READING, PA – Despite numerous increases in efficiencies, demand for energy worldwide continues to rise. At the same time, the use of renewable energy sources is also increasing at the residential, commercial and utility levels. This exposes the worldwide energy grid to a higher rate of intermittencies, with potentially far-reaching effects. With so many choices available, it is important to develop a profile of the specific application to ensure effective protection. This article looks at current trends in renewable power and the role of energy storage providing a reliable energy buffer throughout the generation and delivery system.


According to the BBC, our collective worldwide appetite for energy is expected to rise by at least 50 percent by 2030, as developing countries like China and India seek to fuel their rapid economic growth. China and India have joined the United States and Russia to comprise the top four largest energy consumers in the world, primarily due to energy demand rising to meet the needs of their expanding economies, with coal serving as the leading source of energy.

By Jennifer Eirich, EnerSys

Jennifer Eirich, EnerSys

In the U.S., energy demand also continues to grow, but at a slowing rate due to efficiency gains from new appliance standards and investments in energy efficient equipment. According to the U.S. Energy Information Administration’s Annual Energy Outlook 2013, total electricity demand is expected to grow by 28 percent from 2011 to 2040. Other sources estimate more rapid growth. According to “A Word to the Wise: Know Your Power” in the May 2012 issue of The Data Center Journal, U.S. demand for electricity is forecasted to grow by 40 percent over the next two decades.


Despite the heavy reliance on coal and other fossil fuels, renewable power, including hydropower, is the fastest-growing power generation sector, expected to increase by 40 percent in the next five years — “a bright spot in an otherwise bleak assessment of global progress toward a cleaner and more diversified energy mix,” according to the Medium-Term Renewable Energy Market Report.

As such, by 2018, the report estimates that renewables will make up a quarter of the world’s energy mix, up from 20 percent in 2011. In fact, it is projected that renewable energy will edge out natural gas as the second biggest source of electricity, after coal, by 2016, according to the International Energy Agency (IEA).

Unfortunately, all renewable energy is not equally as beneficial for our fragile ecosystem, as environmentalists and sustainability experts are quick to point out. Hydroelectricity, which represents roughly 80 percent of renewable capacity, has no impact on air quality but requires the construction of dams that can have a negative impact on natural river systems and their fish and wildlife.

Non-hydroelectric sources, such as wind and solar, are a much smaller but rapidly growing portion of the global mix:

• In 2011, non-hydroelectric technologies were just 4 percent of the world’s energy supply. This number is expected to double by 2018.
• In 2011, there were fewer than 200,000 wind turbines worldwide. By 2020, wind power is expected to produce 9.1 percent of the world’s electricity demand. “By 2030, the market could be three times bigger than today…A new turbine every seven minutes — that’s our goal.” — Sven Teske, Senior Energy Expert from Greenpeace International. The strongest growth is expected to be in China/Asia.
• According to IEA analysis, under extreme assumptions solar energy could provide up to one-third of the world’s final energy demand after 2060.

Generation and growth of renewable energy varies widely from one country to another. According to the IEA, developing countries, led by China, will account for two-thirds of the global increase in renewable generation. Growth in much of Europe and the U.S. is expected to slow, although President Barack Obama’s plans released this summer may encourage renewed investment in renewable sources. Germany is also an exception. The German government’s Renewable Energy Source Act (EEG) promotes renewable energy by allowing people to produce and sell renewable energy to the power grid at fixed prices for a period of 15-20 years. Through the EEG Act, the German government’s goal is to achieve 35 percent renewable generation by year 2020.

According to the IEA, policies to decarbonize electricity systems have served to magnify investment risk and uncertainty. At the same time as renewable support schemes have proven effective in facilitating deployment of wind and solar photovoltaic, they also introduce new challenges to design a stable regulatory framework and well-functioning markets.

While it is easy to support renewable energy sources because they are environmentally friendly, they also pose a potential problem. An article by Reuters hints at the question on everyone’s mind… With 40,000 MW+ of wind or solar power at its disposal, what could happen on a windfree, overcast winter day?


While renewable energy sources deliver powerful environmental benefits, some, such as solar and wind, are volatile sources of power with inherent intermittencies. Wind power is affected by wind speeds, wind temperature/air density, and turbine characteristics, among other factors. Intermittency also affects solar energy. Solar output varies throughout the day and by season, as well as cloud cover. The more we increase our reliance on renewable energy, the more susceptible we become to such intermittencies.

