Concentrated Solar Energy-Driven Multi-Generation Systems Based on the Organic Rankine Cycle Technology
Nishith В Descti* and Fredrik Haglind
Design of energy efficient, environmentally friendly and economically viable systems is important for sustainable development. Among the various technology options based on renewable energy sources, concentrated solar power (CSP) systems are considered to be technologies in the development stages. Many small to large-scale power plants (a few kV to a few MW) based on the CSP technology exist in different sun-rich regions worldwide. Due to the high capital cost and high levelized cost of energy (LCOE), CSP plants have not captured a large market share like those of solar photovoltaic (PV) and wind power plants. Concentrated solar power plants with cost-effective thermal energy storage can work as a base load plant with a high capacity factor. In contrast, solar PY and wind power plants with large-scale battery storage are not cost-effective. Patil et al. (2017) reported that the levelized cost of electricity (LCOE) for solar photovoltaic systems with battery storage is about 36.8% higher than that of the parabolic trough collector-powered organic Rankine cycle system with thermal energy storage. Concentrated solar power plants can also avail of the advantage of producing heat and other products, and thus work as a cogeneration, trigeueratiou or multi-generation unit. In contrast, solar PV and wind power plants cannot be used for heat production; therefore, the sub-systems for cooling and/or heating and/or desalination should be electricity-driven. Slialaby (2017) recommended avoiding the use solar photovoltaic systems with batteries to drive RO desalination systems because of the high capital and running costs. Commonly-used small to medium-scale, dispatchable (on demand) distributed generation systems are diesel generator-based or biomass-based systems. Biomass- and diesel-based multi- generation units can have electrical or thermal energy-driven sub-systems, depending on the resulting cost of utilities. For isolated regions and islands, the cost of electricity generation is high, as the diesel is imported from the nearby port. The use of biomass is a major concern in places with water scarcity, due to the large water footprints of biomass energy sources (Gerbens-Leenes et al., 2009).
Multi-generation systems achieve a higher efficiency and a higher energy utilization factor than plants producing only electricity (Karellas and Braimakis. 2016). Concentrated solar energy-driven
Figure 1. Representation of possible energy conversion routes of concentrated solar thermal energy-powered multigeneration systems.
multi-generation systems are also suitable for decentralized installations. Integrated systems powered by concentrated solar energy and biomass energy make up a promising option (Mathkor et al.. 2015). Wu et al. (2019) proposed the integration of a concentrated solar thermal energy and power cycle system with a conventional combined cooling, heating and power system. A representation of possible energy conversion routes of concentrated solar thermal energy-powered multi-generation systems is shown in Figure 1. In the case of a typical parabolic trough collector field, the optical losses (including shading and blocking, cleanliness, shielding by bellows) are about 37% and the thermal losses (including thermal losses from piping) are about 18% (Heller, 2017). For small to medium-scale applications (a few kV to a few MW), organic Raukine cycle power systems have been demonstrated to be efficient solutions for multi-generation plants (Astolfi et al., 2017; El-Emam and Diucer, 2018). Organic Raukine cycle (ORC) power systems can be effectively used for energy sources, like concentrated solar power, biomass, waste heat, geothermal, and ocean thermal. The main advantages of organic Rankiue cycle power systems employing diy and iseutropic working fluids are the high isentropic efficiency of the turbine at design and pail-load conditions, quick start-up, long life-tune of the components, low mechanical stresses in turbine blades, automatic and unmanned operation, low operation and maintenance costs, and flexibility and ability to follow variable load profiles (Algieri and Morroue. 2012). All the mentioned characteristics make ORC units particularly suitable for supplying the electricity demand for a vapor compression refrigeration system and/or for a reverse osmosis system or the thermal energy (using high temperature working fluid vapor available at the exhaust of turbine) demand for a vapor absoiptiou refrigeration system and/or for a water distillation system. When designed for multi-product purposes (thermal energy- driven), the system is designed with a condensation pressure higher than that of systems designed for power generation only. Hoffmann and Dali (2018) reported that the levelized cost of electricity for a solar power tower integrated Raukine cycle increases by 8.8% when used for co-generation. This is because the condensing stream leaving the turbine should be at a higher temperature in order to act as an energy source for the cogeneration application. Hie revenue generated from the other product (heat, fresh water, or cooling) may compensate for this low efficiency.
In this chapter, different concentrated solar energy-driven multi-generation systems based on the organic Rankine cycle technology for small to medium-scale applications are reviewed. Power generation systems are discussed in section 2. Systems generating power, fresh water and heating are presented in section 3. Section 4 describes power, cooling and heating systems. Design considerations and issues in CSP-driven multi-generation systems using ORC technology are presented in section 5. Finally, concluding remarks are given in section 6.