Once again, Elon Musk has prompted a flurry of speculation with a single tweet. But unlike hyperloop or his ridiculous tunneling idea, this one totally makes sense: an electric big rig.

The busiest man in tech already faces looming deadlines for getting a battery factory up to speed, the Model 3 out the door, and a secret payload (probably a spy satellite) into orbit. So you might think he'd resist adding to his to-do list. Nope. Turns out he's got a team working on a battery-powered truck he will reveal in September, as part of his master plan to shift the world to sustainable energy.

I hear you chuckling. But this idea is not crazy as you might think. Plans for such a truck, if they truly exist, almost certainly call for batteries alone, because Musk disdains hybrids and range-extended electrics like the Chevrolet Volt. That makes his idea easier to design and build than a conventional car, SUV, or pickup (which Musk also wants to make). It helps that he's not the first guy to think of this. Nikola Motor Company is pursuing a similar goal.

Semis and the trailers they haul are big enough to hold the ginormous battery pack needed to do the job. The frame of a semi is essentially a pair of long steel rails, which could easily support a battery pack (which also could go behind the cab). Ditching the internal combustion engine saves more space, and lets you use smaller motors on each axle or even each wheel. Electric motors provide oceans of torque, improving acceleration and pulling power, and slinging the battery and motors between the frame rails lowers the center of gravity, improving handling. Tidier packaging increases aerodynamic efficiency, which squeezes more range from the battery.

The biggest drawback? Range. Long-haul truckers typically cover 400 to 600 miles a day, something hard to do with batteries alone—unless you're packing a mighty big one. “I imagine they’ll use a 600-kWh battery, possibly up to 800-kWh,” says Nikola CEO Trevor Milton. (The Model S sedan sports a pack that tops out at 100 kilowatt-hours.) With a little math, Milton figures “Musk’s truck will get around 200 to 300 miles range.” Not much, which explains why Nikola uses a hydrogen fuel cell generator to boost range to 1,000 miles.

Still, 300 miles works for short, repetitive routes. Two hundred miles gets you from the Port of Los Angeles to the vast distribution warehouses in Riverside and back with range to spare. Ditto Oakland, Seattle, and so forth. You can see these things working in urban areas, where diesel trucks create a lot of air pollution and noise. That explains why officials with the Port of LA like the idea of electric trucks powered by overhead lines like trolley buses.

Electric trucks schlepping stuff short distances makes sense because they typically return to a depot, which makes charging a snap. But here, too, Musk's idea makes a certain kind of sense. Long-haul trucks tend to use interstates, where Tesla already has a network of Supercharger stations. The chargers can get a Model S sedan to 80 percent charge in as little as 30 minutes. A truck would need longer, of course, but don't forget that federal rules dictate how long truckers can drive without a break. If they've gotta take a break anyway, why not charge up?

Granted, EV drivers visiting the most popular Supercharger stations often find themselves waiting in a queue. Selling the Model 3 in any significant numbers will exacerbate that problem, so you can imagine what might happen if Tesla starts building big rigs. “They’re also going to run into problems with the grid—just try charging 100 trucks at one location,” says Milton. Dedicated truck charging stations at the most common origins and destinations makes more sense, and could be sold as a package to a fleet management company. Who knows—Tesla could even team up with a chain of truck stops to provide charging.

No one's saying working out the details would be easy. But then again, this isn't rocket science. And it can't be any harder than tunneling under LA or firing people through tubes.