Solar Power for a Greenhouse: Sizing a System for Heaters, Fans, and Grow Lights

Last updated: 2026-08-12

Bottom line up front: a backyard greenhouse rarely gets a real electrical run, but it almost always needs one. A thermostat-controlled heater to stop a frost from wiping out seedlings, a vent fan to keep summer heat from cooking everything on a sunny afternoon, and grow lights to stretch the season all need continuous, weatherproof power — and a trenched conduit run to a structure that's sometimes just a kit bolted to a concrete pad rarely pencils out. A portable power station paired with folding solar panels handles all three loads for a fraction of that cost, as long as you size it around your heater, not your lights.

This isn't the chicken coop power article or the workshop one, even though the hardware overlaps — and if you haven't settled on a brand yet, our EcoFlow vs. Jackery comparison covers how the two product lines actually differ. A greenhouse has one load the others don't: a heater that has to run through the coldest night of the year, at the exact moment your solar panel is producing the least — and if it fails, you don't get a warning, you get a bench of dead seedlings by morning.

What Actually Draws Power in a Greenhouse

Four load categories cover almost every backyard greenhouse setup, and they behave very differently from each other:

Frost-protection heat. A small greenhouse heater sized for a 6x8 or 8x10 structure typically draws 750–1,500W, cycling on a thermostat. This is the load that decides your whole system size — everything else is small by comparison.

Vent fans and circulation. A thermostatically controlled exhaust fan for summer cooling draws 50–150W, and a small circulation fan to prevent fungal disease and even out temperature draws 10–30W. Both often run for hours at a stretch, not just briefly.

Grow lights. LED grow lights for extending a short-season start or overwintering cuttings run anywhere from 20W for a small clip-on unit to 300W+ for a full-bench fixture, usually on a timer for 12–16 hours a day.

Irrigation. A small pump for drip irrigation or a misting system draws 30–100W and typically runs in short bursts rather than continuously.

Combined, a well-equipped hobby greenhouse can draw under 100W most of the year and spike to 1,000W or more on the coldest nights — which is exactly the sizing problem that trips people up if they shop for a power station based on the small numbers.

Why the Extension Cord Doesn't Cut It Here

Running a cord from the house works for a season, the same way it does for a coop or a shed — until a heater trips a breaker at 2 a.m. because the cord's gauge wasn't rated for a sustained 1,000W+ draw, or a freeze cracks the cord where it crosses a garden bed and the greenhouse loses power on the exact night it needed it most.

A permanent electrical run to a detached greenhouse — trenched conduit, a small subpanel, GFCI protection appropriate for a structure that's often warm and humid inside — runs $1,000–$3,000 depending on distance from the main panel, according to typical electrician quotes for outbuilding runs. For a greenhouse that might cost $500–$2,000 to build in the first place, that math rarely works, especially for a hobby setup rather than a commercial operation.

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Sizing the Battery Around the Coldest Night, Not the Average One

The mistake almost everyone makes is sizing off average draw. A greenhouse pulling 100W most of the day looks like it needs almost nothing — until the forecast calls for a hard freeze and the heater runs at 1,200W for eight hours straight to keep the interior above freezing. That single night can draw 9.6kWh, more than most portable power stations hold on their own.

The practical approach: size the battery for your heater's worst realistic night, then add solar to recover that within a day or two of sun, not to cover the heater load directly in real time. A 1,000Wh unit like the EcoFlow Delta 2 covers light frost protection, fans, and lights comfortably, but a 1,200W heater running overnight will drain it in well under an hour if it's the only load the unit is carrying. For anyone in a climate with real hard freezes, that points toward a 2,000Wh-class unit like the EcoFlow Delta Pro or a similarly sized Jackery Explorer 2000 Plus, paired with enough panel wattage to fully recharge it the next clear day.

