The variability of alternative energy sources is one factor that holds back their wider use -- if wind or solar energy decreases and varies widely, then some other energy production has to back it up, and that adds to the overall cost of energy supply.
"Whenever any new form of energy is added, a challenge is to integrate it into the system along with the other sources," said Ted Brekken, an associate professor and renewable energy expert in the College of Engineering at Oregon State University.