Sunny times for University of Ulster
16 February 2009
The University of Ulster in Northern Ireland has advanced the study of photovoltaic systems with a solar simulator facility. The University’s Centre of Sustainable Technologies (CST) is using a half-tonne lamp array to evaluate the performance of photovoltaic panels, solar water heaters, evacuated glazing and similar products.
University of Ulster boasts new solar simulator facility
Standard components from the Rexroth mechanical elements and linear motion range are used to control the lamp array which is hoped to assist with the design of new products. The use of natural sunlight for testing is simply too unreliable, especially in the British Isles where sunshine is all too often in short supply.
In response to the need for dependable and controllable testing, the solar simulator was designed and developed by Dr Mervyn Smyth, Dr Jayanta Mondol and Dr Aggelos Zacharapoulos. In the core of the simulator is an array of high power metal-halide bulbs arranged to produce light of similar intensity and spectrum to the sun.
Because of the high light output it must provide, the lamp array is large and heavy – it measures 3.5 by 2.1 metres, and weighs nearly 500kg without cables. The cables needed to supply power to the bulbs add a further 100kg.
The University of Ulster team commissioned a German supplier to manufacture the simulator itself, but this supplier was unable to offer a mounting frame that would meet its requirements.
The support needed to be stable and mobile so that the simulator could easily be positioned wherever it was needed in the laboratory. Furthermore the simulator needed to tilt so that it can mimic the effects of sunlight reaching the test object at different angles. The simulator also has to be raised to a height of at least six metres, to allow the testing of systems mounted at higher elevations, such as evacuated glazing elements.
In its search for a supplier of a suitable frame, the University invited three companies to submit tenders. One proposal was for a welded frame fabricated from stainless steel, and another suggested the use of a heavily modified hydraulic hoist of the type used in garages to raise cars for servicing.
The proposal that most appealed to the University of Ulster team was, however, submitted by Automation Manufacturing Systems (AMS), a Bosch Rexroth sales partner and a specialist in the development of novel solutions for manufacturing and related applications.
AMS built a robust frame from standard aluminium extrusions, coupling products and accessories in the Rexroth mechanical elements range.
The frame is mounted on castors to allow it to be moved around easily, and the necessary vertical motion for the solar simulator itself is provided by two MKK ball-screw linear motion modules, one on each side of the frame. A small motor is fitted to drive the linear motion modules. Provision is made to tilt the simulator by means of a simple hand-wheel assembly.
Dr Zacharapoulos said the chosen proposal was chosen because of the ‘modularity and flexibility’ the system offered.
“It’s very easy to make modifications, and there is no mess or inconvenience involved. That certainly wouldn’t have been true for a fabricated steel frame, where any but the most trivial modification would have involved welding.”
Ulster University said it also liked the aesthetics of the AMS solution.
‘The solar simulator is the showpiece of our laboratory, so it was important that it should have attractive professional appearance,’ Dr Zacharapoulos said. ‘That’s even truer in the light of our ambition to attract testing and development work from high-profile companies.’
‘With the simulator we can, for example, perform a full experimental characterisation of solar thermal and solar PV products on behalf of manufacturers. Well presented test facilities are an obvious asset when seeking work of this type.’
AMS, the designers and builders of the frame, report that it presented some interesting challenges. In particular, the weight of the simulator and the height to which it had to be possible to raise it meant that a particularly strong and rigid framework was needed. With the light but strong extrusions from Rexroth, however, this requirement was easily met.
During manufacture, the flexibility of the extrusion system proved its worth. After the frame had been built to the original design, it became apparent that an extra safety rail needed to be added at the rear. The work involved in providing this, which would have taken hours with a fabricated frame, was completed in just 20 minutes.
Daivid Murray of AMS described the Rexroth extrusion as ‘very easy to work with’.
Dr Zacharapoulos and his team have placed an order with the company for a second similar frame. Built from Rexroth products also, this frame will support a 2 by 3 metres, 190kg, glass pane used to filter UV and infrared radiation out of the light produced by the solar simulator.
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