Glass has been around for about 5000 years and will probably remain till the doomsday. It is used widely in the industry in its various forms and the household as beautiful vessels, tabletops and transparent walls and windows. In most cases the desirable attribute is its aesthetic value, but in industry, it is transparency, electrical insulation and ability to seal out environmental agents, in addition its non-reaction tendency with most chemicals.
One of the applications is as the transparent insulation (environmental and electrical) on the front side solar panels. This protects the panel and cells against physical stresses, and ingress of dust, moisture etc, while allowing in sunlight. In this application diamond or transparent aluminum may be superior to glass but are beaten badly in price comparison. The backside is generally protected by an opaque sheet called the backsheet. The whole structure is held in place with an aluminum framework which provides strength against accidents and permits installation.
Recently, a trend has started building up to install glass covers on both sides. Solar panels equipped with glass protection on both sides variously called as double glass solar panels, glass on glass solar panels, glass-glass solar panels. They also sometimes called dual glass solar panels. Benefits of replacing the opaque backsheet with glass outweigh its disadvantage of being costlier and heavier than plastic backing.
Bifacial Solar Panels?
While talking about names and terminology, we must make it clear that double glass solar panels are not necessarily bifacial solar panels, although bifacial panels are bound to be of the double glass types, or whatever other of the names you may use. Bifacial solar panels remind one of the Greek God Janus, who could look forward as well backwards without turning. And so do the bifacial solar panels. But it is not the double glass only which makes them bifacial.
Double glass only allows them to receive light from the backside as well as the front side. There must be solar cells to convert the light received from the rear side. Although the efficiency of the rearward system is not as good-some manufacturers do claim the rear face efficiency to be as good as 80 % of the front face efficiency-bifacial solar panels do have advantages under special conditions, albeit, at a cost. Double glass solar panels have several advantages over the standard silicon solar panels with plastic backsheet. Some of these are discussed below.
Durability of double glass solar panels
We have often seen goods cartons marked “Glass, Handle With care”. It is the general perception that glass ware is fragile. It is not really so. Of course, vessel shapes made of glass will be fragile, but in sheet form glass can be very strong, particularly if supported against another smooth surface. The glass protector on the front face of our cell phone is a sheet less than a millimeter thick but last well. The glass sheet used on solar panels of good quality is fit to withstand hails of the size of an inch. These hails can easily dent a car and may be damage the wind screen. But not the sheet on the solar panel.
Solarwatt, a German company claims they use a sheet just 2mm thick on front as well as back, and that makes their panels no heavier than the standard panels. It is claimed that with a total glass thickness of just under four mm (2 mm on each side), these panels will not be damaged when smashed with a hammer or jumped upon!
When solar panels of the standard type are stressed by wind, snow pile-up or other stresses, they flex. This tends to create micro cracks in the panel, reducing conversion efficiency. As claimed by Solarwatt again, double glass solar panels are not affected as readily.
Resistance to Chemical Reactions
Glass does not react with many chemicals, and certainly not with the elements of the environment. That is why wine is stored in glass bottles to stay for thousands of years. Since glass is non-reactive, chemical reactions will not occur between the glass sheet and either the solar cells or the epoxy that holds panels together. Although plastic backsheets are not highly reactive, glass is far superior.
This is another advantage of the double glass solar panels over the standard solar panels- reduced PID. PID is potential induced degradation of performance which can reduce performance by as much as 30% in standard solar panels. The cause is stray currents in modules especially those which have a potential with respect to ground. The effect is increased by moisture penetration and temperature. Since double glass can seal out moisture from both sides, double glass solar panels are virtually immune to PID.
Longer Life-Better Warranties
Since the performance deterioration is much slower than the standard solar panels, double glass solar panels have a longer average life. This means warranties as long as 30 years are available from some manufacturers.
Special Applications-Transparent Roofing Material
Since they are transparent, double glass solar panels can be used as roofing material where partial light transmission is desired, eg, in verandas, carports etc.