Faced with a surge in the number of proposed solar power plants, the federal government has placed a moratorium on new solar projects on public land until it studies their environmental impact, which is expected to take about two years.

The decision has caused widespread concern in the alternative-energy industry, as fledgling solar companies must wait to see if they can realize their hopes of harnessing power from swaths of sun-baked public land, just as the demand for viable alternative energy is accelerating.