Yes, solar water heating is practical. Though I had a solar water heater on my house before I replaced my roof. The quote was $500 to re-mount the water heater (and fix a leaky pipe in it.) Alas, it was saving me only $5/month in gas, and costing electricity, so it could not be justified. But with more modern techniques I think it can be. There is also promising research in thermosolar electricity, and PV panels with reflective panels.

However, the point is not that alternative energy can't be made to work, or that there are not workable systems today. It's that people are not doing their math right, not accounting for the time value of money or total cost when working out which are the right systems to use.