124 in Xcel and Black Hills territory, surplus credits carry forward month to month, so a system sized to the annual total covers cooling season even when summer production and use do not line up hour by hour.

Co-ops and municipals must offer net metering up to 10 kW residential under C.R.S. 40-9.5-118, and beyond that it is utility discretion; most Front Range cooling homes land under that cap. Where an annual true-up pays surplus at a low rate, we size closer to actual use rather than over. Either way, the solar-savings calculator gives ranges, not promises, and we would rather size a little under than sell panels that only produce credits you cannot use.