Over the past 30 years, Americans have experienced a number of major electricity blackouts, the most recent being in August 2003, when 50 million Americans were without power for many hours, costing billions of dollars. In an average year, citizens throughout the United States experience thousands of shorter power outages.

In the wake of the 2003 Northeast outage, Congress held hearings to determine how to mitigate the risk of further blackouts. In those hearings, which were clearly focused on reliability, expert after expert explained the complexities of the grid and its array of vulnerabilities. The grid is susceptible to acts of nature, accidents at the hands of operators, and the increasing threat of sabotage. Much of the testimony focused on various ways to harden the transmission and distribution system, typically using advanced surveillance and control technology.

While reliability is only one of the factors to consider when assessing the integrity of an energy system, there are other essential factors to consider, including safety, security, sustainability, and cost-effectiveness. When this multi-dimensioned approach is applied, interesting and unique visions of the energy future emerge.

We begin this discussion by explaining how the grid developed—in other words, how this situation evolved. We follow by explaining a newly developed technique, the “energy surety methodology,” and how we apply it in examining energy systems. We then show how this methodology has led to the novel proposition that the careful placement of energy generators and associated electric energy and fuel storage near the load can help us not only to improve grid reliability but to address critical needs—including security, sustainability, and cost-effectiveness—all without compromising safety.

This new philosophic approach is not without challenges. Distributed energy generators and current storage technologies, especially electrical storage, are available and workable, but costs are generally high. Energy storage density is low and systems often have relatively short discharge durations. Therefore, we will finish the discussion with some summary information about storage technologies and recommendations for research that will allow storage technologies to become a critical component in America’s energy future.

How We Got Where We Are
The US electric grid has been described as the largest machine ever built. Like many things, it developed over time, starting with small individually dedicated generators connected directly to a load.

Engineers quickly realized that larger generators yielded greater economies of scale with associated improved fuel-to-energy conversion efficiencies. So as demand grew, larger generation plants emerged. However, public concern about pollutants forced them to be located far from urban areas. In response, engineers designed transmission and distribution systems to transport the electricity to the growing number of customers.

In the early days of the grid, only a few generators and their associated loads existed. They were isolated and independent of one another.

However, with an increasing number of customers, the transmission and distribution systems grew, and neighboring systems were connected together to improve reliability.

Smaller grids were tied to neighboring grids to form conglomerates. Slowly, large interconnected electric regions emerged. Today, the grid has evolved into three large interconnection regions.

With these interconnected grids in full production, the utility industry blossomed into a huge business sector upon which the US economy heavily depends. Because of its development from local monopolies, the utility industry tends to be vertically integrated and highly regulated, features large-scale generation and high-voltage transmission with mid- and low-voltage distribution.

Today, electric energy production is largely fueled by coal, nuclear, and natural gas, which we will call the “primary fuels,” most of which are mined in North America. A small amount of the production comes from hydro and other sources.

This system includes three important features. First, there is a huge stockpile of stored energy at or near the large-scale generators. All of the primary fuels are forms of stored energy, most having been created millions of years ago and sequestered in the earth until recently mined.

The majority of the large-scale generators that burn these fuels either are located near the fuel source (e.g., the mouth of a mine) or have a large amount of fuel storage onsite. Others, such as natural-gas generators, depend on a reliably steady supply of gas to operate. While the cost of these primary fuels is rising, they are still relatively abundant.

Second, large-scale generation is highly reliable. The approximately 2,700 generating plants in the United States are well maintained and set up with all the machinery centrally located and have an onsite maintenance staff performing periodic, preventive maintenance. Rarely is a power outage caused by generator failure.

Third, the transmission and distribution (T&D) systems are widely dispersed with over 650,000 miles of transmission lines, 5,600,000 miles of distribution lines, and over 60,000 substations spread throughout the United States, connecting the generation stations to the consumer. In comparison to the generation stations, the T&D system receives little preventive maintenance, especially on the lines themselves, and is much more subject to the whims of nature. Congestion in the transmission system exacerbates these problems.

The T&D system is the source of nearly all electricity disruptions and outages. What is more, there is virtually no storage on the load side of the system to buffer the consumer from the effects of disruption problems. Therefore, when the T&D system fails, the downstream loads are lost. The only exceptions are those loads that incorporate their own energy storage and backup generation.

