"are not efficient enough" is correct and usable in written English.
You can use it when you want to indicate that something is not as efficient as desired. For example: "The current strategies we have in place are not efficient enough to meet our goals."
"Our companies are not efficient enough to compete," said Tomás Iglesias, a retired accountant who now drives a taxi part time.
"This price increase, it is sometimes due to contractor's deliberate acts, and sometimes it is due to the fact that the professional valuation of necessary investments, especially in mountain conditions, for a mountain cluster, are not efficient enough".
Right now, carmakers say they would be able to sell only their smallest, most fuel-efficient cars — models like the Toyota Prius, a hybrid whose sales have fallen sharply since gas prices began dropping last fall — because once-popular vehicles like pickup trucks made by Ford and G.M. are not efficient enough.
In a recent paper, Bradford Cornell, of California Institute of Technology, and James Rutten, of Munger, Tolles and Olson, a Los Angeles law firm, argue that even highly developed financial markets such as the New York Stock Exchange are not efficient enough to allow courts to use declines in share prices to calculate the financial damage caused by a fraud.
Existing prognostic scores are not efficient enough to predict ICU admission in daily practice.
Since the exact algorithms are not efficient enough, we only study the scalability of TTR-Greedy.
Beware: Lots of "energy-efficient" products advertised as meeting Department of Energy standards aren't efficient enough to merit a tax credit.
Of course, solar panels aren't efficient enough to charge you up the way a good ol' 2 prong can, so they include a standard charger in the (recycled) box).
One explanation is that the efficiency of the "hydrogenase valve" is not efficient enough so that the photosynthetic electron transport chain becomes over-reduced resulting in photoinactivation of PSII [ 25].
Those local firms that were not efficient enough to meet Walmex's terms lost market share, and many failed.
Mr. Jeffries makes a straightforward case that the district has not prospered and the district office is not efficient enough for constituents.
