Jennifer Eirich, Marketing Manager, Utilities
According to the US Department of Energy (DOE), growth in peak demand for electricity in the US has exceeded transmission growth by almost 25 percent every year since 1982.1 Today’s utilities are now being challenged to manage increasing consumption with an aging and already compromised infrastructure, congested transmission lines and greater reliance on renewable resources.According to the US Energy Information Administration (EIA), 51 percent of all generating capacity (530 GW) is at least 30 years old.2 This is especially surprising when compared to the telecom industry. For example, just think of the strides that have been made in telecommunications in the past three decades, from portable and cellular technology to smart phones, tablets and more.
Meanwhile, with hundreds of thousands of high-voltage transmission lines connecting the US, only 668 additional miles of interstate transmission have been built since year 2000.1 At the same time, utilities are struggling to incorporate new, renewable sources of energy. According to the EIA, renewable energy will account for about one-third of new electricity generation added to the US grid over the next three years. And yet, despite all of these challenges, spending on research and development is among the lowest of all industries. The result is power outages and interruptions that cost American businesses more than $100 billion each year. Even single incidences can have a significant impact.1
Energy storage works to address these power concerns, especially those striving to incorporate renewable energy sources. Energy is a just-in-time asset in which generation must be matched to demand to maintain reliability and stability. Wind and sun are intermittent by nature, leaving gaps in the utility’s ability to provide constant power. Energy storage helps to bridge this gap by allowing energy to be stored for those times when it is in greatest demand. Energy storage not only helps to prevent service interruptions and downtime, but it also allows for distributed service, placing the energy source closer to the process and equipment that will use it. It also helps utilities postpone and possibly avoid costly expansions or upgrades as demand grows and renewable generation increases.
The Role of Energy Storage
Increasingly, energy storage is being regarded as a way to balance the grid. According to the Energy Storage Association (ESA), energy storage can ease the market introduction of renewables, accelerate the decarbonization of the electricity grid, improve the security and efficiency of electric transmission and distribution (reduce unplanned loop flows, grid congestion, voltage and frequency), stabilize market prices for electricity, while also ensuring a higher security of energy supply.3 Electric utilities already are among the largest owners and users of electrochemical battery systems,4 and the global energy storage market is expected to grow 71 percent per year in terms of capacity from 2014 to 2023, according to a recent study by Navigant research.5
This increased demand for grid-scale storage has opened the door to many new technologies as suppliers compete to fill this need. Utilities must weigh their options carefully to find the optimum solution. Often, traditional technologies offer the most sensible solution. As energy demand continues to increase, today’s utility leaders need to find the right solution and the right partner.
Matching the Right Solution to Your Application
While some forecasters assume that the growth in energy storage will be in newer energy storage technologies, the Electric Power Research Institute (EPRI) holds that â€œno single storage system can meet all of the application needs of the power grid, and a wide variety of storage technology options are being proposed for utility-scale storage uses.â€6 The key is matching the application with the right storage solution. To do this, the utility must develop a clear profile of the application by addressing several key decision-making factors.
Performance: The utility’s first step is to determine how it plans to use the energy storage. Will it be used to generate power, to store energy or both? It is also important to identify other performance needs, such as increasing reliability, improving power quality and/or integrating renewables. Capacity also must be defined as well as required reaction time.
Cycle Life: High energy, high cycling solutions sound impressive, but as some industry engineers quip, not every application requires a nuclear reactor. While some applications require long life cycle, it is just costly overkill if it is not required. Lithium ion batteries, for example, can offer more than twice the life cycle of a lead acid battery. At almost five times the cost, however, it is only cost-efficient for those applications in which size, weight and longevity make it absolutely necessary.
There are three factors that impact cycle life and should be considered when choosing the right storage chemistry. These are:
- Depth of Discharge (DOD): There is a direct correlation between the DOD of the battery and the number of charge and discharge cycles it can perform. The greater the DOD, the fewer cycles the battery can perform.
- Temperature: Temperature plays an important role in battery performance and life. Batteries do not perform as well in temperature extremes. In general, operating at lower temperatures is less harmful to batteries than high temperature operation. As temperatures drop, capacity diminishes due to higher internal impedance. The battery size must be increased to compensate. If the voltage is not temperature compensated (increasing the charging voltage at lower temperatures), it is possible that the batteries may become undercharged, resulting in loss of capacity and life. High temperature operation, however, can shorten battery life, resulting in dry-out and possible failure.
- Charging: It is important to understand how the battery will be used in each application. Will it be left on float for long periods of time or used in short, powerful cycles? The battery must be designed for the right situation, providing the right amount of longevity and/or recharge capability. Users also must be careful not to overcharge the battery, causing overheating, or to undercharge the battery, diminishing the battery’s efficiency.
