Hi Wowser;

DE is more energy efficient, because you can run your pump fewer hours. You also use less water. Sand requires more hours and more water.

Most economical pump depends on piping, operational preferences AND actual electrical rates. It may be something like a 3/4HP 2 speed pump, rather than an Intelliflo. Ramping up the electrical input to compensate for a dirty filter is NOT energy-efficient, but it is convenient.

I'll ask Mas985 to take a look. But, you'll get better answer if you do all the following:
1. mail pictures of the pool AND current equipment, with piping shown to
116085760037372010926.sophocles@picasaweb.com
with the subject "thread 14404"
I'll post them.
2. tell us the KWH rate you are paying.
3. tell us whether the solar system is vented (vacuum relief) or not, and how high above the pool it is.

The