Cramer: Why this stock is getting 'hammered'

Cramer: A tale of two solar energy stocks

CNBC's Jim Cramer sees a big difference between two similar solar energy companies, and he advised investors to heed his observations.

One company, SolarCity, remains a "must buy" for growth managers because of its association with Tesla Motors founder Elon Musk, he said. SolarCity stock exploded 389 percent in the past year, reaching an all-time high Wednesday morning.

The other, First Solar, reported weaker-than-expected earnings Tuesday and projected lower revenue forecasts, sending the stock about 10 percent lower when trading opened Wednesday.

"It's a good company, but you know what, you have to produce," Cramer said Wednesday on "Squawk on the Street."

(Read more: What's making Jim Cramer nervous about stocks)

Cramer said that's because First Solar seems on its way to becoming a more mature company compared with SolarCity, whose appeal lies in its growth potential rather than traditional metrics.

(Read more: Cramer: Don't worry, be happy, buy SolarCity)

"I find this [is] one of the signs of what you have to be careful for when you have a junior growth stock become a senior growth stock," Cramer said. "When you actually have metrics you must beat, First Solar didn't beat them, and the stock got hammered."

Disclosure: Cramer's charitable trust does not own SolarCity or First Solar stock.

—By CNBC's Jeff Morganteen. Follow him on Twitter at @jmorganteen and get the latest stories from "Squawk on the Street."