When somebody writes that a solar electricity-generating facility can provide "enough to supply 100 homes for a year," the phrase "for a year" has no meaning.
Maybe it can or cannot do so all year long — but that's different, and there are ways to write that.
The expression, almost ubiquitous, could make the reader wonder whether or not the writer understands the science well enough to explain it.
"By generating its own electricity — enough to light six homes for a year — the sign could save as much as $12,000 to $15,000 per month."
— New York Times, 14 November 2008.
The story, in this case, was about a combination of wind-turbine generators and photovoltaic panels powering a billboard on Times Square in New York City — but the format of expression is common across English-language media.
The phrase "six homes year-round" would make sense.
"Six homes for a year" does not.
