BMW Manufacturing Plant Process Heat
HBC Group: Co-Generation Solar system with 200 m2 flat plate collector
TOTAL M2 Collctors 200
Tank Storage 24,200
Year Commisioned 2012
Tank Construction Mild Steel
High / Low- Pressure Storage Low Pressure
Litre / m2 110
Energy Savings / Annum kWh 352555
SHORT DESCRIPTION OF THE SYSTEM
BMW South Africa embarked on introducing energy saving technologies at its Rosslyn plant, north of Pretoria. The reason was to reduce the vehicle manufacturing plant’s reliance on the conventional carbon-based, non-renewable energy source. Various interventions have been implemented by BMW engineers and designers to reduce the consumption of their products – the vehicles – and the same ideals are being extended to a number of their fabrication plants around the world.
The Rosslyn plant identified their paint application facility as a major consumer of energy, especially gas used in heat processes for the paint application of the three series vehicles manufactured at the plant. Owing to BMW’s factory location and design, the option of using the high solar radiation levels common to that part of the country, made the option for solar, feasible. At a capital cost of about R1,5 million for this test phase, HBC Group based in Johannesburg, was asked to help design and implement a large-scale solar thermal collector field covering 200m2 on the roof of the paint plant at Rosslyn.
The heated water used in the paint application process needs to be about 90°C when it is applied to get the paint to the correct viscosity. This involves conventional Gas heated water to be circulated through various plate heat exchangers which then heats up the paint.
“Plate heat exchangers allow separate fluids to flow either side of a separator plate, thereby transferring the heat from the water to the paint to allow for better application of the product,” explained Marc Desfontaines, MD at HBC Group.
CHARACTERISTIC’S OF THE SYSTEM
HBC Group was awarded the project to supply and install the system in February 2012 and provided an energy-efficient solution to the process by installing 1 320 solar collector tubes on a 200m2 area. “Most of the design and specification was done by BMW’s engineers in Germany,” said Desfontaines. The system was fitted to the existing boiler system, which was possible because HBC Group installed closed loop systems that transfers energy through plate heat exchangers, using intelligent pump control technology from Resol and valve balancing technology from Danfoss, which meant the system could tie into the return line coming back from the factory to the centralised boiler system, and add energy to the cooler water before it reaches the gas boilers. This allows for the returning water to get preheated during the day by the sun, thereby reducing BMW’s need for gas.
Some of the challenges faced were the structural integrity of the roof and the overall structural load weight, which had not originally been designed to hold the extra weight of the 200m2 bank of collectors. Many of these difficulties were overcome by the introduction of cutting-edge solar thermal collectors.
Using the latest technology in pumped collector systems that combine both vacuum tube technology and reflective backing materials, ensured that the collectors could be laid flat on the surface of the factory roof. Structural engineers tasked with approving the extra load on the roof, sanctioned this additional weight because the flat application meant the sail load of the panels was negligible.
The technology uses evacuated tube collectors, but using the less popular Sydney Tube Method, which is done by fusing together two glass tubes with a high level of vacuum between them. The outer tube is clear and the inner tube has a spiral red copper coating which turns the sunlight that passed through the outer clear tube into heat energy. The heat energy that is generated can’t escape through the vacuum that exists between the inner and outer tube.
The copper inner pipe is installed in each tube in a u – format. This means that the liquid in the boiler can be used directly in the solar collector, and because the system is evacuated there is no chance of freezing during winter months. The Sydney tube will become continually hotter whilst being exposed to sunlight and the liquid inside the copper u-tube heat pipe will continue to increase, temperatures of up to 200°C have been recorded. Due to the industrial nature of this installation, high temperatures of over 100degC can be tolerated but this would not be permissible in domestic applications and is unique to the customer’s requirements.
This simple freeze-resistant technology, coupled with efficient reflector backing enables hot water generation even in low light conditions. Another great advantage with this technology is every tube becomes an individual heating element, which can be plugged in or taken out without affecting the other tubes, or the general operation of the overall system.
REMOTE ACCESABLE DATA LOGGING
BMW requested comprehensive data logging and recording equipment for the whole system. This information was to be made available to their engineers at any time. Resol Thermal Controllers was selected as the technology of choice. Resol controllers would control all pump activation and speed control as well as record and transmit data to BMW’s cloud-based server, which in turn would enable Greencon and BMW technicians to have constant visibility of the system from anywhere in the world.
The results to date have far exceeded expectations and the transition from test facility to full scale plant is now under discussion. Provisions have been made for easy expansion of the current facility, and seamless integration into the existing boiler line. BMW South Africa, in partnership with Greencon Solar Technologies, continues to work towards ensuring their fabrication facilities follow the same modern vehicle ethos of more efficient use of energy.