Energy Surety
Surety is a concept developed for defense applications to describe the attributes of safety, security, and reliability of nuclear systems. In its seminal applications—nuclear weapons and nuclear power plants—“high level of surety” simply meant that the device in question was highly to operate properly and predictably when called upon and to remain quiescent for the remainder of time.

The team at Sandia National Laboratories in Albuquerque, NM, has applied the concept of surety to energy systems. Energy surety is a new philosophic approach to energy system management that can help identify problems that exist in the electric power infrastructure. Energy surety incorporates the original surety concepts of safety, security, and reliability and adds sustainability and cost-effectiveness to describe a complete set of energy system attributes. Within this construct, an energy system is said to have high levels of “surety” if it delivers the energy product to the end user while meeting all of the surety elements.

Energy Surety Elements and Description
The elements of energy surety are described below:

• Safety—Safely supplies energy to the end user
• Security—Uses sources of supply that are secure from attack or disruption
• Reliability—Produces energy of sufficient quality that is available when and where it is needed
• Sustainability—Uses resources and delivery practices that can be reliably sustained over an indefinite period of time
• Cost Effectiveness—Delivers energy at the lowest, predictable cost

This is a conceptual framework, and its elements are not yet completely quantified. Quantification is needed to be able to assess whether improvements are being made by applying new technologies to different applications. Some of the surety elements are more amenable to quantification than others. For example, reliability can be defined in terms of percentage of energy availability, while sustainability is harder to measure. Nevertheless, work is progressing to quantify, to the extent possible, all of the elements so that “energy surety” can be measured.

How the US Electric Grid Measures Up
The major energy systems in the United States include the petroleum, natural gas, and electric power systems. Our surety efforts are currently focused on the electric power system, because it is vulnerable to immediate outages and other problems, such as market perturbations with fluctuating prices of fuel and odd behavior, such as a contango condition (one in which distant delivery prices for futures exceed spot prices, often due to the costs of storing and insuring the underlying commodity).

If one examines the current energy generation-supply system with respect to each of the five surety elements, some problem areas emerge. We call this examination process our Energy Surety Methodology.

Outlined below are our observations from this examination.

Safety—Safety has always been a high priority in the electric power industry, and the current system has a good safety record, both in the generating plants and in the transmission and distribution system. However, some segments of society are concerned about disposal of waste byproducts, such as spent nuclear fuel and carbon dioxide.

Security—The hurricanes of 2005 exposed the vulnerabilities of the existing system. Energy supplies were interrupted and supply systems were damaged, leaving large numbers of people without energy and fuel. More importantly, great upward pressure was created on refined fossil fuel prices, especially those for liquid fuels.

Additionally, there are many single points of failure in the existing system, where events in one location affect users many miles away. One event—a tree touching a high-voltage line or a lightning strike—can cause a cascading outage not only on the immediately affected line but on neighboring lines as well.

A growing concern is sabotage, where humans perpetrate a well-planned attack on one of the single points of failure. One such attack may have been recently thwarted in December 2003, when six transmission line towers were found to be unbolted in the Nevada desert. It is possible that saboteurs were planning to topple the towers, causing an energy supply disruption.

Reliability—The overall reliability of the electric grid system today is around 99.99%, which means that it is available 99.99% of the time. Robert Arno explains that, from the perspective of an energy consumer, this means that the system is available for all except 53 minutes per year. This outage could occur as one 53-minute outage or 53 one-minute outages. It could also mean one 159-minute outage over three years (Arno, R., et al. “What Five 9s Really Means and Managing Expectations.”  IEEE 2006 Industry Applications Society Conference, Tampa FL, October 8–12, 2006).

Many people accept whatever reliability the utility provides, but businesses and some civil protection organizations are beginning to demand more control over their energy systems’ availability. This is especially true in critical manufacturing and service sectors, such as computer chip factories and financial data centers. The US military is particularly concerned about how the vulnerabilities in the energy infrastructure may affect mission readiness.

In any case, nearly all of the outages originate in the transmission and distribution system and are due to one of three causes: a) accident, b) act of nature, or c) sabotage. The existing system reliability—essentially a one-size-fits-all offering—is not sufficient for all users.

