The present study analyzes the influence that market conditions have on determining optimum molten salt solar tower plants with storage that maximizes profits (in terms of plant configuration, sizing, and operation) for a location in South Africa. Three different scenarios based on incentive programs and local wholesale electricity prices are considered. A multi-objective optimization modeling approach was followed, showing the tradeoff curves between minimizing investment and maximizing profits when varying critical size-related parameters (such as nameplate capacity, solar multiple (SM), and storage capacity) together with power-cycle design and operating specifications including dynamic startup curves and different storage dispatchability strategies. Results are shown by means of a comparative analysis between optimal plants found for each scenario, highlighting the value that storage has under the current two-tier tariff scheme and the relevance of designing a suitable policy for technology development. Finally, a final analysis is performed with regard to the indicators used for economic evaluation of power plants, by comparing the differences between optimum designs found when using the levelized cost of electricity (LCoE) solely as performance indicator instead of cash-flows and profit-based indicators, such as the internal rate of return (IRR).
Levelized Cost of Electricity (LCOE) is an important metric which provides one way to compare the economic competitiveness of different electricity generation systems, calculated simply by dividing lifetime costs by lifetime production. Hidden behind the simplicity of this formula are various assumptions which may significantly alter results. Different LCOE studies exist in the literature, although their assumptions are rarely explicitly stated. This analysis gives all formulas and assumptions which allow for inter-study comparisons. The results of this analysis indicate that CSP LCOE is reducing markedly over time and that given the right location and market conditions, the SunShot 6¢/kWh 2020 target can be reached. Increased industrial cooperation is needed to advance the CSP market and continue to drive down LCOE. The results also indicate that there exist a country and technology level learning effect, either when installing an existing CSP technology in a new country or when using a new technology in an existing CSP country, which seems to impact market progress.1 Excluding combined cycle plants.
The operation of steam turbine units in solar thermal power plants is very different than in conventional base-load plants. Due to the variability of the solar resource, much higher frequencies of plant start-ups are encountered. This study provides an insight to the influence of thermal energy storage (TES) integration on the typical cycling operation of solar thermal power plants. It is demonstrated that the integration of storage leads to significant reductions in the annual number of turbine starts and is thus beneficial to the turbine lifetime. At the same time, the effects of storage integration on the electricity costs are analyzed to ensure that the designs remain economically competitive. Large storage capacities, can allow the plant to be shifted from a daily starting regime to one where less than 20 plant starts occur annually. Additionally, the concept of equivalent operating hours (EOHs) is used to further analyze the direct impact of storage integration on the maintenance planning of the turbine units.
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