Balcony Solar Kit Size: How Many Watts Do You Need?

The right balcony solar kit size for most renters is 400 to 800 watts: enough to cover the power your home draws all day, without paying for panels whose output mostly flows to the grid unpaid. Size up only if someone is home using power in daylight, your state cap allows it and your railing has room.

To choose your balcony solar kit size, check four things in order: your daytime baseload, your state’s wattage cap, your balcony space and the direction your panels will face.

How to choose a balcony solar kit size in 4 steps

You choose a balcony solar kit size by matching it to the power your home uses while the sun is up, then trimming it to your legal cap and the space you have. Kit size is the inverter’s AC output in watts, which is the number state laws count.

Find your daytime baseload. This is the power your fridge, router and standby devices draw all the time.
Check your state’s cap. Most states with a law allow 1,200 W, but a few set different limits.
Measure your railing or floor space. Each standard panel needs roughly 3.7 feet of width.
Check the direction and mount. A vertical railing panel makes much less than a tilted one.

EnergySage says most plug-in systems on the market fall between 400 and 800 watts. Solar United Neighbors gives the full range as 200 to 1,920 watts.

Step 1: Find your daytime baseload

Your daytime baseload is the steady power your home uses when nobody is cooking, washing or running the AC, and it sets the useful size of a balcony kit. Solar power that your home uses saves you money; the rest leaves through the meter.

Two figures to start from:

164 watts: the average always-on load an NRDC study measured across 70,000 California homes.
Under 100 watts: Germany’s environment agency, the UBA, says constant load in average apartments is mostly well under 100 watts.

Your total use matters less than you’d think. The EIA’s 2020 Residential Energy Consumption Survey puts electricity use in apartments in buildings with 5 or more units at 20.8 million Btu per household. At the EIA’s 3,412 Btu per kWh, by my math that’s about 6,096 kWh a year, or 16.7 kWh a day.

That big number is spread over evenings, heating and cooling. What a solar kit can offset is the part you use between roughly mid-morning and late afternoon. If you work from home, run a dishwasher at noon or charge an e-bike in daylight, your daytime load is higher than the always-on figure, and a bigger kit earns its keep.

Step 2: Check your state’s wattage cap

Your state’s wattage cap is the legal ceiling on balcony solar kit size, and it counts the inverter’s AC output, not the panel watts. Most states with a signed plug-in solar law cap kits at 1,200 W, but several differ in ways that change what you can buy.

State	Cap or rule	What it means for size
Most signed states (California, New Jersey, Utah, Virginia and others)	1,200 W	800 or 1,200 W both fit
Colorado	1,920 W (HB26-1007)	The highest cap in the country
Maine	Up to 420 W DIY (LD 1730)	Above 420 W, up to 1,200 W, needs an electrician on a dedicated circuit
Maryland	1,200 W, one system per meter (Chapter 353)	You can’t add a second kit later on the same meter
Delaware (pending)	800 W per meter proposed (SB 270)	Still awaiting consideration in committee

In Maryland, if you buy 400 W now, you can’t simply plug in a second kit next year, so pick the size you’ll want to keep. Our balcony solar laws by state page lists every state’s status, cap and bill number.

Step 3: Measure your balcony space

Balcony space limits kit size because each standard 400 W panel is about 44.6 by 67.8 inches. Our panel weight and size guide has the full spec table, including lighter flexible panels that make less power per square foot.

By my math, using 400 W modules side by side on a railing:

Kit size	Panels	Railing width needed	Panel area
400 W	1	about 44.6 in	about 1.76 m²
800 W	2	about 89.2 in (7.4 ft)	about 3.52 m²
1,200 W	3	about 133.8 in (11.2 ft)	about 5.28 m²

Measure your railing before you shop. By my math, an 8-foot railing fits two panels side by side, not three. Panels that overhang a neighbor’s space or block an exit can turn a size decision into a lease problem.

Step 4: Factor in direction and mounting

Direction and mounting change how many kWh each watt makes, so they change the size that makes sense. A south-facing panel tilted outward makes far more than the same panel hanging flat on a railing.

In Baltimore, PVGIS gives 921.3 kWh per kW a year for a vertical south railing panel and 1,378.4 kWh per kW tilted at 35 degrees. A tilted 800 W kit there makes about as much as a vertical 1,200 W kit.

East and west railings shift output toward mornings or evenings, which can line up better with when you’re home. Our panel direction guide compares the four directions and the best tilt.

Why a bigger balcony kit mostly exports unpaid power

A bigger balcony kit mostly exports unpaid power because your home only uses solar power at the moment it’s made, and the surplus earns nothing in most states with a plug-in law. Maryland’s Chapter 353, Utah’s HB 340, New Jersey’s S2368 and Virginia’s Chapter 1052 all keep plug-in kits out of net metering.

Some top guides get this wrong. As of October 2026, EnergySage says balcony panels don’t feed excess electricity back to the grid. They do: the surplus flows out through your meter, as our guide to extra power from balcony solar explains.

So each extra watt is worth less than the last. Once your kit’s midday output passes your baseload, every additional panel adds output you give away.

By my math: self-used kWh for a 400, 800 and 1,200 W kit

A 400 W kit uses most of its output at home, while a 1,200 W kit exports more than half of it, for a renter whose daytime load is the 164 W always-on average. I modeled a south-facing apartment balcony in Baltimore, Maryland, a state with a 1,200 W cap.

