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Electrochromic materials & devices for buildings

Kapil Menghrani, Co-founder, Econaur/ Director, Prakriti Sustainable Building Services Private Limited

An electrochromic device (ECD) controls optical properties such as optical transmission, absorption, reflectance and/or emittance in a continual but reversible manner on application of voltage (electrochromism). This property enables an ECD to be used for applications like smart glass, electrochromic mirrors, and electrochromic display devices.

Electrochromic (sometimes called electrochromatic) devices are one kind of electrochromic cells. The basic structure of ECD consists of two EC layers separated by an electrolytic layer. The ECD works on an external voltage, for which the conducting electrodes are used on the either side of both EC layers. Electrochromic devices can be categorized in two types depending upon the kind of electrolyte used viz. Laminated ECD are the one in which liquid gel is used while in solid electrolyte EC devices solid inorganic or organic material is used.

The basic structure of an electrochromic device embodies five superimposed layers on one substrate or positioned between two substrates in a laminated configuration. In this structure there are three principally different kinds of layered materials in the ECD: The EC layer and ion-storage layer conduct ions and electrons and belong to the class of mixed conductors. The electrolyte is a pure ion conductor and separates the two EC layers. The transparent conductors are pure electron conductors. Optical absorption occurs when electrons move into the EC layers from the transparent conductors along with charge balancing ions entering from the electrolyte.

Electrochromic windows, also known as smart windows, are a new technological arrangement for achieving energy efficiency in buildings, with variable transmittance of light and solar energy. These ‘‘smart windows’’ can automatically control the amount of light and solar energy passing through the windows which subsequently improves indoor comfort; for example, electrochromic glass provides better glare resistance than fritted glass in most direct sunlight applications.[4] The efficiency of these windows will vary depending on their placement, size, and local climate conditions since these factors influence the amount of sunlight that comes in contact with these windows.[5] Electrochromic windows generally achieve their control over light and heat through their layered design. These layers within the window allow for tinting of the glass in response to increases in incoming sunlight as well as protection against UV radiation. An example of this layered design is the electrochromic glass developed by Gesimat, where multiple layers of material (i.e. tungsten oxide, polyvinyl butyral, and Prussian Blue) are sandwiched by two dual layers of glass and fluorine-doped tin oxide-coated glass.[6] Together, the tungsten oxide and Prussian Blue layers form complementary electrochromic layers; essentially, this means they form the positive and negative ends of a battery using the incoming solar energy.[7] The polyvinyl butyral (PVB) forms the central layer in this configuration, and it serves as a polymer electrolyte (this allows for the flow of ions which, in turn, generates a current).

PROVEN ENERGY BENEFITS

Buildings and construction together account for 36 percent of global final energy use and 39 percent of energy-related carbon dioxide (CO2) emissions when upstream power generation is included, according to UN Environment and the International Energy Agency in their Global Status Report 2017.

Due to the ability of Electrochromic window glass to adapt to solar heat and light depending on the seasons and needs, it brings a level of efficiency to a project that adds up to significant long-term savings over the course of a building’s life cycle.

In addition to reducing the up-front material costs of shading systems, Electrochromic glass can also help reduce building operating costs. It reduces overall energy loads by an average of 20 percent and peak energy demand by up to 26 percent over a building’s life cycle.

How Electrochromic Glass Works

Electrochromic glass’s coating consists of five layers of ceramic material. Applying a low voltage of electricity darkens the coating as lithium ions and electrons transfer from one electrochromic layer to another electrochromic layer.

Reversing the voltage polarity causes the ions and electrons to return to their original layer, causing the glass to return to its clear state.

This solid-state reaction is controlled through a very low voltage (less than 5V DC) power supply. A darkened state enables Glass to absorb and reradiate away the sun’s unwanted heat and glare. A clear state allows you to maximize daylight and solar energy.

STATIC GLASS VS. ELECTROCHROMIC GLASS

Energy lost through conventional windows accounts for approximately 30 percent of heating and cooling energy, according to the U.S. Department of Energy. Not with Electrochromic Glass. By adapting to the external climatic conditions, Electrochromic glass minimizes energy use by reducing heating loads in winter, air conditioning in summer and electrical lighting all year long.

Conventional windows also cause glare and heat gain and require blinds and shades to offset the negative effects of the sun. Electrochromic glass eliminates the need for additional solar shading systems, hence the use of additional energy and resources for their manufacturing, transportation and installation.

Also, if shades and blinds are used, not only does one have to clean the window but also clean and maintain the blinds. With Electrochromic glass, there are no additional maintenance requirements besides keeping the glass clean, thus limiting the environmental impact of the building.

The market for electrochromic glass is expected to have a strong trajectory. According to third-party researcher n-tech, by 2020 the electrochromic glass market should reach $3 billion in revenue and will keep growing to over $4 billion by 2023.

And, the greatest potential for growth in the electrochromic industry is in smart windows, which should surge from a currently $40 million industry to a $500 million industry by 2019.

Greater Adoption of Electrochromic Glass

The adoption of electrochromic glass has accelerated in recent years. And, we believe this acceleration will increase in the New Year as more installations serve as proof points for architects and building designers. It’s common for architects to be risk-averse to new building technologies – they’ve been utilizing traditional glass and glazing for many, many years. And, it can be difficult to break old design habits. However, we’re seeing that the growing number of reference point projects are helping to ease concerns around adopting electrochromic glass.

Electrochromic glass is present in a wide variety of buildings, but is mainly concentrated in higher education and healthcare facilities as well as commercial office space. Electrochromic glass will continue to expand in these sectors. However, we believe the electrochromic glass industry will become more diverse and expand further into the retail market, including hospitality venues and restaurants. There is also significant potential for electrochromic glass in transportation-related structures such as weigh stations and airports, and we predict that dynamic glass will have the potential to create a positive impact in overseas markets where sun glare and extreme heat are pressing issues.

About author

The author is the co-founder of Econaur and Director – Prakriti Sustainable Building Services Private Limited. He is an experienced consultant providing sustainability strategies for the Construction Industry. He specializes  in AutoCAD, Green Buildings, and Market Research.

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