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Title: Performance and operational effectiveness of evacuated flat plate solar collectors compared with conventional thermal, PVT and PV panels
Authors: Moss, Roger
Henshall, Paul
Arya, Farid
Shire, Stan
Hyde, Trevor
Eames, Philip C.
Keywords: Evacuated
Flat plate
Solar collector
Organic Rankine cycle
Issue Date: 2018
Publisher: Elsevier Β© The Author(s)
Citation: MOSS, R. ...et al., 2018. Performance and operational effectiveness of evacuated flat plate solar collectors compared with conventional thermal, PVT and PV panels. Applied Energy, 216, pp.588-601.
Abstract: The concept of an evacuated flat plate (EFP) collector was proposed over 40 years ago but, despite its professed advantages, very few manufacturers have developed commercial versions. This situation suggests both technical difficulties in manufacturing a competitively-priced sealed for life panel and a lack of awareness of the benefits of such panels. This paper demonstrates an evacuated flat plate simulation that closely models experimental efficiency measurements. Having established the validity of the model, it compares published data for a commercial EFP collector with predictions for an optimal design to investigate whether any further efficiency improvement might be possible. The optimised design is then evaluated against alternative solar energy devices by modelling a number of possible applications. These comparisons should inform choices about solar options for delivering heat: EFP collectors are well-suited to some of these applications. An evacuated flat plate solar thermal collector with a 0.5x0.5 m absorber was tested under a solar simulator. The test conditions spanned the range 200<G<1000 W/m2, 0≀𝑇𝑇𝑀𝑀≀52℃. Evacuating the enclosure reduced the measured heat loss coefficient by 3.7 W/m2K: this was a close match to predictions and corresponds to an increase in aperture efficiency from 0.3 to 0.6 at 𝑇𝑇𝑀𝑀𝐺𝐺⁄=0.06 m2K/W. Further model predictions incorporating commercial solar coating properties suggest that evacuated flat plate collectors should have a 50% greater efficiency than conventional flat plates for an absorber mean surface temperature 100Β°C above ambient. As a measure of installed performance, the mean annual heat output was predicted by a transient analysis scheme using efficiency curves, absorber heat capacity and historical weather data for Coventry, UK. An optimised evacuated flat plate collector could supply 104% more heat to an 85℃ district heating main than a conventional flat plate. The availability parameter increased by 120% due to the reduction in critical radiation level. In Winter if the necessary absorber temperature is above 58℃ an optimised EFP collector requires the least panel area to meet a heating demand. Conversely if temperatures below 58℃ can be utilised a smaller panel area is possible using a heat pump powered by a PVT panel. A further option would be to replace each 1m2 of PVT panel with 0.3m2 of PV panel in a country receiving more solar radiation. Evacuated flat plate collectors are a possible alternative to concentrating collectors for Organic Rankine Cycle power generation. The annual output for all the modelled collectors was found to be a quadratic function of delivery temperature: this enabled a novel optimisation of ORC source temperature. Predictions for concentrating and non-concentrating ORC plant are compared with a PV/thermal alternative. The ORC output is significantly less than a PV panel would achieve; applications needing both heat and power are better served by PVT panels. This is an original and novel result.
Description: This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/.
Sponsor: The authors are grateful to the Engineering and Physical Sciences Research Council (EPSRC) for funding this work as part of a collaborative programme between Warwick, Loughborough and Ulster universities, reference EP/K009915/1, EP/K010107/1 and EP/K009230/1.
Version: Published
DOI: 10.1016/j.apenergy.2018.01.001
URI: https://dspace.lboro.ac.uk/2134/28226
Publisher Link: https://doi.org/10.1016/j.apenergy.2018.01.001
ISSN: 0306-2619
Appears in Collections:Published Articles (Mechanical, Electrical and Manufacturing Engineering)

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