On-Site Power

Are Ultracapacitors the Next Big Trend in Backup Generator Starting?

Issue 10 and Volume 121.

By Jeff Brakley, Maxwell Technologies Inc.

Among generator starting professionals, it is widely accepted that the most prevalent reason for generator set (genset) failure-to-start is issues with the lead-acid battery starting system. Service providers have said that approximately 80 percent of genset failures-to-start can be attributed to battery system failure resulting from poorly maintained batteries, charger failure, or cable and terminal corrosion. After several decades of these challenges, the genset industry is embarking on a new trend toward ultracapacitor-based starting systems, which offer advantages over traditionally used lead-acid battery-based starting systems.

Ultracapacitors are fast-responding, power-packed energy storage devices that have been adopted in a variety of applications and industries, including commercial truck engine starting. Ultracapacitors are successful in starting large truck engines in the face of problems unique to the trucking industry, like dead or discharged batteries. Depending on operation, an ultracapacitor stores energy in a static electric field, rather than in a chemical reaction like batteries do, which can slow dramatically in very cold weather. Because they don’t depend on a chemical reaction to produce electricity, ultracapacitors can operate in much lower and higher temperatures than batteries.

When a power outage happens, commercial transaction-based businesses can be susceptible to exorbitant expenses related to data loss and customer service downtime. Power failure in hospitals or hotels presents a high risk of injury or loss of life to people in the facility. Ultracapacitors installed in emergency or standby backup generator sets can provide a more reliable way to meet strict starting requirements, avoid losses associated with power failures, and improve building safety. When used to start backup generators, ultracapacitors can either completely replace lead-acid batteries or operate alongside them, providing primary or backup assistance to the battery system. Seamless transition from ultracapacitors to batteries in a hybrid installation can take place during cranking, yielding the fastest possible starts.

Applying ultracapacitors to gensets also reduces battery maintenance costs. Ultracapacitor-based genset starting systems require minimal maintenance due to their high cycle life and ruggedness in wider temperature ranges. Depending on operation and use, ultracapacitors can achieve 10 or more years without replacement versus much more frequent battery changes. Batteries for genset starting generally have to be replaced every two to three years. Generally speaking, batteries must be inspected and tested on a weekly or monthly basis. This involves checking all cables and connections for corrosion caused by sulfuric acid fumes, checking water levels in each battery, and load testing each battery individually to ensure that its cold cranking amperage (CCA) rating is still within specification. In addition to costs of replacing batteries that fail testing, the cost of technician hours spent on maintenance is thrown in the mix. With ultracapacitors, there is no sulfuric acid to cause corrosion, no water levels to check and no load test requirements. As a result, maintenance costs are significantly less than those of batteries.

Because of their low internal resistance, ultracapacitors are capable of sourcing higher current with lower voltage drop during cranking than batteries. As a result, cranking revolutions per minute can be as much as 20 percent higher than with batteries alone. This results in starting the genset in a shorter period of time, often in the range of 10 percent to 20 percent less cranking time.

Electric utilities are beginning to adopt ultracapacitors to start large engines that, in turn, start gas-fired turbines. This benefits utilities because their smaller plants are in remote locations. The engine and turbine are started remotely by the grid manager in response to increased demand. In this case, failure of the lead-acid battery system to start the engine has significant consequences to the utility because power to the grid is not supplied on demand. Alternate arrangements must be made quickly to obtain power from another source. Most often, personnel need to make an emergency service call from the central site to the remote site to diagnose and correct the problem.

Lead-acid batteries have been the standard technology for starting commercial engines since the 1930s and now, ultracapacitors are emerging as an alternative starting technology for critical applications like backup generators. Ultracapacitors make a strong business case for replacing batteries in a genset or specifying the starting system for a new installation, leading genset professionals to increasingly rely on the technology. Ultracapacitor-based systems for genset starting give building owners and facility managers confidence that operations will always run smoothly – even in periods of power outages.