Simulator testing of evacuated flat plate solar collectors for industrial heat and building integration

The concept of an evacuated flat plate collector was proposed over 40 years ago but, despite its professed advantages, very few manufacturers have developed commercial versions. This paper demonstrates the reduction in heat loss coefficient and increase in efficiency resulting from evacuating a flat plate collector: it is hoped that these results will stimulate interest in the concept. Evacuated tubes are now mass-produced in large numbers; evacuated flat plate collectors could in principle replace these tubes if the technical difficulties in creating extended metal-glass seals can be overcome. The experimental experiences described here should indicate targets for future research. Two different designs of evacuated flat plate solar thermal collector, each with a 0.5x0.5m flooded panel black chrome plated absorber, were tested under a solar simulator. The cover glasses were supported by an array of 6 mm diameter pillars. Inlet and outlet temperatures were monitored via PT100 RTDs and glass temperatures were measured using thermocouples. Inlet temperature was controlled by a fluid circulator connected to a header tank with a Coriolis mass flow meter to measure fluid flow rate. Testing was conducted indoors with and without the use of a fan to cool the top cover glass. The test conditions spanned the range 200<G<1000 W/m², 0 less than or equal to TM/G less than or equal to 52°C. 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 TM/G = 0.06 m2K/W. The poor efficiency under non-evacuated conditions was due to the black chrome absorber coating being less selective than commercial panel coatings. The solder seals were developed from experience with vacuum glazing but the increased gap led to reliability issues. A vacuum pump maintained the enclosures under a high vacuum (<0.1 Pa) during testing. The enclosure based on a thin rear metal tray proved to be more effectively sealed than the more rigid enclosure with glass on both sides: the latter developed leaks as the front to rear temperature difference increased. The biggest challenge in the manufacture of evacuated flat plate collectors is to ensure a long-term hermetic seal such that no pumping is required

Design and commissioning of a virtual image solar simulator for testing thermal collectors

A solar simulator has been designed and built for testing prototype (0.5×0.5 m) flat plate thermal collectors. An internally reflecting light tube generates multiple virtual images of the four halogen floodlights to ensure uniform illumination. Ray-tracing simulations were used to choose the tube dimensions and maximum allowable clearance. Illumination measurements agree well with these predictions. The visible & near IR spectrum appears to follow a black body curve. In the absence of a “cold sky” IR filter there is a secondary, long wavelength IR spectral component that causes heating of the cover glass on a solar flat plate collector. The cover glass temperature can be maintained at typical outdoor levels using a cooling fan. The design would be well suited to LED illumination. Simulation of solar collector response to this spectrum shows that an efficiency based on pyranometer readings is approximately 1% higher than would be obtained with an AM1.5 spectrum

On generation-integrated energy storage

Generation-integrated energy storage (GIES) systems store energy at some point along the transformation between the primary energy form and electricity. Instances exist already in natural hydro power, biomass generation, wave power, and concentrated solar power. GIES systems have been proposed for wind, nuclear power and they arise naturally in photocatalysis systems that are in development. GIES systems can compare very favourably in both performance and total cost against equivalent non-integrated systems comprising both generation and storage. Despite this, they have not hitherto been recognised as a discrete class of systems. Consequently policy decisions affecting development or demonstration projects and policy approaches concerning low-carbon generation are not fully informed. This paper highlights that policy structures exist militating against the development and introduction of GIES systems-probably to the detriment of overall system good

Performance and operational effectiveness of evacuated flat plate solar collectors compared with conventional thermal, PVT and PV panels

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 bene fits 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. 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

Design and development of lead-free glass-metallic vacuum materials for the construction and thermal performance of smart fusion edge-sealed vacuum glazing

Advancement in hermetic (vacuum-tight) edge-sealing materials has been one of the challenges since decades because of the existing cost, use of hazardous substance and complexity-to-construct issues in vacuum glazing. This paper presents novel experimental findings with designs and methods developed to construct and analyse thermal performance of the fusion edge-sealed vacuum glazing. The novel concept of fusion edge-seal consists of forming a thin glass-metallic rigid textured layer, in which the formation processes and experimental glass-metallic textured surface bonding property tests of 15 samples are microstructurally analysed using FIB-SEM and optical microscopy and succeeded the correct mixture of B2O338-Sn62 wt%. Experimental analyses of at least 60 samples conducted using different techniques and Pb-free materials, among which five vacuum glazing samples of various designs and techniques discussed in this paper. The fusion edge-sealed vacuum glazing, constructed with bonded Sn62-B2O338 wt% surface textured fused with Sn90-In10 wt% alloy at 450 °C, achieved at the hot-plate surface heat induction of 50 ± 5 °C and the cavity vacuum pressure of 8.2 · 10−4 Pa. Validated 3D FEM employed and the centre-of-sheet and total thermal transmittance values of fusion edge-sealed vacuum glazing (sample ‘A5’), area of 300 · 8300 mm with 10 mm wide fusion edge-seal, predicted to be 1.039 and 1.4038 Wm−2K−1, respectively

Integrated collector storage solar water heaters

The Integrated Collector Storage Solar Water Heater (ICSSWH) developed from early systems comprised simply of a simple black tank placed in the sun. The ICSSWH, by its combined collection and storage function suffers substantial heat losses to ambient, especially at night-time and non-collection periods. To be viable economically, the system has evolved to incorporate new and novel methods of maximising solar radiation collection whilst minimising thermal loss. Advances in ICS vessel design have included glazing system, methods of insulation, reflector configurations, use of evacuation, internal and external baffles and phase change materials.Optical efficiency ICSSWH Thermal performance Technological development

A unified numerical model for optics and heat transfer within line-axis concentrating solar energy collectors Development, validation and parametric analysis

2 volsAvailable from British Library Document Supply Centre- DSC:DX93781 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo