Не пойму, вроде флот тут совсем ни при чем. Может, имеется в виду "общая работа всех установок"?
Контекст:
Results from the operating units as of August, 2000 are as follows: total fleet operation stands at
more than 3.5 million hours. The plants achieve 40% LHV electric efficiency, and overall use of
the fuel energy approaches 80% for cogeneration applications (8).

Заранее спасибо!