Energy Storage: The Basics

Welcome to Energy Storage Trends. In this first post, I'll provide a basic overview of energy storage trends with plenty of links to more in-depth reports and features. Subsequent blogs will focus on new developments. A few words about me, Pete Singer: armed with a degree in electrical engineering from the University of Illinois, I've been reporting on high tech topics for 26+ years, primarily focused on the semiconductor industry and related fields in electronics. I'm now the editor-in-chief of Solid State Technology and Photovoltaics World, which is part of PennWell's Renewable Energy World network.

So what's so cool about energy storage? Analysts see a strong, upcoming demand for energy storage as part of the grid. This will likely be a combination of some kind of central storage (i.e., a 20MW flywheel installation near a power generation station) and distributed storage (i.e., batteries or supercapacitors next to the familiar green transformers in people’s yards). These types of energy storage are primarily driven by a need on the part of utilities for load balancing, since it's expensive for them to constantly adjust the output of traditional power generation systems as the load varies. Energy storage may even allow them to offset or delay the requirement of additional power plants, such as a gas-fired "peaker" plants.

According to a report from Pike Research, the demand for energy storage is driven by several trends, including the proliferation of intermittent renewable energy sources such as wind and solar, the move toward smart grids, and the coming rise of plug-in hybrid and electric vehicles, to name just three. While storing electricity was once thought a practical impossibility, a variety of technologies have now emerged to disprove that theory, and the global energy storage market is poised to grow from $329 million in 2008 to $4.1 billion by 2018, according to Pike.

“About a dozen technologies are currently vying for a piece of the utility-scale energy storage market,” says managing director Clint Wheelock. “In our analysis, the greatest potential for growth lies with advanced battery technologies, especially Lithium Ion (Li-ion). Sodium Sulfur (NAS) batteries, Pumped Hydro, and Compressed Air Energy Storage (CAES) will also be important technologies in the years ahead.”

In some markets, there may also be value for companies and people on "the other side of the meter" to buy and store power when it is least expensive, and use the stored power during peak demand when prices are highest. Called “time shifting,” this is an interesting concept, although it may be a bit ahead of its time. Jaime Smith of SunEdison (Beltsville, MD), who runs the installer/developer’s North American PV commercial operations, said “as far as taking a solar curve and shifting it and it being worth the value of that shift for the cost of the storage, we have not seen that yet. We’re keeping our eyes and ears open for the right technology but we haven’t seen anything yet that is cost-effective.”

To a lesser extent, the need for energy storage will also be driven by the inherently intermittent nature of many renewable energy sources, such as solar power and wind. As more of this kind of power generation comes on-line, it makes sense to store the energy for times when the wind isn’t blowing or the sun isn’t shining.

Proponents of solar power, however, like to point out that although PV is intermittent (due to clouds and of course darkness), it’s actually highly predictable. Clouds don’t cause that much variability if the PV is spread out over a wide enough area, and because they are visible, it’s relatively straightforward to predict the impact on power generation on a short-term basis and even easier to predict the amount of power that will be generated the next day based on weather reports. That’s fine because power markets operate on a day to day basis. Dan Shugar, CEO of Solaria (Fremont, CA), a supplier of PV modules, said: “In PG&E’s territory alone, which is pretty much north of LA up to Oregon, there’s about 30,000 solar plants. If you look at a 10 x 10 mile area, statistically there’s no variability.”

Also, depending on location, peak demand is often in near-perfect sync with demand, since it’s the heat of the sun that creates the need for air conditioners which are the primary source of demand. “Solar is not available when you want it, but it’s available when you need it,” quips Smith of SunEdison. “It does have intermittency, but the reality is when the demand is the highest – which is when air conditioning demand is the highest – we are the strongest,” he said. Shugar agrees: “Do we need storage today? No. Solar is generating in a very high correlation with when the grid is needing power.”

While that’s true in most of California, it can be a little different in other States. “We’re not perfectly correlated because people come home and flip on their air conditioning in Western States at 5:00 and we’re peaking earlier than that, so storage could be very interesting for us to try to shift that curve,” Smith said.
In the future, 5-10 years from now, when PV and other renewables come to represent a significant percentage of the overall power generated for the grid, energy storage could play an increasingly important role. “As you go from a scenario where 2% of the peak load is generated by PV to 20-30-40%, you start to get into a situation where you need storage,” Shugar said. But he also points out that there are many other ways to control demand with a smart grid in place. “Instead of building dedicated storage systems, there are other things you can do. For example, all the commercial buildings with over 50 kW/h of load have time of use metering now. It’s very simple to install some demand response – there are programs that exist right now that are doing that – where you might let the temperature go from 71 degrees to 72 or 73 when electricity prices are highest.”

Electric vehicles will also come into play, in part by helping to advance battery technology, but also by becoming an integral part of the smart grid. Andy Chu, director of marketing at A123 Systems (Watertown, MA) envisions a time when utilities are so linked into the grid that they can monitor and control electric vehicle battery chargers, and charge them quickly or slowly so as to optimize the load/generation equation. “Electric cars already have a computer in there that can control the charging rate,” Shugar said. “My car is charging right now out in the parking lot from a solar array coupled with the building. I could easily control the rate at which that car is charging based on the availability of solar or a demand signal from the utility.”

Energy storage applications

The two main applications of energy storage technologies are for power – driven by the needs for power quality and bridging power – and for energy management. In power applications, stored energy is only applied for seconds or less to assure continuity of quality power, or it might be used for slightly longer (a few minutes) to assure continuity of service when switching from one source of energy generation to another. For energy management applications, storage media is used to decouple the timing of generation and consumption of electric energy, as previously described. A typical application is load leveling, which involves the charging of storage when energy cost is low and utilization as needed.

Table 1, developed by the Electricity Storage Association, lists various types of energy storage technologies, describes main advantages and disadvantages, and provides a rough measure of relative feasibility.





A new report issued earlier this year by Sandia National Labs, titled, “Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide,” goes even further, describing five main applications for energy storage, with 17 subcategories.

• Electric supply (electric energy time-shift, supply capacity)
• Ancillary services (load following, area regulation, reserve capacity, voltage support)
• Grid Systems (transmission support, congestion relief, upgrade deferral, substation on-site power)
• End user/utility customer (time-of-use energy cost management, demand charge management, service reliability, power quality)
• Renewables Integration (energy time-shift, capacity firming and wind generation grid integration).

Figure 1 shows financial benefits and maximum market potential estimates for the U.S. for each of the 17 subcategories. Clearly, renewable energy sources represent one driver for energy storage, but they will not be the primary driver.




When it comes to renewables, the report notes that one of the main objectives of energy storage is “capacity firming.” Here, the goal is to get a fairly constant output from combination of renewable energy generation and storage. The resulting firmed capacity offsets the need to purchase or ‘rent’ additional dispatchable (capacity) electric supply resources. Depending on location, firmed renewable energy output may also offset the need for transmission and/or distribution equipment.

One important challenge associated with intermittent renewable energy generation is that the generation’s power output can change rapidly over short periods of time. Photovoltaic (PV) output can drop quite quickly as clouds pass. Wind generation output can change rapidly during gusty conditions. These rapid changes (also known as ramping) can lead to the need for dispatchable power sources whose output can also change rapidly. Most non-renewable energy generation facilities (i.e., coal, nuclear, natural gas) are best operated at a constant output. Rapid changes from intermittent renewable energy generation can lead to ramping of these sources, which increases wear, fuel use and emissions. In some regions, there may not be enough dispatchable generation capacity to offset renewable energy generation’s ramping, which creates addition problems – again, potentially solved by energy storage.