In the U.S., our increasing appetite for power and our aging infrastructure further compromise reliability. Power outages are a significant problem today in the U.S. A 2012 Ernest Orlando Lawrence Berkeley National Laboratory study, entitled, “An Examination of Temporal Trends in Electricity Reliability Based on Reports from U.S. Electric,” analyzed 10 years of electricity reliability information collected from 155 U.S. electric utilities (accounting for roughly 50 percent of total U.S. electricity sales). The study reported “reliability is getting worse, on average, over the [past] 10 years.”

Decreasing reliability and increasing outages cost consumers and businesses money. According to the U.S. Environmental Protection Agency (EPA), “cost of a service interruption varies by customer and is a function of the impact of the interruption on the customer’s operations, revenues, and/or direct health and safety.” In one study, Pacific Gas & Electric Company (PG&E) estimated the total annual cost of power outages to its customers at $79 billion per year.

These fluctuations can impact the stability of the power grid as a whole, potentially leading to widespread blackouts. According to a joint report by Allianz insurance company and the Chief Risk Officer Forum, an action-focused Independent Industry Network of 13 European insurance companies, aging infrastructure combined with cross-border electricity networks have “heightened the likelihood of a devastating collapse of power supplies lasting months and covering several continents.” Furthermore, leading risk analysts modeled a worst-case scenario in which transformers are knocked out in the U.S., causing outages to cascade through the grid into Canada, Russia and Scandinavia. In this scenario, electronic banking services would stop immediately, and gasoline pumps and refineries would shut-down within six hours and back-up generators powering hospitals, stock exchanges, emergency services and sewerage plants could run out of fuel within days. Longer lasting blackouts could create significant impacts on society and economy. The analysts even wrote about “supranational blackouts” with even larger economic losses. These outages could be trigged by cyber attacks, terrorist action, natural disasters or even solar storms.


So how do we avoid these worst-case scenarios? Energy storage can provide the solution by serving as a buffer or shock absorber. Frost and Sullivan’s research predicts “electric energy storage technologies will be an inseparable part of smart grids and distributed energy generating systems in the future.” This is coming to bear as electric utilities already are among the largest owners and users of electrochemical battery systems.

Choosing the right energy storage can be challenging, however. It is important to understand where the storage is needed and the role it will play in each position within the energy delivery system.

Generation: At the point of generation, energy storage can help support peak generation capacity deferral, energy arbitrage and spinning/non-spinning reserve requirements. It also can serve as an intermittency buffer for renewable integration and to regulate service support (frequency and volume). Batteries have evolved in recent years and there is a wide selection of cost-efficient, reliable and familiar energy storage solutions, including flat plate and tubular lead acid batteries, to meet a wide range generation and integration needs.

T&D: On the transmission side, energy storage provides fast relief for congestion by subsidizing loads in congested areas (downtown NYC). It also enables capital deferral. Meanwhile, energy storage can improve the distribution system efficiency through power factor correction, reducing system losses and providing more stable voltage for sensitive customers while maximizing asset utilization by reducing current needed to supply electrical loads.

However, the greatest challenge is likely to come from the duty cycle to which these batteries will be exposed. A typical energy storage installation on the T&D side must be capable of handling frequent discharges to the grid and frequent charging cycles from the grid. It is important to choose a battery that is optimized to handle these short, recurrent cycles. There are several battery systems that are capable of meeting these demanding conditions. When selecting an energy storage supplier, beware of those that claim to be “battery agnostic.” The right vendor should be “battery intelligent” and be able to discuss how to treat the battery, how to measure the battery charge and how to proactively manage the battery system.

Consumer: At the consumer’s residence or business, energy storage can provide back-up power for use during renewable downtime and to improve power quality by augmenting existing energy supplies. Selecting the rightsized battery is one of the most critical decisions in setting up backup storage for all energy storage systems including residential or commercial renewable system. However, when factors, such as cost, play a big role, proper sizing sometimes takes a back seat. It’s no surprise then that one of the most common mistakes in battery selection is the improper sizing of the battery. This occurs when the installer miscalculates the number of days of autonomy and the size of the renewable generation needed to support the load and charge the batteries.

