CASE STUDY - STEERABLE SOLAR ARRAY FOR CIRCADIAN SOLAR
The objective of this project was to present a large photovoltaic array at 90 [+/-1] degrees to the sun at all times. This required two key features. Firstly the ability to mount all the individual cells flat [to within one degree] and secondly to move the array to follow the Sun’s position [within a similar tolerance]. For construction efficiency each array needed to be large [with a size of 5 x 6 metres].
- The Customer’s challenge was further extended to include:
- 6 sub assembly units at 2 x 2.5 m
- Mass of each sub-assembly unit no more than 35 kg
- Each unit flat within 3 mm
- Each unit to package more than 16 photovoltaic cells per sub-assembly and 96 per array
- Units to be capable of simple but accurate assembly to a steerable mounting beam on site within 5 mm overall flatness across the array
- Resistant to high wind loads
- Units to have long term corrosion and thermal fatigue durability
- Low cost initial solution
- Volume extendable concept
Creating an excellent solution required simultaneous input from both the Finite Element team and our Manufacturing Feasibility team. Modelling the adhesive performance is important to achieving a realistic model for fatigue and wind loads, and this is an area where we have developed a good interaction with FE teams over several projects to achieve effective outcomes. As with an aircraft wing, the assembly needs to demonstrate elastic flexibility associated with the lightest possible mass.
The main supports for each of the sub assemblies are operating in shear and a folded sheet solution was the obvious approach for these components and at higher volumes a pressed solution is planned.
The photovoltaic cell support rails are based on extrusions which provide the predictable levels of sub assembly straightness required to meet the overall flatness tolerances required by the Customer.
Bonding the anodised sub components with a single part epoxy provides the structural performance and long term mechanical and thermal durability required for the space frames. All critical joints are backed up with mechanical fasteners for added peel resistance and robustness during the final assembly process on site and for maintenance loads.
Sub assembly fixturing appropriate to the initial volumes is based on simple aluminium plates.
A number of full and partial demonstrator arrays have been produced by Circadian based on our low volume route for the sub assemblies and these are in field trials in a number of sunny locations. Feedback on the system performance is now being accumulated to confirm that all predicted measures are capably achieved.
We are pleased to have supported the team at Circadian Solar in this challenging and environmentally relevant project. www.circadiansolar.com