Necessity may be the mother of some people's inventions, but the truth is that Billy Mitchell doesn't really need a solar water heater.

That hasn't stopped Billy from inventing one, though. The elaborate contraption, made up of tiny mirrors, a number of pipes and some anti-freeze, is Billy's entry in the eighth annual Electric Contest, sponsored by Utah Power and Light.The contest is open to junior high students in Utah and in parts of Idaho, Wyoming and Colorado.

Hundreds of students have entered the contest, which will be judged in regional competitions between now and the end of April. Judging for the Salt Lake region will be April 18 at the South Towne Mall.

In each of the seven geographic judging areas there will be a grand prize awarded, as well as first, second and third place prizes for each grade level.

Midvale Middle School has been particularly prolific in contest entries over the years, spurred on by science teachers Mike Gourley, Nancy Kuhn and Joanne Ackerman.

Like generations of scientists before them, Midvale eighth graders Daniel Bennett and Greg Hansen have devoted their efforts to creating a perpetual motion machine, based on what they call the Independently Run Electricity Producing Generator Theory (probably best known as the IREPG Theory).

"It's a theory," explains Greg, "because we haven't proved it works yet."

Utah Power and Light judges don't require that the students' models actually produce electricity. But practicality of application is one of the four judging criteria.

"Some of these things aren't practical now," admits Julie Thornton, the power company's home energy advisor. "But in the future they could be."

Not all the entries are original inventions. Some explore current research into new alternative energy sources - such as Aparna Reddi's review of Ocean Thermal Energy Conversion (OTEC).

OTEC utilizes solar energy absorbed by the ocean, making use of the temperature difference between warmer surface water and cooler water underneath.

An OTEC plant would cost $100 million to build, "and that's kind of a lot of money," notes Aparna. But cost per kilowatt hour using the OTEC method is 8.2 cents compared with 11.7 cents for fission plants and 10.7 for coal-fired plants.

In the past, says Thornton, some entries have even taken a whimsical look at energy. "The Furry Furnace will always stand out in my mind," she says. This contest entry pondered how many rabbits, producing how much body heat, it would take to heat the average home. It was quite a few, remembers Thornton.