An encapsulant is used to bond or join the top and bottom layers of the solar panels, the glass and back-sheet respectively, to the main middle layer which has the solar cells. This is a very important component because it unites the layers into one solid layer but does not reduce the properties of the three main layers especially their transmittance and low thermal resistance.
The encapsulant material is usually made of EVA (ethyl vinyl acetate) and there are many good reasons why it became the material of choice by many solar panel manufacturers. The most important feature of EVA is its high optical transmittance allowing maximum light transmission to the solar cells. EVA is also known for its stability at elevated temperatures and high ultraviolet exposures. It is also very easy to handle because it is not adhesive at room temperature. You will have to heat it to around 150 degrees Celsius before it can properly and effectively bond with the other layers of the solar panel. It also comes in thin sheets which are a breeze to lay on the surfaces of the other layers in preparation for heating and pressing. And just like any other encapsulant, the EVA can also provide added support to the tempered glass helping to hold it together in case it breaks.
There are two encapsulant EVA layers; the first is sandwiched between the glass and solar cell layers, and the second one is in between the solar cell and back-sheet layers. They are aligned and heated then pressed and finally cured at a certain temperature depending on the EVA brand. Once cured, the EVA also contributes to the overall rigidity of the solar panels.
Home-made or DIY solar panels can be difficult to make if you want to use EVA thin sheets as your encapsulant. You would need an industrial grade machine to apply it. The alternative would be a clear liquid silicone adhesive which can be use to bond the solar cells to whatever back-sheet substitute material you plan to use. We don’t recommend that you try to apply this liquid adhesive between your solar cells and glass because it will not be equally distributed across the surface and will significantly affect light transmission. A better way to solve this limitation is to just apply a protective coating on your back-sheet and then place your solar cells on top of it. What we did on our straight-forward tutorial on how to make a solar panel was to glue in place using a silicone adhesive the solar module (group of solar cells connected in series) on a perforated hardboard (Pegboard) which was fitted on top of a substitute back-sheet which was a plywood. Both the Pegboard and plywood were painted with latex acrylic paint which protected them from external environmental elements.