Peter Fairly has recently suggested that attempts to harden the grid—to improve reliability and resiliency against attack—may in fact be making it more vulnerable to failure (Fairley P. “The Unruly Power Grid: Advanced Mathematical Modeling Suggests That Big Blackouts Are Inevitable.” IEEE Spectrum, August 2004). Basically, his argument is that complexity begets failure in any system and the existing grid is already highly complex. Hardening, it appears and increases its complexity, which begets more potential failure.

Sustainability—The energy surety team at Sandia has defined “sustainability” as meaning that one can carry on an operation for seven generations (about 150 years) without compromising the ability of future generations to meet their own needs. Generally, we consider this period to be sufficiently long as a distant horizon but short enough to be considered within the planning horizon of today’s thinkers.

It is clear to most people who are knowledgeable of energy systems that the world cannot continue to use fossil fuels at the current rate for 150 years. Although these fuels continue to be relatively abundant and some of them, such as coal, are in very high reserves, the cost for accessing them over the long term is becoming objectionably expensive. Additionally, environmental costs are rising as the impact of fossil emissions becomes known. We believe that the current system is nonsustainable over the defined period.

Cost-Effectiveness—The current system is cost-effective, but recent increases in fuel costs and high price volatility, especially in natural gas, are creating a burden to industry worldwide. As noted above, a nonsustainable system is one in which the fuel costs become oppressively high. Thus, sustainability and cost-effectiveness go hand-in-hand, and the current system is destined for problems in the near future.

Based on this energy surety viewpoint, today’s energy generation and supply system is badly out of balance and is ripe for new ideas and approaches.

Systems of the Future
Sandia is developing a new concept for energy generation and delivery systems called the Energy Surety Microgrid. This concept is designed to put into play the energy surety concepts outlined above on an electric power system. The Energy Surety Microgrid will supplement the existing grid structure by adding high-reliability generation near critical loads, by adding storage at critical locations and by introducing sustainable generation on a local scale.

Storage in the microgrid is essential to stabilize the operation of the system. Fuel storage allows for the generation of electricity without dependence upon the grid. Electricity storage provides fast response to the changing needs of the microgrid. It also raises the level of security and reliability of surety microgrid’s generators. Thermal storage might also be included, if waste heat is to be recovered from onsite generators and subsequently applied to loads.

Fuel, electrical, and thermal storage near the load balances the storage on the generation side of the grid, creating a more reliable system. The level of desired reliability can be chosen by the consumer with the appropriate selection of generators and amount and type of associated storage.

Also, additional distribution system interties may be incorporated in the microgrid to allow energy to be shared between local generation nodes, especially if the existing distribution system is unreliable. Currently, when power is interrupted, a building with a backup generator cannot share its energy with a neighboring building, even if the load in that building is of high priority. The surety microgrid addresses this need by introducing intelligent control of resources and loads on the consumer side of the distribution system.

In short, our vision of the future energy generation-and-supply system is one in which there is more small generation near the load, abundant storage near the consumption points, and intelligently controlled microgrids that integrate these resources into a system. This will provide consumers a viable alternative to the limited energy menu currently offered by utilities.

Prototype surety microgrids can be built today using current generation and storage technologies but with some limitations and constraints on operational flexibility. Advanced surety microgrids are expected to employ plug-and-play concepts allowing different generation and storage devices to be seamlessly removed and introduced into the system.

Increasing Surety With Storage
We have applied the Energy Surety Methodology to our vision of the future that presumably includes energy surety microgrids integrated into the existing grid system. We considered each of the five surety elements relative to this hypothetical system, just as we did when we examined the conventional one. Our perspectives are outlined below.

Safety—The surety microgrid does not add any untested or unproven components to the system. One may argue, however, that dispersing the generation and fuels renders the system potentially less safe.

Security—By applying a variety of generators and different fuels, dependency on single fuel supplies is reduced and security is increased.

Reliability—The surety microgrid concept is potentially much more reliable than the current system because it incorporates different sources of power for critical loads than the current grid. Dispersed generation and an abundance of storage located near critical loads allow continued operation during an outage or other disruption. More important, the user would finally have choice in developing a system that would be flexible in meeting unique needs, especially for businesses and military organizations.

