Parabolic Trough Solar Field Research Articles

Solar–geothermal hybrid system

The Cerro Prieto Geothermal Power Plant is located in the northwest of Mexico, lat. 32°39′, long. 115°21′ in the northern hemisphere. A solar–geothermal hybrid system is proposed in order to increase the steam flow during the present geothermal cycle, adding a solar field of parabolic trough concentrators. Energy is supplied to the geothermal flow from wells in order to increase the steam generation rate. This configuration will increase the capacity factor of the system by generating additional steam during the peak demand hours. The parabolic trough solar field is evaluated in North–South and East–West orientation collector alignments. A proposal to obtain an increase of 10% in steam flow is evaluated, as the increase in flow is limited by the content of dissolved salts, so as to avoid a liquid phase with high salt concentrations. The size of the parabolic troughs field was obtained.

Engineering aspects of a molten salt heat transfer fluid in a trough solar field

An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating large-scale solar parabolic trough plants in the USA currently use a high temperature synthetic oil in the solar field consisting of a eutectic mixture of biphenyl/diphenyl oxide. The scope of the overall investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems existed, and the quantification of performance and electricity cost using preliminary, but reasonable, cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO 3 and 40% KNO 3) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% Ca(NO 3) 2, 7% NaNO 3, and 45% KNO 3). Operation and maintenance (O&M) becomes an important concern with molten salt in the solar field. This paper addresses that concern, focusing on design and O&M issues associated with routine freeze protection, solar field preheat methods, collector loop maintenance and the selection of appropriate materials for piping and fittings.

Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field

An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating SEGS (Solar Electric Generating Systems located in Mojave Desert, California) plants currently use a high temperature synthetic oil consisting of a eutectic mixture of biphenyl/diphenyl oxide. The scope of this investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems exist, and the quantification of performance and electricity cost using preliminary cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO3 and 40% KNO3) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% CaNO32, 7% NaNO3, and 45% KNO3). Assuming a two-tank storage system and a maximum operation temperature of 450°C, the evaluation showed that the levelized electricity cost can be reduced by 14.2% compared to a state-of-the-art parabolic trough plant such as the SEGS plants. If higher temperatures are possible, the improvement may be as high as 17.6%. Thermocline salt storage systems offer even greater benefits.

Thermal gradient avoidance under stratified two-phase flow in DSG by capillar structures

The benefits of substitution of thermal oil with water in two phase flow for electricity production in parabolic trough solar fields have been pointed out in several papers, [1]. The need of covering a wide range of flow masses to cope with variable solar isolation, means low mass flows, that provide an insufficient cooling of the horizontal pipes, when stratification occurs. The large differences between the heat transfer coefficients for wetted (liquid to solid) and dry segments (steam to solid) will lead to very large thermal stresses and absorber misalignment from the focal axis of the parabolic trough collector, Between the solutions to avoid the drawbacks just mentioned, the mcrease of the wetting perimeter by capillary forces is found. Capillary pressures, developed by internal porous coated or microgrooved pipes, lift up a thin liquid film, that rewets all the perimeter of the pipe and whose thermal resistance, because of boiling, is very low. In this paper, a model of the theoretical wetting film behaviour and its relation to the characteristic of the system (microgroove's depth, permeability of porous coatings...) is shown. Experimental set up for measurements under temperature and pressure ranges for DSG conditions (311°C, 100 bar) is shown.

96/06232 Passive solar, country-style

In the present paper a tri-dimensional non-linear dynamic thermohydraulic model of a parabolic trough collector was developed in the high-level acausal object-oriented language Modelica and coupled to a solar industrial process heat plant modeled in TRNSYS. The integration is performed in an innovative co-simulation environment based on the TLK interconnect software connector middleware. A discrete Monte Carlo ray-tracing model was developed in SolTrace to compute the solar radiation heterogeneous local concentration ratio in the parabolic trough collector absorber outer surface. The obtained results show that the efficiency predicted by the model agrees well with experimental data with a root mean square error of 1.2%. The dynamic performance was validated with experimental data from the Acurex solar field, located at the Plataforma Solar de Almeria, South-East Spain, and presents a good agreement. An optimization of the IST collector mass flow rate was performed based on the minimization of an energy loss cost function showing an optimal mass flow rate of 0.22 kg/s m2. A parametric analysis showed the influence on collector efficiency of several design properties, such as the absorber emittance and absorptance. Different parabolic trough solar field model structures were compared showing that, from a thermal point of view, the one-dimensional model performs close to the bi-dimensional. Co-simulations conducted on a reference industrial process heat scenario on a South European climate show an annual solar fraction of 67% for a solar plant consisting on a solar field of 1000 m2, with thermal energy storage, coupled to a continuous industrial thermal demand of 100 kW.