Solar energy is clean, renewable, abundant and free. The light and heat energy can be harnessed by using several technologies such as solar heating, photovoltaic cell and photosynthesis. Solar collectors are used for collecting solar thermal energy by heating and reheating a stream of water. This paper focuses on improving performance of solar flat plate collector using twisted tape. Flat plate collectors have a wide range of usage in industrial, public as well as residential sectors. Solar water heaters are environment-friendly, cheap to operate and need very little when compared with other solar applications. Many researchers are working to enhance the thermal efficiency of solar water heaters. The thermal efficiency enhancement can be done by modification of design of parts of solar flat plate collector such as absorber plate, STs, working fluid, thermal insulation, efficiency of fin and selective coating of an absorber plate. Use of twisted tape is an efficient method to increase the thermal efficiency by increasing the heat transfer by increasing the contact surface area between the water and metal tubes (inserted tape tubes) and also by promoting turbulence of flow. © Springer Nature Singapore Pte Ltd 2021.