An example of the daily operation profile for wind generation plus storage on a summer day is shown in Fig. 2. For the scenario depicted, winder generation output occurring at night, when the energy’s value is low, is used to charge storage. In this example, about ½ of the energy used on-peak is from wind generation that occurs off-peak. The result is constant power for five hours.



The utility factor

The vision of the smart grid with renewable sources and energy storage working in harmony is complicated by one main factor: The U.S. electric industry includes over 3,100 electric utilities. Investor owned utilities are privately-owned, represent 8% of the total, approximately 75% of generation capability and revenue. There are 2,009 municipal utilities, supplying approximately 10% of the generating capability and 15% of retail revenue. There are 912 cooperatives, operating in 47 States, accounting for 9% of total revenue and around 4% of generation.

Some utilities have embraced the concept of energy storage and already implementing it. New York Independent System Operator published a published a paper earlier this year, titled “Energy Storage in the New York Electricity Markets,” in which they note that integration of all types of energy storage technologies into the modern electric grid is becoming a priority. Storage resources can complement intermittent renewable resources such as wind and solar power by storing excess power for delivery when it is most needed. Some storage resources, particularly limited energy storage resources (LESRs) where energy output is measured in minutes, are well suited to providing regulation service that has traditionally been supplied by conventional hydroelectric and thermal units. “The use of storage for services that require fast response helps to improve system efficiency while reducing the need to burn fossil fuels to provide this service,” the report notes.

Beacon Power (Tyngsboro, MA) is constructing a 20-megawatt flywheel energy storage facility designed to provide regulation service to the electric grid. Beacon’s system utilizes 1 megaWatt flywheel modules consisting of 10 individual 25kWh flywheels integrated into a plant that can provide up to 20 megaWatts of regulation service. Beacon received a conditional commitment for a $43 million loan guarantee from the U.S. Department of Energy and broke ground in Stephentown, New York on November 19, 2009.

AES Energy Storage (Arlington, VA) has proposed three 20-megawatt battery storage facilities in the upstate New York counties of Broome, Onondaga and Niagara. AES has previously developed a 2 x 1 megawatt grid-scale energy storage system constructed with battery cells manufactured by Altair Nanotechnologies. The system has the capability to deliver one megaWatt of power to the grid for 15 minutes.

Energy storage also made notable progress recently in California, with the passage of AB 2514 legislation at the end of September by the California State Assembly. The bill requires the Public Utilities Commission by March 1, 2012, to “open a proceeding to consider establishing investor owned utility procurement targets for viable and cost-effective energy storage systems to be achieved by December 31, 2015, and an additional target to be achieved by December 31, 2020.” Publicly owned utilities would have comparable requirements, and would be required to develop plans to maximize shifting of electricity use for air-conditioning and refrigeration from peak demand periods to off peak periods. "Energy storage improves the overall efficiency of our electric power system which will lower costs for consumers," said Assembly Member Nancy Skinner.

Janice Lin, Director of the California Energy Storage Alliance, said “This landmark bill puts California at the forefront of a growing global market that will spur economic development. Given major advances in energy storage, the industry is now ready to provide affordable, reliable products for California's utilities and consumers.” The California Energy Storage Alliance is an association of companies committed to the rapid expansion of energy storage to promote growth of renewable energy and a cleaner, more affordable, reliable and secure electric system. Members include a diverse group of companies ranging from mechanical, thermal and chemical storage companies to system integrators and renewable energy component manufacturers and developers.

Another element that is essential to widespread use of energy storage in the grid (and renewable energy in general) is standardization. One standard of importance is IEEE P1547.8, which is focused on high-penetration, grid-connected photovoltaic technology, including energy storage aspects.

Suggested Additional Reading:

Solar and energy storage - a perfect match

Energy Storage takes on the Variability Conundrum

Basic Research Needs for Electrical Energy Storage

Grid Scale Frequency Regulation Using Flywheels Free whitepaper (registration required)