Gases as Working Fluid in Parabolic Trough CSP Plants

AbstractThe energetic dimension of actual economy is massively oriented towards the use of fossil fuels: they cover a share of 87% of the energy needs and the trend of this share is increasing, in spite of the commitments adopted by almost all the Countries in the World. Most crucial concern is CO2 levels in the atmosphere and the positive feedback between Earth's temperature increase and carbon. Actual technologies which make use of renewable sources seem to be not fully suitable to invert this continuous increase of fossil fuels.Concentrated Solar Power plants (CSP) have had, recently, a huge attention as a technology able to give, in the mean future, a strong contribution to the electrical energy generation. CSP technology has an intrinsic superiority with respect to the other renewable plants but actual plants suffer of many drawbacks which slow down a massive diffusion: these aspects increase costs and do not insure the reliability levels required to make the investments profitable.Gas as heat transfer fluid inside solar receiver in a CSP Parabolic Trough (PT) type plant is discussed in this paper: this would simplify actual technology in the conversion section, downstream the solar energy collecting phase. The use of gases calls for a new conversion section discussed in this paper based on a direct expansion in gas turbine plants.The success of this concept is related to the possibility to increase the fluid (gas) temperature above the actual operating maximum values. The paper discusses the performances of a new gas cycle, the performances of actual receivers when fed with gas and introduces and discusses an optimization design parameter which allows a cost decrease and industrial reliability improvement