I'm collecting parts for one of these.
Solar Hot Water Batch Collector - DIY Solar Shower - Homemade Hot Water Heater - Tankless Water Heaters ? ByExample.com
Some extra storage included!
My initial October tests yielded 50 gallons from 70degrees to 125degrees in 4.5 hours (0930-1400). I'm thinking about a small flat plate copper (4x4') with recirc to supplement heat from 1400-1600 since I can mount it remote.