Potential applications of inserts in solar thermal energy systems – A review to identify the gaps and frontier challenges

•Potential applications of inserts in solar thermal energy systems are reviewed.•Mechanism, advantage, and disadvantage of each insert are studied in solar systems.•Usage of inserts is effective measure to amend efficiency of solar thermal systems.•Some recommendations together with a pathway for future research are introduced. Solar energy systems are recognized as promising alternatives for fossil fuels due to their economic viability and environmental benefits. Efficient converting and harvesting of solar energy is a key target in solar energy systems. The implementation of inserts is an effective technique to amend the thermal efficiency of solar thermal energy systems. Thereby, the objective of this paper is to carry out a review on the recent investigations on the potential applications of different inserts including baffles, wire coils, vortex generators, and twisted tapes, in different solar thermal energy processes. The latest state-of-the-art developments are deeply discussed and some recommendations are made for further investigation in this field.