Can you expand on that?
Ive got solar HW, and being nerdy/geeky I have an intimate knowledge how my system works, and I manage it accordingly. Not disparaging your post at all, just keen to hear more
sorry not a whole lot. i never went into details on the systems. even mates one was a long time ago. afaik the problem they mentioned was boiling the water in summer due to the solar. so its kept small to avoid that and they used wetback in the winter. most likely it would have been low pressure system. we used to boil our wetback so i know how much fun that is. the company i spoke to said they used things like outdoor swimming pool or even house water tank, to dump the hot water into to stop the hot water cylinder from overheating.
the idea of the PV is you can use a simple thermostat to turn it on/off. (except dc is problematic). if you want to work well in winter put bigger panels in as in summer the thermostat just turns it off. a waste of generation it may be.
cost wise i have no idea.
On-grid folks I know shifted off their solar HW and onto PV HW when they couldn't figure out how to get the solar HW system running quietly enough during summer. It was on a roof just above the master bedroom; burbling during summer afternoons was loud enough to be *really* annoying to the one who worked night shifts. A bog-standard electric HWC runs very quietly; but (as I posted when resuscitating this thread) the iBoost+ has a noisy fan so you'd definitely want to have that positioned where its fan-noise won't disturb anyone's daytime sleep. Alternatively you could contact Paladin NZ. as its principal has assured us (in this thread) that they're still in business.
Personally I'd be very cautious about a DC PV HWC system, unless it was designed by someone who really knows what they're doing. DC arcs are pretty dangerous -- they don't self-quench like AC ones... as Nicola Tesla had pointed out more than 100 years ago, when duking it out with Thomas Edison regarding the relative merits of AC v DC distribution. Well nowadays there's a resurgence of interest in DC-coupled PV systems (and I'd be keen to get one, someday, when they're productised into a DC slow-charger for my BEV that'll make efficient use of my household's wimpy PV array), and DC microgrids are now in the pilot-stage (see e.g. https://pcmp.springeropen.com/articles/10.1186/s41601-020-00157-9) but I personally wouldn't want to rely on my own (or some cowboy's) DC circuit-breaker offering anything more than a "security theatre" level of assurance against DC arcing in my home!
And... if perchance you're a DC/AC geek who hasn't seen the
Nikola Tesla vs Thomas Edison. Epic Rap Battles of History
you're in for a treat ;-) https://www.youtube.com/watch?v=gJ1Mz7kGVf0