Electrochromic Glass

In a Nutshell

Electrochromic (EC) smart glass changes its visible light transmittance (VLT) and solar heat gain (SHGC) when we activate it with a low-voltage electrical signal. This tints the glass, limiting visual glare and HVAC costs, yet preserving exterior views.

After changing tint, the glass needs no further electrical current, making EC technology extremely low-power. (Typical figures range from 0.1 to 1 W/sq.m).

The gradual change in tint (30 seconds to 30 mins) is ideal for building facades, since it avoids distracting city centre traffic and wildlife, protecting biodiversity.

Finally, since the driving voltage is typically 3-5Vdc, electrochromic glass can be powered sustainably by photovoltaics located directly in the window frame.

This reduces cable routing costs during installation and minimises the risk of electrical fire during the lifetime of the building.

How does Electrochromic Glass work?

As you can see from the diagram below, an electrochromic glass panel comprises a stack of layers, somewhat resembling a battery.

Electrochromic glass layers; Image attribution: Keyur.tithal, CC BY-SA 3.0, via Wikimedia Commons

This stack is normally a few thousandths of a millimetre thick and is deposited onto the glass during manufacture. The layers comprise:

• transparent conductive electrodes normally of indium tin oxide (ITO)
• the ion storage layer
• the electrolyte
• the tinting electrochromic (EC) layer

When you apply a direct (DC) voltage to the structure, charged particles (normally lithium ions) migrate from the ion storage layer, through the electrolyte to the electrochromic layer (often tungsten oxide, which is transparent in its inactive state).

This causes the electrochromic layer to undergo electrochemical reduction-oxidation (‘redox’) which results in absorption of light.

This causes the change in tint.

When you reverse the voltage, the lithium ions migrate back from the electrochromic (EC) layer, through the electrolyte, and back to the ion storage layer, returning the glass to its transparent state.

If you are looking for a deeper dive, check out our article: What Is Electrochromism.

Why does Electrochromic Glass tint?

When we apply a voltage across the electrochromic stack, lithium ions ‘insert themselves’ into the electrochromic (EC) layer.

The inserted lithium ions reduce the ‘band gap’ of tungsten oxide to roughly 2 electron-Volts (eV).

This means that electrons can absorb photons having at least that energy, which energises the electrons into a higher energy state. The photon is absorbed, not transmitted, and the photon energy is passed to the electron.

Since visible light photons have 1.6 eV to 3.2 eV, the EC layer absorbs visible light and the EC glass appears tinted.

Why is Low Voltage Important?

If a product operates below 50 Vac / 60Vdc it is considered a ‘Safety Extra-Low Voltage’ (SELV) by IEC 61140.

If the system operates below 12 Vac / 30Vdc, as does EC glass, it can be safely used even in wet areas, such as bathrooms or swimming pools, without requiring protection against direct human contact.

The lower the voltage (and current), the lower the risk to safety and the cheaper the cables.

For a large electrochromic glass installation, you can see how smaller cable widths reduce installation costs and operational maintenance costs due to lower current use.

Electrochromic Glass Applications

Architects and engineers who specify electrochromic glass should bear in mind that wiring regulations differ in each country.

Vehicle OEMs must bear in mind the cost and weight of cabling. Also important is the voltage transformation needed from 48Vdc (aircraft) or 24Vdc (automotive) to the operating voltage of the glass (typically 3Vdc).

Consumer appliance OEMs must bear in mind the carbon footprint when mass manufacturing devices based on electrochromic glass.

Environmental Impact

One obvious benefit is a substantial reduction in air conditioning costs, thanks to the infrared (i.e. solar heat) rejection by electrochromic smart glass when installed in building facades (and vehicles).

The fact that the behaviour can be dynamically controlled allows owners, managers and users to tune the electrochromic smart glass facade to their needs, which can change over the course of a day and of course seasonally.

Switching Time

It is worth repeating that electrochromic smart glass takes anything from 30 seconds to 30 minutes to fully change state, whereas SPD and PDLC smart glass take less than 1 second.

However, in architectural facades, a gradual change in tint can be an advantage since it allows our eyes to adjust. Also, buildings can avoid step changes which may distract people, traffic or wildlife.

Electrochromic Glass Manufacturers

Please note that a Google search for ‘electrochromic glass’ returns manufacturers who are not making electrochromic smart glass.

This is caused, in part, by recent US legislation that equates ‘electrochromic glass’ with ‘any electrically-operated smart glass’, which is simply not correct.

If you are looking specifically for electrochromic glass manufacturers, distributors or installers, look no further than our parameterised Search.

This is our own database of vendor-neutral curated data, sourced from supplier datasheets by Smartglass World engineers. No AI-generated results, so no hallucination.

If you press the ‘Show Results’ button, you will find relevant companies and products. You can contact them directly, or post a request on our Marketplace.

References

[1] “Smart Switchable Glazings for the New Millennium” – Carl M. Lampert, Star Science

[2] “Colour and the Optical Properties of Materials”, Richard Tilley

[3] https://www.commercialwindows.org/electrochromic.php