# Concentrating Solar Collectors for a Trigeneration System--A Comparative Study
## 1 Introduction  
Solar irradiation exploitation is an effective weapon in order to face critical issues such as population growth which leads to higher energy consumption [1], the need for sustainable energy systems [2] and various environmental problems related to greenhouses emissions [3]. Concentrating solar power is an efficient way to produce high quantities of useful heating at various temperatures in order to fulfill the energy needs of numerous applications such as space-heating, industrial-heating, air-conditioning, refrigeration, electricity, desalination, industrial heat and methanol-reforming [4], while a lot of interest exists in hybrid solar concentrating systems [5]. The cogeneration [6] and the trigeneration systems [7] are highly efficient technologies because they produce many useful outputs by utilizing waste heat quantities from one subsystem to another, and so overall there is lower entropy generation. The exploitation of solar energy in order to drive or to assist a trigeneration system seems to be a sustainable choice in order to create efficient systems that are also environmentally friendly [8]. Solar-driven trigeneration systems are usually applied in the building sector which is responsible for a great part of worldwide energy consumption [9]. The building sector needs mainly electricity, heating and cooling; three kinds of energy which are usually produced by the trigeneration configurations. Moreover, it must be stated that the trigeneration systems aid the efficient operation of the utilized devices and the exploitation of solar irradiation reduces fossil fuel consumption and grid electricity consumption. Moreover, it is useful to state that there are extra ways of enhancing theenergy behavior of the buildings such as sustainable ventilation strategies [10] and novel architecture techniques [11]. In the literature, the utilization of solar concentrating power for feeding trigeneration systems has been examined by many researchers. Usually, the organic Rankine cycle (ORC) is used as a primary mover, and it is combined with heat pumps which can be vapor-compressors or absorption heat pumps. [PERSON] et al. [12] carried out thermodynamic studies of a solar-fed trigeneration unit with a parabolic trough collector (PTC), absorption machine and ORC. The solar collectors give useful heat in the ORC, and the ORC condenser transfers heat to the absorption heat pump. According to their findings, the system presents exergy efficiency close to 20%. In addition, [PERSON] and [PERSON] [13] examined a similar system and they calculated that the optimized configurations present 29.4% exergy efficiency and approximately 150% energy efficiency. The high value of the system energy efficiency is explained by the use of the absorption chiller as a heat transformer in order to exploit the cooling production as the energy input and partially to make heating production. [PERSON] et al. [14] carried out a study of a system with an organic Rankine cycle and a double-stage absorption machine, and they found the maximum exergy efficiency to be approximately 13% while the respective energy efficiency is about 95%. [PERSON] et al. [15] conducted a comparative work of the optimum way for combining an absorption chiller, ORC and parabolic trough collectors. They found that feeding the absorption chiller by the waste heat of the ORC is the best way to achieve a maximum exergy efficiency of around 41%. [PERSON] et al. [16] examined the use of an absorption chiller and an ORC in the solar field loop. Moreover, there is an assisted vapor compression cycle for heating production which is driven by the ORC waste heat, while geothermal and wind energy are included in this work. They found that the exergetic performance of the unit is 7.3% and the energetic 76.1%, while the system net present value is USD 345,000. [PERSON] et al. [17] examined a unit with a vapor compression heat pump coupled with an organic Rankine cycle.