Sustainability—Because a surety microgrid would incorporate various types of generators and fuels, it is likely that many renewable resources would be integrated into the mix. Most renewable generation systems meet the definition of
sustainability.

Cost-Effectiveness—The cost of energy from a surety microgrid has potential to be more cost-predictive than that from the current system. One advantage is that surety microgrid systems will use more indigenous fuel resources that are not as price volatile as the traditional fuels that originate from a limited number of suppliers. Another advantage is that onsite systems might be able to supply both electricity and heat, which would potentially double the efficiency of most currently available grid generators. While heat is created in abundance in large conventional generators, it cannot be effectively transported over great distances to reach the consumer. When the value of additional reliability is added to these advantages, the energy surety microgrid is potentially more cost-effective than the existing system.

Current Storage Practice and Practical Limitations
As we have stated above, energy storage is an important factor to the success of the Energy Surety Microgrid concept. However, there are some practical limitations to today’s storage technologies. Before we discuss these limits, we present below a brief primer on the common storage technologies of the day. For the purpose of energy surety microgrids, there are primarily three basic types of storage: fuel, thermal, and electrical.

Fuel storage is quite common, as we noted above, especially on the generation side of our grid system. Fuel tanks, both above- and belowground, are ubiquitous in our society.

Thermal storage is also quite common. Nearly every home or commercial building has a store of hot water in a water heater. Some commercial operations store heat or chilled fluid to heat or cool buildings when conventional systems are not available or when the price is high.

Both fuel and thermal storage systems are well developed, relatively inexpensive, very reliable, and commonly available. These technologies can be easily integrated into a surety microgrid.

Because of its complexity and cost, the situation with electricity storage is different. Electric energy can be stored in electrochemical devices (e.g., batteries), electrostatic devices (e.g., capacitors), and mechanically in flywheels.

Capacitors are used extensively in the electrical industry, but most of their applications are for short-term storage and very rapid discharge, as well as to improve power quality. And while super-capacitor storage is thought to have a future for storing large amounts of electrical energy for grid and microgrid applications, few exist today.

Batteries are the mainstay for energy storage in today’s electrical systems, and we expect that to continue in the near future. Through a process of electrochemical reactions involving certain chemicals and metals, batteries can produce a steady stream of electrical energy. The most common batteries, such as the ones in cars, produce large amounts of electrical energy for a short period of time in order to start engines.

However, batteries in stationary applications, such as those in a microgrid, must supply lower levels of electrical energy for a longer period of time. These are less common, but are most often found in uninterruptible power supply (UPS) systems. Usually coupled to a diesel generator, the UPS is activated during a power outage and uses the battery to supply power for critical building loads during the time that the generator is firing up and coming online. Many of these types of applications would be incorporated into a surety microgrid.

Battery storage is an excellent companion for intermittent generators (solar or wind) that might be found on a surety microgrid. Energy stored at times of high production can be used when the renewable resource is not available. Storage can also supplement temporary decreases in output caused by variations in the wind or passing clouds, giving the renewable generators a more predictable output.

Emerging New Electrical Storage Technologies
Several electricity storage technologies are emerging. These range from large-scale sodium-sulfur (Na/S) batteries (5–10 MW, 30–80 MWh) to medium-scale flowing electrolyte batteries (100–500 kW, 2 MWh), to short-duration, high-power systems (flywheels and electrochemical capacitors).

Larger-scale systems are designed for peak shaving in utility or surety microgrid applications. NGK Insulators Inc., of Japan, has manufactured Na/S batteries that can deliver rated power output for six to 10 hours and over 150 MWh of them are operational. American Electric Power is installing a 1.2-MW, 7.2-MWh system in West Virginia that will operate near the load and will defer for six years the upgrade of the substation.

Several companies are developing battery systems where the electrolyte is stored in tanks and pumped through a reaction cell. The advantage here is that the energy storage rating and power rating are decoupled.

To gain additional storage capacity, one simply increases the volume of the associated storage tank.

In early 2004, PacifiCorp installed a 250-kW, eight-hour discharge vanadium redox battery system in Castle Rock, UT, to stabilize a long rural distribution line that was suffering voltage stability problems due to load growth. This state-of-the-art system was manufactured by the Vancouver, BC–based VRB Power Systems Inc.

