How many solar panels do you need to run a space heater?

By the SmartSolarSizer team · Published 20 October 2026

How much electricity does a 1500 watt heater use?

Exactly 1.5 kWh for every hour it runs on full power. Eight hours is 12 kWh, four hours is 6 kWh. No other appliance on this site is so easy to work out, because a heater's watts don't change with the weather or the model.

Electric space heaters range from 400 to 1,500 W (US Office of Congressional Workplace Rights), and the plug-in models Consumer Reports tests top out at 1,500 W (Consumer Reports). So whatever it's sold as, an electric heater, room heater or portable heater, a US plug-in model will use 1,500 W or less, and many have a 750 W low setting. On 230 V sockets in the UK and Europe you'll see higher ratings, such as 2 kW fan heaters. A 1,500 W heater warms roughly 185–215 square feet (Yukon Energy Solutions Centre).

Every resistance heater turns electricity into heat at 100% efficiency, whether it's oil-filled, ceramic, fan or infrared. An oil heater feels gentler because the oil holds heat and keeps radiating for a while after the thermostat clicks off, but it makes no more heat per kWh than a fan heater. What does lower the total is the thermostat: once the room is warm the heater cycles on and off, so if yours runs half the time, halve the hours in the estimator above.

Over a month the figures add up quickly. A 1,500 W heater on for 8 hours every day uses 360 kWh in 30 days. Cut it to 4 hours on the 750 W setting and it's 90 kWh. Before you price panels for a heater, it's the hours and the setting that are worth questioning.

Why winter decides the number of panels

Most appliance pages here size panels for an average day. A heater can't be sized that way, because nobody runs one in July. In New York one 430 W panel makes 1.66 kWh on an average day but 1.21 kWh in December. The 12 kWh heater goes from 8 panels to 10. The last column below is each location's darkest winter month:

Further north the gap becomes impractical. Berlin's December output of 0.96 kWh per kW a day means 30 panels for one heater, which is a whole roof for one room. Lahore, Karachi, Delhi and Johannesburg are the opposite case: there, the darkest winter month needs no more panels than an average day of the year.

What happens when a cloud passes (no battery)

Run a heater straight off panels and an inverter, with no battery or grid behind it, and it only works while the array delivers at least 1,500 W at that moment. That's 4 panels at full rated output, and panels reach their rating only in strong sun. When a cloud crosses, output can fall well below that within seconds; the inverter shuts down or the heater cuts out, then the cycle repeats as the sun returns. A heater gives no warning and can't run at "half power" on its own.

So a solar-only heater needs either a battery to smooth the dips or a grid connection to fill them. A hybrid inverter that can draw from the grid when the panels fall short handles this automatically, which is one more reason heaters are far easier on a grid-tied home than off-grid. On the inverter side, a resistance heater has no start-up surge, so a 2,000 W continuous inverter covers a 1,500 W heater and 3,000 W covers a 2 kW one. The main calculator sizes more cautiously and may suggest a larger unit.

Can a solar generator run a space heater?

For an hour or so, yes. Overnight, rarely. A solar generator (portable power station) stores energy in its battery, and a 1,500 W heater empties it fast:

Assumes a lithium (LiFePO4) battery, using 90% of its capacity at 90% efficiency. A power station's rated Wh is its battery size; its inverter must also be rated for the heater's watts.

Eight hours at 1,500 W needs 12 ÷ 0.81 = 14.8 kWh of battery, and refilling that from panels in a New York December would take 13 panels on top of everything else.

Don't buy a power station just because its inverter is rated above 1,500 W. That only tells you it can power the heater. The battery's Wh decides how long it runs. Take a cabin used on winter weekends with a 750 W heater on its low setting overnight: 8 hours is 6.0 kWh, which needs about 7.4 kWh of battery. If you want warmth from a power station, use the low setting, heat a small space, and consider an electric blanket, which warms you rather than the air.

The best heaters to use with solar panels

For heating you do every day, the honest answer is a heat pump, usually a ductless mini split. It moves heat in from outdoors rather than making it. A 1,500 W heater produces about 5,100 BTU an hour; the 12,000 BTU model on our mini split page has a coefficient of performance at full output of 4.24 at 47 °F (8 °C) and 2.74 at 17 °F (−8 °C) (Mitsubishi submittal). The same heat therefore takes about 354 W in mild weather and 547 W in a hard frost. The US Department of Energy says heat pumps can easily cut heating electricity by 50% compared with resistance heaters (DOE).

A space heater still earns its place for short, occasional use, like an hour in a cold office or a bathroom before a shower, where a small battery or the grid covers it. Buying panels to run one for hours every evening is the expensive way round.

DC heaters and "solar-powered" heaters

A 12 V or 24 V DC heater is still a resistance heater, and its heat output equals its watts whatever the voltage. Running it straight from a battery saves the small inverter loss, and that's all. Check the watt rating before you buy: a low-wattage DC heater gives a fraction of a 1,500 W heater's warmth, which suits a van or a small cabin, not a living room. If something is sold as a "solar heater", check whether it's a DC resistance heater, a solar thermal air collector or an ordinary heater bundled with a power station, because the maths is different for each.

If you want to use direct DC solar for heat, water is the better target, because a tank stores the heat for later. Our water heater page covers DC geyser elements.

Garages, greenhouses and grid-tied homes

A garage workshop or greenhouse heater uses the same sum, watts × hours, and the hours depend on insulation far more than on the heater. Sealing draughts and heating only the hours you need is cheaper than adding panels.

On a grid-connected home, the winter column overstates what you need, because net metering lets summer surplus pay for winter heating. A 1,500 W heater used 8 hours a day for four winter months uses about 1,440 kWh, which 3 panels offset over a year in New York. Whole-home electric heating, such as an electric boiler or underfloor heating, is a bigger sizing job; start with the heat pump page.

Common questions

Sources

Solar output for every location comes from the European Commission's PVGIS 5.3 (1 kW system, panels at the best fixed angle facing the equator, 14% system losses), retrieved 20 October 2026. Panel counts assume 430 W panels, the most common size in 2025 home solar quotes (EnergySage).

• US Office of Congressional Workplace Rights: space heater fast facts
• Consumer Reports: space heater buying guide
• Yukon Energy Solutions Centre: electric heaters
• US DOE Energy Saver: electric resistance heating
• Mitsubishi MSZ-FS12NA submittal (COP at 47 °F and 17 °F)

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