Is sealant alone enough to waterproof a roof-penetrating solar mount?

Do not assume so. DOE/PNNL guidance warns that sealant alone can deteriorate from sunlight, oxidation, thermal movement and vibration, and recommends additional weatherproofing, including flashing. Use the complete waterproofing detail specified for the roof type and selected mounting system. This does not mean every system needs a separate metal flashing sheet: IronRidge's HUG, for example, uses an integrated foam-and-mastic sealing assembly. That example does not establish approval or performance for another product. Confirm the roof material and slope, applicable local code and roof-warranty requirements, and follow the current mounting-system and roofing-manufacturer instructions. Do not replace specified components or installation steps with a bead of caulk.

Sources: U.S. DOE/PNNL Building America Solution Center, 'Roof Anchor System for Solar Panels': https://basc.pnnl.gov/resource-guides/roof-anchor-system-solar-panels IronRidge, 'QuickMount HUG': https://www.ironridge.com/component/halo-ultragrip/