The demand for energy in cities will continue to rise, especially with 70% of the world population expected to become urbanised by 2050. This can produce significant impact to the environment and climate. To mitigate this issue, smart and energy efficient buildings with autonomous energy management and green architectural design are now becoming more common.
I believe there should also be more discussions on how to make buildings in cities to become a major source of renewable energy generation. In particular, through the deployment of the so-called building integrated photovoltaics (BiPV).
Building integrated photovoltaics (BIPV) are solar PV devices that are, as the name suggests, integrated into buildings. These devices replace traditional building materials with a power generating hardware. The hardware also provides additional return on investment (ROI) to property owners.
BiPV can turn buildings into power plants that generate clean and free energy from the sun. Particularly, in large cities where, due to land scarcity, there are usually little space left for the installation of conventional solar PV. Tall buildings with large vertical surface area, on the contrary, are ideal for BiPV.
Transparent solar glasses
A notable example of BiPV is transparent solar glasses. These solar glasses are made from novel thin film materials such as amorphous Si, dye-sensitize and more recently perovskite. These glasses function both as windows and power generating devices.
Transparent solar glasses can turn buildings into a source of green energy generation, especially in large cities. Due to land scarcity, there are usually little space left in large cities for the installation of conventional solar PV. Tall building with large vertical surface area, on the other hand, are ideal for solar glasses.
As a replacement to windows, transparent solar glasses are usually installed vertically. As a result, these devices generally do not receive the optimum amount of sunlight. The sun also does not always shine on the same face of the building. Additionally, obstructions/shading from other nearby high rises/structures will also affect the amount of power that can be generated from solar glasses.
Therefore, transparent solar glasses are currently considered to be an expensive and risky investment. In addition, technological complexity, building regulations and smaller scale of manufacturing also further increase the cost of these devices.
Crystalline Si based BiPV
On the other hand, there is a low cost and emerging type of BiPV that is based primarily on crystalline Si solar technology. The main power generating components of this technology are made from crystalline Si solar cells. These solar cells are the same as the ones used for conventional Si solar modules. They are mass produced, and can be found in large scale PV farms and residential roof tops. Hence, they are much cheaper in price, more stable and enjoy a higher power conversion efficiency than transparent solar glasses.
Furthermore, the colour of crystalline Si based BiPV can also be changed so that it is easier to be “camouflaged” into buildings. Instead of the typical dark-blue, the colour can be tuned via glass tinting, metal nanoparticles, or thickness changes in the anti-reflection layers. However, this may affect the efficiency and power output of the device.
A major limitation of crystalline Si based BiPV compared to solar glasses, is its non-transparency. As a result, Si based BiPV devices are more suitable to be integrated into non-viewing parts of buildings. These include glass façade, roof top (e.g. Tesla’s solar roof shingles) and semi-transparent glazing/windows.
Another trade-off for low cost in crystalline Si based BiPV is the aesthetics of the device. Compared to the clean and clear looking transparent solar glasses, the metal contacts (wiring) and empty spaces between cells are hard to be concealed. Nonetheless, this can be improved with cleaver designs such as shingling to pack cells close together to eliminate empty spaces, black Si technology or light-capturing ribbon/wiring.
With growing concerns on climate change, continuous drop in the price of solar PV, and a projected market CAGR>15%, BiPV could be the next technological focus of the solar PV industry. I also believe that, in the next few years, there will be more attentions on how to integrate the cheaper but more efficient crystalline Si solar technology into, not only building, but also other surfaces such as vehicles and roads. Hopefully, this will help to reduce the climate impact from energy usage, and to create cities that are greener and more sustainable.