[mercutio2]

Are you including the maintenance costs of the water panel in your estimate?

I used to buy this argument, but then:

A) PV panels got ridiculously cheap

B) everyone I know with solar hot water has emptied their systems because the maintenance hassles were not worth dealing with

Using high grade intermittent current to produce resistive heat isn’t high on my list of efficient things to do, but unfortunately neither is maintaining hot water panels.

[defrost]

Might be a location thing; there are vast numbers of solar hot water systems here in W.Australia and typical maintainence is maybe just replace the tank outright and flush the lines every 20 years or so.

How 'clean' of salts, etc. is the water being put through your panels?

Hard water clogs up faster.

[mattclarkdotnet]

As you allude to, our water in WA is notably soft, maybe that helps? I mean it's full of iron but that mostly just seems to cause staining not clogging.

That said, a heat pump running at 4:1 COP coupled to 20% efficient solar panels gets you right back to the same efficiency as solar thermal, with a lot more flexibility.

[defrost]

I'd rather run both in parallel, and I do, as do most of the people here abouts.

No single point of failure, sun heats the water directly and provides power, with a breakout box that accepts power in from the grid (if required), exports excess for points, hopefully that gets better over time, and accepts a local generator input if the PV panels are offline for some reason when there's a local grid power outage.

This is pretty good for now, there's loose neighbourhood discussion about perhaps getting a local area battery in a sea container that can buffer ~200 standard homes to further secure the town's energy stability.

Flexibility, in rural settings, is about having options not a single point of failure | dependency.

Eg: Way up the hill it's good to have PV panels on the bore pumps and better to have these independant of the house circuits with cables in place to route power "in case" .. along with option to use a generator if needed.

[mattclarkdotnet]

Totally agree. I'm in the city so don't have roof space for both. If I could I would totally do it.

[stdbrouw]

Yeah, when I was looking into this a couple of years ago, thermal panels were about 4 times as efficient as photovoltaic panels, but they were also 4 times as expensive. The ratio has probably shifted in favor of photovoltaics since then. If you have very limited space on your roof solar thermal can still be a good idea, but otherwise why prefer low grade energy (heat) over high grade energy (electricity) if you can get the same capacity at the same price?

[palmfacehn]

The most I've had to do is clear the dust from the tubes during the dry season.