The most important rule is that “energy in” must be greater than “energy out.” Without enough power generation in the system, the batteries become depleted. With no recharge period, they plateau and then discharge again, creating a downward “stair step” cycle pattern. For example, continuously discharging lead acid batteries greater than 80 percent will cause the battery life to decrease. Therefore, the more cycles anticipated, the lower the depth of discharge (DOD) should be designed into the battery system. For maximum investment, it is best to not discharge the battery more than 40 to 50 percent in a diurnal system.


The key to choosing the right energy storage solution is a solid understanding of the application at hand. Following are five key decision-making factors to help develop a clear profile of the application:

Performance: The first step is to determine whether the user needs to generate power and/or store energy. Also, it is important to identify other performance requirements that need to be addressed, such as increasing reliability, improving power quality and/or integrating renewables. The user also needs to have a firm idea of how much capacity is needed and how quickly it needs to respond to a signal to dispatch/absorb (reaction time).

Period (Cycle Life): In some applications, long life cycle is critical; in others, it’s costly overkill. Lithium ion batteries, for example, can offer more than twice the life cycle of a lead acid battery. However, at almost five times the cost, it is only cost-efficient for those applications in which size, weight and longevity make it absolutely necessary.

Three factors impact cycle life and must be considered when choosing the right chemistry:
• Depth of Discharge: There is a direct correlation between the depth of discharge and the number of charge and discharge cycles a battery can perform.
• Temperature: Some batteries are less tolerant of cold and/or heat; others operate at higher temperatures and need to be insulated against the cold to prevent degradation.
• Charge: Charging methods vary; Charge management is key, as overcharging can shorten the lifecycle.

Peril: Risk management means weighing one’s appetite for risk. With so many new technologies come safety risks. Storing energy involves understanding what to do when there is a failure, how to control it and how to avoid the potential catastrophic results. Like water in a pool, the more energy stored in a device, the more will be released in a catastrophic failure. Electrical shorts also generate heat that can spread to surrounding cells. Effective monitoring is critical. Some systems monitor individual cells, while others monitor strings of devices. The former is more effective at spotting spikes, identifying trends and avoiding failures.

Power: High energy, high cycling solutions sound impressive, but as industry engineers like to quip, not every application requires a nuclear reactor. Likewise, energy density is attractive, but it comes at a significant premium and is only required when space is limited. For example, in many applications, lead acid batteries may deliver the necessary performance requirements at greater savings than other high-energy storage solutions.

Price: Cost is a key determining factor in storage selection. Users may be surprised to find that familiar technologies may be more cost-efficient than newer solutions at addressing energy storage needs.

In addition to the five P’s, maintenance is also a key consideration. Maintenance requirements differ based on the type of technology, the amount of runtime and the physical environment. While some technologies are widely familiar, others may require hard-to-find specialists that can result in added cost and downtime.


Despite improved efficiencies, demand for electricity in the U.S. is anticipated to grow over the next few decades, with renewable energy growing faster than any other power generation sector. Our dependence on renewable energy sources is making us increasingly susceptible to power outages and other intermittencies. A buffer is needed to help maintain reliability. Energy storage can provide the solution by serving as a shock absorber against service interruptions. Today’s utilities have more choices than ever for energy storage. A good understanding of the application is the key to choosing the right energy storage solution. With a well-defined understanding of the application, users may be pleased to find that there are multiple ways to incorporate energy storage and that conventional technologies can still provide cost-efficient solutions that work.

About the Author

Jennifer A. Eirich, is a marketing manager, Utilities/product manager, Optigrid, at EnerSys. Eirich joined EnerSys a year ago as part of the team responsible for launching OptiGrid™ Stored Energy Solutions, the company’s first utility-scale energy optimization system. Eirich has more than a decade of experience in mixing and systems engineering, previously serving as a sales engineer and project manager at Komax Systems Inc. She began her career as a territory sales manager for Philadelphia Mixing Solutions, Ltd. is one of the world’s most experienced fluid mixing equipment and process optimization firms. Eirich is a member of the U.S. Technical Advisory Group to IEC TC120 for the standardization of Electrical Energy Storage Systems. She also supports her local community as a member of Rotary International. Eirich holds a Bachelor of Science degree in Chemical Engineering from the Pennsylvania State University.

About EnerSys

EnerSys® (NYSE:ENS), the world leader in stored energy solutions for industrial applications, manufactures and distributes reserve power and motive power batteries, chargers, power equipment, and battery accessories worldwide.