SAN JOSE, Calif. — Nanosolar, a heavily financed Silicon Valley start-up whose backers include Google’s co-founders, plans to announce Tuesday that it has begun selling its innovative solar panels, which are made using a technique that is being held out as the future of solar power manufacturing.

Nanosolar’s founder and chief executive, Martin Roscheisen, claims to be the first solar panel manufacturer to be able to profitably sell solar panels for less than $1 a watt. That is the price at which solar energy becomes less expensive than coal.

According to the Energy Department, building a new coal plant costs about $2.1 a watt, plus the cost of fuel and emissions, he said.