Wireless Monitoring Solutions in Large-Scale Projects
As the solar industry matures, there is a fundamental shift in how large-scale solar projects are funded, constructed and operated. While government programs in the form of tax credits, initiatives, legislations, subsidies and general funding encouraged renewable energy and environmental action, the financing model is now squarely set on mandatory ROI and guaranteed payback over the operational lifespan of the solar plants. As a result, sound operational models have to be put in place at the outset of the business case, along with the capital investments of labor and equipment.
As the industry evolves, it has become standard practice to enter into multi-year operation and maintenance (O&M) contracts following the commissioning of the solar plant. Often bundled with the construction contract, engineering, procurement and construction firms (EPCs) are increasingly required to guarantee the performance to the specifications for years after construction. Consequently, it becomes important for EPCs to include optimization of the operation and power production as key design criteria of the solar farm, while figuring out how to be competent in the O&M business.
Fortunately, wireless technology exists to help address these new requirements. Easily installed and scalable — invaluable in brownfield projects — a mesh network of thousands of nodes is highly secure and reliable, providing robust insight into the operation of solar panels, tracking systems and “smart” combiner boxes, which are fast becoming a requirement for utility-scale PV deployments. Wireless is becoming a critical component of highly-efficient solar farms of the future, measuring a wide variety of factors from fractional changes in the current in each string of a solar panel to environmental factors such as wind speed and sun intensity. With wireless technology in place, expected output generated from predictive model can be compared against actual output — allowing investors to measure ROI performance and operators to identify potential issues before they cause real problems. With real-time access, operators can take immediate action remotely and respond quickly to maintain power generation and protect investments.
With critical access to real-time information and the ability to predict and diagnose problems, utilities and other end-users are increasingly requiring solar farm data and connection controls in order to better manage their own power generating assets. In Europe, monitoring is increasingly becoming an integral component of the solar installations. At present, 80 to 90% of large-scale solar projects require monitoring all the way down to the combiner box string level.
Yet, wireless technology is not being fully tapped in solar installations due to skepticism and misconceptions about costs. Contrary to the belief of many, one of the greatest benefits to come out of wireless solutions is the considerable cost-savings for installation and commissioning. Monitoring solutions at the transformers, inverters, all the way down to individual strings in solar combiner boxes are proven technologies deployed in mission critical applications including mining, oil and gas, smart grid and water/wastewater management.
Smart combiner boxes equipped with wireless radios and solar DC/DC power supplies eliminate the need to lay AC mains and data cables or low-voltage DC communications cabling from combiner boxes. As a result, savings of up to 94% have been recorded during installations — the larger the project, the bigger the benefit. For example, in a utility-scale project, you may have 2,000 to 3,000 combiner boxes, which equates to nearly 2,000 to 3,000 cables. That large quantity of cable can create even bigger and more expensive maintenance issues.
A second fallacy among those in favor of a wired solution is that data and power cables may be installed simultaneously and in parallel to one another. There is this misconception that it is no trouble to add another cable since you are already running one anyway. While this may be somewhat true, the cost of the extra cable for long runs is significant for low-voltage communications. Further, these cables need to be separated to avoid data corruption due to interference, which adds costs.
Fewer cables also help reduce overall maintenance. For example, corrosion is often the main cause of data interruptions and is completely eliminated with a wireless solution. Also, with wireless technology, there is no need to open combiner boxes during commissioning to clamp on each string to measure the output current; all the information is readily available at the monitoring stations. The commissioning time could be cut by half or more.
Getting smart: solar monitoring
Advanced wireless solutions include an industrial-grade mesh network, smart wireless combiner box and a comprehensive supervisory control and data acquisition system (SCADA) designed to meet utility-scale PV system requirements. Specific components need to be selected to ensure easy integration so operators are not locked in to a single-manufacture solution and the system can continue to be enhanced and upgraded with best-in-class solutions.
Solutions like Eaton’s solar monitoring products and services are based on a comprehensive SCADA platform and are an example of a robust solar control and monitoring solution that can help optimize safety and efficiency by providing real-time access to system-wide parameters. With a SCADA system, operators can monitor PV system productivity and verify generation against predictions. The system can also enable operators to recognize gradual degradation in solar panel performance and take measure of overall system productivity. The SCADA system interfaces with a weather station to provide ambient temperature, wind speed, humidity and solar irradiance. It monitors individual string currents, total string currents, busbar voltage, temperature as well as a host of other parameters.
Analysis of critical parameters allows operators to rapidly determine the cause of a system fault and helps provide the information required to get the system back online. The list to the left gives examples on the parameters being monitored, respective probable causes in the event of an alarm from the SCADA system and the most likely actions (some of which could be taken remotely with the control functions built into the SCADA).
SCADA provides powerful, user-friendly reporting and alarm features, as well as historical information that can store decades of crucial information. Alarms triggers and the display of the alarms are custom-defined by the operators to fit their operation needs. Additionally, the system provides extensive historical information for various different user groups.
Industrial wireless networking
Wireless mesh networking technology utilizes 900 MHz radio to carry data from combiner boxes and inverters reliably and securely to a central SCADA monitoring system workstation.
Innovative wireless technology provides a robust alternative to signal and data wiring. Today’s best-in-class technology includes mesh networking with intelligent auto-determined best signaling paths overcoming the highly challenging solar-field environments loaded with concentrated objects and metal work reflecting RF signals. It is also highly scalable, so that simply adding communications nodes can easily extend networks.
Smart monitoring and control in utility-scale PV applications provides powerful business and system advantages — supporting enhanced safety and efficiency, reduced costs and improved reliability. By monitoring critical components, these systems can help enhance safety and take action remotely.
Simplifying and enabling monitoring and fault isolation reduces the risk of total system shutdown due to ground faults; further, granular wireless string-level monitoring identifies under-producing panels so appropriate action can be taken to maximize generation. Wireless solutions also help reduce the costs of connecting sensors by 90% or more. And critically, wireless technology are scalable — as the installation grows and evolves, the system continues to provide crucial data to make intelligent power management decisions that improve system reliability and profitability.
Patrick Ho is director of system solutions at Eaton.
— Solar Builder magazine