Electric carmaker Tesla Motors raised the number of shares it will sell in its initial public offering by 20 percent, an early sign that investor interest in the startup is strong.

The increase, which comes the same day the shares are expected to price, increases the number of shares being offered to 13.3 million from 11.1 million, according to a regulatory filing.

Tesla maintained the expected price range at $14 to $16 a share. Based on the midpoint of $15 a share, the IPO could raise about $200 million.

The Palo Alto, California-based company's public debut comes amid growing interest in green technology and battery-powered vehicles, and as major automakers are gearing up to launch electric cars.

The final pricing of the shares is expected later on Monday, and the stock is set to trade on the Nasdaq exchange on Tuesday under the symbol TSLA.

Tesla Chief Executive Officer Elon Musk, during the company's roadshow last week, characterized the IPO as a technology play rather than a traditional carmaker stock.

But many analysts are skeptical, saying the shares may not appreciate in value until the money-losing company launches its second car, the Model S.

The company has yet to make a profit, and does not expect to do so until the $50,000 Model S sedan starts selling in significant volume. As of March, it had sold a little over 1,000 of its trademark $109,000 Roadsters.

The equity markets are a bit fickle and this is somewhat of a speculative deal, given the company doesn't generate any profits. So I think at the margin the firm may not be able to go out there with some blockbuster size of a deal, said Morningstar IPO analyst Michael Gaiden. Institutions, however, may want some exposure to this revolutionary-type name, he added.

Despite the considerable risks facing Tesla, the company is generating enthusiasm among investors, and the shares could price above the $14-$16 range.

Investors are indicating a willingness to pay around $17 per share, IPO Boutique senior managing partner Scott Sweet said.

The IPO represents about 14 percent of the company, excluding additional shares the underwriters have an option on. At $15 a share, Tesla would have a market capitalization of $1.4 billion.

Tesla's losses widened to $29.5 million for the quarter ended March 31, from $16 million a year earlier.

The company's business plan is fraught with risk. Tesla has said in regulatory filings that it faces a production gap in its Roadster after 2011 due to tooling changes at a supplier.

Musk, talking to investors last week, said Tesla was closer to Silicon Valley giants than traditional automakers.

We are a Silicon Valley company. Closer to an Apple or Google than to a GM or Ford in the way we operate the company, he said.

Tesla would be the first U.S. car company to go public since Ford Motor Co made its public debut in 1956.

Investors will be betting on the Model S. Tesla plans various cars based on the Model S, including a minivan, SUV and a mass market car, Musk said at the investor meeting, but he did not give a timeline for the launch of these vehicles.

Jeremy Anwyl, chief executive of Edmunds.com, which tracks the car market, said Tesla operates in a capital-intensive business that is highly competitive, with major automakers poised to enter the electric car market.

The deck is stacked against them, he said last week. They are not Google. They are in manufacturing.

Underwriters on the IPO are led by Goldman Sachs & Co, Morgan Stanley, JPMorgan, and Deutsche Bank Securities.

(Reporting by Poornima Gupta; Editing by Derek Caney and John Wallace)

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