Distributed m-CHP generation from a small scale concentrated solar power installation

The present work describes the realization of a modular 1-3 kWe, 3-9 kWth micro Combined Heat and Power (m-CHP) system based on innovative Concentrated Solar Power (CSP) and Stirling engine technology. The cogeneration of energy at distributed level is one of leading argument in large part of energy policies related to renewable energy resources and systems. This CSP m-CHP will provide electrical power, heating and cooling for single and multiple domestic dwellings and other small buildings. The developed system integrates small-scale concentrator optics with moving and tracking components, solar absorbers in the form of evacuated tube collectors, a heat transfer fluid, a Stirling engine with generator, and heating and/or cooling systems; it incorporates them into buildings in an architecturally acceptable manner, with low visual impact. Some good results have already been achieved, while developments on several technology subcomponents will be finalized through first part of 2013. Two Cer.Met. have been modelled, realized and tested. The up scaled receiver, in form of Cer.Met. coating based on TiO2 - Nb, has been confirmed an absorptance of 0.94 and emittance of 0.1 (@350C). A second Cer.Met. coating based on SiO2 - W has demonstrated an absorptance of 0.93 and emittance of 0.09 (@350C). A full-evacuated solar tube has been designed and realized, with absorber of 12 mm in diameter and length in 2 meters. The system is provided of a concentration ratio 12:1, and a single module is 200 cm long, 40 cm wide and 20-25 cm high. Two or more modules can be combined. The evacuated solar tube, located on the focus, has the selective absorber on a tube of 12 mm in diameter. A very thin glass mirror has been developed (< 1 mm). The overall mirror reflectivity has been measured, the verified value is 0,954. Research has proposed a high energy density, double acting Stirling engine, provided of innovative heat exchangers realized through Selective Laser Melting process. The engine is a low speed (250 RPM), high pressure (130 Bars) and compact solution able to be run at 300C and generate 3,5 kW nominal power. The solar technology has been fully proven in a demonstration site. The solar plant has been installed in Malta, by Arrow Pharm company, supplying the industrial process of generated steam at 180C and 3.5 absolute pressure in a first phase and supporting the tests of improved technologies at a second stage. The solar collector's efficiency is around 50% in presence of 900 W/m2 of direct solar radiation and at 300C. During 2013, solar evacuated tubes with innovative Cer.Met. coating, together with new thin glass mirrors has upgraded the demonstration site, together with a new and innovative low temperature difference and high energy density Stirling. By end-2013, the system has been demonstrated. At the beginning of 2014 it will be transferred to Trento for further optimization, with the overall objective to achieve a minimum of 65% in solar collectors efficiency at 300C, and 12-15% of overall electrical efficiency by the Stirling cycle. The actual work is part of a FP7 European Funded project, DIGESPOBajada New Energy, General Membrane, EcoGroup, Econetique, Energy Investment, JMV Vibro Blocks, Solar Engineering, Solar Solutions.peer-reviewe

Solar flux map distribution of a parabolic-spheric dish based on photographic method

This paper presents a novel method to derive solar flux map of irradiation near to the focal plane of an innovative concentrating point focusing technology facility. The system has a reflector covered by mirrors focusing sun radiation on a Stirling engine. It has been designed and manufactured from the sketch. It consists of a novel dish of 8.6 m in diameter, whose reflector is made of glass mirrors and has a focal distance of about 4.5 m. The profile is the innovative part of this facility where the mirrors have been designed in order to reduce manufacturing costs. The inner part of the concentrator consists in a spherical shape profile and the external part represents a parabolic profile. Flux measurements is obtained integrating photogrammetric and photometric procedures. The approach used here is presented in a real case application which provides pixel values of radiation for the receiver plane. The solar flux map achieved for a sunny day is reported and compared with the one obtained by a ray-tracing analysis

Model-Based Design of an Energy-System Embedded Controller Using Taste

Model-based design has become a standard practice in the development of control systems. Many solutions provide simulation, code generation, and other functionalities to minimize the design time and optimize the resulting control system implementation. In this paper, we report on the experience of using Taste as the design environment for the controller of an energy system comprising a parabolic dish collector and a Stirling engine. Besides standard advantages of model-based design, an appealing feature of Taste is the possibility of specifying the design model with a formal language such as SDL. The complexity of the designed system stressed the tool’s performances and usability. Nevertheless, the functionalities provided by Taste were essential to manage such complexity

Numerical Analysis of Radiation Propagation in Innovative Volumetric Receivers Based on Selective Laser Melting Techniques

Volumetric absorbers constitute one of the key elements in order to achieve high thermal conversion efficiencies in concentrating solar power plants. Regardless of the working fluid or thermodynamic cycle employed, design trends towards higher absorber output temperatures are widespread, which lead to the general need of components of high solar absorptance, high conduction within the receiver material, high internal convection, low radiative and convective heat losses and high mechanical durability. In this context, the use of advanced manufacturing techniques, such as selective laser melting, has allowed for the fabrication of intricate geometries that are capable of fulfilling the previous requirements. This paper presents a parametric design and analysis of the optical performance of volumetric absorbers of variable porosity conducted by means of detailed numerical ray tracing simulations. Sections of variable macroscopic porosity along the absorber depth were constructed by the fractal growth of single-cell structures. Measures of performance analyzed include optical emission losses from the absorber front and rear faces, penetration of radiation inside the absorber volume, and radiation absorption as a function of absorber depth. The effects of engineering design parameters such as absorber length and wall thickness, material reflectance and porosity distribution on the optical performance of absorbers are discussed, and general design guidelines are given