Image generated with Claude. Why have we juxtaposed a bicycle with balcony solar? Read on.

First it was Plug-In Solar. Then it was Balcony Solar. Now it’s Guerrilla Solar, at least according to Inside Climate News, which yesterday proclaimed that The ‘Guerrilla Solar’ Era Has Arrived.

“It,” of course, is Modular solar panels. They’re the hot new photovoltaic solution: cheap enough to buy at Home Depot, easy to hang or prop to catch maximum rays, and small enough to fit on a balcony (if you’ve got one) and plug into your “home grid.” But, alas, too meager a generator of electricity to be more than a bit player in decarbonizing most U.S. homes.

How do I know? I’ve done the math.

A standard, lower-end 220-watt balcony solar array will produce 337 kilowatt-hours a year, or 28 kWh a month averaged over the course of a year. That’s for a 220W unit measuring 3.5 feet by 3.5 feet. (220W x 1/1000 x 17.5% x 8760 hours per year = 337 kWh. Calculation assumes a 17.5% full-year capacity factor, which is arguably generous for New York, where I live. )

Our balcony solar mashup. Top: an install in Germany. Bottom: Home Depot advert.

A typical U.S. home consumes 10,500 kWh a year, or 28 to 29 kWh per day, says Solartech, drawing on U.S. Energy Information Administration data. That puts a home’s daily power needs on par with a balcony solar unit’s monthly output. In effect, once each month the balcony array gifts a homeowner or renter a bit more than day’s full complement of electricity. And earth’s atmosphere gets the same respite: a 3 percent reduction in carbon emissions caused by the home’s electricity usage.

(The 3 percent figure could also be calculated directly by dividing 337 kWh per year of solar production by 10,500 kWh per year to run the home. For bigger or smaller arrays, just prorate your assumed wattage by my 220W; for 440W, say, double my figures.)

Balcony Solar metrics

Why write about balcony solar if it’s so inconsequential? CTC’s mission includes puncturing would-be climate balloons before they ascend too far. In the same vein, we practice quantification to make clear what does and doesn’t move the climate needle. (More on that further below.)

The best way to depict balcony solar’s climate value is to express it in terms of tangible metrics. We’ve selected two. Both assume the basic, lower-end PV array I assumed at the top: a 3.5 foot-square array whose peak output is 220 watts.

1. It would take 50 million 220W balcony solar units (bsu’s) to restore the climate benefit we destroyed in 2020-2021 when we shut the high-performing Indian Point nuclear power plant 32 miles from Midtown Manhattan.

2. A single person cutting back their driving by a mile a day would provide the same climate benefit over the course of a year as a single 220W bsu.

(Calculations in sidebar. Now you know why we led with images of an urban dweller as cyclist and balcony solar user.)

Yes, it’s dense — as befits a sidebar. The numbers tell a story. Follow the color co-ordination.

Ponder that: It would take fifty million smallish bsu’s to level up to the fossil fuel carbon emissions that Indian Point was keeping at bay by supplying the New York City area year in and year out with abundant carbon-free power. Deploying that many balcony solar units would entail 10 bsu’s for each of the 5 million households in the MTA’s service territory. (The Metropolitan Transportation Authority provides subway, bus and commuter rail transit in the five boroughs and seven suburban counties.) Or, if those same households upgraded to 1100-watt bsu’s, collectively they would still make up only half of the lost Indian Point power.

The second comparison, involving driving, is perhaps trickier to grasp but more interesting, since it relates to people’s behavior. Living differently isn’t part of public discourse, at least not in the USA, and especially when what’s being served up is using less. But “reducing,” as we might call it (remember “Reduce, Reuse, Recycle”? or, “Insulate, then Insolate”?) is just as potent for cutting emissions as switching to renewables — even more so when the reducing means driving less, considering the multitude of benefits that accrue from diminishing cars’ imprints on our communities. Still, staying on topic: driving just one fewer mile per day brings about the same shrinkage in carbon emissions as deploying one 220W solar array.

