Energy is constant, but not always instant. The same goes for the composure of singer-songwriter Mark Kozelek. The San Francisco musician has perfected the slow-release — first through six albums with fuzzed-out, introspective quartet Red House Painters, then on four solo albums, and most recently fronting folk-rock ensemble Sun Kil Moon for its third release, April. He bundles his fingerpicked guitar with layers that breathe, sighing from relief and resignation simultaneously. He creates vignettes that overlay desire and regret, evoking loneliness and a flood of fond remembrances in casts of sepia and selenium tones. As emotional wells go, this one is deep, as is the catalog from which Kozelek can pull songs when he performs on Saturday, April 26, at Palace of Fine Arts at 8 p.m. Admission is $30; call 567-6642 or visit www.palaceoffinearts.org.