Building-integrated photovoltaics is steadily entering the market. It allows for solar cells to be an integrated part of the building itself, contrary to installing the photovoltaic modules onto the finished building. Unfortunately, several challenges such as the creation of thermal bridges and moisture intrusion hinder the rapid development of building-integrated photovoltaics into a mainstream mass product. Wireless power transfer systems could solve some of these challenges and contribute to an accelerated use of building-integrated photovoltaic solar cells.
A building-integrated solar module, whether it takes the form of a window, or a roof shingle, is located at the exterior of the building envelope. It contributes to realizing the physical barrier between the unconditioned outside and the conditioned inside environment. It protects the inside climate of the building against unwanted water, heat, light, noise or air. Unfortunately, a prerequisite for any BIPV system is the wired electrical connectivity from the solar panel to the inside of the building. This implies two consequences.
- First, the electric cables are breaking the thermal envelope of the building by the creation of thermal bridges. This reduces the building insulation and creates unwanted heat loss or gain. As an example, consider the figure above which shows a representation of BIPV roof shingles. The separate shingles are connected with each other (usually in different strings) by electric wires which have to be connected to the inverter in the interior of the building. These connections breach the thermal envelope of the building. Thermal bridges are created and impact the energy requirements to heat or cool the building. This can result in thermal discomfort. Notice that thermal bridges are not restricted to roof shingles, but apply to all BIPV applications, for example, the frame of a window covered with semitransparent solar cells will have to be pierced for the electric connections.
- Second, the perforation of the electric cables through the insulation potentially causes condensation and water penetration. This results in moisture intrusion, as well for the building as for the BIPV installation, leading to a faster degradation of the PV cells, and thus a shorter lifetime of the BIPV system.
By installing a WPT system, the produced energy from the solar modules can be transferred wirelessly over the building envelope, without the creation of any physical piercings. In this way, a nearly perfect thermal, air, and water tightness can be created, resulting in a better conditioned indoor environment and a longer lifetime of the total system.
Moreover, BIPV systems with WPT could allow for an easy “plug-and-play” mechanism for installation. Nowadays, discussions arise over who is responsible for the BIPV construction elements: the construction worker or the electrician. In practice, construction workers are now educated to correctly handle the different wiring schemes of WPT. A plug-and-play system would facilitate the set-up of the system.
Aside from the plug-and-play and improved insulation, WPT would also contribute to solving the problem of reduced efficiency caused by, a.o., partial shading
The project WPT4BIPV develops a BIPV plug-and-play module that wirelessly transports the energy produced from the solar cells over the building envelope.
Source: Ben Minnaert, Simon Ravyts, Johan Driesen and Nobby Stevens. Challenges for Wireless Power Transfer in Building-Integrated Photovoltaics. IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (Wow). Montréal, QC, Canada, 3-7 June 2018, pp. 1-5.