• Operating Temperature Range of Flat-Plate Collectors:
• Design Range: Flat-plate solar collectors are non-concentrating stationary collectors designed for domestic water heating, space heating, and low-temperature agricultural crop drying.
• Temperature Attained: Under typical sunny ambient conditions, thermal losses through the front glass cover and casing limit operating fluid temperatures to a maximum of approximately $80 - 90^\circ\text{C}$ (rarely exceeding $100^\circ\text{C}$ without concentration or high vacuum).
• Conclusion: 90°C (Option 1).

Correct option: (1) 90°¢

• Loss Suppression in Evacuated Tube Collectors (ETC):
• Structure: An Evacuated Tube Collector consists of parallel double-walled borosilicate glass tubes. The annular space between the outer transparent tube and inner selective absorber tube is evacuated to a permanent high vacuum ($p \lt 10^{-3}\text{ Pa} / 10^{-5}\text{ torr}$).
• Physical Mechanism:
• Convection: Completely suppressed because there is no air medium to support natural convective buoyant circulating currents.
• Conduction: Gas molecular conductive heat transfer across the vacuum envelope is eliminated.
• Conclusion: Both conduction as well as convection losses are suppressed (Option 2).

Correct option: (2) Both conduction as well as convection losses are suppressed