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Smart Window Coatings

University of Texas at Austin (UT Austin)

Low-Cost Solution Processed Universal Smart Window Coatings

Program: 
ARPA-E Award: 
$2,986,199
Location: 
Austin, TX
Project Term: 
03/28/2013 to 09/26/2016
Project Status: 
ALUMNI
Technical Categories: 
Critical Need: 

Buildings account for 40% of all energy used in the U.S., and the energy lost through typical windows can boost a building's energy bill as much as 25%. Today's best window technologies--which dynamically control transmittance of sunlight to reduce both cooling requirements in the summer and heating requirements in the winter--can be cost prohibitive for homeowners and commercial building managers. In order to support the widespread installation of efficient window technologies, we need to make substantial improvements in the heat- and light-transmission properties of windows while achieving significant reductions in price.

Project Innovation + Advantages: 

The University of Texas at Austin (UT Austin) is developing low-cost coatings that control how light enters buildings through windows. By individually blocking infrared and visible components of sunlight, UT Austin's design would allow building occupants to better control the amount of heat and the brightness of light that enters the structure, saving heating, cooling, and lighting costs. These coatings can be applied to windows using inexpensive techniques similar to spray-painting a car to keep the cost per window low. Windows incorporating these coatings and a simple control system have the potential to dramatically enhance energy efficiency and reduce energy consumption throughout the commercial and residential building sectors, while making building occupants more comfortable.

Potential Impact: 

If successful, UT Austin's low-cost window coatings would yield a 5-fold reduction in the cost of "smart window" production, enabling more consumers to adopt the technology and drive down building energy consumption.

Security: 

Improving the energy efficiency of buildings reduces pressure on the electrical grid, improving its stability and also reducing the nation's dependence on imported oil for heating.

Environment: 

Better building efficiency would limit electricity and fuel consumption and reduce greenhouse gas emissions.

Economy: 

Improvements in heating and cooling efficiency could save homeowners and businesses thousands of dollars on their utility bills.

Innovation Update: 

(As of December 2016) 

The UT Austin team is exploring new approaches to the fabrication of a dual-band window coating with electrochromic (EC) properties to control the passage of light from the visible spectrum through near-infrared (NIR), reducing energy use for air conditioning. The team’s successes have been recognized through both awards and investment, including financing from Prelude Ventures, a 2013 R&D 100 Award, a $1 million Small Business Innovation Research (SBIR) award, and $250 thousand from Wells Fargo’s Innovation Incubator program. The team is currently working on transitioning its dual-band window technology to a commercial product. Due to window market needs, the UT team is experimenting with variants of their chemistries to achieve improved coloration and durability. 

In parallel, the team is using its new solution-processed techniques to manufacture single-band EC windows that have the potential to be fabricated at a significantly lower cost than incumbent vacuum deposition technologies. The team has established agreements with window fabricators to produce or sell EC panes rather than competing directly with full insulated glazing unit (IGU) window assembly manufacturers. They plan to establish themselves in the EC window market with a single-band product while work continues on the dual-band product. Their work demonstrates commercial promise with the potential to enable projected U.S. energy savings up to 0.6 quads using EC windows in certain climate areas. 

Prior to ARPA-E support, the UT team demonstrated a prototype dual-band EC material capable of independently modulating visible and NIR light transmission. Early experiments combined indium tin oxide (ITO) nanocrystals within an Nb2O5 polyoxometalate (POM) cluster-derived matrix. The device could transition to a “cool” state via the application of modestly negative voltages, resulting in an approximate 65% decrease in NIR transmission while maintaining visible light transmission at approximately 96%, reducing solar heat gain but allowing daylighting. The project team goals were to develop devices based on these materials approaches that improve optical properties, switching speed, and durability. 

The project focused on scaling up fabrication of devices from 4cm2 to 25 cm2 using a lower cost, higher-throughput solution-processable technique (such as spray coating) to fabricate all three major components of the device: the electrochromic electrode, the counter electrode, and the electrolyte. The targets for these films included demonstrating +/-5% film uniformity, <15 minute switching time, 30% NIR transmission modulation while maintaining visual light transmission at >50%, and cycling the transitions at least 100 times. The team identified a new materials set that, combined with their work on the counter electrode and electrolyte, substantially improves performance. 

Simultaneous efforts at partner organization Heliotrope focused on translating the materials and devices to solution-processed manufacturing techniques. Heliotrope developed a process to reliably charge the devices at the outset via a built-in electrochemical reaction and were able to fabricate ~100cm2 devices with a blade coating process. 

For a detailed assessment of the UT Austin project and impact, please click here.

 

Contacts
ARPA-E Program Director: 
Dr. Eric Schiff
Project Contact: 
Delia Milliron
Partners
Heliotrope Technologies, Inc.
Lawrence Berkeley National Laboratory
Release Date: 
11/28/2012