Glass on Glass PV Modules: (All You Need to Know)
There are two main structural designs for PV modules: glass backsheet and glass-glass.
Although the glass-glass PV technology is older, it was faced out due to weight issues but has recently come back due to its long-term reliability.
Traditional solar panels with synthetic backsheets are vulnerable to damage from outdoor conditions, including moisture, dirt, and extreme temperatures, so their power output declines over time.
A glass on glass (glass-glass) PV module, on the other hand, is properly cushioned from all these outdoor elements by double layers of glass, so it maintains its optimal performance for a very long time.
So, are you interested in making the most of every square foot of roof surface with solar panels for an extended period?
Then you might want to read this article about glass-glass PV modules that will help you achieve this goal.
What are Glass-Glass PV Modules?
Glass-glass PV modules, also known as glass on glass, double glass, or dual glass solar panels are modules with a glass layer on both the front and the backside.
Glass on glass solar panels eliminate the need for a laminated backsheet and the problems it comes with.
After prolonged use of solar panels with laminated backsheets, degradation eventually occurs and the backsheet material delaminates or discolors, compromising the modules' integrity.
The same can’t be said for dual glass solar panels since the double layers of glass are robust and stable to withstand environmental and general outdoor pollutants, so their degradation is drastically reduced.
The following characteristics of glass make it an ideal structural material for solar panels:
High mechanical strength
This ensures that the solar cells are well guarded against mechanical stresses and pressures.
Although the glass itself may break when handled poorly during transportation or installation, its mechanical-structural properties are still better than standard solar panels.
High heat resistance
Solar panels made with glass only can withstand very high temperatures, so even in scorching conditions, they maintain optimum output.
No chemical elements in the environment can damage the solar cells sandwiched between the glass layers. As a result, glass-glass modules are very stable and reliable when it comes to solar power production.
The glass allows light to pass through it, so if transparent solar panels are needed, only the distance between the solar cells needs to be altered during production.
Several outdoor structures, such as pergolas and car parks, can be fitted with partially transparent solar panels for illumination as well as power production.
Poor conductor of electricity
Due to glass' low conductivity, electricity produced by solar cells can’t be lost through the glass. This means that there's no risk of electrical shock when there’re some minor faults with the array.
Impenetrable and damp proof
Glass is impervious to environmental elements such as oxygen and moisture. Consequently, solar cells can’t be harmed by induced reactions caused by the infiltration of these elements.
Glass Glass vs. Glass-Foil PV Modules
The following are the main differences between glass-glass PV modules and laminated (glass-foil) PV modules:
|Factors||Glass – Glass PV Modules||Laminated (Glass-Foil) PV Modules|
|Stability and robustness||Extremely stable and robust due to the extra support provided by the glass layer on the back||Can't withstand extreme pressure and physical stressors|
|Degradation rate||0.45% per year||0.7% per year|
|Micro-cracks formation||Since the material used to cover solar panels is the same on the front and back, solar cells are unaffected. As a result, microcracks are less likely to form||When under pressure, foil expands more than glass putting pressure on solar cells that consequently lead to the formation of microcracks|
|Lifespan||20-25 years of standard power production||25-30 years of standard power production|
|Durability||The added protection makes these solar panels highly durable||Relatively low durability as the back foil is unlikely to stand outdoor stresses|
|Guaranteed performance||From high as 87% after 25-30 years||80% after 20-25 years|
|Suitability for use on pergolas/ patios||The transparency of glass-glass solar panels allows for use on solar pergolas and patios||The back foil doesn't allow light to pass through making these modules unsuitable for use on pergolas and patios|
|CO2 emissions||420Kg of CO2 per kW||480Kg of CO2 per kW|
Characteristics of Glass-Glass PV Modules
The cost of PV glass per square meter currently averages at $6. Considering that double-glass PV modules use glass on both sides, the cost of glass alone doubles if compared to glass-foil solar panels.
A benefit of most glass-glass solar panels is that they are frameless, which reduces their price.
The weight of glass-glass PV modules with 2.5mm glass on each side is around 50 pounds (23 kg).
Standard glass-foil solar panels weigh around 40 pounds (18 kg). These weights suggest that glass-on-glass PV modules are around 20% heavier than glass-foil solar panels.
The back layer of glass-glass solar panels is transparent and allows the light that enters the front of the module and isn’t absorbed by the solar cells to pass through.
This increases cell to module losses reducing the power generated considering the amount of light that reaches the solar cells as the only determining factor to power generation.
Glass-glass solar panels utilize polyolefin encapsulants since EVA encapsulants release free radicals that can be trapped between the glass layers.
As free radicals can reduce module efficiency, polyolefin encapsulants are used to eliminate this problem.
Number of solar cells
The number of solar cells used in a glass-glass solar panel can vary depending on the targeted capacity and size. The common number of solar cells used on dual glass solar panels are 48, 60, and 72.
The number of solar cells in a module also determines how they’re spaced out to alter the level of light transmission.
Long term stability
Glass on glass PV modules can withstand severe weather, and outdoor elements hence are very stable over the long term.
