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Virtual Energy Storage:
Using Buildings as Batteries

by Greg Kats and Andrew Seal, October 11, 2012

Thomas Edison once remarked "When we learn how to store electricity, we will cease being apes ourselves; until then we are tailless orangutans." True to Edison's insights, recent investment in battery banks, compressed air systems and ultra-capacitors show interest in solutions that improve energy storage technologies. Utilities and the venture capital (VC) community are spending vast sums in search of solutions to curb peak power loads and to address the intermittency of renewable power sources. Edison would likely view these expensive investments in hard storage technologies as noble but misguided efforts to transcend our collective simian roots.

Better solutions within our grasp

The rush to invest in new capital-intensive storage technologies overlooks a larger, lower cost and lower risk opportunity -- what we call virtual storage. Unlike hard storage technologies, virtual storage does not require large capital costs. Instead, virtual storage proposes creating intelligent distributed energy efficiency as well as harnessing the latent potential in building structures and systems to dynamically modify building energy usage. Virtual storage promises to reshape energy demand to match a variable energy supply.

Virtual storage offers a far more cost-effective and lower-risk solution than hard storage technologies to solve most power supply and demand mismatches. The rapid rise of virtual storage will more effectively meet energy storage needs at a lower cost than most hard-storage technologies now receiving investment from utilities and VC firms. Shifting to a virtual storage strategy can save tens of billions of dollars, serve as a catalyst for the renewable energy industry, improve utility profitability, strengthen security and slow global climate change.

Buildings as batteries

Buildings represent close to 75 percent of electricity consumption. Building energy demand peaks during hot summer afternoons when the need for air conditioning is greatest. While buildings are the dominant source of unbalanced load demand, buildings -- through virtual storage -- also represent the largest opportunity to cost-effectively reshape load, thereby saving tens of billions of dollars by avoiding costs relating to both inefficient generation and costs of transmission and distribution (T&D) infrastructure.

Some new technologies are designed to reduce peak power consumption. These will be part of "building as battery" designs meantl to achieve zero net energy. The new technologies are varied, including hardware solutions, energy efficiency control devices and smart grid solutions.

At one end of the sophistication scale is the application of cool paints (typically white) which reflect 80 or 90 percent of the solar radiation falling on a roof.

This simple change very cost-effectively cuts solar heat gain and peak air conditioning load while reducing ambient local temperature. For example, in Washington DC, making roofs on city owned buildings cool would reduce ambient city temperature by 0.3 to 0.4 degrees.

Dynamic electrochromic glass

One of the most effective of these hardware solutions is dynamic electrochromic glass which allows building occupants to control the amount of light and heat allowed through the glazing. A small electricity current passing through an electrochromic layer on glass causes the window to shift from clear to tinted and back. In the clear state, up to 63 percent of light passes through -- ideal for an overcast winter day when the solar heat gain helps warm the building and natural light reduces need for artificial lighting. In the tinted state, as little as two percent of light and solar heat gain comes through the window glass -- keeping out almost all unwanted heat in summer afternoons while providing sufficient light to keep internal lights off.

For an average commercial building in areas where peak demand occurs during the summer afternoons, electrochromic windows can cut total commercial building electricity peak load between 15 and 20 percent. Additionally, this technology can make windows a net energy saver by increasing solar heat when needed and rejecting it when not wanted.

A hybrid load-shifting efficiency technology such as Calmac or Ice Energy uses ice storage as a way to shift peak AC load. Ice Energy devices use low cost electricity at night to cool water into ice and then reverse the process to deliver coolth during peak cooling hours. Because temperature is lower at night, this is more energy efficient as well as less expensive than daytime cooling. Both electrochromic glass and ice storage systems can be managed as part of a building or campus-wide energy management system which includes a building load demand shaping strategy.

Commercial building monitoring management services represent a major avenue for large virtual storage gains. These systems allow all aspects of building energy use and generation to be monitored, linked, and managed efficiently.

One challenge for most building energy management systems, however, is that they cannot use the thermal mass of buildings to optimize energy use. Thermal mass refers to the large concrete, brick, stone or other materials that make up the building structures. These structures absorb and emit significant amounts of heat. The best of new virtual storage building control systems, such as BuildingIQ, can use the thermal mass of buildings as an integral part of achieving occupant comfort at lowest energy costs.

Operating in demanding environments such as Rockefeller Center, BuildingIQ incorporates real-time energy measurement with projected energy (e.g. next day temperature), the thermal mass of the building and current energy prices to optimize building energy use to achieve desired comfort. BuildingIQ typically delivers total building electricity savings in the 25 percent range. It is able to integrate multiple energy elements -- including generation and onsite storage -- to provide desired comfort in a way that is most efficient and lowest cost. In effect the building itself becomes a battery.

An example of smart building management providing virtual storage is illustrated in graph of a homes hourly use of electricity. Intelligent building controls also enable large cost-effective virtual storage at campus-wide levels. The capacity to shift building and campus-wide energy load has been demonstrated in residential buildings. Tendril, a leading US residential smart grid firm, works with utilities to demonstrate the potential for peak load reduction and shifting across multiple buildings. An example of smart building management providing virtual storage is illustrated in the test results (see graphic to the right):

In a fall 2011 test run by Colorado-based residential smart grid firm Tendril, which is illustrated in the graph above, 60 buildings responded to utility incentives to reduce peak demand. The goal was to reduce demand by 2.5 KW on average, or approximately 2.0 kWh during the three-hour peak period from 3 pm to 6 pm (as indicated by the grey band). The average peak load reduction is about 40 percent, a dramatic reduction considering that participation in events is voluntary and occupants may opt-out at any time before or during an event. This virtual storage capacity costs far less than hard storage solutions such as batteries. Virtual storage capacity is available for both residential and commercial buildings.

Energy storage shows great promise in addressing the variability of power supply, lowering peak power usage and ultimately helping to mitigate the effects of climate change. Currently, energy storage is characterized by capital intensive hard storage technologies, which are expensive and soon-to-be obsolete.

The future of energy storage, however, lies in with virtual storage solutions that are flexible, adaptive, and low-cost. The sooner utilities and VC firms can grasp the potential of virtual storage, the sooner we will cease to be the "tailless orangutans" of Thomas Edison.

This article was adapted by the co-authors from a longer version published in October 2012 in Electricity Journal.

Greg Kats and Andrew Seal
Virtual Energy Storage: Using Buildings as Batteries, October 11, 2012

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