A figure of merit for selective absorbers in flat plate solar water heaters

Roberts, D.E.

doi:10.1016/j.solener.2013.10.012

Cited by 20 publications

(6 citation statements)

References 7 publications

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“…Taking residential applications as an example, heat and cooling energy are produced for domestic use in different time periods and/or seasons. Solar water collector [38] 0.728~0.790 -Radiative cooling collector [39] -20~80 SH-RC collector 0.627 50.3…”

Section: Nocturnal Collector Tests On An Overcast Nightmentioning

confidence: 99%

Field test and preliminary analysis of a combined diurnal solar heating and nocturnal radiative cooling system

et al. 2016

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A type of composite surface was manufactured for trial to achieve integrated solar heating and radiative cooling functions. The spectral properties of the composite surface present a relatively clear selectivity in the spectra of solar heating and radiation cooling wavelengths. A combined system for both solar heating and radiative cooling (named SH-RC system) based on the composite surface was mounted together with a traditional flat-plate solar heating system. Comparative experiments were carried out to investigate their thermal performances both at daytime and nighttime. Results showed that the composite surface has a relatively evident spectral selectivity. In diurnal collector testing mode, the thermal efficiency of the SH-RC collector was 62.7% at zero-reduced temperature, which was about 86.4% of that of the traditional flat-plate solar heating collector. In nocturnal collector testing mode, the SH-RC collector had net radiative cooling powers of 50.3 W/m 2 on a clear night and 23.4 W/m 2 on an overcast night; by contrast, the traditional flat-plate solar heating collector exhibited very little radiative cooling capacity. In diurnal system testing mode, the daily average thermal efficiency of

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Section: Nocturnal Collector Tests On An Overcast Nightmentioning

confidence: 99%

Field test and preliminary analysis of a combined diurnal solar heating and nocturnal radiative cooling system

et al. 2016

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“…Finally, the simplified calculation of the optical efficiency was performed using two parameters: selectivity (f ) and figure of merit (FM, e.g., in [39,40]) according to Equation ( 4). The first parameter can practically and effectively characterize performance as the selectivity parameter [41] with higher f indicating more selective material.…”

Section: Spectral Optical Measurementsmentioning

confidence: 99%

“…Table 2 sums the results of the spectral reflectance analysis: thermal emissivity and solar absorbance of the tested absorbers. In addition, the table also shows the selectivity of the absorbers (the ratio between both parameters) and figure of merit (FM; calculated based on [39,40]). This shows that all evaluated absorbers have almost the same solar absorbance (from 0.90 to 0.95), whereas their emissivity notably varies.…”

Section: Evaluation Of Spectral Optical Parametersmentioning

confidence: 99%

Preparation and Characterization of a Selective Polymer-Based Solar Absorber for Building Integration

2020

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Recent technological advances in solar absorber production may have created opportunities for new applications of these materials in buildings. A low-emissivity enhanced polymer-based absorber foil was developed and prototyped to demonstrate feasibility of the concept. This paper describes key development factors leading to a particular composition of the prototype and its testing, specifically spectroscopy measurements (both for shortwave and longwave regions) and environmental impact assessment of its production. It also provides comparison of the tested parameters with commercially available absorbers. The results show that the developed absorber has relatively good thermal emissivity (approx. 0.3), high solar absorption (0.95) and selectivity (3.2), and significantly lower (up to 98%) environmental impacts compared to the commercially available metal-based solar selective absorbers.

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“…This was done through the measurement of global irradiance and water temperature. Furthermore, Roberts [27] showed that irradiance, inlet water temperature and ambient temperature are vital parameters for determining the merit for absorbers used in solar water heating systems.…”

Section: Introductionmentioning

confidence: 99%

Decoupling the Monitoring of Solar Water Heaters and their Usage Profiles

Nwodo

Overen

Meyer

2021

Water

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South Africa is the most technologically advanced nation in Africa. However, the country is plagued with constant load shedding. The country receives about 2500 sunshine hours annually, with daily average irradiation levels of 4.5–6.5 kWh/m2. Despite these potentials, the use of electricity for domestic water heating is still prevalent in the country. The mass rollout of solar water heating (SWH) technologies in the low-cost housing sector across the country were met with massive failures. This study aims to assess the energy yield of a passive flat plate and an evacuated tube solar water heating system by evaluating the performance of these systems to address the energy crisis in South Africa. The flat plate (FP) and evacuated tube (ET) solar water heating systems were monitored for four days, characterised by varying sky conditions through instantaneous data measurement at 5 s. The parameters measured were water temperature, ambient temperature, irradiance at the plane of array, relative humidity, wind speed and direction. The results obtained show that a maximum irradiance of 1050 W/m2 was obtained on a clear day and corresponded to a hot water temperature of about 58 °C and 65 °C for the FP and ET, respectively. However, a cloudy day with a maximum irradiance of 400 W/m2 produced about 22 °C and 29 °C of hot water for the FP and ET, respectively. The results obtained in this study will guide stakeholders in the renewable energy sector towards employing SWH systems to replace or augment the electric geyser. Solar water heaters (SWH) can be used in the low-cost housing sector to provide hot water. Hence, the assessments in this study offer essential information for the deployment of these systems to reduce demand on the ailing South African electricity utility, Eskom, and mitigate climate change.

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A figure of merit for selective absorbers in flat plate solar water heaters

Cited by 20 publications

References 7 publications

Field test and preliminary analysis of a combined diurnal solar heating and nocturnal radiative cooling system

Field test and preliminary analysis of a combined diurnal solar heating and nocturnal radiative cooling system

Preparation and Characterization of a Selective Polymer-Based Solar Absorber for Building Integration

Decoupling the Monitoring of Solar Water Heaters and their Usage Profiles

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