Investigating an Integrated Solar Combined Cycle Power Plant

Using solar energy standalone to generate electricity has high investment risk. This is due to the need to energy storage systems to ensure electricity generation during the night. For this reason the hybridization of renewable energy resources and fossil fuel has been motivated. In an Integrated solar combined-cycle (ISCC) the solar thermal energy is integrated into combined cycle gas turbine (CCGT) power plant. The aim of this study is to evaluate the impact of addition of solar energy to a CCGT at both design and off design conditions of solar thermal input and ambient temperature.

The evaluation was fulfilled by studying the main performance indicators for hybridization of combined cycle (CC) with solar energy. These factors are the solar conversion efficiency, solar fraction, and boosting factor.

The study was implemented on Kurymat ISCC, in Egypt. The plant is designed to produce 135 MWe. It composed of parabolic trough solar field integrated with a conventional CCGT power Plant. The design solar heat input is 50 MWth at 20 °C dry bulb ambient temperature. The CCGT consists of one gas turbines of 70 MWe, one HRSG that produce steam at pressure 90 bar and a steam turbine of 65 MWe. The study shows that, for night mode operation (no solar) changing the ambient temperature from 5oC to 35 °C, the plant efficiency drops from 0.53 to 0.51 and the output power changes from 119.2 MW to 99.69 MW. Also, for day mode (with solar) at design solar thermal input and ambient temperature the ISCC efficiency is higher than CC efficiency when we neglect the solar fuel cost, while the efficiency drops below that of the CC if the solar fuel cost is considered. The power output reduces with increasing the ambient temperature and increases with increasing the solar thermal input.

Keywords:Parabolic trough; Integrated solar combined cycle; Thermodynamic analysis

Abbreviations

CCGT - combined cycle gas turbine

CST - Concentrated solar thermal

DSG - direct steam generation

HPEC - High pressure economizer

HPEV - High pressure evaporator

HPSH - High pressure super heater

HRSG - Heat recovery steam generator

HTF - Heat transfer fluid

ISCC - Integrated solar combined cycle

LCOE - Localized cost of energy

LEC – Levelized energy cost

MENA - Middle East North Africa

NGCC - Natural gas combined cycle

SAPG - Solar aided power generation

SSG - Solar steam generator

Nomenclature

dQ_solar Increase of solar heat input MW

dη_steam Increase of steam cycle efficiency -

F_solar Solar fraction -

LHV_gas Lower heating value of natural gas MJ/kg

Q_solar Solar heat input MW

W_fossil Output power of the NGCC MW

W_fossil+solar Output power of the ISCC MW

W_net The net power of the whole plant MW

W_solar The output power of the steam turbine with solar hybridization MW

η_plant Overall plant efficiency %

η_solar Solar conversion efficiency %

Θ _s Boosting factor of the steam cycle efficiency