Cleantech investors hailed on Monday the passage of a long-awaited energy bill in the U.S. House of Representatives as a step toward a more cohesive national energy policy, even as they lamented what it left out.

Among the more striking provisions of the bill is a national renewable energy standard requiring utilities to generate 15 percent of their electricity from renewable energy sources by 2020. But the legislation, which passed in a 241-172 vote Saturday just before the summer recess, fell short of calling for an increase in fuel economy. Those and other results drew mixed reactions from venture capitalists and other investors who closely monitor the cleantech sector.

“There’s a real need for us to rethink how we use personal transportation,” said Peter Grubstein, managing member at NGEN Partners. “Changing the CAFÉ [Corporate Average Fuel Economy] standard would have been a push to both producers and consumers.” Mr. Grubstein also expressed disappointment the bill didn’t mandate a carbon cap-and-trade system.

The Senate passed an energy bill in June that lacked a renewable energy mandate but hiked the nation’s fuel economy standard to 35 miles per gallon by 2020. When lawmakers return to Washington this fall, they will wrangle the House and Senate versions into law, so much uncertainty lies ahead. Add to impending political showdowns on Capitol Hill the threat of a presidential veto over concerns that the bill doesn’t do much to boost domestic oil and gas production.

“We’ll see what it takes to actually get something signed,” said Rob Day, a principal with @Ventures in Wilmington, Massachusetts, who nonetheless called the passage of the House energy bill “another sign of the overall trends in favor of clean technologies.”

Whatever happens in the next step, the bill revived hope that a renewable energy mandate could be part of that eventual legislation, a prospect that cheered cleantech investors.

“If a national RPS [renewable portfolio standard—or renewable energy mandate] goes through, that’s huge,” said Neal Dikeman, a partner at Jane Capital Partners. “That would basically double the total potential for renewable power in the country from a demand perspective.” It would also add another layer of complexity for companies already dealing with state renewable energy portfolios, he added.

Twenty-three states “each have their own rules as to what constitutes renewable power,” Mr. Dikeman said. “A federal standard would set a 24th standard—the question is what takes precedence.” Established renewable energy providers with tried-and-true technologies, like wind and solar, stand to benefit along with companies positioned to supply and build new transmission lines, he said.

Also passed as part of the House package is a provision to shift $16 billion in tax breaks for the oil and gas industry to renewable energy, energy efficiency, and biofuels development as well as allocations to install ethanol pumps and push cellulosic ethanol production. But some VCs are already looking ahead to the next big policy fight.

“All of these efforts are only half-measures until we can get a serious climate change policy put in place in the U.S.,” said Mr. Day. “Even major energy companies and manufacturers are starting to make noise in favor of a cap-and-trade scheme for carbon emissions.”