Abstract
The operation of a power plant based on solar energy can vary significantly with time because of the intrinsic intermittency of the energy resource. Hence, a smart management is required to deal with the complex dynamic variations of the different subsystems. In order to do that, different control logics can be implemented but their effectiveness strictly depends on the temporal evolution of the parameters considered. For a given plant configuration, their exact estimation can be obtained through experimental tests during the commissioning of the plant. However, any change in the design parameters of the plant reflects in a different time constant, whose preliminary knowledge may be of support in tuning the control logic of the plant during the design stage. Therefore, based on the configuration of a small-scale concentrated solar combined heat and power plant as designed and built under the EU funded project Innova MicroSolar by several universities and companies, in this study a prediction of the time constant of several plant configurations with varying solar multiple and size of the storage tank is performed. By making use of the dynamic simulator previously developed by some of the authors, an estimation of such characteristic is assessed in case of potential redesign of the plant, providing also useful suggestions into the design of the control logic.
Highlights
An energy transition based on renewable technologies is required in order to meet the challenging targets set out by the Paris Agreement [1]
The reference configuration of the plant consists of: (i) a 146 m2 solar field based on Linear Fresnel Reflectors (LFR) producing heat at temperatures in the range 250 - 280°C; (ii) a 2kWe/18kWt regenerative Organic Rankine Cycle (ORC) unit; (iii) a 3.8 tons of Phase Change Material (PCM) thermal storage tank equipped with reversible heat pipes; and (iv) a balance of plant (BOP) with a total length of 49 m pipes connecting all the different subsystems
Based on the specifications defined by ASHRAE 93-2003 [17] test standard and according to [18], the time constant, τLFR, of the receiver tube is determined using either a step input of solar energy when the collector is focused or a withdrawal of solar energy while it is defocused
Summary
An energy transition based on renewable technologies is required in order to meet the challenging targets set out by the Paris Agreement [1]. Among the different renewable sources, solar energy represents the most promising and clean energy for future power generation. The use of solar energy in decentralized energy systems (micro-Combined Heat and Power, mCHP) is foreseen as a valuable alternative to substitute the thermal and electric power generation from fossil fuels. An example is the system here presented: a small-scale concentrated solar combined heat and power plant, developed within the Innova MicroSolar EU funded project [4]. In a previous work by some of the authors of the present paper [5], the annual performances of this novel micro concentrated solar ORC CHP system have been numerically evaluated, finding that proper control of the system was fundamental to optimize the operation of the different sub-systems with varying ambient conditions and user needs. The obtained results are expected to provide useful insights for the optimal design of the control of similar plants
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