ZBB Energy Corp., of Menomonee Falls, WI, manufactures zinc-bromine (Zn/Br) battery energy storage systems and is currently certifying a 2-MWh system for a substation upgrade deferral application for Pacific Gas & Electric. The project is funded by the California Energy Commission (CEC) and the US Department of Energy (DOE).

High-power, short-duration products are also coming into the marketplace in the form of supercapacitors and flywheels. San Diego–based Maxwell Technologies Inc. and several other manufacturers produce electrochemical capacitors that combine the high power output of traditional capacitors with significantly higher energy storage capacities.

Maxwell, with DOE and CEC funding, is installing a supercapacitor energy storage system in a microgrid to stabilize output from a wind turbine and a hydroelectric plant and to provide bridging power to the utility.

Finally, in the arena of flywheels, Beacon Power Corp., located in Wilmington, MA, is demonstrating seven flywheels in a small-scale frequency stabilization system.

Beacon also intends to develop a 20-MW system for frequency regulation services. Active Power Inc., of Austin, TX, is commercially successful in selling flywheels for power quality applications, both as stand-alone systems and as an integral part of one Caterpillar product line.

Ensuring Readiness
There is much additional work needed to fully incorporate the various storage devices, especially advanced ones, into surety microgrid systems. A number of problem areas exist.

First, methods for optimizing the storage components (fuel, thermal, and electric) and tying them to the surety metrics have not been developed. Questions remain about how much of the various kinds of storage should be included in a surety microgrid to meet certain surety requirements. The problem is compounded by difficulties in quantifying some of the surety elements. Sandia National Laboratories is teaming with the Army’s Construction Engineering Research Lab, New Mexico State University, and the University of New Mexico to address this challenge.

Second, the best methods for controlling the storage devices on the surety microgrid are not known with certainty. A CEC-sponsored consortium including the University of Wisconsin, Sandia National Laboratories, and American Electric Power have created basic microgrid control systems to maintain reliable operation in a reasonably controlled environment.

However, we believe that additional control system sophistication is needed to apply advanced generation storage devices effectively within a surety microgrid concerned with five fundamental surety elements.

We envision that an energy surety microgrid should be capable of dynamically changing its operational features while serving loads.

Properly controlled storage devices are an essential feature to maintain power stability on a surety microgrid.

Third, technical, economic, and regulatory challenges remain. Many regulatory systems do not have provisions for including energy storage in a utility’s rate base, preventing utilities from installing energy storage systems on a distribution system where it could benefit an energy surety microgrid.

Fourth, while fuel and thermal storage is relatively inexpensive, electrical storage costs remain relatively high. Research and development in both the private and the government sectors is striving to improve the performance of storage and microgrid products and bring down the capital and operating costs to allow more market penetration to occur.

Finally, with the exception of tanks that store fuel and lower-temperature thermal liquids, as well as ordinary batteries used mostly for motive power, advanced energy storage systems lack the extensive field experience needed to secure the confidence of surety microgrid designers.

Advanced thermal technologies, such as molten salt, have only been demonstrated in limited settings. New electric storage technologies are also lacking in the number of systems successfully demonstrated.

The DOE Energy Storage Systems (ESS) program is currently investing in these areas but is severely limited in its discretionary budget. The DOE ESS program estimates that a $20 million-per-year budget would significantly change the nature of energy storage systems within a period of five years.

Conclusion
Today’s grid is an evolutionary artifact that has worked reasonably well for more than half a century. However, rapidly changing economic conditions in the US are requiring a more robust system, one that meets all of the energy surety elements. By applying the Energy Surety Methodology to the existing system, the weaknesses become more clear.

The Energy Surety Microgrid under development at Sandia has the potential to improve the overall level of surety in the system. Nevertheless, the concept is highly dependent on storage to realize its full potential.

While there are sufficient existing storage technologies available to begin implementation, there are many technological challenges that lie ahead. The most important research needs include reducing the cost and size of electrical storage systems, improving the component and system capability and reliability, and demonstrating these improvements.

As these research needs are met in the lab and the results rolled out to the field in the form of energy surety microgrids, levels of surety in our power generation systems will steadily rise.

John Boyes and Dave Menicucci are research engineers at Sandia National Labs.

DE - January/February 2007