The aging of these panels is also significantly lower than that of solar panels with a foil backsheet, making them more reliable in the long run.
The warranty of double glass modules is higher than the average warranty for standard solar panels.
Since the output level of glass-glass solar panels stays over 85% even after 30 years of operation, this should be the average output power guarantee period for these solar panels.
Glass-glass solar panels have impressively low CO2 emissions. Generally, their CO2 emission is around 7.5-12% lower than that of standard modules with a laminated backsheet.
By using inert glass and frameless construction, CO2 emitting processes are reduced in glass on glass solar panels.
Many solar companies are now producing glass-glass solar panels, and it's best to purchase directly from them for the best deals. Here are some examples to get you started:
- JA solar
- Onyx Solar
- Luxor solar
Applications of Double Glass PV Modules
Thanks to their stellar characteristics, glass-glass solar panels can be used for a wide array of applications.
Here are the most common areas where glass on glass PV modules are used:
- Agriculture (greenhouses) and fishing due to excellent resistance to high humidity
- High salt fog areas due to their excellent corrosion resistance
- Deserts because they have great wear resistance, high temperature, and UV resistance
- For outdoor structures such as car parking lots, pergolas, and patios as the light transmission and shading levels of glass on glass solar panels can be altered during solar cells assembly.
Pros of Glass-Glass Solar Panels
Exceptionally long lasting
Glass-glass PV modules are built to produce power for generations. These solar panels are very robust and will withstand prolonged exposure to harsh outdoor elements such as snow and strong winds.
While glass-glass solar panels may only last a few years more than glass-foil solar panels, the additional period might mean a lot for you as a solar consumer.
Reduced potential induced degradation
Glass and glass PV modules have no frame so the chances of potential induced degradation are reduced.
This is a common problem with traditional solar panels where the current eats away the frame degrading the power output.
Glass on glass modules looks better when installed on a roof since the glass back matches most roof tiles.
The same can't be said for traditional laminated solar panels, a reason why many solar consumers are preferring glass-glass modules nowadays.
A reliable way to reduce electricity bills
For anyone trying to reduce power bills, double glass solar panels are the perfect solution.
These solar panels produce free solar power more efficiently than other types of modules reducing the amount of money you spend on electricity from the grid.
Cons of Glass-Glass PV Modules
Special clamps and racks are needed for glass-glass PV modules. To ensure that glass on glass PV modules is properly supported without damage, careful calculations must be performed to determine the best mounting position.
Lack of expertise is the other major constraint. Installation of a double-glass solar panel array is a big challenge for many solar installers and technicians who are used to the traditional glass-foil solar panels.
Heavy modules are the tradeoff for double glass stellar characteristics. To install these solar panels, good structural support must be provided.
Consequently, very few applications are suitable for glass-glass panels. In fact, only new installations that include all mounting and support structure needs are most suitable for using double-glass PV modules.
High installation costs
The installation process for double glass solar panels is pretty expensive due to the complex mounting structures and additional support requirements.
Therefore, even if there’s no significant difference in market prices between glass-glass modules and traditional ones, installation may be expensive.
Frequently Asked Questions
Are glass-glass PV modules more effective when mounted on a shiny surface?
You can expect to get 2 to 3% better solar power production when you install glass on glass solar panels on a shiny surface.
This is because cell to module losses are reduced as light passing the solar cells can be reflected by the surface beneath the module.
So despite the installation constraints that come with installing dual glass solar modules, you can get really good output if you install them on a shiny surface.
What glass is used for double-glass PV modules?
Tempered glass, also known as strengthened glass, is the preferred glass type for double-glass solar panels. Compared to normal glass, toughened glass is 6 times stronger.
Tempered glass can be produced by either thermal or chemical treatment, making the final product more expensive than standard glass.
Even so, tempered glass is still a more affordable option than laminated glass. Fortunately, solar panel manufacturers are working on bringing tempered glass costs down.
How can the ROI of glass-glass PV modules be improved?
One way to improve the ROI of glass on glass solar panels is to integrate them with PERC technology. This technology adds a dielectric passivation layer on the rear of the solar cells resulting in high energy conversion efficiency.
Glass on glass solar panels can also be made with bifacial solar cells to increase the output.
Solar panels that track the sun on both sides could produce 35% more energy than single-sided modules. Lastly, high-efficiency solar cells need to be designed to leverage the full potential of glass on glass solar panels.
Glass-glass PV modules have a rear and front layer of heat strengthened glass to protect the solar cells.
As a result of this structural modification, these modules are resistant to microcracks, snail trails, and any other issue associated with glass-foil solar panels.
Most glass-on-glass modules have a frameless design and hence don't suffer from potential induced degradation. There is no doubt that glass-glass solar panels are the most reliable and stable solar panels you can buy today.
Glass-glass PV modules have some drawbacks, such as higher costs, weight problems, and complex installation, but all of these are outweighed by the benefits these PV modules have in the long run.
From a solar consumer standpoint, the main reason why it's totally worth it to invest in these modules is the reduced degradation rate. It means you'll get optimum power production from the solar panels for an extended period.