The 16kw unit would be ridiculously under-powered for serving more than a kichen sink or a single shower with the flow throttled way back. It's just not enough juice to boost the temp enough at even modest flows at YOUR wintertime in coming water temperatures.
For serving a 2 bathroom house in a 4-person household on lake Erie, fuggedaboudit- not enough flow for more than 1 scaled down shower load at a time in January.
For serving a 3- head shower ANYWHERE fuggedaboudit- not enough flow to run all 3 heads at once.
Hard water can also lime up any tankless pretty quick too- call that strike-3.
Or maybe strike- 9, new inning, since you'd also be spending money upgrading the panel, and maybe even the service drop or transformer to provide the peak power all to run even that inadequate tankless.
As finish-heat to a solar thermal nstallation it can make sense, provided also have backup elements keeping the solar tank up to at least room temp.
Running even a 40 gallon a gas fired tank would provide more hot water gallons than a big electric tank, but since you're bound for all-electric, not that bigger electric tanks don't have dramatically higher standby losses than smaller tanks. For a 4 person family, go with an 80 gallon unit.
How are you heating the place? There are various options for heating hot water (or pre-heating) with the heating system that might be more satisfactory or effient than another electric tank.
If your's is mostly a showering type family rather than tub-bathers, a drainwater heat recovery heat exhanger can more than double the apparent capacity (and efficiency) of any water heater, with much shorter payback than any solar-electric. To compare efficiencies between models, see: http://oee.nrcan.gc.ca/residential/p...ain.cfm?attr=4 These are standardized numbers at 2.5gpm (single shower) flows. Efficiency goes up a bit with lower flow, down a bit at higher flow, but a 50% unit would still be delivering better than 40% energy return with 3 showerheads running. Without drainwater heat recovery you can run into capacity issues with 3-head shower, even with an 80 gallon tank, and the recovery time on a depelete 80 gallon electric can be fairly long. The walk-in shower is likely to account for well over half your hot water use, and an electric tank + drainwater heat recovery would give you both the peak flow you need, and run BETTER efficiency than a tankless.