The appropriations bill signed Friday contains a "Buy American" clause for Pentagon purchases of solar panels, The New York Times reports.
Green-energy technologies are likely to be an issue in Hu's talks with President Barack Obama.
China produced at least half of the world's solar panels last year, and its share is rising. The United States accounts for $1.6 billion of the world's $29 billion market.
The American military is shifting rapidly to renewable energy technologies since it is expensive and often dangerous to ship fuel into remote war zones such as in Iraq and Afghanistan.
The perception that China unfairly subsidizes its solar industry has drawn concern in Congress. The administration already is bringing a case against China before the World Trade Organization over wind turbines.
The solar panel provision was drafted to comply with the WTO's free-trade rules.