Seventeen years ago, ponies discovered that leycrystals could be used to create magic essence if charged with raw magical energy. Only a small amount of energy was needed to create larger quantities of essence, which unicorns draw from to conjure magical energy. Overtime, methods were discovered to artificially mimic the biological process of magical energy creation from magic essence; these reactors, unfortunately, are large and bulky, limiting their practical use.
 
The reactor requires an “essence rod” containing a special gel that can hold magic essence. It is here that the essence created from the leycrystals in a magilec-reactor is gathered. The rod stores a generous amount to be used when the magilec-reactor needs to be restarted, then shunts a small amount to a perpetual matrix shell to be converted back to magical energy, and the remaining to powerful magilec converters to be changed into ever useful magilectricity.
 
This technology was considered a breakthrough, and the Princesses personally observed the assembly of the first reactor for use in an airship. Today’s Royal Equestrian Aeronautical Corps vessels utilize this method for power.
 
-A Consolidated History of Earth Pony Engineering in Equestria, p. 256  
(Also published in Magilectricity Operations for Dummies vol. XI)