How I ran it:

Output: PVGIS 5.2 hourly data for a vertical south railing and a 35-degree tilt, PVGIS-NSRDB, 14% system losses, all 96,408 hours from 2005 to 2015.
Load: a steady 164 W, the NRDC always-on average, as if you’re out during the day.
Self-use: for each hour, the smaller of the kit’s output and the load, averaged over the 11 years.
Value: Maryland’s August 2026 residential price of 21.40 cents per kWh.

Kit (vertical south railing)	Made per year	Used at home	Share used	Exported	Saved per year
400 W	369 kWh	314 kWh	85%	55 kWh	$67
800 W	737 kWh	423 kWh	57%	314 kWh	$91
1,200 W	1,106 kWh	470 kWh	42%	636 kWh	$101

The step that matters: going from 400 to 800 W adds 109 kWh of self-used power. Going from 800 to 1,200 W adds 369 kWh of output but only 47 kWh of self-use, about 13% of the extra. That’s about $10 a year.

Tilting the panels widens the gap. At 35 degrees, self-use is 417, 506 and 546 kWh for the three sizes, while the 1,200 W kit exports 1,108 kWh, by my math. The UBA’s lower baseload shrinks the useful size further: at 100 W, the three sizes use 242, 292 and 316 kWh.

The other extreme shows when a big kit pays. If your apartment drew the RECS average of about 696 W evenly around the clock, a 400 or 800 W kit would use 100% of its output and a 1,200 W kit about 96%. Real homes sit between the two cases, so watch your own daytime use for a week before you buy.

Is 800 watts or 1,200 watts better for balcony solar?

For balcony solar, 800 watts is better for most renters who are out during the day, and 1,200 watts is better only if someone is home using power in daylight, the railing fits three panels and the state allows it. The 1,200 W kit makes 50% more power but, in the example, saves only about 11% more.

Factor	800 W	1,200 W
Panels (400 W each)	2	3
Output, vertical south, Baltimore	737 kWh a year	1,106 kWh a year
Output, tilted 35°, Baltimore	1,103 kWh a year	1,654 kWh a year
Self-used with a 164 W load (vertical)	423 kWh (57%)	470 kWh (42%)
Yearly savings at 21.40 cents	$91	$101
Price at $1.47 to $1.87 per watt	$1,176 to $1,496	$1,764 to $2,244
Current added to the circuit at 120 V	6.7 A	10 A
Legal fit	Every state cap, including Delaware’s proposed 800 W	Most signed states; Maine above 420 W needs an electrician
Clipping with extra panels	Loses more if you overload it with panels	Little clipping with 1,600 W of panels

Cost. Canary Media found kits at $1.47 to $1.87 per watt before taxes, including a two-panel 800 W system at $1,499 in April 2026. By my math, the extra 400 W costs about $588 to $748. At $10 a year of added savings, that step takes about 59 years to pay back, longer than the panels last.

Circuit current. By my math, a 1,200 W kit adds 10 amps at 120 volts, two-thirds of a 15-amp circuit’s rating. UL Solutions warns in IAEI Magazine that combined utility and solar current “can exceed conductor ratings without tripping the circuit breaker.” An 800 W kit adds about 6.7 amps, which leaves more headroom for whatever else shares that outlet.

Clipping. Some buyers get an 800 W inverter and hang more panels on it. NREL’s PVWatts manual says output above the inverter’s rating “is clipped to the nameplate value.” Our microinverter guide found 1,600 W of panels on an 800 W inverter lost 13% to 18% of the year’s energy.

Pick 800 W if you’re out on weekdays, your railing is under 11 feet, you live in Maine or Delaware, or you’d rather keep circuit load low. Pick 1,200 W if you work from home, run laundry or charge an e-bike at midday, and your state allows 1,200 W.

My take, and the limits of this math

My take: start at 400 to 800 W and buy for the baseload you can prove, not the cap you’re allowed. The UBA reaches a similar view, saying a single module of around 450 W can be the most economical choice. By my math for Baltimore, the third panel added about $10 a year for a renter who’s out all day.

A flat 164 W load is a simplification: your fridge cycles, and evenings and weekends add load the model ignores, so your self-use is likely higher. PVGIS also assumes open sky, with no balcony above you or neighboring building casting shade. To see your own output by city, use our balcony solar output guide.

FAQ

What is the typical size of a balcony solar kit?

Most plug-in kits sold today are 400 to 800 watts, usually one to three panels, according to EnergySage. State laws allow more: 1,200 W in most states with a law and 1,920 W in Colorado. A standard 400 W panel is about 44.6 by 67.8 inches.

What can 800 watts of balcony solar run?

At full sun, an 800 W kit can cover roughly a fridge or a few small appliances, as Canary Media puts it. Over a year it covers your always-on load for much of the daylight hours, but it won’t run an oven or air conditioner on its own.

What will a 1,200 watt balcony solar system run?

At peak, a 1,200 W kit can cover more appliances at once, but only while the sun is strong. If your home mostly runs a 164 W always-on load during the day, most of the extra output from 800 to 1,200 W goes out to the grid instead.

Is a bigger balcony solar kit always better?

No. In most states with a plug-in law, exported power earns nothing, so watts beyond what your home uses in daylight add little value. By my math for a Baltimore railing kit, going from 800 to 1,200 W adds about $10 a year of savings.

What Size Balcony Solar Kit Do I Need?