Markus Eck

Direct Steam Generation in Parabolic Troughs Final Results and Conclusions of the DISS Project

This paper presents a summary of the main results and conclusions achieved in the DISS (Direct Solar Steam) project. The test facility implemented at the Plataforma Solar de Almeria (PSA) in 1997–8, the so-called PSA DISS test facility, was operated for more than 3000 h in 1999–2000 and 2001 to investigate the Direct Steam Generation (DSG) process under real solar conditions. The feasibility of the DSG process in horizontal parabolic trough collectors has been proven and an important know how has been acquired by the project partners regarding the thermo-hydraulic parameters of the water/steam flow in DSG solar fields.

The DISS Project: Direct Steam Generation in Parabolic Trough Systems. Operation and Maintenance Experience and Update on Project Status

The DISS (DIrect Solar Steam) project is a complete R+TD program aimed at developing a new generation of solar thermal power plants with direct steam generation (DSG) in the absorber tubes of parabolic trough collectors. During the first phase of the project (1996-1998), a life-size test facility was implemented at the Plataforma Solar de Almeria (PSA) to investigate under real solar conditions the basic DSG processes and evaluate the open technical questions concerning this new technology. This paper updates DISS project status and explains O&M-related experience (e.g. main problems faced and solutions applied) with the PSA DISS test facility since January 1999.

Direct steam generation in parabolic troughs: First results of the DISS project

This article presents the latest experimental results of the European DISS (DIrect Solar Steam) project. The experiments are subdivided into steady state and transient tests. The goal of the steady state tests is the investigation of the thermohydraulic phenomena of the occurring two phase flow, whereas the transient tests are needed for the controller design. The experimental results are compared to simulation studies. Implications for the plant operation will be discussed.

A Direct Steam Generation Solar Power Plant With Integrated Thermal Storage

For the future market potential of parabolic trough power plants with direct steam generation (DSG), it is beneficial to integrate a thermal storage system. Heat storage media based on phase change materials offer heat transfer at constant temperatures needed for the evaporation process. Different options for a plant layout are presented and discussed. The interactions between the three subsystems—solar field, power block, and thermal storage—are analyzed, and boundary conditions arising from the thermal storage system are identified. Compared with a system without storage the number of operating points increases significantly since different combinations of storage charge and discharge operations go along with a varying power output of the solar field. It is shown that the large number of theoretical operating points can be reduced to a subset with practical relevance. Depending on the live steam parameters a reheat is necessary within the power block. Compared with parabolic trough fields with a single phase heat transfer medium such as oil, a special heat exchanger configuration is needed for a DSG plant. Different alternatives based on available technologies are presented and evaluated.

Heat Transfer Fluids for Future Parabolic Trough Solar Thermal Power Plants

Parabolic trough solar thermal power plants are at present the cheapest option for utility scale solar electricity production. At present several projects are under development in Spain, in the USA, Egypt, Morocco, Mexico, Algeria and Iran. The levelised cost of electricity (LCE) for solar thermal power plants is in the range of 13-21 €Cts/kWh. Accordingly, subsidies are necessary to bridge the gap between current LCE’s and market price. To achieve a sustainable competitiveness significant cost reduction is required. One possibility for cost reduction is increasing the efficiency. So far synthetic oil is used as a heat transfer fluid (HTF) in the absorber tubes of the collector field. This HTF limits the upper temperature of the power cycle to 370°C and thus the achievable efficiency to approx. 38%. Alternative HTF’s are under investigation. This paper compares the different HTF’s with respect to the operation temperature, overall operation aspects, storage concepts safety aspects and of course costs.

Thermal energy storage - overview and specific insight into nitrate salts for sensible and latent heat storage.

Summary Thermal energy storage (TES) is capable to reduce the demand of conventional energy sources for two reasons: First, they prevent the mismatch between the energy supply and the power demand when generating electricity from renewable energy sources. Second, utilization of waste heat in industrial processes by thermal energy storage reduces the final energy consumption. This review focuses mainly on material aspects of alkali nitrate salts. They include thermal properties, thermal decomposition processes as well as a new method to develop optimized salt systems.

THERMAL MODELLING AND SIMULATION OF PARABOLIC TROUGH RECEIVER TUBES

Receiver tubes (or heat collecting elements — HCE) are a key component of parabolic trough solar thermal power plants. They are mounted in the focal line of the collectors, absorb the concentrated solar irradiance and transfer the absorbed energy to the heat transfer fluid flowing through them. During the design phase of the receiver tubes and for the performance prediction of solar thermal power plants it is helpful to derive their technical properties, like the thermal losses or the temperature field in the receiver tubes, from their physical and geometrical properties. For this purpose, several models have been developed in the past [1–3]. In this paper, the different existing models are presented, compared and assessed. It is found that a simple analytical model is a helpful tool for the fast prediction of the temperature distribution in the receiver tube. Furthermore, a 2-dimensional and a 3-dimensioanl model are compared regarding the heat losses of a HCE at different operation conditions. Both tools show a good agreement with available measurements. Finally with these tools the efficiency factor F′ is calculated that considers the heat losses of an irradiated receiver compared to that of an un-irradiated receiver. According to the performed calculations, the efficiency factor of parabolic trough receivers is higher than expected.Copyright

Thermal Load of Direct Steam-Generating Absorber Tubes with Large Diameter in Horizontal Linear Fresnel Collectors

Solar thermal power plants are presently the cheapest technology for solar electricity production. Today, level electricity costs of 15 ct/kWh are achievable at good sites with high levels of direct normal irradiation. Nevertheless, further cost reductions are necessary to make solar thermal power plants economically feasible. One possibility for a further cost reduction might be the use of so-called Linear Fresnel Collectors in solar thermal power plants. Preliminary cost estimates of this option show that this is a promising potential for cost reduction. The technical feasibility of the linear Fresnel collector has to be checked in theoretical studies as well as during the operation of a life-sized prototype under real solar conditions. This paper presents results of preliminary theoretical studies regarding the thermal load of the absorber tube used in a linear Fresnel collector with a secondary concentrator.

20 – High-Temperature Molten Salts for Solar Power Application

Solar thermal power plants are a key technology for electricity generation from renewable energy resources. Thermal energy storage (TES) systems correct the mismatch between the solar supply and the power demand. TES makes it possible to meet the intermediate load profile with dispatchable power, a benefit that has a high value to power utilities and that gives concentrating solar power (CSP) technology an edge over photovoltaic and wind power. Hence, TES is a key technology for solar thermal energy utilization with growing present and future importance. This chapter focuses on material aspects of alkali nitrate salts. They include thermal properties, thermal decomposition processes, steel corrosion issues, and phase diagrams of multicomponent salt systems. In addition, two CSP applications using molten nitrate salts as sensible and latent TES are discussed.

Maximum Temperature Difference in Horizontal and Tilted Absorber pipes with Direct Steam Generation

The direct steam generation (DSG) in parabolic trough collectors is a promising option for the im provement of the reliable parabolic trough technology for solar thermal electricity generation. The DISS (DIrect Solar Steam) test facility at the Plataforma Solar de Almeria is a full-scale solar steam generator consisting of parabolic trough collectors, used to investigate the DSG process under real operating conditions. According to theory and results from lab-scale experiments it was expected that the tilt of the absorber tubes can improve the thermohydraulic behavior of the DSG process significantly. Within the DISS project a test campaign has been performed to investigate the influence of tilt. The evaluation of the test data showed, that the horizontal absorber tube guarantees sufficient cooling confirmed by low temperature differences even at very high steam qualities.