Small Hybrid Solar Power System: First Field Test Results

Daniel Favrat, El Hadj Malick Kane
2002
Conference paper

Abstract

This paper presents field tests of an original concept of a small hybrid solar power plant integrating three technologies: hermetic volumetric scroll expander-generators installed in two superposed Organic Rankine Cycles (ORC), a (bio-)Diesel engine with heat recovery exchangers and a solar field made of two rows of sun following flat plate concentrators with vacuumed isolated collector tubes. The basic idea of the concept is to exploit the synergy between equipment, use cheap and maintenance free expander- generators, guaranty power availability at all time and improve the efficiency of the engine when it has to operate alone at night time by converting the waste heat with the solar ORC. This type of hybrid power plant is intended for rural electrification purposes in developing countries or cogeneration in applications like heated swimming pools in other countries. Pressurized hot water is used at this time as a thermal fluid in the collectors with HCFC123 in the topping cycle and HFC134a in the bottoming cycle. The field tests have been performed during the summer 2001 in Lausanne (Switzerland) and the pland proved operationally reliable. However performance results (with exergetic efficiencies up to 45%) did not meet the expectations but measures to improve the concept have been identified.

Official source

https://infoscience.epfl.ch/record/53437?ln=en

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts

Related publications

Related publications (25)

SPS: Projet d'une minicentrale pilote électro-thermo-solaire de 10 KWe.

Daniel Favrat, El Hadj Malick Kane

This report presents the field tests synthesis of a small Hybrid Solar Power Plant integrating three technologies : hermetic volumetric scroll expander - generators working with two superposed Organic Rankine Cycles (ORC) a cogeneration group composed by a Diesel engine coupled with an asynchronous generator with heat recovery at two levels of temperature and a solar field made of plate concentrators. This type of hybrid power plant is mainly intended for rural electrification purposes in developing countries or cogeneration in applications like heating swimming pools in other countries. After having been tested separately, the three main components of the plant (Concentrators, ORC and cogeneration group) have been coupled in a field on the EPFL campus in Lausanne (Switzerland) in order to allow experimentation of the entire installation with real conditions. The general concept is promising, thermal cycles being quite robust and adapting well to the very variable solar conditions, and this for the two working modes (Solar and Hybrid). In terms of performances, results have been encouraging, even if improvements are still necessary. Expanders worked at part load, the concentrating surface having been under-dimensioned and there are no doubts results could be achieved with better adaptation between these two elements. In hybrid mode, fuel energy was transformed up to 40.5 into electricity, opening good perspectives for the future including with other cogeneration technologies like micro gas turbines or medium to high temperature fuel cells.

2001

A new concept of small hybrid solar power system (HSPS) has been successfully demonstrated in the context of a project called SPS (Solar Power System). This plant integrates two rows of solar collectors, two superposed Organic Rankine Cycles (ORC) each equipped with a scroll hermetic expander-generator and a heat engine. In operation with solar energy only, the heat is supplied by a thermal fluid (presently pressurized water) heated in the vacuum insulated focal tubes of sun following, flat concentrators made of series of thin plate mirrors (CEP). In hybrid mode additional heat is supplied by heat recovery from the exhaust gases of the engine in series with the solar network and by a separate network recovering heat from the cooling of the engine block at an intermediate temperature level. This paper presents the results of a multi-criteria optimization of a 22 kWe HSPS, including aspects such as energy performance, economic and financial analysis, and environemental aspects. The so called mini-maxi methodological approach with genetic algorithm is used considering three principal criteria such as the energy efficiency of the superposed ORCs, the minimal cost of the installation and the minimum emission of CO2 . Taking into account of the solar radiation time dependence, the elecricity supply variation and the change of configuration (night and day operation), the performance analysis is based essentially on the yearly energy simulation in which the off-design physical models of components are considered. A comparison of HSPS with pure fossil fuelled Plants (DEPU-Diesel Engine Power Unit) is reported for the same electrical power load curve, with an economic sensitivity analysis. Results show that the solar electricity costs are still high and depend considerably on the size of the Solar Field (the HSPS Levelized Electricity Cost with 5 to 16% of annual solar share is about 17% to 49% higher than a similar size Diesel Engine Power Unit). However, a reduction of CO2, emission up to 26% could be obtained when replacing the Diesel Engine Unit by a similar HSPS. Those hybrid solar thermal power systems may already be competitive if a tax of about 42 Swiss cts/kgCO2 would be considered.

2002

Small Hybrid Solar Power System

Daniel Favrat, El Hadj Malick Kane, Diego Larrain

This paper introduces a novel of mini-hybrid solar power plant integrating a field of solar concentrators, two superposed Organic Rankine Cycles (ORC) and a (bio)Diesel engine. Turbines for the organic Rankine Cycles are hermetic scroll expander-generators. Sun tracking solar collectors are composed of rows of flat mirror bands (CEP) arranged in a plane, which focus the solar energy onto a collector tube similar to those used in SEGS plant in California. The waste heat from both the exhaust gases and block cooling of the thermal engine are also heat sources for the ORCs. Such units are considered to meet electricity, cooling and pumping needs of remote settlements in the sun belt areas or on special sites requiring low temperature heating such as swimming pools or greenhouses. The thermal engine guaranties a minimum level of both power and heat availability at night or during cloudy periods. Laboratory tests, made with the superposed ORCs only, confirmed adequate operational characteristics with good performances over a broad range of conditions. A few preliminary tests on the site of the solar power plant when coupled with the engine confirmed a reasonable behavior and the interest of the concept even at part load or during sharp variations of the thermal supply.

2003

2002