PERC solar modules are growing in the market, but what is PERC cell technology and what are its advantages? To better understand the importance of PERC cell technology, let's first review some of the inefficiencies commonly found in standard silicon solar panels.
Simplified cross-section of a silicon solar cell. Sunlight (orange) hits the solar cell, and the light loosens electrons (blue) within the silicon material. Electrons entering the electrical contacts can then flow through the connected circuit, providing electrical energy.
Solar cells built with only two layers of silicon wires experience some efficiency loss. The first type of loss comes from inefficiencies in capturing sunlight; sunlight may be reflected by the solar cell itself, blocked by wires, or sometimes travel all the way through the cell and be converted into heat, reducing cell efficiency. Another type of loss stems from the random motion of electrons scattered by light strikes. Electrons may recombine with the silicon material on the front and back of the solar cell, or sometimes miss passing through the circuit.
Within a solar cell, when light is not converted to electrons, some efficiency is lost, or the resulting electrons cannot reach the backside for contact. Researchers have been working to reduce these losses.
Fortunately, technology can mitigate some of the efficiency losses. For example, adding a front-side passivation layer prevents front-side recombination and prevents some reflections. To prevent unwanted electron movement through the battery to the backside contacts, you can add a backside field layer during production or place all wires on the backside of the panel. The tricky part of managing inefficiencies is converting sunlight into heat at the back of the panel and back compounding.
Most silicon modules have layers that help avoid losses; the front layer reduces reflection losses and also prevents electron loss at the front edge. The backside backside field repels electrons, reducing the number of them making contact with the backside.
What is PERC?
PERC stands for "Passivated Emitter and Back Contact" or "Back Cell". Solar panels made with PERC cells have an extra layer on the back of conventional solar cells. This extra layer captures more sunlight and converts it into electricity, making PERC cells more efficient than conventional cells. PERC modules also mitigate backside recombination and prevent longer wavelength heat from becoming heat that can compromise cell performance.
PERC technology has been around since 1989, but commercial implementations have encountered increased light-induced degradation. However, with steady improvements over the years, PERC modules are now 1 percentage point more efficient than standard modules. Given that standard modules are typically 20% efficient, other things being equal, a system using PERC modules will generate about 5% more energy than a system using standard modules.
Like other high-efficiency modules, PERC modules can be used to maximize production on a limited roof area. A PERC module would be a good choice if you are installing on a small partially shaded roof area or building.
Even if roof space is not a major issue, installation time and cost can be saved by using more efficient PERC modules. If a site requires 40 standard modules or 38 PERC modules to achieve the expected annual output, you can reduce the amount of racks, cabling and MLPE equipment needed to tie everything together.
PERC module production
PERC solar modules are structurally very similar to other silicon modules on the market, which is a distinct advantage for manufacturers. Panel makers are able to largely reuse existing production equipment, although there is some added cost to produce new passivation layers and back contact cover layers. According to cost reports from NREL and PV Magazine, the manufacturing cost per watt of a PERC module is about the same as that of a conventional silicon panel. PERC modules may cost slightly more than traditional modules, but they are slightly more efficient and power rated.
The global demand for monocrystalline PERC module production has increased significantly in a short period of time. In 2014, single PERC module production reached ESS greater than 1 GW to 64 GW in 2018, with production reaching a forecast of 168 GW by 2022.
PERC modules are becoming more popular and are likely to take market share in the coming years.