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Solar Space Heater Calculator

Calculate panels needed to power a space heater using winter peak sun hours — the critical difference from other calculators. Includes heat pump comparison.

Space heater inputs
hrs/day
months
$/kWh
Solar for space heater — and the better alternative
6 panels needed (winter PSH: 3.5)
Daily heater usage6.00 kWh/day
Annual heater electricity cost$117.00/yr
Panels needed (WINTER PSH)6 panels
Solar system cost$6,720
Annual savings (heating months)$117.00/yr
Payback period57.4 yrs
Better option: Solar + Heat Pump (3x more efficient)
Heat pump kWh/yr300 kWh (vs 900 for heater)
Panels needed for heat pump2 panels (vs 6 for heater)
Annual savings vs space heater$78.00/yr
Payback (solar + mini-split)67.2 yrs
A mini-split heat pump + fewer solar panels beats solar + space heater on payback, panels needed, and roof space.
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How to Use This Calculator

Enter your heater wattage and usage pattern

Select your space heater's wattage — most portable heaters have a 750W low and 1500W high setting; garage and workshop heaters are typically 2000W. Enter how many hours per day you run it during the heating season and how many months per year. These inputs determine your annual heating electricity cost and how many solar panels are needed to offset it.

Use WINTER peak sun hours — this is critical

This calculator uses winter-specific peak sun hours, not the annual average. This is the most important distinction from general solar calculators. In Chicago, winter PSH is 2.8 — significantly lower than the annual average of 4.4. Using annual average PSH would suggest you need fewer panels than you actually do, leaving your system undersized precisely when you need heat most. The locations list shows winter-specific PSH values.

Read the heat pump comparison

The calculator automatically computes the heat pump alternative. A mini-split heat pump produces the same amount of heat as a resistance space heater using 3 times less electricity (COP of ~3). The comparison shows how many fewer panels you'd need to power a heat pump versus a space heater, and the payback period for a solar + heat pump combination. In nearly every scenario, solar + heat pump beats solar + space heater on ROI.

The Formula

Daily kWh = Heater Watts × Daily Hours ÷ 1000 Annual Heater kWh = Daily kWh × 30 days × Heating Months Annual Heater Cost = Annual kWh × Electricity Rate System Watts = Daily kWh × 1000 ÷ WINTER PSH ÷ 0.80 Panels Needed = System Watts ÷ Panel Watts (round up) Annual Savings = min(Annual Production, Annual Heater kWh) × Rate Payback = System Cost ÷ Annual Savings — Heat Pump kWh = Annual Heater kWh ÷ 3 (COP = 3) Heat Pump Panels = Panels Needed ÷ 3 (round up) Heat Pump Payback = (Panel Cost + $3,000 mini-split) ÷ Heater Cost Savings

The formula uses winter-specific PSH to size the solar system for worst-case heating season conditions. If you sized panels using annual average PSH (e.g., 4.4 for Chicago), you'd get the wrong answer — your panels produce only 2.8 hours equivalent in January when you need heat most. The 0.80 efficiency factor accounts for inverter losses and panel temperature derating.

Example

Tom — 1500W living room heater in Chicago

Tom runs a 1500W space heater in his Chicago living room for 10 hours per day during 5 winter months. He pays $0.15/kWh and wants to know how many panels he needs.

Heater1500W, 10 hrs/day, 5 months
LocationChicago, IL (winter 2.8 PSH)
Rate$0.15/kWh

Space heater result

Annual heater cost~$337/yr
Panels needed (winter PSH 2.8)9 × 400W panels
System cost~$10,080
Payback~29.9 years

Heat pump alternative

Heat pump electricity (COP 3)750 kWh/yr (vs 2,250)
Panels needed3 × 400W panels
System cost (panels + mini-split)~$6,360
Annual savings vs old heater~$225/yr
Payback~28.3 years

The solar + space heater combination has a 30-year payback — nearly the entire lifetime of the panels. The heat pump alternative needs only 3 panels instead of 9. Both paybacks look long in this scenario because Chicago's low winter sun means more panels are needed, and the heating cost per year doesn't justify a large solar system used only for heating. The real lesson: solar ROI is best when panels are used year-round for all loads, not dedicated to seasonal heating only.

FAQ

Solar + space heater has poor ROI for three compounding reasons: (1) Winter is the worst time for solar — panels produce significantly less in winter due to shorter days and lower sun angles, so you need more panels to cover the same load. (2) Space heaters are energy-intensive — running a 1500W heater 10 hours/day uses more electricity per month than running an entire home's lighting. (3) Heating is seasonal — unlike a year-round load (refrigerator, EV charging), your solar investment sits idle in summer and is undersized in winter. The math works out to very long paybacks — typically 20-35 years — in any climate with real winters.
A resistance space heater converts electricity directly to heat at 100% efficiency — 1 kWh of electricity becomes 1 kWh of heat. A heat pump (mini-split) doesn't create heat; it moves heat from outside air into your room. Even at 20°F (-7°C) outside, there is still thermal energy in the air that a heat pump can extract. A modern mini-split in mild-to-moderate cold has a COP (Coefficient of Performance) of 2-4 — meaning it delivers 2-4 kWh of heat for every 1 kWh of electricity consumed. At COP 3, a heat pump is 300% efficient by the resistance heater measure. In climates below -10°F (-23°C), COP drops significantly and heat pump efficiency advantage diminishes.
Solar + space heater makes sense when: (1) You already have a solar system sized for other loads — the heater is an extra load you're adding to an existing system with surplus capacity. (2) You're in a mild climate (South/Southwest US) where winter PSH is still 4+ and heating is only 2-3 months. (3) You're off-grid with no alternative and solar + battery is already installed. (4) The heater use is during daylight hours only — running it directly from panels without batteries maximizes efficiency. In any other scenario, the combination doesn't pencil out vs just buying a more efficient heat pump.
Annual average PSH represents solar production spread over 12 months. If you're sizing solar specifically to power a space heater used only in winter (the worst solar months), annual average PSH gives you a false sense of security. Example: Seattle has an annual average of 3.6 PSH but a winter PSH of only 1.8 — half the annual average. A system sized using 3.6 PSH would produce only 50% of what you expect in January. For dedicated seasonal loads, you must size using the PSH of the months when the load actually runs. This calculator uses winter PSH specifically to avoid this dangerous underestimate.
In order of efficiency and ROI: (1) Solar + heat pump (mini-split) — best combination by far. One system heats AND cools, and COP of 3-4 means fewer panels needed. (2) Solar thermal collectors for radiant floor heating or hydronic systems — directly converts sunlight to heat with 50-70% efficiency (much better than PV's 20%). Good for new construction. (3) Solar + resistance space heater — worst of the options. The only scenario where this makes sense is if you already have a large PV system with excess capacity in winter.

Related Calculators

☀ Solar Panel Calculator
Size your full home solar system for year-round loads.
❄ AC Solar Calculator
Panels needed to run air conditioning.
⚡ Power Consumption Calculator
Calculate daily kWh for any appliance including heaters.
📈 Solar Savings Calculator
Full home solar savings including all seasonal loads.

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