How much solar does it take to offset AC use in a Phoenix home?

By Michael Fitzgerald, Founder & Editor, Phoenix Cooling Guide
Technically reviewed by Tom Mattingly, Owner & President, AZ Trusted Air LLC (ROC 317368)
Published 2026-09-18

Solar and air conditioning are sold as separate purchases in the Valley, and they are usually bought that way — a panel quote in one folder, a replacement quote in another, six months apart. They are not separate problems. In a Phoenix home the air conditioner is the load that decides how large an array has to be, when that array's production is worth the most, and whether a battery can do anything useful during a monsoon outage.

Most solar-and-AC advice online was written against retail net metering, where every exported kilowatt-hour was worth what a purchased one cost. That is not how SRP's export plans work today. SRP credits exported energy at a fixed 3.45 cents per kWh, and its summer on-peak window runs 2 to 8 p.m. weekdays from May through October — the exact hours a Phoenix roof is losing sun and a Phoenix house is at its hottest. That mismatch is what this page is about.

What is an AC soft-start kit and why do solar and battery owners install them?

The device is often confused with a hard-start kit at the quoting stage, and they do opposite jobs. A hard-start kit adds starting torque so a tired compressor breaks away faster, which raises the current draw for that instant. A soft starter ramps the voltage so the same compressor comes up to speed more gradually and pulls less current doing it. A Valley homeowner sizing a battery wants the second device; a homeowner nursing a twelve-year-old condenser through one more August is sometimes sold the first.

The number that decides everything is printed on the outdoor unit's data plate. Enphase's design brief for running HVAC on stored energy points to locked rotor amps — the nameplate startup figure — as the sizing input for a backup system, and notes that LRA can run four to eight times the running amperage depending on the make, model and age of the unit. The surge lasts a moment, and the battery either carries it or drops the load. In the large share of Phoenix housing stock cooled by a rooftop package unit, that plate is on the roof, which is the most common reason the figure never gets read before a battery is ordered.

Manufacturers publish reduction percentages for their soft starters, and those claims vary by device and by compressor. The honest position is that no percentage from a brochure should be treated as a fact about a particular Phoenix condenser. The useful move is contractual rather than technical: ask the installer to write down, on the proposal, which LRA figure the inverter was sized against and what the measured start current was after commissioning. A number in writing survives the argument that follows a failed start in August; a number in a brochure does not.

Not every system needs one, and reputable designers disagree about how often they do. Florida Solar Design Group argued in a 2026 update that soft starts are mostly unnecessary when a battery backup inverter is properly sized, and that they were the default answer in an era when inverters were the weak link. Enphase's brief separately notes that variable-speed HVAC systems typically do not present the same startup inrush. So the answer turns on two specific pieces of hardware — the compressor and the inverter — both of which have their ratings printed on them.

Can I run my AC on battery backup during an outage?

The arithmetic is short. EcoFlow's own guidance for matching batteries to air conditioners describes the method: take the LRA from the compressor label, multiply it by the unit's voltage to get surge volt-amps, then confirm the inverter can sustain that level for at least a second rather than for a split-second peak. A system whose headline peak wattage looks comfortable can still trip, which is why the one-second figure is the one to ask for. Nothing in this calculation is proprietary — it is a label, a multiplication and a spec sheet.

Runtime is a separate question and it is where Phoenix departs from the national write-ups. At a 115°F design temperature the air conditioner is not cycling gently; it is running long and hard, and a battery sized to carry a refrigerator and some lights overnight in a mild climate will not carry a four-ton condenser through a July afternoon. A homeowner can estimate this without a salesperson: take a July daily kWh figure from the SRP or APS account, divide by 24 for an average hourly draw, and compare that against the battery's usable capacity.

Partial cooling is the more realistic goal, and it is worth saying plainly rather than being talked past. Backing up one zone — a mini-split serving a bedroom, or a single window unit on a critical circuit — asks far less of a battery than backing up a whole-house condenser. Pre-cooling the house before a forecast outage buys hours of thermal coast in a well-insulated Valley home and costs nothing. Both approaches sidestep the surge problem entirely instead of trying to pay for it.

Timing matters here too. Valley outages cluster in monsoon season, roughly July through September, when microbursts take down lines on the same afternoons the cooling load is highest. That is also the season when an underspecified backup system fails its first real test. The LRA check belongs before the battery contract is signed, not after the first storm, and any contracting work on the electrical or HVAC side should be done by a contractor whose licence status a homeowner has confirmed at roc.az.gov.

