Solar HVAC Sizing Considerations: How to Match Systems with Rooftop PV

Load Calculation & Energy Matching

Start with a rigorous room-by-room load calculation (Manual J or ASHRAE), then map that expected hourly cooling demand to your site’s solar production curve. In practice, peak solar output overlaps with peak cooling hours exactly when the compressor needs it most. For a typical 1.5-ton split system, instantaneous draw is roughly 1,200–2,200 W depending on efficiency. The goal is not just matching nameplate kW; it’s aligning when the kW is available. Build a 24-hour profile of sensible/latent loads, occupancy, internal gains, and envelope performance. Overlay PV output (by month) and identify gaps you’ll cover with grid power, batteries, or precooling strategies.

Related: See our Help Center.

Converting HVAC Load to PV Array Size (with a 1.5-ton example)

A practical first pass for PV sizing uses the unit’s steady-state electrical input. Example for a 1.5-ton AC:

Typical compressor + fan input: 1.2–2.2 kW

Loss factor (inverter, wiring, heat): ×1.25

PV DC to target (peak hour): ~1.5–2.75 kW

On modern 250–400 W panels, that’s ~8–12 modules for daytime compressor coverage, assuming good irradiance and minimal shading. Confirm with local peak-sun-hours and the system’s duty cycle (how long the compressor actually runs during peak). If your Manual J load and climate indicate long, hot afternoons, size toward the higher end—or plan to supplement with grid or storage.

Quick estimator (rule-of-thumb)

PV_kW_required ≈ (HVAC_kW_peak × 1.25) ÷ Inverter_eff

Shopping links: R32 Condensers.

Panel Count, Sun Hours, and Roof Constraints

Panel count depends on module wattage, tilt/azimuth, local peak-sun-hours, and string/inverter limits. Warmer roofs reduce module efficiency; plan for thermal derate on hot afternoons. In 5–6 peak-sun-hour regions, 8–12 panels (250–400 W) typically cover a 1.5-ton system’s peak-hour operation; higher latitudes or partial shading push counts up. Confirm setback codes, rail layout, and conductor sizing before finalizing string lengths.

Visual (conceptual):

[PV Strings]─DC→[Inverter]─AC→[Disconnect]→[Panelboard]→[Air Handler & Condenser]

                           └─CTs→[Smart Controller]

Related products: Accessories.

How SEER/EER Shrink the Array You Need

Efficiency directly drives PV size. Moving from an older unit to SEER 16+ can cut power draw ~30–40%, which proportionally lowers required array kW and shortens payback. Premium systems now reach SEER 22+, especially inverter-driven heat pumps. Remember: EER reflects fixed test conditions (e.g., ~95°F ambient), while SEER averages seasonal performance. For hot-climate design, weigh both; EER is a stronger predictor of peak-hour solar matching.

Explore high-efficiency options: R32 Air Conditioner + Air Handler Systems.

Variable-Speed (Inverter) Gear + Solar: The Perfect Pair

Inverter-driven condensers and ECM blower motors modulate capacity to match both load and available PV power. Instead of hard on/off cycling, the system ramps, extending compressor run time at lower watt draw—ideal for riding the solar curve. With smart controls, you can bias stages when PV is abundant, then trim capacity as clouds move in, keeping comfort steady without oversizing the array.

Control ideas:

• PV-aware staging: Use PV power/irradiance as a control input.

• Setpoint glide: Nudge setpoints during surplus PV to bank a few degrees of precooling.

• Enhanced dehumidification: Lower blower speed at mid-day for latent control with minimal watt penalty.

See compatible formats: Ductless Mini-Splits.

Net Metering Realities & Right-Sizing Under New Rules

Classic net metering credited exports at retail. Many utilities now offer reduced export rates sometimes ≈$0.10/kWh and impose capacity limits (commonly up to 1.5× of sanctioned load). That changes the optimal PV/HVAC ratio. Instead of maximizing annual kWh, design to self-consume mid-day production with the HVAC first, then trim array size to minimize low-value exports.

Design levers:

• Size PV to your peak cooling window, not just annual totals.

• Favor high-SEER equipment; watts saved are watts you don’t need to generate.

• Consider battery a la carte: only if export credits are weak and your peak rates are high.

Planning help: Our Design Center can review tariff rules and propose a right-sized package.

Designing for Time-of-Use (TOU) Rates

TOU schedules commonly set peak pricing from ~12:00–8:00 PM in summer—exactly when solar is strongest. A PV-first HVAC design captures high-value kWh during that window, then relies on precooling or limited storage later.

Mid-day strategy timeline (example):

Noon–3 PM:  Run on PV, start setpoint glide (-1 to -2°F)

3–6 PM:     Maintain comfort; trim fan CFM for latent control

6–8 PM:     Let setpoint drift back; rely on building mass

Options to enhance TOU performance:

• Direct PV coupling for compressor priority mid-day.

• Battery sized for 1–3 hours if your evening rates spike.

• Smart thermostats/controls that sync with irradiance or inverter APIs.

Learn more: Blog: HVAC Tips.

Hybrid Architectures & Controls That Actually Work

Most solar-HVAC installs land in one of three architectures:

1. Direct Connection: Daylight PV feeds the HVAC; grid supplements as needed. Simple, efficient.

2. Grid-Tie Hybrid: PV prioritized, seamless grid backup; ideal when export credits exist.

3. Battery-Enhanced: Add storage for late-peak rates or resiliency.

Control stack (practical):

• PV → Inverter → PV-priority relay for condenser.

• Current transformers (CTs) to monitor whole-home load and avoid backfeed surprises.

• Thermostat logic with PV/price inputs: comfort first, exports last.

Size conductors and breakers per NEC for both continuous compressor load and inverter interconnection. Don’t forget rapid shutdown requirements for rooftop arrays.

Compatible equipment categories: Residential Packaged Heat Pumps.

Load Profile Matching: Residential vs. Commercial vs. Industrial

Residential: Cooling peaks ~3–7 PM; occupant-driven internal gains. Strategy: slightly oversize PV for mid-day surplus, then precool to bridge the late peak. Ductless and multi-zone inverter systems excel here.

Commercial: Loads track business hours with steadier internal gains. Strategy: strong alignment with PV; right-size PV to average daytime kW and use controls for demand limit. Packaged RTUs with VFD fans and demand-control ventilation pair well.

Industrial: Process-dependent; may run 24/7. Strategy: PV covers daytime fraction; consider thermal storage (ice or chilled water) or targeted battery to shave afternoon demand charges.

Application links:
Homeowners: Ductless Systems • Room & Window AC

Step-by-Step Sizing Workflow & ROI Guardrails

1. Conduct load analysis (Manual J or equivalent) and generate hourly cooling profiles.

2. Assess solar resources (roof orientation, shading, local peak-sun-hours).

3. Set PV target = HVAC peak kW × 1.25 loss factor, adjusted for inverter efficiency and climate.

4. Select equipment: Favor SEER 16+ (SEER 22+ where budget allows) to reduce array size.

5. Design controls: PV-aware staging, setpoint glides, and dehumidification modes.

6. Check tariffs: Map net metering and TOU to a self-consumption strategy.

7. Run economics: Cooling cost reductions of ~70–80% are common with 3–6 year payback; lifespan 25+ years supports long-term value.

8. Commissioning: Verify airflow, charge, and control logic under real sun.

Use our Design Center to translate loads and tariffs into a bill-of-materials. If you already know your model, shop R32 Packaged Systems.