I grew up in a cottage in Florida where we put a 2x4 frame encompassing 10 sqft of area on the roof, painted the 2x4's and the space inside with Brea (tar), ran black heater hose in tight "esses" to fill the frame, layed glass over the whole thing (sealing with Brea again), and voi-la! We had solar heated water for under $15 (in today's money) that lasted for years.
On the other hand I lived in Indonesia and France with instant propane (tankless) heaters and in the Caribbean for years with instant electric (tankless). All worked superbly well, cost under $150 (in today's money) and never caused problems.
On still another hand, you can put in a $1500 solar unit, buy a Chevy Volt and dream you're saving a polar bear.
On the other hand I lived in Indonesia and France with instant propane (tankless) heaters and in the Caribbean for years with instant electric (tankless). All worked superbly well, cost under $150 (in today's money) and never caused problems.
On still another hand, you can put in a $1500 solar unit, buy a Chevy Volt and dream you're saving a polar bear.