Supercapacitors paired with microcontrollers forge an intelligent power-management solution for distributed networks.
As we modernize our power grids, we become increasingly reliant on Smart Energy, which integrates renewable energy generators to improve reliability and resource efficiency on distributed power networks. At the same time, we need to move toward a better energy-storage technology that’s cleaner and lasts longer than lead-acid batteries. The emerging class of hybrid supercapacitors are superior to lead-acid batteries in both respects. To function on a smart grid integrating locally stored power seamlessly for the user, supercapacitors require embedded controls to balance power production on a distribution network based on supply and demand.
Figure 1: Smart Energy storage unit containing multiple Hybrid-Supercapacitors requiring individual monitoring and control
ZigBee mesh networks for Smart Energy are an important and well-established market for embedded control. But with the explosive growth of distributed power networks and power-backup systems for mission- critical applications, Smart Energy storage is playing a pivotal role in expanding the makeup of today’s complex power grid. This key role presents a great opportunity to developers of embedded electronic sensors and controls.
Good-bye to “Battery Shortfalls Included”?
Local customer storage of both on-grid and renewable energy has evolved from electrochemical energy storage to alternative technologies for safety, environmental, cost and regulatory reasons. Off-grid and localized microgrids, which operate either in parallel or autonomously to mitigate disturbance on the grid, share similar storage and load-leveling Smart Energy needs. Though time-tested lead-acid batteries are robust and simple from the standpoint of electronic control, they’re unreliable due to a short lifespan of two to three years. And their toxicity makes them environmentally unfriendly.
Similarly, new paradigms have emerged as alternatives to traditional battery-based transportation methods such as Wayside Energy Storage systems, which are substations that buffer power for electric rail applications. Supercapacitors and on-train regenerative power-storage systems are challenging the cost of ownership of lead-acid batteries and the efficiency/cost of extended grid storage. Instead of transporting recovered energy through a low efficiency third rail to remote locations, light power-dense technologies such as hybrid-supercapacitors may be incorporated within the power-train to significantly reduce the transient delivery burden on the power grid.
For a grid increasingly powered by renewables, where timing of peak energy demand can further diverge from peak production, the need for local grid energy storage becomes an imperative. Opportunity has sprung up for safe and reliable power dense-storage solutions, along with better controls, sensors and feedback loops throughout the Smart Energy grids.
Today, alternatives such as mechanical flywheel and capacitive solutions address the shortfalls of lead-acid batteries and can anticipate greater inroads into these and other energy-storage markets. Capacitive solutions are especially interesting for peak power and energy storage applications in that they have the higher power and energy-delivery capabilities for a given volume, when compared to lead-acid batteries. They also have lifecycles that are two to three times longer and are eco-friendly and safe alternatives.
Achieving TCO Advantages
As often happens, the downside to integrating new technology is that more complex system controls and management are required to achieve a total cost of ownership advantage over existing solutions. Hybrid-supercapacitor solutions are no exception. Where older battery technologies are tolerant of over-charge, new system controllers accommodate strict-use constraints while providing reliability monitors for state-of-health and operational-condition communication for hybrid supercapacitors.
A simplified example of embedded control for stacked-cell energy systems is shown in Figure 1. To accommodate elevated voltages and energy requirements, either battery cells or supercapacitors are series-parallel connected to meet specifications. Inherently, cells in a series stack, in some applications supporting voltages up to 800Vdc, are mismatched with regards to their storage characteristics and require constant monitoring and control to ensure maximum storage capability, long life and safety. Specifically, the control processor function of Figure 1 must monitor for imbalance and redistribute energy within the stack when appropriate. The telemetric requirements for this system will include total capacity and capacity utilization, servicing requirements and fault conditions.
Indeed, if you think that Smart Meters are the only embedded process controls useful in grid power systems, think again! With the advent of Smart Energy, applications for process control abound in local power storage as we experience explosive growth in new energy models that bring with them rich opportunities for embedded control. You can liken this challenge to the evolution of power-storage solutions for mobile computing devices in the 1990s, where the need for new, safe and reliable power storage hastened in the era of fuel-gauges and smart-chargers, creating unparalleled opportunity for embedded controls that continues to this day.
Gene Armstrong is the Sr Director of Applications for Paper BatteryCompany. He has consumer industry knowledge in battery integration and management from world leading semiconductor companies such as Maxim, TI, Benchmarq and Sharp.