  Advanced linear accelerator design may use Optical Transition Radiation (OTR)
screens to measure beam spot size; for instance, such screens are foreseen in
plasma based accelerators (EuPRAXIA@SPARC_LAB) or Compton machines (Gamma Beam
Source@ELI-NP). Optical Transition Radiation angular distribution strongly
depends on beam energy. Since OTR screens are typically placed in several
positions along the Linac to monitor the beam envelope, one may perform a
distributed energy measurement along the machine. Furthermore, a single shot
energy measurement can be useful in plasma accelerators to measure shot to shot
energy variations after the plasma interaction. Preliminary measurements of OTR
angular distribution of about 100 MeV electrons have been performed at the
SPARC_LAB facility. In this paper, we discuss the sensitivity of this
measurement to beam divergence and others parameters, as well as the resolution
required and the needed upgrades of conventional OTR diagnostics, using as an
example the data collected at SPARC_LAB.
