Fuel cell fuel cells so efficiencies vary, but most are between 40% and 60% energy efficient. However, when the fuel cell's waste heat is used to heat a building in a cogeneration system this efficiency can increase to 85%. This is significantly more efficient than traditional coal power plants, which are only about one third energy efficient. Assuming production at scale, fuel cells could save 20–40% on energy costs when used in cogeneration systems. Fuel cells are also much cleaner than traditional power generation; a fuel cell power plant using natural gas as a hydrogen source would create less than one ounce
Interlanguage fossilization 1) why fossilization occurs, 2) the precipitating conditions, 3) what kind of linguistic material is likely to be fossilized, and 4) what type of learners are more prone to fossilize. However, there has been almost no investigation by SLA theorists on the possibilities of preventing or overcoming fossilization, and little explanation related to those adult second language learners who overcome one or more "areas of stability" in interlanguage—those learners whose interlanguage does not fossilize, and who reach a high level of proficiency in the second language. One factor of obvious relevance is motivation, and studies have been conducted regarding motivation