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Energy Storage Solving Power Quality Problems

Issue 2 and Volume 88.

by Chad Hall, Ioxus

Energy production and storage are in the midst of some major changes. During the past decade, energy production and storage have become a high priority for business and government because of concerns relating to the environment and sustainability of energy sources. The power quality problems that have occurred on the existing, aging system will continue to worsen as intermittent, renewable energy systems are added. Fast-acting energy storage is required to help combat this problem.

Although most of the nation’s electricity is provided by fossil-fueled and nuclear power plants, both fuel sources have fallen into disfavor because of environmental concerns, as well as the question of sustainability in the case of fossil fuels. The latest policies are designed to reduce fossil fuel use in favor of clean, green electrical energy, and current government policy is designed to promote this approach by encouraging energy conservation and the use of more renewable energy sources for electricity production.

In 2008, about 3 percent of electrical energy in the U.S. was from renewable sources. According to the American Wind Energy Association (AWEA), 20 percent of the nation’s electrical energy supply will come from wind energy by 2030. In 2008 alone, an additional 8,500 MW of wind capacity was added, increasing the cumulative total of wind generated electricity by nearly 50 percent. Photovoltaic systems still lag far behind wind when it comes to commercial energy production, but efforts are underway to make it a substantial contributor to green energy. The sun shines during the day, and the wind blows at night. Both of these green energy sources have intermittency problems; the clouds reduce solar production, and wind speed and direction change infinitely. A storage system with high cyclability, high energy and power density is required to provide system stability.

With the shift toward intermittent renewable energy sources comes a new set of technical problems. The primary shortcoming of such power sources is that with intermittence comes the urgent need to develop reliable energy storage. The challenge to any commercial electricity producer is the requirement to meet current demand because it is difficult and expensive to store electricity. The most desirable situation for an electricity generator is to supply energy at a constant rate. Reality, however, requires utilities to respond to rapid changes in demand, and they need reserves to meet demand increases.

Demand changes come in two flavors: long- and short-term. The long-term changes occur at a gradual rate and are illustrated by the summertime increase in demand that accompanies a period of sultry weather resulting in widespread air conditioner use. This type of demand increase can be handled by a utility, provided it has sufficient capacity or can buy reserves from a neighboring utility. More ubiquitous are short-term demand increases, resulting from a sudden change in load that might occur when large machinery is brought online in a manufacturing facility. Most fluctuations occur for less than two seconds, and such momentary changes in demand represent the biggest headache for utilities because they lead to reduced power quality. Power quality is a major issue, as most customers require high power quality to ensure proper equipment operation. In its 2007 report “Provides Power Quality for 21st Century Needs,” the Department of Energy’s National Energy Technology Laboratory estimates that power quality problems cost U.S. companies more than $100 billion annually.

Spinning reserve, pumped hydro, flywheels and high-pressure air all are used to provide energy storage. Spinning reserve is the practice of having a generating station running but offline until demand increases require additional generating capacity to be brought online. Spinning reserve is expensive and inefficient, requiring a utility to use fuel to run a generating station that is idling for long periods. Pumped hydro allows a utility to produce energy at a relatively constant rate and use periods of low demand to pump water into an elevated holding area. When demand increases, the water can be used to produce hydroelectricity by recapturing the gravitational potential energy. Flywheel systems use power during periods of low demand to put energy into flywheels whose energy is recaptured when demand increases, and in a like manner, high-pressure air is accumulated when demand is low and used to drive a turbine under conditions of increased demand. These last three methods require specialized conditions and are expensive. For example, in the case of pumped-hydro storage, a facility with a large reservoir is required along with the ancillary hydro generating equipment. High-pressure air generally is stored in a large natural cavern or abandoned mine, and because these are not readily available, the usefulness of this approach is limited. Flywheel farms require high maintenance. Several prototype facilities were taken out of service because of that issue. All of these methods have significant drawbacks and generally, because of their expense and limited availability, require a smart grid network to make them viable. The investment, for example, in a high-pressure air system requires a cavern or abandoned mine, the installation of the machinery to operate the system, and a cost-benefit analysis to ensure the system will be cost-efficient. This then will require that the energy produced be conveyed to regions of the country needing extra capacity and thus the need for a reliable and efficient grid network.

The systems described thus far are not portable, require an expensive infrastructure and added transmission, and are not efficient for addressing the short-term sags described earlier. More suitable solutions for short-term sags are batteries, ultracapacitors or both. They are portable, allowing them to be installed in virtually any location or substation. They also are efficient for short-term sags and provide for faster return-on-investment than large installations. A megawatt of capacity that will function well with an associated power electronics interface to address the short-term interruptions previously mentioned is relatively easy to build using batteries, ultracapacitors or a combination of both.

Energy storage methods can be divided into two categories: one suitable for longer-term demand increases and one for short-term fluctuations. With the increase in electricity generated by renewable energy sources, both methods will be required. As the electrical infrastructure evolves, however, using renewable energy sources will need to include an intermediate storage media that can function in both arenas and will make local electricity production more practical. Financial drivers dictate this trend; local production that uses renewable sources will go a long way to relieve stress on the grid infrastructure and will use resources more efficiently. To make this a reality, robust energy storage media must be developed that includes improved batteries and high-energy density ultracapacitors. The future of energy storage appears exciting and filled of endeavor, but necessary in a world that will continue to consume energy at an exponential rate.

Author

Chad Hall is CEO of Ioxus Inc. Previously, he spent 14 years with Ioxus’ parent company, Custom Electronics Inc. Reach him at [email protected]

 


 

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