ETC have demonstrated that the combination of a
selective surface and an effective convection suppressor
can result in good performance at high temperatures [21].
The vacuum envelope reduces convection and conduction
losses, so the collectors can operate at higher temperatures
than FPC. Like FPC, they collect both direct and diffuse
radiation. However, their efficiency is higher at low
incidence angles. This effect tends to give ETC an
advantage over FPC in day-long performance