Solar Windows and Solar Buildings: Understanding Building Integrated Photovoltaic Systems

Semi-transparent solar cells are a relatively new solar technology that allow light to partially pass through the panels while also delivering light-to-electricity conversion. The possibilities offered by semi-transparent solar panels include their integration as skylights and windows of buildings, referred to generally as building-integrated photovoltaic (BIPV). The semi-transparent characteristics of BIPV technology also has the potential to improve the efficiency (conversion rates) for the photovoltaics themselves.

Building integrated photovoltaic (BIPV) systems

Crystalline silicon-based modules are presently used for making building-integrated photovoltaics (BIPVs). But due to the opaque nature of silicon, other photovoltaic candidates with the potential to be made truly semi-transparent are quickly gaining attention.

These include kesterite-, amorphous silicon-, chalcopyrite-, cadmium telluride- (CdTe-), organic-, dye-sensitized-, and perovskite-based systems. Of these, amorphous silicon-systems have been extensively researched in the semi-transparent solar cell field, because of their low-temperature fabrication processes.

Lately, researchers are showing interest in alternative systems like perovskites as well as their inorganic counterparts, owing to the greater efficiency gains that these systems have exhibited. The main challenges with these alternative chemistries for photovoltaics are the instability or degradation of the materials over time, compared to the leading silicon-based solar cells.

In the context of BIPV, these systems present a unique set of challenges and opportunities. Let’s examine those.

Challenges of Transparent Solar Technologies

Two key challenges faced by researchers of transparent solar technologies are the limited efficiency of transparent solar panels and their tendency to change colors of the light that enters them.

Several experiments have been performed to repurpose conventional solar cells for use on glass. However, it is difficult to achieve the kind of transparency that is necessary for this type of use with conventional solar cells.

Transparent Luminescent Solar Concentrator

Professor Richard Lunt at Michigan State University decided to take a different approach than conventional solar cells. He made the concentrator using thin-film with organic materials that can be placed on any flat, clear surface. It is capable of harvesting energy from ultraviolet and near infrared wavelengths, which are invisible to the eye. The visible spectrum of light passes through the concentrator unhindered thus achieving a high level of transparency.

This was developed and named by researchers at Michigan State University in 2017. The concentrator looks like normal glass and is capable of providing clean electricity with minimal impact on the building aesthetics.

“Highly transparent solar cells represent the wave of the future for new solar applications,” said Richard Lunt, the associate professor who was heading the research team at MSU.

Image Photo Credit: Michigan State University (

Thin-Film PV Technology

Thin-film PV technology is being used to develop BIPV photovoltaic solar glass to harness electricity production and visible light transmission. The thin-films used for making BIPV systems can be transparent or opaque. For this reason, thin-film BIPV systems are increasingly being sought for a wide range of purposes, including:

  • Solar greenhouses
  • Facades
  • Canopies
  • Skylights
  • Curtain walls
  • Electric vehicles
  • Electronic displays

Thin-film offers the following advantages compared to traditional silicon modules:

Efficiency at poor angles

Thin-film solar remains efficient even when it isn’t optimally positioned to receive direct sunlight. This allows thin-film solar to be used in unconventional ways, for instance, vertically on buildings.

Performance in low lighting

Thin-film solar needs as little as 10% sunlight to operate. This translates into increased annual electricity production as well as a more consistent energy yield.

Comparable costs

The installation costs for thin-film solar cells are nearly the same as their traditional alternatives.

Robust panels

Thin-film solar panels are rigid and tough. They use laminated glass to increase their overall functionality, which is highly resistant to weather damage.

Increased heat resistance

Thin-film solar has higher tolerance for heat. You don’t need to ventilate them to achieve optimal efficiency.

Wavelength-Selective vs Non-Wavelength-Selective Semi-Transparent Photovoltaic Technologies

Semi-transparent photovoltaic technologies can be grouped into wavelength-selective and non-wavelength-selective variants depending on how they absorb sunlight.

Non-wavelength-selective systems generate electricity through the absorption of a broad spectrum of solar rays, including the visible spectrum of photons. At the same time, they’re also able to transmit light through the segmented placement of opaque solar cells. In some cases, the transmission of visible light is achieved via the use of thin photoactive materials. Non-wavelength-selective systems include amorphous silicon-, chalcopyrite-, kesterite- and cadmium telluride-based systems.

Wavelength-selective transparent & semi-transparent solar panels use photoactive materials that harvest near-infrared (NIR) or ultraviolet (UV) light preferentially while emitting the visible spectrum of light. These solar cells convert the NIR and UV light into electricity while allowing the visible spectrum of light through, which can be used for illuminating any space, including greenhouses with plants requiring certain light wavelengths for growth.

The Future of Transparent and Semi-Transparent Solar

Transparent and semi-transparent solar panels are a new and exciting form of solar technology that delivers solar energy from a material that resembles clear glass. This type of solar is a work in progress. Research is underway to further refine these technologies and increase their efficiency rating.

When transparent solar glass is placed on conventional glass, the two become indistinguishable. The widespread adoption of these systems is being considered in windows and ceilings of buildings as well as automobiles and electronic device displays.

If you would like to discuss the integration of semi-transparent solar panels to your next innovative building project, get in touch with Dandelion Renewables, the solar contractors for numerous Canadian communities, farms & businesses. Contact Dandelion Renewables today.