Tomorrow night, if its strong hints are accurate, Tesla Motors will announce that it plans to offer lithium-ion battery packs for home and business energy storage.
Such storage comes at a cost on top of that of the photovoltaic solar panels that generate the energy.
But the promise is that such batteries vastly increase the utility of solar panels by allowing the energy they generate to be held on site, and drawn upon when needed.
Today, most residential solar panels feed excess power into the electric grid--a process known as "reverse metering."
Many states require utilities to accept power from solar panels, which the homeowner "sells" to the utility (often at a wholesale rate) while continuing to buy electricity (at retail) when demand exceeds supply.
In broad plan, the same applies as well to large commercial buildings, making it notable that Tesla has prototyped its energy-storage systems with Wal-Mart, among other large corporations.
Photovoltaic solar power field at Volkswagen plant in Chattanooga, Tennessee
The company has installed batteries in more than 100 pilot programs "really without anyone noticing," according to analyst Andrea James of Bernstein Securities as quoted last week by Bloomberg.
Tesla Motors CEO Elon Musk tweeted that tomorrow night's announcement--"not a car"--would be a "major new Tesla product line."
The unveiling will happen at 8 pm Pacific / 11 pm Eastern at Tesla's Southern California design center in Hawthorne.
But while those batteries will represent a "major new product," estimates of the size of the energy-storage market remain far lower than the auto market.
Xtreme Power energy storage battery, installed at Ford's former Wixom Assembly Plant
Last year, roughly 16.5 million vehicles were sold in the United States, at an average price slightly over $30,000, giving a market size of roughly $500 billion.
According to a recent report from GTM Research and the Energy Storage Association (ESA), however, the total U.S. market for energy storage in 2019 will grow to $1.5 billion--11 times its size in 2014.
So what's driving the Tesla announcement?
Several possibilities present themselves.
First, sale of Tesla home batteries offers an outlet for any excess lithium-ion cell production from the company's Nevada gigafactory.
That plant's main mission is to provide battery packs for the Tesla Model 3 compact electric car that is expected to launch two to four years hence.
Two, it may also kick-start the home energy-storage business by attaching the red-hot Tesla brand to a product that so far has very little consumer recognition.
2015 Tesla Model S 70D, Apr 2015 [photo: David Noland]
No large consumer brand thus far markets batteries for storing solar energy onsite to consumers, as far as we know.
And there's a strong correlation between electric-car ownership and use of residential solar panels, according to data from California user surveys.
So a Tesla battery pack could make a Tesla electric car more appealing, especially if it comes with a solar-panel installation deal from Solar City--whose board chairman happens to be one Elon Musk.
Tesla Motors CEO Elon Musk at Tesla Store opening in Westfield Mall, London, Oct 2013
Finally, the announcement may serve to keep Tesla Motors in the media eye (and indirectly promote its electric cars) during a publicity lull.
With the all-wheel-drive versions of the Model S now launched (representing three of the four available versions), Tesla isn't likely to have a major product launch before the arrival of production versions of its Model X electric SUV.
It could still be several months hence before it starts delivering that utility vehicle to the first buyers.
That assumes, of course, that Tesla launches the Model X in accordance with its announced schedule of deliveries in the second half of this year.
Tesla Model X testing on California road, Mar 2015 [Twitter: ModelXnews]
With Tesla, you never know--but it's clear that tomorrow evening's unveiling will attract the same rapt attention and social-media outpouring that's associated with anything at all labeled "Tesla" or "Elon Musk."
Let the show begin.