For Phoenix-area homeowners who want this looked at on their own system, Phoenix Cooling Guide recommends AZ Trusted Air LLC (ROC 317368), whose owner Tom Mattingly reviews this guide. (623) 252-6403 · second opinion on a quote.

How do solar export rates interact with afternoon AC loads?

SRP publishes two export plans for solar customers. The Time-of-Use Export Price Plan has no monthly demand charge and applies a credit at the end of the billing cycle for all accumulated export generation at a fixed rate of 3.45 cents per kWh. The Electric Vehicle Export Price Plan uses the same fixed 3.45 cents and also has no demand charge, with credits applied instantly whenever solar output exceeds household load. Both rely on metering that tracks kWh delivered and kWh exported separately, which SRP distinguishes from the netting used on its Customer Generation and Average Demand plans, where exported kWh are subtracted from delivered kWh to reach a net figure.

On the netting plans the air conditioner drives a second charge entirely. Under the standard Customer Generation Price Plan (E-27) the demand charge is set by the single highest 30-minute on-peak interval in the month; the Average Demand Price Plan (E-15) instead averages the daily on-peak maximum demands. In practice that means one compressor start stacked on a dryer and an oven at 4 p.m. in July can set the month's demand charge on E-27, while the same behaviour is diluted across the month on E-15.

The export credit is worth running the arithmetic on before assuming surplus generation pays for the summer. At SRP's fixed 3.45 cents per kWh, 100 kWh exported in a month earns $3.45, 500 kWh earns $17.25, 1,000 kWh earns $34.50, 1,500 kWh earns $51.75 and 2,000 kWh earns $69.00. Compare that against the plan sheet's on-peak energy price for the same kilowatt-hours consumed inside the house, and the conclusion writes itself: in Phoenix, using solar output directly — pre-cooling before 2 p.m., running the pool pump at midday, charging the car on the roof's production — is worth more than selling it.

Two dates belong in any current calculation. SRP is temporarily lowering prices by $0.0038 per kWh for the May through October 2026 billing cycles, citing lower-than-expected natural gas and market power costs, with prices returning to published levels with the November 2026 billing cycle; the published plan sheets do not reflect the reduction. Separately, SRP's publicly elected Board approved the retirement of select price plans on Feb. 27, 2025, and both the Time-of-Use Export Price Plan and the Customer Generation Price Plan are flagged for discontinuation as of the November 2029 billing cycle. APS uses a different structure and its own export rate, which secondary sources report inconsistently — an APS customer should confirm the current figure with APS directly rather than from a solar proposal.

Should I upgrade the AC before or after going solar?

Load first, generation second, is the order that holds up. An array sized against a house cooled by an oversized, duct-leaking, twenty-year-old system is an array sized against waste, and the panels stay on the roof for decades after the condenser is scrapped. Correct sizing on the HVAC side is also a rebate condition rather than a nicety: SRP requires Manual J load calculations to be submitted with the Cool Cash application for single-stage systems, and states that applications without them will be delayed or denied. Load calculations are not required for multi-stage or variable-capacity equipment.

The federal picture has changed and it no longer argues for rushing either purchase. Public Law 119-21, signed 4 July 2025, terminated the Residential Clean Energy Credit under Section 25D for expenditures made after 31 December 2025, replacing the previous 2034 horizon. The IRS has confirmed that paying in 2025 does not preserve the credit if the work finished later, because Section 25D(e)(8)(A) treats an expenditure as made when the original installation is completed. The Energy Efficient Home Improvement Credit under Section 25C, which covered high-efficiency AC and heat pump equipment, is likewise unavailable for property placed in service after 31 December 2025. Taxpayers who did qualify before the cutoff may still carry forward unused 25D amounts; the carryforward rules were not changed.

What survives is the utility money, and it comes with its own conditions. Cool Cash is advertised at up to $1,125, and to qualify a customer must be a permanent SRP residential electric customer, must have the system installed by a contractor licensed in Arizona to install residential air-conditioning systems before April 30, 2027, and must be replacing or supplementing an existing central heat pump or central AC. Per-ton amounts and efficiency thresholds are set by SRP and move between program cycles, so the figure to rely on is the one on SRP's rebate page on the day of signing, not the one printed on a proposal.

There is a physical argument for the same order, and it is specific to Valley roofs. A large share of Phoenix homes are cooled by rooftop package units, and panels laid out without regard to that equipment can leave a crane, a curb and a service path fighting for the same square footage later. Replacing a package unit under an installed array can mean panel removal and reinstallation, which is an avoidable cost if the two trades are sequenced in one direction. Where a roof is nearing the end of its life, that work belongs before the panels as well.