What Balcony Solar boosters are really saying

To be fair, our friends at Inside Climate News and, yes, The New York Times appear to be trying to modulate their balcony solar enthusiasm.

ICN‘s Dan Gearino, whom we cited up front, said he looked to Germany, the birthplace of balcony solar, to see if the units made sense for U.S. households. His takeaway: “It may make more sense financially to spend the cost of plug-in solar on insulation, air sealing or other basic measures to reduce energy use.” Hooray: insulate before you insolate.

Gearino helpfully interviewed renewables guru (and U.S. emigré) Craig Morris, who currently heads Germany’s plug-in solar trade association, Bundesverband Steckersolar. To Morris, balcony solar’s main advantages are that it provides power without taking up land, and that it affords people a way to “become participants in the transition to clean energy.” Behold, guerrilla solar. That, in turn, bolsters “the political consensus that supports the transition.” But Morris also made clear that widespread adoption of plug-in solar would only meet “about 2 percent of Germany’s electricity demand.”

Morris’s “about 2 percent” feels right for Germany. But not for the U.S., where widespread adoption of virtually any individual carbon alternative seems forever out of reach, and where the energy pie is so much larger — think giant fridges, freezers for beer, steroidal homes bursting with piles of powered toys, not to mention industrial and institutional electricity use that Morris correctly excluded from his figure.

Don’t forget to micro-dose. NYT headline + image for David Wallace-Wells’ guest essay (see text). Image by Rui Pu.

Both Gearino and Morris seem more measured than climate journalist Robinson Meyer, founding editor of Heatmap and frequent contributor to The Times, where he wrote about balcony solar in mid-June.

“New zero-carbon power kits will allow Americans to make their own energy choices,” declares the callout to the print version of Meyer’s NYT guest essay, The Tiny Solar Panel That Could Change America. (The even more expansive print headline invites us to “Forget Roofs. Backyard Solar Is the Next Frontier.”)

Wallace-Wells is of two minds. He calls balcony solar “a small way that apartment- and condo-dwelling Americans can take ownership of their energy choices and cut down their pollution on the margins.” No quarrel there, thanks to his qualifiers “small” and “on the margins.” Earlier, though, he opines that balcony solar units “have the potential to change how Americans understand and consume energy,” But read further and you’ll again see Wallace-Wells cautioning that “Balcony solar will play one small role in [the] drama” of transiting to the new world of clean, abundant energy.

Any such caveats are welcome these days, amid widespread solar hoopla. Still, it doesn’t seem to be in Wallace-Wells’ toolkit — or that of Inside Climate News and other mainstream climate journalists — to tutor their audiences as to the  true limits of balcony solar and other panaceas. Just like it wasn’t in their field of vision a decade ago to lay out the true stakes of shutting Indian Point as Riverkeeper was singing its siren song.

What’s Next for NY Balcony Solar

Meantime, as Canary Media reported recently (and helpfully), New Yorkers concerned with climate and affordability are waiting for NY Gov. Kathy Hochul to sign the recently passed SUNNY (Solar Up Now New York) Act legalizing balcony and other plug-in solar. It would be head-spinning (and politically suicidal) if she didn’t, given near-universal support ranging from Con Edison to DSA Assembly Member Emily Gallagher, who told Canary Media, “This is the most popular bill I’ve [ever] worked on.”

My guess is that Hochul is waiting for the right moment, and perhaps the right “package,” that can advance and not undercut her push to launch five large new nuclear power plants around the state — one to be built by the public New York Power Authority, the others to be constructed and operated privately. A little bit of math, a la what we offered here a la Indian Point, might help her out.

The governor also must manage the veritable hot potato of her deferred implementation of the landmark 2019 Community Leadership and Climate Protection Act. She might do well to consider jettisoning the act’s unwieldy cap-and-invest centerpiece in favor of a straight-up carbon tax (with the revenues distributed pro rata to the state’s households) in its place. That, far more than balcony (or guerrilla) solar, could blow open the door to the “innovations and technologies we cannot yet imagine” that Wallace-Wells fantasized about in his Times essay.