A rule that works for most three-season climates: assume two to three consecutive cloudy or freezing days with minimal solar recovery, and size the battery to survive that stretch on heater load alone before assuming solar bails you out mid-freeze. Add panels to close the gap afterward, not to carry the load during it. The same worst-case-first logic applies to whole-home backup — our 72-hour outage sizing guide walks through the math in more depth if you're sizing a unit that needs to cover the house as well as the greenhouse.

Where Solar Panel Placement Gets Tricky

A greenhouse's own roof is usually the worst place to put a solar panel — greenhouse glazing is there specifically to let light through, and shading part of it to mount a panel defeats the purpose and can shadow plants underneath. Ground-mount or a small rack near the structure, angled for your latitude and kept clear of the greenhouse's own shadow as the sun moves through the day, works better for most backyard setups than trying to integrate panels into the greenhouse itself.

If the greenhouse sits within panel-cable range of your home's existing rooftop solar array, it's worth asking whether a small dedicated circuit off your home battery makes more sense than a standalone portable setup — especially if you're already running near capacity on backup power and considering an expansion. That's a conversation worth having with an installer rather than assuming a portable station is automatically the cheaper path; comparing quotes through EnergySage costs nothing and shows whether a small dedicated circuit prices out lower than a dedicated portable system once you factor in a multi-year lighting and heating habit. If you're weighing a bigger disconnect-from-the-grid move rather than just one outbuilding circuit, our off-grid solar system cost guide breaks down what that actually takes.

Battery Chemistry and Cold Matters Here Too

Like coop and outbuilding setups, a greenhouse power station is often stored somewhere unheated — a garden shed, a covered corner of the greenhouse itself, or outdoors under a weatherproof cover. LiFePO4 batteries, standard in current EcoFlow and Jackery units, tolerate cold far better than older lithium-ion packs, but usable capacity and charge speed still drop as temperatures fall, and most manufacturers recommend charging above freezing when possible. On the exact nights you need full heater capacity most, a cold-soaked battery may deliver less than its rated number — one more reason to size with margin rather than to the label spec.

Bring the unit inside overnight during the hardest freezes if you can, or keep it in an insulated enclosure near the greenhouse rather than fully exposed. A unit that's warm when the heater load hits will outperform and outlast one that's been sitting at 15°F all evening. Your solar panels take a similar hit in cold, low-light months — see our breakdown of real winter production numbers for what to actually expect from the recharge side of this equation.

A Few Things to Check Before You Wire It Up

Confirm your heater's actual wattage, not the box's rounded number. Small ceramic and fan-forced greenhouse heaters vary widely — check the nameplate rating, not a generic "greenhouse heater" wattage assumption, before sizing anything.

Put the heater on its own thermostat, not a timer. A timer runs the heater whether it's needed or not, wasting battery capacity on a mild night and potentially running short on the coldest one. A thermostat only draws power when the temperature actually calls for it.

Test the full setup through one real cold snap before you trust it. Run the greenhouse off battery and solar through a normal cold night early in the season, so you know your actual recharge rate and runway before the first hard freeze that actually matters.

Don't assume your home backup unit can double duty during a freeze. If you already own a portable power station for house backup, it's tempting to run an extension cord to the greenhouse during a cold snap — but a genuine hard freeze is also exactly when winter storms and grid outages are more likely, and you don't want your home backup half-drained by a heater the same night you need it for the house.

Start Here

A greenhouse is a different sizing problem than a coop, a workshop, or camping gear: small day-to-day draw, one large and unforgiving overnight load, and a battery that has to actually deliver on the coldest, lowest-sun night of the year. Size the battery for your heater's worst night first, add solar to recover from it, and keep the unit somewhere it won't cold-soak below its rated performance.

Check current pricing on the EcoFlow Delta 2 for light frost protection and lights, step up to the Delta Pro or Jackery Explorer 2000 Plus if you're running real heat through winter, and if you're weighing a dedicated home-battery circuit instead, get a few quotes through EnergySage before committing to either path.

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