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Solar + Geothermal Calculator

Enter your home size, climate zone, and current HVAC — get geothermal kWh consumption, solar panels needed, combined system cost with 30% tax credit, and payback period.

Home details
sqft
$/kWh
Solar + Geothermal system sizing
13 × 400W panels — 5.0 kW solar to offset geothermal
Geothermal annual kWh (COP 4.0)6,594 kWh/yr
Solar kW to offset geothermal5.0 kW (13 panels)
Geothermal system cost$16,000
Solar system cost$14,052
Combined system cost$30,052
ITC 30% tax credit (geo + solar)-$9,016
Net cost after tax credit$21,036
Current annual HVAC cost$324/yr
Annual cost with geo + solar$857/yr (solar offsets electricity)
Combined annual savings$-533/yr
Fossil fuels eliminated100% — fully electric net-zero HVAC
Net-zero home HVAC threshold5.0 kW solar
CO2 eliminated vs current HVAC1,165 kg/yr
Simple payback (after tax credit)N/A
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How to Use This Calculator

Enter your home size and climate zone

Start with your conditioned floor area in square feet — this drives both the geothermal heat pump sizing and the solar panels needed to run it. Select your climate zone: cold zones (Chicago, Minneapolis) need far more heating capacity than hot zones (Phoenix, Miami). Mixed climates balance heating and cooling loads roughly evenly.

Select your current HVAC and geothermal loop type

Your current HVAC type determines the savings — switching from expensive oil or propane saves far more than replacing a heat pump. Horizontal loops (trenched 4-6 ft deep) cost less but need yard space. Vertical bores suit small lots or rocky terrain but require drilling, adding $3,000-5,000 per bore hole.

Read the results

The calculator outputs geothermal annual electricity at COP 4.0, the solar kW needed to offset it entirely, combined system cost before and after ITC 30% tax credits, annual savings versus your current HVAC, CO2 eliminated, and payback period. Both geothermal and solar qualify for the 30% federal Investment Tax Credit through 2032.

The Formula

Heating Load (kBtu/yr) = Home sqft × Climate Heating Factor Cooling Load (kBtu/yr) = Home sqft × Climate Cooling Factor Geothermal kWh = Load (Btu) ÷ 3412 ÷ COP (4.0) Solar kW = Daily kWh ÷ Peak Sun Hours (4.5) ÷ 0.80 efficiency Panels = Solar kW ÷ 0.40 kW per panel (round up) Combined Cost = Geo Cost ($8-12K per 1,000 sqft) + Solar Cost ($2.80/W) Net Cost = Combined Cost × 0.70 (after 30% ITC) Payback = Net Cost ÷ Annual Savings

Climate factors used: Cold = 35 kBtu/sqft heating + 10 cooling; Mixed = 22 + 16; Hot = 10 + 28. These are annual totals — geothermal handles both seasons with the same equipment. COP 4.0 means for every 1 kWh of electricity, the heat pump delivers 4 kWh of heat (or removes 4 kWh of heat for cooling).

Example

The Hendersons — Cold climate, 2,000 sqft, replacing gas furnace

The Hendersons live in Minneapolis (cold climate zone) in a 2,000 sqft home. They currently pay for gas heating and standard central AC. They want to go fully electric with geothermal and offset it with solar.

Home size2,000 sqft
ClimateCold (Zone 6)
Current HVACGas furnace + AC
Loop typeHorizontal
Rate$0.13/kWh

Result

Geothermal annual kWh~5,900 kWh/yr
Solar to offset geo4.5 kW (12 panels)
Geothermal cost~$16,000
Solar cost~$12,600
ITC 30% credit-$8,580
Net cost~$20,020
Annual savings~$1,800/yr
Payback~11 years

The Hendersons achieve a fully fossil-fuel-free home: geothermal handles all heating and cooling at 4x efficiency, and the solar array offsets all the electricity it consumes. With a 25-year system life and 11-year payback, they get 14 years of free heating, cooling, and electricity production.

FAQ

Yes — residential geothermal heat pumps qualify for the same 30% Investment Tax Credit (ITC) as solar panels through 2032, then step down to 26% in 2033 and 22% in 2034. The Inflation Reduction Act extended and expanded this credit. Both the geothermal system and the solar array can be claimed together. For a $28,000 combined system, that's $8,400 back as a tax credit — not a deduction. You must owe enough federal tax to claim it, though unused credits can carry forward.
Ground-source (geothermal) heat pumps maintain COP 3.5-5.0 year-round because ground temperature stays constant at 50-55°F regardless of air temperature. Air-source heat pumps drop to COP 1.5-2.5 in extreme cold. This is why geothermal excels in cold climates — while an air-source heat pump struggles at -10°F, the geothermal system delivers the same COP 4.0 it achieves in summer. This calculator uses COP 4.0 as a conservative average across heating and cooling seasons.
Horizontal loops need approximately 1.5 times your home's square footage in yard area. A 2,000 sqft home needs about 3,000 sqft of trenching area — trenches run 4-6 feet deep in parallel rows. Vertical bores use a 5×5 ft footprint per bore hole but require a drilling rig. Each bore goes 150-300 feet deep, and a typical home needs 3-6 bores. Vertical costs more ($3,000-5,000 per bore vs $2,000-3,000 for horizontal) but works for small urban lots or rocky soil that's hard to trench.
Yes — geothermal heat pumps connect to existing ductwork, making them a direct swap for gas furnace + AC. The heat pump unit replaces both your furnace and AC condenser. You keep your existing air handler and ducts. You do need to upgrade your electrical panel for a 240V heat pump circuit if you don't have one — typically $500-1,500. If you have radiant heat (no ducts), you can use a water-to-water geothermal system to supply radiant floors or baseboards instead.
The climate zone affects the geothermal's annual kWh consumption, which determines how much solar is needed to offset it. In cold climates, heavy heating demand means geothermal uses more electricity, requiring more solar panels. In hot climates, cooling dominates — still significant but somewhat lower total load. The solar sizing uses an average 4.5 peak sun hours nationally; if you know your specific location's PSH, the actual panel count may differ slightly. Cold climate homes often need 20-40% more solar than hot climate homes of the same size.

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