what are the disadvantages of solar water heaters?I would like atleast 5-7 points

The things in our household where we use heat and cold are
among the things that soak up the most electricity, so this includes our washer and
dryer, our refrigerator, and of course, the water
heater.

To go completely solar for your water heater needs
has some definite disadvantages:

1)  A typical system can
heat about 50 gallons of water per day.  If you have more than two people living in your
household, or take a lot of showers, you will need a backup conventional water
heater.

2)  Typical system purchase and installation costs
run about $5000 - $6000, and it will take a long time for the system to pay for itself
with the money you save on your utility bill

3)  With that
kind of cash, you can buy all new energy efficient appliances (Energy Star program) and
get a rebate on those, plus you'll save more money in the short and long
run.

4)  The technology has not yet been perfected to make
this cost effective.  Better to wait a few years and see what kind of advances they make
in the later models.

5)  Sometimes hard to find qualified
installers and dealers in your area.  Coming out from the larger cities can cost
extra.