How Many Solar Panels to Run a Space Heater? (Calculator + Examples)
A space heater uses 4.5 to 12 kWh per day depending on its wattage setting (750W or 1,500W) and how many hours it runs. You need 3 to 8 standard 400W solar panels to cover it at 5 peak sun hours. However, if you are investing in solar for heating, a heat pump is roughly 3 times more efficient and should be your first consideration.
Quick answer
A 400W solar panel produces about 1.66 kWh per day at 5 peak sun hours (400W x 5h x 0.83 derate). A 1,500W space heater running 6 hours at 50% duty cycle uses 4.5 kWh per day, so 3 panels cover it. At 8 hours or higher duty cycles, you may need up to 8 panels.
| Peak Sun Hours | 750W (low setting) | 1,500W (50% duty) | 1,500W (100% duty) |
|---|---|---|---|
| 3 PSH (very cloudy) | 4 panels | 6 panels | 13 panels |
| 4 PSH (cloudy) | 3 panels | 5 panels | 10 panels |
| 5 PSH (US average) | 3 panels | 3 panels | 8 panels |
| 6 PSH (sunny) | 2 panels | 3 panels | 7 panels |
| 7 PSH (desert SW) | 2 panels | 2 panels | 6 panels |
Formula: panels = daily kWh / (panel watts x PSH x 0.83 derate), rounded up. Assumes 6 hours of daily use.
Space heater energy breakdown
All electric resistance heaters -- ceramic, oil-filled radiator, infrared, fan-forced -- convert electricity to heat at 100% efficiency. The difference between types is how they distribute that heat, not how much energy they consume. A 1,500W ceramic heater and a 1,500W oil-filled radiator use the same energy over the same period.
| Specification | Low Setting | High Setting (cycling) | High Setting (constant) |
|---|---|---|---|
| Wattage | 750W | 1,500W | 1,500W |
| Hours per day | 6 | 6 | 8 |
| Duty cycle | 100% | 50% | 100% |
| Daily energy use | 4.5 kWh | 4.5 kWh | 12.0 kWh |
| Monthly energy use | 135 kWh | 135 kWh | 360 kWh |
| Yearly (5-month season) | 675 kWh | 675 kWh | 1,800 kWh |
The duty cycle depends heavily on room insulation. In a well-insulated room with the thermostat set to 68 degrees F, the heater may cycle at 40-50%, reaching the target temperature and shutting off periodically. In a drafty room or uninsulated garage, the heater runs at nearly 100% duty and still struggles to maintain temperature.
Try the calculator
Adjust the panel wattage and your location's peak sun hours to see exact production numbers for your setup.
Benchmarks: U.S. avg 4.98 · Phoenix 6.54 (highest) · Seattle 3.95 · Anchorage 3.17 (lowest). Above ~5.5 = sunny · 4.5–5.5 = average · below 4.5 = cloudy.
Tap to see sensitivity analysisSensitivity analysis
| Scenario | Value |
|---|---|
| Low (-20%) | 1.3 kWh |
| Expected | 1.6 kWh |
| High (+20%) | 1.9 kWh |
Your daily production scales linearly with both panel wattage and peak sun hours. A 10% change in either input changes your result by 10%.
Running it off-grid
Running a space heater off-grid with solar has a fundamental timing mismatch: heating demand peaks in the evening and at night when solar panels produce zero power. This makes battery storage essential and significantly increases system cost.
Battery bank sizing (for 4.5 kWh/day use):
- Daily consumption: 4.5 kWh
- Autonomy target: 1.5 days (heating is needed on cloudy days when solar output drops)
- Total energy needed: 6.75 kWh
- At 12V with lithium (LiFePO4) batteries at 80% depth: 6.75 kWh / 12V / 0.80 = 703 Ah
- At 48V: 176 Ah
Inverter sizing: Space heaters are pure resistive loads with no startup surge. A 1,500W heater needs an inverter rated at 1,500W or above -- no need to oversize for surge. A 2,000W pure sine wave inverter works well. Modified sine wave inverters are acceptable for resistive heaters, unlike compressor-based appliances.
Charge controller: Three to four 400W panels need an MPPT charge controller rated for at least 25A at 48V. A 30A MPPT controller is adequate.
Important caveat: In winter, peak sun hours are reduced by 30-50% compared to summer. If you live in a northern state with 3 PSH in winter, you will need twice as many panels as the summer calculation suggests. This makes solar-powered resistive heating one of the least practical off-grid applications.
See our battery charging calculator for exact sizing.
Running it grid-tied
Grid-tied solar can offset space heater costs, but the seasonal mismatch is significant. Your panels produce the least energy in winter (when you need heating most) and the most in summer (when you do not need heating at all).
In practice, grid-tied systems handle this through annual net metering. You build up large credits during summer months when your panels overproduce, then draw those credits down in winter when you underproduce. The economics still work out because total annual production offsets total annual consumption.
For a space heater using 4.5 kWh per day over a 5-month heating season (675 kWh total), 3 panels producing about 1,815 kWh per year generate more than enough annual energy to cover the heater. The surplus 1,140 kWh offsets other household loads.
Why a heat pump is a better investment
Before sizing a solar array for a space heater, consider this: a mini-split heat pump delivers the same heating with one-third the electricity. The DOE rates modern cold-climate heat pumps at a COP (coefficient of performance) of 2.0-3.0, meaning they produce 2-3 kWh of heat for every 1 kWh of electricity consumed.
- Space heater: 4.5 kWh electricity produces 4.5 kWh of heat. Needs 3 panels.
- Heat pump: 1.5 kWh electricity produces 4.5 kWh of heat. Needs 1 panel.
A ductless mini-split costs $1,500-$4,000 installed and also provides cooling in summer, eliminating the need for a separate AC. When paired with solar, a heat pump requires far fewer panels for the same comfort level.
Energy-saving tips for space heater use
If you do use a space heater, these strategies reduce energy consumption by 20-40%:
- Heat only the room you are in. Close doors and lower the central thermostat. Heating one room with a space heater while keeping the rest of the house at 60 degrees F is more efficient than heating the whole house to 68 degrees F.
- Use the low setting when possible. The 750W setting provides adequate warmth for small, well-insulated rooms. At half the wattage, you need half the solar panels.
- Insulate the room. Draft stoppers under doors, weatherstripping on windows, and heavy curtains can reduce heat loss by 20-30%, allowing the heater to cycle less frequently.
- Use a heater with a built-in thermostat. Models with thermostatic control cycle off when the room reaches the set temperature, reducing average energy consumption compared to units that run at full power continuously.
- Place the heater strategically. Put it near where you sit, not across the room. Radiant and infrared heaters work best for direct heating of people rather than warming entire rooms.
- Consider heated blankets or foot warmers. A heated blanket uses only 100-200W and keeps you warm at a fraction of the energy cost of heating an entire room.