Hybrid Solar Gas-Turbine Power Plants – A Thermoeconomic Analysis

Abstract:

The provision of a sustainable energy supply is one of the most important issues facing humanity at the current time, and solar thermal power has established itself as one of the more viable sources of renewable energy. The dispatchable nature of this technology makes it ideally suited to forming the backbone of a future low-carbon electricity system.

However, the cost of electricity from contemporary solar thermal power plants remains high, despite several decades of development, and a step-change in technology is needed to drive down costs. Solar gas-turbine power plants are a promising alternative, allowing increased conversion efficiencies and a significant reduction in water consumption. Hybrid operation is a further attractive feature of solar gas-turbine technology, facilitating control and ensuring the power plant is available to meet demand whenever it occurs.

Construction of the first generation of commercial hybrid solar gas-turbine power plants is complicated by the lack of an established, standardised, power plant configuration, which presents the designer with a large number of choices. To assist decision making, thermoeconomic studies have been performed on a variety of different power plant configurations, including simple- and combined-cycles as well as the addition of thermal energy storage. Multi-objective optimisation has been used to identify Pareto-optimal designs and highlight trade-offs between costs and emissions.

Analysis of the simple-cycle hybrid solar gas-turbines revealed that, while electricity costs were kept low, the achievable reduction in carbon dioxide emissions is relatively small. Furthermore, an inherent trade-off between the design of high efficiency and high solar share hybrid power plants was identified. Even with the use of new optimised designs, the degree of solar integration into the gas-turbine did not exceed 63% on an annual basis.

In order to overcome the limitations of the simple-cycle power plants, two improvements were suggested: the integration of thermal energy storage, and the use of combined-cycle configurations. Thermal energy storage allowed the degree of solar operation to be extended, significantly decreasing carbon dioxide emissions, and the addition of a bottoming-cycle reduced the electricity cost. A combination of these two improvements provided the best performance, allowing a reduction in carbon dioxide emissions of up to 32% and a reduction in electricity costs of up to 22% compared to a combination of conventional power generation technologies.