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Solar technologies have been increasing in popularity for many years. Whilst the primitive forms didn’t offer much in the way of efficiency, they did open a new renewable energy source. Since then, solar cells have constantly been advancing and are now one of the most widely implemented renewable energy technologies around the world.
The Solar Cell
The solar cell, also known as a photovoltaic cell, is at the core of every solar module. The solar cell is directly responsible for the direct conversion of light into electrical energy. Solar cells contain a semiconducting material that can specifically absorb sunlight, which enables an efficient production of electricity.
Solar cells generally have two layers of semiconducting materials with a junction at the interface. To create a junction, the solar cell has one n-type semiconducting material (one with charge carrying electrons) and a p-type material (a material with holes). When light hits the solar cell, a portion of the light is absorbed within the cell and the energy of the absorbed light is transferred to the semiconducting material. The charge carriers then become excited, and the junction sustains the internal field that arises from the splitting of the photo-excited carriers in opposite directions.
The splitting of the charge carriers generates a current and voltage across the junction. The internal electric field enables the movement of electrons in a single direction and the current is then drawn out of the cell using metal contacts.
Solar cells also come in many forms, from silicon-based solar cells, graphene solar cells, organic-polymer solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells and thin-film solar cells.
Traditional Solar Panels
Solar panels can only absorb light from one side of the panel. A large number of photovoltaic cells are combined together to create a solar module. These modules are then placed together in a periodic array to create a solar panel. The more photovoltaic cells present on a solar panel, the more sunlight that can be absorbed, and therefore the greater the amount of electricity that can be produced.
Traditional solar cells are limited in their efficiency, and this is a result of the junction. Estimates state that conventional solar panels will only reach up to 33-34%, but many current commercially available solar panels rarely meet this, even now. Solar panels are getting cheaper to make but their limited efficiency is a problem.
Additionally, solar panels can only capture sunlight from one side of the panel. This means that the efficiency is also determined by the positioning of the solar panel, and the positioning affects how much sunlight is absorbed throughout the day.
Bifacial Solar Modules
As the name suggests, these solar panels have two faces, or rather, they can absorb light from both sides of the panel. A lot of potential energy transfer is lost in traditional solar cells when the light hits the back of a solar panel. Most bifacial solar panels use monocrystalline cells, whereas traditional cells use polycrystalline materials. The monocrystalline materials, alongside the clear light pathway on both sides of the panel, enable the light to be absorbed from either side of the cell, and it is thought that, that the overall efficiency of these cells can be up to 30% greater in commercial applications.
Although, the exact amount is variable depending on the surface that they are installed on. The front side of the solar panel still absorbs most of the solar light, but the back side of the solar panel can absorb between 5-90% of the light absorbed by the front of the solar panel.
Traditional solar panels use an opaque backsheet. By comparison, bifacial solar panels either have a clear/reflective backsheet or have dual panes of glass. Most of these solar panels are frameless so any issues with potential-induced degradation (PID) are reduced. To efficiently convert light into electricity from both sides, bifacial solar cells have selective-area metallization schemes that enable light to pass between the metallized areas, rather than the conventional thick metal collectors as seen with monofacial solar panels.
Bifacial solar modules can be installed both vertically and horizontally. In the hortizontal plane, any light reflected off nearby surfaces can be picked up through the back of the solar panel. In the vertical plane, the cell can be tilted at an angle to pick up the maximum amount of solar rays possible from the east in the morning, and from the west in the evening.
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