In Hawaii a combination of PV + hybrid tank hot heaters actually MORE efficient than a thermal hot water, and lowers the cooling load inside the building too.
In heating-dominated climates there's always the issue of hybrid tanks adding to the space heating load, but in cooling dominated climates with high-priced electricity (such as in HI) they're a slam-dunk.
Some independent testing seems to indicate that the larger the tank the more efficiently the hybrid heat pump tank works, but I don't have web-published data on that. The 80 gallon Steibel Eltron Accelera tests better than any of the smaller- tank hybrids out there, and has good first-hour ratings for an electric tank- you can even fill a decent sized soaking tub with it before the resistance elements would kick on.
A couple grand for a hot water heater may seem like a lot, but at Hawaii's electricity rates it'll pay back well within it's anticipated lifetime, since it uses dramatically less power for hot water while reducing your cooling power use at the same time. The installed cost will still be less than that of a fossil-fired tankless, (and less than even an in-line batch-solar hot water heater of lower net efficiency.)