Solar thermal engineering lab

Description

The solar thermal engineering lab aims to experimentally characterize solar thermal collectors. Throughout the years, several experimental tests were carried out on parabolic trough collectors (PTC), taking the standard ANSI/ASHRAE 93-2010 as reference.

Figure 1. PTC UNIVPM.01 prototype

 

Figure 2. PTC UNIVPM.02 prototype

To date, the research is focused on the assessment of the performance of solar cookers, thermodynamic systems able to convert solar energy into thermal energy that can be exploited to heat up and cook food.

Solar cookers can be classified according to the type of solar concentration:

  • solar box cookers, with or without booster mirrors;

  • concentrating (open) solar cookers, e.g. parabolic cookers or with a different geometry.

Figure 3. Solar box cooker with booster mirrors

 

Figure 4.  Concentrating (open) solar cookers,“Heliac”

Research activity

Solar cookers are characterized by carrying out outdoor tests on the DIISM roof. Two tests are necessary to characterize a solar cooker:

  • no-load tests;

  • load tests.

No-load tests allow to determine the maximum temperature achievable by a solar cooker. Load tests, instead, are generally conducted with water (or other testing fluids, such as natural or diathermic oils) and allow to estimate the cooker specific/characteristic boiling times, power, optical and thermal efficiency.

Figure 5.  Experimental results obtained with water

Experimental tests with thermal storages based on phase change materials (PCMs) are carried out, too. PCMs are substances with a high latent heat of solidification/fusion, which can be used in solar cookers to improve their thermal stabilization during absence/intermittence of solar radiation.

Facility

To date, five solar cookers are under testing in the lab:

  • a solar box cooker with high concentration ratio;

  • a solar box cooker with medium concentration ratio;

  • an “open” concentrating solar cooker;

  • two low-cost solar box cookers with booster mirrors.

Figura 7. Solar box cooker with high concentration ratio

Al fine di simulare carichi termici variabili, il laboratorio dispone di speciali pentole in grado non solo di alloggiare diversi fluidi di prova (acqua, oli naturali, oli diatermici, ecc.) ma anche sistemi di accumulo termico a base di materiali a cambiamento di fase (PCM, phase change material). Ad oggi, sono stati effettuati test col sale solare HITEC (miscela di nitrato di sodio e nitrato di potassio) e con diversi zuccheri (eritritolo, xilitolo). Il laboratorio dispone anche di un sistema di acquisizione per la misura di temperatura tramite termocoppie e di pireliometri NIP per la misura della radiazione solare diretta.

Figure 7. Flow chart of the acquisition system

Figure 8. NIP pyrheliometers used to measure direct solar radiation

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