The materials cost was about $1400, half of that is the panels the rest is wire, conduit, brackets, etc. A solar permit in my area costs $1200+ . The high permit costs would make a system this small uneconomic. Local codes vary but in my jurisdiction I could avoid need for permit by putting the panels on my shed instead of my house and using the power for the water heater instead of connecting to the grid.

The payback is 3-6 years depending on what ratio of peak/off-peak power pricing you assume.

very cool, thank you. Payback is also hot water when the power goes out :)

This is would be fairly inexpensive to do. DC heating elements are < $40 and used panels can be had for ~0.20$ a watt or less.

You'd wire the PV panels directly to the heating element. (Of course you'd have to size your element to match the volts/amps of your panels)