Thermodynamic advantages of using solar energy in the regenerative Rankine power plant

Use of solar energy is of great importance in reducing greenhouse gases emission. Although there are some advances in solo solar power systems, the efficiencies and costs of these systems are not so attractive. This paper presents a new approach for solar power utilization, i.e, using solar heat to replace the extracted steam to heat the feedwater in the regenerative Rankine plant. The exergy merit index EMI (the ratio of the work generated by the saved steam to the exergy supplied by the solar heat) of such solar-aided systems can be greater than 100% while the maximum exergy efficiencies of the solo solar power systems can never reach 100%. The analysis of a three-stage regenerative Rankine plant shows that, by using solar energy, the work generated can be increased up to 30% while the EMI reaches 101.28%. Therefore low-grade heat and other waste heat can be utilized as a valuable source of work in this way. The "aided" concept has special meaning for solar power utilization. In summer, both the solar radiation and the electrical load demand reach their peaks. The increased solar radiation can generate increased power to meet the increased power demand. In addition, the solar aided system can also eliminate the variability in power output in solo solar power systems. (C) 1999 Elsevier Science Ltd. All rights reserved.