The current flat-plate solar collectors perform best when their absorbers rotate around their axis. However, with their concentrators, reflectors, and tracking mechanisms, they take up a lot of space and are thus commercially speaking, not the best solutions. This paper proposes a novel solar collector design which employs the (relative) rotation of absorbers, but strives to combine the benefits of fixed and (absolute) tracking solar systems, i.e. volume occupancy from the former and thermal performance from the latter. The findings of our numerical analysis show that, the solar irradiance efficiency of this novel design is 20% higher than that of a fixed flat-plate collector during clear-sky days, and it is equally lower than that of an absolute tracking collector. This paper also introduces a new criterion for describing single-axis tracking solar collectors which should be included in the classifications of solar collectors. Finally, the article, which represents a continuation of our research in the field of solar energy utilization, can contribute to the future development of solar technologies and solve some of the current challenges.

In this paper the energetic and economic performance assessment of residential application of IC engine based cogeneration system in the Serbian climatic conditions using building energy simulation software was performed. The performance of IC based system was compared with the performance of the two other conventional systems for DHW preparation: gas and electric water heater. Comparing the IC based system with gas water heater the period required to return investment costs of IC engine is relatively high (11.7 years). The main barriers for widespread residential application of IC engine cogeneration system are related to the high capital costs and low price of purchased or sold electricity. In this respect, the investment cost reduction in small scale cogeneration systems has to be achieved. In relation to the current price in Serbia the price of purchased and sold electricity (feed-in tariff) should be increased by 37.5% and 67.5%, respectively, in order to achieve the value of payback period of five years. Comparing the IC based system with electric water heater the application of the IC engine is economically feasible since the payback period amounts 3.42 years. According to the simulation results, the IC engine cogeneration system ensured a primary energy saving of 28.81%.