Energy Density: As with cycle life, energy density is attractive, but it comes at a premium and should only be considered when space is limited. Here again, lead acid batteries may deliver the necessary performance requirements at greater savings than other high-density storage solutions.
Monitoring and Risk Management: In energy storage systems, the amount of stored energy is equivalent to the amount of potential risk undertaken. The more energy stored in the device, the more can be released in a catastrophic failure. For this reason, utilities must understand how to avoid and control potential failures. Even a seemingly isolated electrical short can be a major concern. An electrical short not only damages the immediate cell, but it can generate heat that spreads to surrounding cells.
Effective monitoring is critical to the energy storage system. Some systems monitor individual cells, while others monitor strings of devices. Individual cell monitoring is much more effective at spotting spikes, identifying trends and avoiding thermal runaway.
Enclosure: Utilities may be tempted to compromise when specifying the enclosure, the last piece of the energy storage system. However, the enclosure protects your investment. For this reason, it is best to buy the most robust structure the budget will allow. For outdoor installations, this should include a watertight and sealed enclosure mounted on a thick concrete pad with a grounding structure. Direct Current (DC) ground fault monitoring and protection should be added to provide safety, security and reliability. Utilities also may want to consider other built-in safety features, such as fire suppression, spill containment and gas detection, as well as a climate control system to optimize battery life.
Budget: Cost is an important determining factor in storage selection. As previously mentioned, power and density may come at a considerable price. For this reason, familiar technologies may be more cost-efficient than newer solutions at addressing the energy storage needs of many utilities. Utilities also should be sure to account for all project needs, thinking beyond initial installation to include training, first year maintenance and contingency planning.
Choose the right partner: Choosing the appropriate DC chemistry is a science and requires as much, if not more, due diligence than specifying the Alternating Current (AC) electronics. A systems integrator can help build a customized solution, including the battery storage solution and related support systems. Ideally, we recommend that utilities align themselves with an experienced DC integrator or, better still, a DC supplier who offers a range of storage chemistries and can recommend the ideal match from several available choices. The latter may be better suited to making recommendations on the merits of the individual technologies rather than force-fitting a single solution.
For added convenience, many DC suppliers promote a one-stop shopping option that provides the control hardware and supportive services, such as shelter construction, thermal management, monitoring and controls software, installation and maintenance services, and even financing. Others simply provide a list of recommended vendors.
Some DC suppliers go a step further, offering expertise in both AC and DC technologies and offering a truly integrated solution. They also may be able to provide a demonstration, allowing the customer to see the system in operation and to review real world data. This offers a reliable, seamless and time-efficient solution.
On the flip side, it is wise to be wary of integrators who approach energy storage from the AC perspective only, leaving the DC chemistry decision up to the end customer. Some may promote a one-size-fits-all approach to chemistry and/or battery form factor, a sign for the customer to proceed with caution. Suppliers refer to these integrators as battery agnostics, as this demonstrates an overly simplistic view of the DC market.
Lastly, with so many new vendors flooding the market, it is also important to choose a partner with a firm financial history to ensure long-term security of supply.
Today’s utilities are balancing just-in-time energy demands while coping with an aging infrastructure and budget limitations. Renewable energy helps fill the gaps, but it also presents challenges due to its intermittent nature. Energy storage provides a convenient and practical solution. Choosing the right system and partner, however, is a critical and daunting task. The key is understanding the application requirements. While new energy storage solutions may offer sleek packaging and greater energy density, today’s utility leaders must be careful not to overlook familiar technologies that can still deliver proven, cost-effective results. For more information on utility-scale storage, visit www.optigrid.enersys.com.
1 The Smart Grid: An Introduction,â€ http://energy.gov/sites/prod/files/oeprod/DocumentsandMedia/DOE_SG_Book_Single_Pages%281%29.pdf
2 US Energy Information Administration, Form EIA-860 Annual Electric Generator Report , and Form EIA-860M (see Table ES3 in the March 2011 Electric Power Monthly) http://www.eia.gov/todayinenergy/detail.cfm?id=1830
4 Renewable Energy: Clean, Secure, Reliable,â€ The National Renewable Energy Laboratory, May 2003
5 Energy Capacity of Advanced Batteries for Utility-Scale Energy Storage Applications Will Grow 71 Percent per Year through 2023, Forecasts Navigant Research,â€ May 29, 2014, http://finance.yahoo.com/news/energy-capacity-advanced-batteries-utility-160700608.html;_ylt=A0LEVyu2HuVTVC0AMCFXNyoA;_ylu=X3oDMTEzOHZ0NGlwBHNlYwNzcgRwb3MDNgRjb2xvA2JmMQR2dGlkA1ZJUDA3N18x
6 Electricity Energy Storage Technology Options – A White Paper Primer on Applications, Costs, and Benefits,â€ D. Rastler, EPRI Project Manager, EPRI, Dec. 2010