Turboefficiency: An enhancement to improve existing solar thermal plants with readily available technology

This paper studies a method to enhance the performance of solar thermal parabolic trough power plants. The method can be applied to new designs and existing plants at a low cost and with minor modifications. It is called the turboefficiency concept because it is based on increasing the solar–electric efficiency of the plants by means of standard, low pressure turbines. These turbines would only be used at periods of high solar radiation, during which the solar resource exceeds the nominal power of the plant. By letting the solar field generate a minimal excess steam, and using it to power the small turbines coupled to pumps, the heat transfer fluid can be driven across the solar field saving the consumption of electricity of the normal electric pumps. This electricity would be sent to the grid, thus increasing the net production of the plant. The turboefficiency concept is based on standard, low cost components, and is conceived so as to be installed on an existing plant with minor modifications, during any of the programmed stops. A well known 50 MW plant design has been modelled and the turboefficiency concept has been modelled onto it. Then the increase in net electricity production has been estimated on two locations with slightly different solar irradiation profiles. This has been carried out for several sizes of the solar field. Results show that a minimum increase of several hundred of MWh can be expected in the case of a small solar field, in the order of 0.8% of the total annual production. Large solar fields, as those used with plants with thermal energy storage systems, can increase their annual production up to 2.1%. A preliminary economic assessment of installing the turboefficiency concept on an existing plant shows an improvement on the LCOE of a conventional plant can range from just over 0.1% to well over 1.3% for larger fields.