Let’s start with the different types of solar panels currently on the market (mono-, polycrystalline and thin film) and list their benefits and downsides.
The term “solar panels” will be used to describe photovoltaic solar panels (the type that generates electricity), not solar thermal collectors.
Almost 90% of the World’s photovoltaics today are based on some variation of silicon. The silicon used in PV takes many forms. The main difference is the purity of the silicon.
But what does silicon purity really mean? The more perfectly aligned the silicon molecules are, the better the solar cell will be at converting solar energy (sunlight) into electricity.
The efficiency of solar panels goes hand in hand with purity, but the processes used to enhance the purity of silicon are expensive. Efficiency should not be your only concern, as cost- and space-efficiency are the determining factors for most people.
Crystalline silicon forms the basis of mono- and polycrystalline silicon solar cells:
Solar cells made of monocrystalline silicon (mono-Si), also called single-crystalline silicon (single-crystal-Si), are quite easily recognizable by an external even coloring and uniform look, indicating high-purity silicon.
Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. To optimize performance and lower costs of a single monocrystalline solar cell, four sides are cut out of the cylindrical ingots to make silicon wafers, which is what gives monocrystalline solar panels their characteristic look.
A good way to separate mono- and polycrystalline solar panels is that polycrystalline solar cells look perfectly rectangular with no rounded edges.
- Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. The efficiency rates of monocrystalline solar panels are typically 15-20%.
- Monocrystalline silicon solar panels are space-efficient. Since these solar panels yield the highest power outputs, they also require the least amount of space compared to any other types. Monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels.
- Monocrystalline solar panels live the longest.
- Tend to perform better than similarly rated polycrystalline solar panels at low-light conditions.
- Monocrystalline solar panels are the most expensive.
- The Czochralski process is used to produce monocrystalline silicon. It results in large cylindrical ingots. Four sides are cut out of the ingots to make silicon wafers. A significant amount of the original silicon ends up as waste.
Unlike monocrystalline-based solar panels, polycrystalline solar panels do not require the Czochralski process. Raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers.
- The process used to make polycrystalline silicon is simpler and cost less. The amount of waste silicon is less compared to monocrystalline
- The efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels.
- Lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon. However, this does not mean every monocrystalline solar panel perform better than those based on polycrystalline silicon.
- Monocrystalline and thin-film solar panels tend to be more aesthetically pleasing since they have a more uniform look compared to the speckled blue color of polycrystalline silicon.
Depositing one or several thin layers of photovoltaic material onto a substrate is the basic gist of how thin-film solar cells are manufactured. They are also known as thin-film photovoltaic cells (TFPV). The different types of thin-film solar cells can be categorized by which photovoltaic material is deposited onto the substrate:
- Amorphous silicon (a-Si)
- Cadmium telluride (CdTe)
- Copper indium gallium selenide (CIS/CIGS)
- Organic photovoltaic cells (OPC)
Depending on the technology, thin-film module prototypes have reached efficiencies between 7–13% and production modules operate at about 9%. Future module efficiencies are expected to climb close to the about 10–16%.
- Mass-production is simple. This makes them and potentially cheaper to manufacture than crystalline-based solar cells.
- Their homogeneous appearance makes them look more appealing.
- Can be made flexible, which opens up many new potential applications.
- High temperatures and shading have less impact on solar panel performance.
- In situations where space is not an issue, thin-film solar panels can make sense.
- Thin-film solar panels are in general not very useful in most residential situations. They are cheap, but they also require a lot of space. Monocrystalline solar panels can produce up to four times the amount of electricity as thin-film solar panels for the same amount of space.
- Low space-efficiency also means that the costs of PV-equipment (e.g. support structures and cables) will increase.
- Thin-film solar panels tend to degrade faster than mono- and polycrystalline solar panels, which is why they typically come with a shorter warranty.
Rather than an individual type of solar cell technology, building-integrated photovoltaics have several subtypes (or different methods of integration), which can be based on both crystalline-based and thin-film solar cells.
Some homeowners are turned off by how solar panels affect the appearances of their homes. Building-integrated photovoltaics – basically solar panels incorporated into the construction of new buildings – can eliminate the negative visual impact of traditional solar panels; improve appearance and boost resale value.
The installed capacity of building-integrated photovoltaics is expected to boom over the next couple of years.
There are many different categories of BIPV today. Here are the most common ones:
- Thin-film solar panels integrated with a flexible polymer roofing membrane.
- Flexible thin-film solar panels integrated into roof shingles/tiles.
- Thin-film or crystalline-based solar panels mounted on the façade of a building.
- Semi-transparent solar panels that replace windows and skylights.
Generally, BIPV systems are less efficient and more expensive compared to traditional solar panels. However, if you want to seamlessly integrate solar panels with your home, and have the extra money that is required, building-integrated photovoltaics can be a great solution.