"Powerhouse", like any other metaphor, has a figurative meaning implied by the literal meaning; however, in the case where there are several possible meanings you have to look at how it's most commonly used. Some examples pulled from the internet:
Damon had appeared in eleven other films before winning his first Oscar, but it was his role as a heroin addict veteran in 1996's Courage Under Fire that won him the respect and admiration of many powerhouse actors.
Each process does leech some nutrients, but the beet is a veritable nutritional powerhouse to begin with, so a certain degree of deterioration doesn't negate the vegetable's positive properties.
From his haunting acoustic material as heard on the albums Harvest and Harvest Moon to his garage rock powerhouse band Crazy Horse, Neil Young has been following his own inspired musical compass for the better part of four decades.
From these (and many others) we should assume that "powerhouse" refers to something "full of power", or, depending on the context, significance, usefulness, influence, and other applications of power.
It does not seem to be used to mean something that "produces power", as in a "power plant", so it's unlikely your sentence implies he is a "source of ideas" as in someone who inspires ideas in other people.