Energy needs in a broad range of applications inside a plant are becoming more complex. For that reason, those responsible for ensuring reliable, clean, cost-effective energy supplies within their organizations are constantly looking for solutions that can increase efficiencies while enhancing power quality and reliability.
Clean, uninterrupted power is the goal of every plant manager overseeing continuous business operations and processes. While battery-based uninterruptible power systems (UPSs) are a long-proven backup solution, batteries require constant maintenance, take up valuable plant real estate, require a controlled temperature environment and can often fail long before their suggested life span. Keeping batteries from being cycled often – which degrades battery life, as well as keeping them at their recommended operating temperature– can be problematic for facilities that experience frequent power sags and interruptions.
Many plant managers are turning to kinetic energy storage as a clean and environmentally friendly solution to improve system or process continuity. In many cases, incorporating kinetic energy storage technology (also known as flywheels) in a new or retrofit electrical system design can serve as an excellent foundation for achieving the goals of maximizing facility and process uptime while reducing operating costs. With the added benefit of providing an environmentally friendly energy source, it may be worth taking a look at using flywheels in any demanding application where peak loads or utility sags and surges provide a challenge for ongoing operations.
A flywheel system stores energy mechanically in the form of kinetic energy by spinning a mass at high speed. Electrical inputs spin the flywheel rotor and keep it spinning until called upon to release the stored energy. The amount of energy available and its duration is governed by the mass and speed of the flywheel.
In a rotating flywheel, kinetic energy is a function of the rotational speed of the flywheel and the mass moment of inertia. The mass moment of inertia relates to the mass and diameter of the flywheel. The kinetic energy of a high-speed flywheel takes advantage of the physics involved, resulting in exponential amounts of stored energy for increases in the flywheel rotational speed.
The advantages of flywheel-based systems include:
- High-power density, small footprint
- Parallel capability that allows for future expansion
- Low total cost of ownership(TCO)
- 20-year useful life
- High efficiency (99%)
- Low maintenance &simple installation
- Seismic rating options (Shaker table tested)
- Wide operation temperature tolerance
- Fast recharge (under 150 seconds)
- No special facility requirements
- N+1 redundancy options
- Quiet operation
The rest of this article explores the benefits of flywheel technology in several applications: energy recycling, power quality, variable speed drives, and repetitive industrial applications.
Energy recycling is the process of taking the energy component of an application that would otherwise be wasted and converting it into usable electricity or thermal energy. Sizeable power generation facilities often rely on combined heat and power (CHP) cogeneration, waste heat recovery, and other technologies to enhance efficiency. However, more targeted technologies, such as kinetic energy recycling, can cost-effectively bring similar efficiencies to industrial operations. For plants, energy recycling can not only improve operational efficiency to significantly cut operating costs, but also reduce greenhouse gas emissions to address sustainability initiatives set by an increasing number of organizations.
Across the spectrum, energy recycling can reduce energy use. Studies from the U.S. Department of Energy (DOE)and Environmental Protection Agency (EPA) indicate that energy recycling could meet up to 40 percent of U.S. electricity needs with as much as one-third of that (65,000MW) coming from recovery of waste energy using such technologies as kinetic energy storage. Other storage technologies such as super-capacitors, also referred to as ultracapacitors, and batteries also offer advantages; however, as Figure 1 shows, flywheels can offer greater overall benefits.
Flywheels used in conjunction with a UPS instead of batteries are ideally suited for industrial plant applications to provide protection against all types of power disturbances from power line voltage spikes to complete power outages. These systems provide high power density, and thus have a very small footprint, require very little maintenance, operate in up to 40°C environments, and have a life span of 20 years.
Variable speed drives
Traditionally, UPS systems with batteries were typically placed in front of the variable speed drive to provide backup power for critical operations. However, using a UPS in this application adds inefficiencies of 6 to 8 percent due to losses from conversion electronics (AC to DC and back to AC), reducing efficiency gains from the variable speed drive. Because variable speed drives use the same rectifier, DC bus, and inverter components, such as a UPS, flywheels can be placed directly on the variable speed drive without the added expense and complexity of placing a UPS in the front of the drive. The flywheel can provide backup power as well as regenerative energy absorption, offering a very efficient (99.3%) power solution. Another advantage to using flywheels is that many variable speed drives are located in harsh environments that can greatly reduce UPS battery life, which is optimized at 20°C (68°F). High operating temperatures are not a problem, as flywheels can operate up to 40°C (104°F).
Repetitive industrial applications
Punch presses, auto-insertion equipment, and other pulse power applications demand high power from the grid in very short bursts on a continual basis. Operators of such equipment must typically pay a premium for the constant availability of the maximum power required. In addition, tracking this power use and related cost allocations can be very complicated. These applications can benefit from an energy storage device that takes out the peaking altogether (also known as peak shaving). By supplying the load during the peak power demands when the higher power is needed, demand on the grid only reflects the baseline power usage – not the peaks. A flywheel continues to cycle (with short bursts of high power) with rapid recovery and a duty cycle of as long as 20 years with minimal routine maintenance. While battery-based systems can provide similar peak-shaving functionality, the battery banks themselves must be oversized (by factors of as much as four to 20 times, depending on the equipment) to address the peak loads.
Flywheel implementations comply with the highest international standards for performance and safety, including those from UL, CUL and CE. As industrial and commercial users continue to seek improved process operations and efficiencies, kinetic energy recycling can offer an ideal solution for a wide variety of applications that demand higher reliability along with frequent energy discharge/recharge cycling.