Comparative system analysis of direct steam generation and synthetic oil parabolic trough power plants with integrated thermal storage

Abstract

Parabolic trough power plants are currently the most commercially applied systems for CSP power generation. To improve their costeffectiveness, one focus of industry and research is the development of processes with other heat transfer fluids than the currently used synthetic oil. One option is the utilization of water/steam in the solar field, the so-called direct steam generation (DSG). Several previous studies promoted the economic potential of DSG technology (Eck et al., 2008b; Price et al., 2002; Zarza, 2002). Analyses' results showed that live steam parameters of up to 500°C and 120 bars are most promising and could lead to a reduction of the levelized electricity cost (LEC) of about 11% (Feldhoff et al., 2010). However, all of these studies only considered plants without thermal energy storage (TES). Therefore, a system analysis including integrated TES was performed by Flagsol GmbH and DLR together with Solar Millennium AG, Schott CSP GmbH and Senior Berghö fer GmbH, all Germany. Two types of plants are analyzed and compared in detail: a power plant with synthetic oil and a DSG power plant. The design of the synthetic oil plant is very similar to the Spanish Andasol plants (Solar Millennium, 2009) and includes a molten salt two-tank storage system. The DSG plant has main steam parameters of 500°C and 112 bars and uses phase change material (PCM) for the latent and molten salt for the sensible part of the TES system. To enable comparability, both plants share the same gross electric turbine capacity of 100 MWel, the same TES capacity of 9 h of full load equivalent and the same solar multiple of the collector field of about two. This paper describes and compares both plants' design, performance and investment. Based on these results, the LEC are calculated and the DSG plant's potential is evaluated. One key finding is that with currently proposed DSG storage costs, the LEC of a DSG plant could be higher than those of a synthetic oil plant. When considering a plant without TES on the other hand, the DSG system could reduce the LEC. This underlines the large influence of TES and the still needed effort in the development of a commercial storage system for DSG.

Second test campaign of a pilot scale latent heat thermal energy storage – Durability and operational strategies

“…This could reduce the Levelized Cost Of Electricity (LCOE) of the power plant and simplify the operation of the storage [6]. The Alsolen Sup® test section can be used as a combined sensible-latent thermal storage by keeping an intermediate water level in the test section when charging: doing this the upper part of the module (where steam is condensed) is used as a latent storage, while the lower part of the module (where liquid water is subcooled) is used as a low temperature sensible storage.…”

Transient performance of direct steam generation solar power plants

“…The LEC can be estimated as in for both DSG and oil plants for the same solar field and power block; the collector type and area are assumed to be identical. The technical specifications and size of the power block equipment are considered to be identical.…”

“…Feldhoff compared a power plant with synthetic oil and a DSG power plant. The LEC of a DSG plant was larger than that of a synthetic oil plant with thermal storage, whereas without storage, the synthetic oil plant had a larger LEC value.…”

Materials-Related Aspects of Thermochemical Water and Carbon Dioxide Splitting: A Review

“…A mixture of molten salts is used as the heat transfer fluid and storage media. Such molten salts are e.g., currently used in some commercial solar power plants like the GemaSolar Plant or the Andasol Plants in Spain [150,151]. Similar to the process in those plants, here a binary mixture of 60% NaNO 3 and 40% KNO 3 was considered.…”