Tesla CEO Elon Musk announced on Twitter on Wednesday that the company’s solar roof panels would be available for pre-order that afternoon. In a press conference Wednesday afternoon, Tesla and SolarCity executives said the roof would be cheaper, on the whole, than installing a regular tile roof (although not cheaper than an asphalt roof). Pre-orders require a $1,000 payment to secure a place on the list.

Tesla

Tesal

Tesla also rolled out a calculator on its website using data from Google Sunroof , a 2015 project from the search giant that used 3D modeling to map out every house’s potential for solar panel output. Tesla’s calculator factors in the cost of a 14kWh Powerwall, although purchase of a Powerwall is not required to get a solar roof, as well as any tax incentives that a customer might receive in their state. The "energy value" number featured most prominently is calculated over 30 years, which is the length of the warranty covering power production from the tiles. (Tesla is offering an "infinity warranty" on the tiles themselves.)

A press release from Tesla claims that, on average, a solar roof will cost $21.85 per square foot, if 35 percent of the panels are active and the rest are inactive. Inactive panels are about $11 per square foot, and active panels are $42 per square foot, according to Peter Rive, SolarCity’s co-founder and CTO (and Elon Musk’s cousin). The 35 percent number was derived from Consumer Reports calculations to estimate approximately $53,500 worth of electricity production over 30 years. "Looking at the roof from street level, the tiles look the same," Tesla states on its blog. "Customers can select how many solar tiles they need based on their home’s electricity consumption. For example, households that charge an electric vehicle every day may want more solar tiles on their roof."

Homewyse estimates an average tile roof to cost somewhere between $12-$16 per square foot without solar capabilities, and asphalt shingle roofs are significantly cheaper.

Musk noted on Twitter that the roof panels can be purchased in “almost any country,” and deliveries would begin this year to US purchasers. Deliveries outside of the US would start next year, Musk said.

The CEO also noted that only two styles of panels would be available today: smooth and textured black glass. Tuscan glass and French slate panels would be available “in about six months.”

Tesla announced the solar roof panels, which are intended to be a sleeker and more attractive version of regular solar panels, at a Los Angeles event in October 2016. Musk said at the time that the panels would initially be about 98 percent as efficient as regular solar panels, although he expressed hope that they would eventually be more efficient than standard panels. Musk didn’t mention the panels’ efficiency rate in today’s press conference.

The October announcement came at a time when Tesla had offered to buy solar panel installer SolarCity in a $2.6 billion all-stock deal. It was unusual to have Tesla announce a product without a pre-order being available at the same time, and some suggested that the announcement was a bid to convince skeptical investors to approve of the merger.

In the call today, Musk and Rive focused mostly on the value of the roof once electricity generation was factored in. “Just before installation, we’re going to design, custom design the solar roof for a customer’s home… it’s going to be an all-inclusive contract,” Rive said, addressing what happens after a customer puts down a pre-order payment. Musk chimed in: “This is much like the way we sell the cars, when you buy a Tesla car there’s no haggling, you don’t have to worry about if you’re getting a good deal or bad deal.”

“It’s important that people compare the true cost of a roof as opposed to the highly optimistic cost that ends up coming in twice as much,” Musk added.

Rive and Musk also tried to assuage worries about the sturdiness of the tiles. Musk said that on average, a solar tile roof weighs about a third less than a regular tile roof, and the tiles had been tested to be three times more durable than tile. Musk suggested that, as a supplier, Tesla would “save considerably on logistics and breakage,” compared to other tile roof installers due to the solar tile’s weight and durability.

This article was updated to add the average price per square foot of other tile roofs.