Known for producing electric cars, Tesla is expanding the range of products it offers with a low-cost solar panel package that the company claims pays for itself in energy savings. The "Solar Roof" is now available for pre-orders in Delaware.

The Solar Roof combines solar panels with roof tiles using tempered glass. The roof is integrated with Tesla's proprietary battery, Powerwall, which allows energy collected during the day to be used at night.

Installation takes 5-7 days. The cost is $21.85 per square foot. The company is offering an "infinite warranty"  that extends to the lifetime of the house, or infinity -- an absurd but confident pitch for the quality of the product.

Tesla acquired SolarCity last year in a deal that opened up the home energy market to the car maker.