Tracking systems
The most effective solar photovoltaic systems turn and face the sun throughout the day using single- or dual-axis solar tracking systems. All solar power plants employ such smart tracking systems, whether they are photovoltaic, concentrated photovoltaic or concentrated solar systems. These systems rely on sensitive electronic components: integrated electronics to regularly determine whether the angle of incidence of the sunlight is correct, plus a DC or brushless DC (BLDC) motor and a gearbox.
Naturally, the service life of these tracking systems needs to be as long – typically 20 to 25 years – as it is for the power systems they manoeuvre. But this is no easy task, considering where solar power plants tend to be installed: in locations that experience extreme weather conditions such as long hours of direct sunlight, wide temperature ranges, high winds, dust, hail and driving rain.
There are various ways to protect the system’s electronics and motors against such environmental factors, yet many of them do not address the key problem of temperature fluctuations: pressure differentials. Exposure to direct sunlight in the daytime and cold air at night causes significant temperature changes outside the housing. In addition, a sudden rainstorm on a hot sunny day can cause the outside temperature to drop rapidly. These changes can cause significant pressure differentials inside the housing, thus producing a vacuum that puts stress on the housing seals. Over time, this fatigue can lead to failures – creating leak paths for liquid and particulate contaminants.
Partial solutions to the problem
Because the measures currently taken to protect the electronics in solar tracking systems suffer from certain drawbacks, they are at best partial solutions. For instance, desiccants may be placed inside the housing, but while they will successfully bind the relative humidity within the enclosure, they do nothing to equalise the pressure differentials. Also, because they need regular replacement, these desiccants incur maintenance costs.
Another approach is to pot the electronics. While potting encapsulates them and protects them from contaminants, it also subjects them to the stresses that arise from the different thermal expansion coefficients of the potting, housing and PCB materials used. What’s more, it requires labour-intensive chemical processes and prevents later maintenance or recycling.
Vacuum formation can be avoided by not hermetically sealing the enclosure, but instead providing an opening to allow air to flow easily in and out of the housing – in other words, to let it breathe – via a tortuous path. The problem with this is that the tortuous path cannot stop water and contaminants from entering, so the housing will not achieve the higher ingress protection (IP*) ratings that solar tracking systems require.
Venting is the answer
One approach provides a comprehensive solution and avoids the drawbacks of other protective measures: venting. Vents rapidly and continuously equalise pressure differentials while effectively reducing condensation. At the same time, vents effectively block the ingress of dust, dirt and water to sustain enclosure integrity and maintain high IP ratings over the lifetime of the housing.
Dunkermotoren, a global manufacturing company with operations in Germany, the United States and China, provides solar tracking motion solutions that are installed worldwide. The company engineered a sealed housing with O-rings and connector seals to protect its motor components from liquid and contaminant ingress; however, once installed in the field, the motors were experiencing corrosion issues. These issues increased customer returns and warranty claims. When developing its new STM™ system, Dunkermotoren focused on improving the motor’s durability to meet the intended service life and increase customer satisfaction.
GORE® Protective Vents
For the new design, Dunkermotoren’s engineering team decided to test various venting options to eliminate potential seal failure due to pressure differentials. Based on feedback from their customers, the engineering team decided to evaluate GORE® Protective Vents. Gore’s application engineers collaborated with the Dunkermotoren team to evaluate several GORE® Protective Vents in both environmental chamber tests and field tests.
Based on the results of these tests and the need to integrate the vent into an existing product design, Gore recommended a GORE® Metal Vent. This vent equalises pressure within the motor by maintaining sufficient airflow to allow air and moisture vapour to pass in and out of the enclosure freely. At the same time, the vent serves as a barrier to provide a high IP rating against liquid, dirt, dust, salt and other contaminants. The rugged screw-in construction of GORE® Metal Vents extends the system’s service life and it is easy to integrate into new or existing product designs.
According to Will Vinson, President of Dunkermotoren USA, Inc., their goal was to develop a more durable product to exceed service-life expectations. “With our new STM™ product, we wanted to deliver a tracking system that would last for the expected life of the solar energy system – more than 20 years. GORE® Protective Vents extended the life of our motors by achieving the durability of IP67 protection against exposure to harsh environments. Gore’s engineers understood our requirements and worked like part of our team to ensure that our products deliver the performance our customers expect.”
(*IP ratings depend on the design of the product housing. Please contact a Gore representative for more information.)
ABOUT THE AUTHOR
Sara Ellis and Thomas Guldin are Applications Engineer at W. L. Gore & Associates.
FURTHER INFORMATION
W.L. Gore & Associates, http://www.gore.com/en_gb/