Homebuilders might one day offer Tesla’s new Powerwall as part of an energy-efficiency package that includes rooftop solar panels and promises to slash a new homeowner’s electricity bills. But it might be a while before the carmaker’s power pack, designed to store solar electricity for use after dark or during a power outage, boots backup generators from the builder’s menu of optional upgrades.

A week after Tesla CEO Elon Musk announced the $3,000 to $3,500 high-tech battery earlier this month, he told investors that the company had already sold out after taking 38,000 orders and wouldn’t be able to fill new requests for another year.

Due to such high demand for all versions of the Tesla batteries, including the larger utility option, the company is considering expanding its $5 billion gigafactory currently under construction in Nevada, according to Utility Dive.

However, Bloomberg has reported that the devices “don’t work well with rooftop solar — at least not yet.”

Best intentions

Bloomberg explained that storing the unused electricity generated by a home’s rooftop solar panels with the battery’s smaller version, which can store 7 kWh of power and is intended for daily use, isn’t as cost-effective as selling that extra juice to the local utility.

So suppliers, including Musk’s own SolarCity, will not be installing it in homes for the time being. That means owners of houses that rely on solar panels for at least some of their electrical needs won’t be able to use Tesla’s celebrated high-tech device to store the excess energy they generate on sunny days for use after dark.

Instead, the company will be promoting the larger, 10 kWh version for home use as a backup power source during the occasional electrical outage. That one is not equipped for daily use.

Cool factor

Still, some builders will likely latch onto the smartly designed, cutting-edge device to add some "cool" factor to their list of energy-efficient, premium-priced extras, like solar water heaters and solar panels, or as an alternative to permanently installed standby generators.

Those hard-wired generators — a different product from gasoline-powered portable units — have become a fairly popular option since Generac, the largest manufacturer of standby home generators, started working directly with homebuilders to install them during new construction.

Generac estimates that just 3% of homes have a standby generator to keep the lights and appliances on during a power outage, and a slight 7.5% of new homes came equipped with them in 2013, according to Builder Magazine. Large standby units are powerful enough to keep a whole house up and running.

"It can … become a cool selling point and a way to differentiate your product," the magazine advised homebuilders last year. That was before the unveiling of the 3-by-4-foot Powerwall, which techies are calling “revolutionary” and crediting in advance with making American homes energy self-sufficient and far less reliant on the electricity grid.

Early adopters among residential contractors almost certainly will find a way to get the Powerwall into their new homes. And construction companies that have built their reputations as "green" builders will be watching for future developments that might make the Powerwall suitable for storing and delivering  solar power that is generated — but not needed — during the day for use at night.

Riviera Beach, FL,-based Mesocore, whose sustainable factory-built homes feature solar energy, rainwater harvesting and "allow … for off-grid applications," is one of those builders.

The Powerwall, the company noted in a press release after Musk unveiled the device, "offers perfect synergy for solar battery backup systems that are currently being used by sustainable homebuilders."

Still, Bloomberg noted, "the Powerwall product that has captured the public's imagination has a long way to go before it makes sense for most people." Yet the financial writers there predicted that homeowners will line up to buy the batteries nonetheless.

"There's a tremendous amount of interest in backup power that's odorless, not noisy and completely clean," a SolarCity executive told the publication.

And if homeowners want them, builders are likely to figure out a way to be part of that purchase.