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Solar Mini Split Calculator

Enter your mini split's BTU and SEER rating — get solar panels needed, inverter size, annual savings, and payback period for grid-tied or off-grid systems.

Mini split specifications
hrs/day
$/kWh
Solar system
Solar sizing for your mini split
1 × 400W panels to offset usage
Running watts (AC draw)195 W
Daily kWh usage1.56 kWh/day
Annual kWh usage571 kWh/yr
Annual grid cost (no solar)$74.17/yr
Annual savings with solar$74.17/yr
Recommended inverter size500 W
Est. system cost$1,120
Payback period15.1 yrs
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How to Use This Calculator

Enter your mini split's BTU and SEER rating

The BTU rating determines your mini split's capacity — find it on the unit nameplate or product spec sheet. The SEER (Seasonal Energy Efficiency Ratio) is equally important: a 12,000 BTU SEER-25 unit draws only 469W while a SEER-15 model draws 782W for the same cooling output. Both values are on the Energy Guide label. If you don't know your SEER, most units sold after 2015 are SEER 16-18; high-efficiency models reach 22-25.

Set usage hours and electricity rate

Enter the realistic hours per day the unit runs (compressor on, not just standby). Bedrooms: 8-10 hrs. Living rooms: 10-14 hrs. Always-on cooled spaces: 16-20 hrs. Your electricity rate is on your utility bill — look for "energy charge" or "rate per kWh." The national average is $0.13/kWh but ranges from $0.09 (Louisiana) to $0.28 (Hawaii).

Choose system type and read results

Grid-tied systems use net metering — solar offsets your bill without batteries. Off-grid sizing adds a battery bank sized for 12 hours of overnight operation. The results show running watts, panels needed, annual savings, inverter recommendation, and payback period.

The Formula

Running Watts = BTU ÷ (SEER × 3.412) Daily kWh = Running Watts × Hours ÷ 1000 Annual kWh = Daily kWh × 365 Annual Cost = Annual kWh × Electricity Rate System Watts = Daily kWh × 1000 ÷ Peak Sun Hours ÷ 0.80 Panels Needed = System Watts ÷ Panel Wattage (round up) Inverter Size = Running Watts × 1.25 (round up to 500W) Battery (off-grid, 48V) = Running Watts × 12 hrs ÷ 0.80 DoD ÷ 1000 kWh

The 3.412 conversion factor comes from the BTU-to-watt relationship (1W = 3.412 BTU/hr). Dividing BTU capacity by (SEER × 3.412) gives actual watts drawn at rated SEER. System efficiency of 0.80 accounts for inverter losses, wiring losses, and real-world temperature derating — meaning you need 25% more solar capacity than the pure math suggests.

Example

Marcus — Living room 18,000 BTU mini split in Dallas

Marcus has a 1.5-ton (18,000 BTU) mini split in his living room rated SEER 18. He runs it 10 hours per day and pays $0.12/kWh in Dallas (5.4 PSH). He wants to go grid-tied with 450W panels.

BTU / SEER18,000 BTU / SEER-18
Daily usage10 hrs/day
LocationDallas, TX (5.4 PSH)
Rate$0.12/kWh

Result

Running watts293 W
Daily kWh2.93 kWh/day
Annual cost on grid$128/yr
Panels needed2 × 450W panels
Inverter recommended500W minimum
Annual savings$128/yr
Payback~8 years

Two 450W panels are sufficient to offset Marcus's living room mini split. The SEER-18 rating makes this unit quite efficient — if he had a SEER-13 unit, he'd need 3 panels instead. Upgrading to SEER-20+ would reduce both his panel count and operating costs significantly.

FAQ

Most mini splits need 1-4 solar panels (400W each) to offset their electricity use, depending on BTU capacity, SEER rating, and location. A 9,000 BTU SEER-18 unit running 8 hours/day in Los Angeles typically needs 1-2 panels. A 24,000 BTU SEER-15 unit running 12 hours in Seattle needs 4-5 panels. The SEER rating has a large impact — upgrading from SEER-15 to SEER-25 reduces electricity consumption (and panel count) by 40%.
Yes, with the right inverter. A grid-tied system with net metering effectively offsets your mini split costs without batteries. For truly off-grid operation, you need a hybrid inverter or a DC-to-AC inverter plus batteries to handle nighttime and cloudy-day operation. Some manufacturers (like Mr. Cool and Midea) make solar-ready mini splits with DC inverter technology that can run directly on DC power from panels with minimal conversion loss.
SEER (Seasonal Energy Efficiency Ratio) measures how many BTU of cooling you get per watt-hour of electricity. A SEER-20 unit is 33% more efficient than a SEER-15 unit. For solar sizing, this directly affects panel count: a 12,000 BTU SEER-15 unit draws 781W, while SEER-25 draws 469W — requiring 40% fewer panels. When sizing solar for a mini split, maximizing SEER is often more cost-effective than adding panels.
Yes — mini splits are heat pumps, so they provide both heating and cooling. Heating mode is typically 2-4x more efficient than cooling (measured as COP, or Coefficient of Performance). A unit with COP 3.0 produces 3 kWh of heat per 1 kWh of electricity — meaning you need even fewer panels for heating. However, heat pump efficiency drops in very cold temperatures (below 20°F), and some units stop working below -4°F. For cold climates, size your solar system for the cooling season (usually higher draw) to ensure year-round coverage.
Size the inverter at 1.25-1.5x the running wattage of the mini split to handle startup surge. Mini splits use variable-speed inverter compressors with relatively low startup surge (unlike traditional AC), so a 1.25x multiplier is usually sufficient. For a 12,000 BTU SEER-18 unit drawing 469W, a 600-750W pure sine wave inverter works. For a 36,000 BTU SEER-16 unit drawing 1,465W, use a 2,000W inverter. Always use pure sine wave — not modified sine wave — inverters with mini splits.

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