{"id":13282,"date":"2017-07-28T10:43:40","date_gmt":"2017-07-28T00:13:40","guid":{"rendered":"https:\/\/www.solarquotes.com.au\/blog\/?p=13282"},"modified":"2024-01-25T08:01:09","modified_gmt":"2024-01-24T22:31:09","slug":"perc-solar-panel","status":"publish","type":"post","link":"https:\/\/www.solarquotes.com.au\/blog\/perc-solar-panel\/","title":{"rendered":"What is a PERC Solar Panel?"},"content":{"rendered":"
\"perc

34 years after it was invented ‘PERC’ is\u00a0now a big deal in solar panel technology. But what the hell is it?<\/p><\/div>\n

Update 16th April 2019:\u00a0<\/strong> Many PERC panels have suffered from LeTID deterioration problems since this article was written.\u00a0 This article here<\/a> goes into the problem and this article on the MC Electrical blog<\/a> covers it in detail and gives information on which PERC panels are resistant to LeTID.<\/em><\/p>\n

Solar panel manufacturers crave efficiency.\u00a0 I’m not talking about the labour efficiencies they receive from building new production lines that are robot-heavy and people-light, although they like those too.<\/p>\n

The efficiency I am referring to is turning light into electricity. \u00a0 The higher a solar panel’s efficiency, the more watts of power you can get from the same amount of silicon.\u00a0 As solar panels are sold by the watt, mo’ watts means mo’ money.<\/p>\n

This is why the holy grail of the PV industry is increased solar cell efficiency.<\/p>\n

\"holy

And you thought I’d put a Monty Python video here. Or at least an Indiana Jones clip.<\/p><\/div>\n

One of the most cost effective methods of improving efficiency that has caught on this decade is PERC.\u00a0 While it’s not quite a holy grail, it has to at least count as a holy beer stein and is definitely better than a mere holy shot glass.<\/p>\n

PERC stands for Passivated Emitter and Rear Cell1<\/a><\/sup>.\u00a0 It improves efficiency by allowing electrons to flow more freely and also by increasing the reflectiveness of the back of solar cells.\u00a0 I’ll explain how it works later in the article.\u00a0 (Provided I actually understand it myself by the time I get to that point.)<\/p>\n

Currently, around one quarter of new solar panels are PERC and the figure may reach 50% in 2020.\u00a0 The reason it has become popular is because it adds little to the cost of solar panels<\/a> while increasing their efficiency by around one whole percentage point.\u00a0 That is, it can turn a boring old 16% efficient panel into an exciting 17% efficient one.2<\/a><\/sup><\/p>\n

In this article I will explain, or possibly fail to explain, just what PERC is, why the majority of panels may be PERC in the future, and if you should give a damn whether your panels are PERC or not.<\/p>\n

Spoiler Alert:<\/strong>\u00a0 Frankly my dear, you shouldn’t give a damn.<\/p>\n

PERC Is An Australian Invention<\/h2>\n

PERC was invented in Australia because we’re so awesome.\u00a0 Or at least that subset of us who were working on solar cell technology in the University of New South Wales<\/a> in the 80s, many of whom came from overseas, are awesome.\u00a0 But that’s okay.\u00a0 I’m sure it is a kind of contagious, nationalistic awesomeness that has since spread to us all.<\/p>\n

Sure, some Americans<\/a> deserve a quantum of credit for producing the first actual paper on the topic, but that’s okay, we can just make them honorary Australians in much the same way we claim Russell Crowe is Australian, right up until the point he starts pegging his phone at people,<\/p>\n

And how we used to say Mel Gibson was Australian until he went freaking nuts.<\/p>\n

\"Mel

Despite once playing a smurf, Mel Gibson would later go on to blame everything on “the Blues”.<\/p><\/div>\n

How PERC Works<\/h2>\n

If you want to read an in depth and detailed description of how PERC solar cells work then I recommend this article<\/a> by Australia’s master of green technology, Martain A. Green.<\/p>\n

If you want a simplified and possibly laughably botched explanation, then don’t stop reading now.<\/p>\n

How Solar Cells Work<\/h2>\n

Most solar panels use P-type cells while some high efficiency and higher cost panels use N-type cells.\u00a0 You can read about the difference between the two in P and N’s excellent article here<\/a>.<\/p>\n

When light hits silicon atoms in a solar cell it can knock electrons free.\u00a0 These electrons are negatively charged and the atoms that lose them become positively charged.\u00a0 Since opposites attract the two want to recombine to make themselves whole again. But solar cells are made so electrons gather on one side and can’t reach the positive atoms on the other side.<\/p>\n

\"Silly<\/p>\n

In P-type cells, the most common sort, the base of the cell is positive and the top is negative.\u00a0 The top layer of silicon where the electrons gather is called the emitter.\u00a0 Since the negative electrons at the top are blocked from taking the shortest path to the positive atoms below, they pass through a fine grid of wires on the surface of the cell and keep traveling until they arrive at the bottom of the solar cell.\u00a0 As they travel on their merry way we can exploit them to provide power to run lights, laptops, solar inverters, and potentially many other things.<\/p>\n

But if electrons and atoms recombine under the metal contacts on either the surface or rear of the cell, it reduces the voltage and limits the cell’s output.\u00a0 This effect can be reduced by passivation, which is what the first letter in PERC stands for.<\/p>\n

P is For Passivation<\/h2>\n
\"PERC

The difference between a PERC solar cell and a regular one is the passivation on the top and bottom. (Note to nitpickers: this is a simplified diagram)<\/p><\/div>\n

Passivation involves creating a layer of oxidized material.\u00a0 The layer under the grid of wires on the surface of the cell is usually aluminium oxide<\/a>.\u00a0 On the rear of the cell it is either aluminium oxide or silicon oxide<\/a>, followed by a layer of silicon nitride<\/a>.\u00a0 And that’s all the four letters in PERC — Passivated Emitter and Rear Cell.<\/p>\n

On the rear of the cell, the metal contacts still need to touch the silicon of the cell, so a “laser<\/a>” is used to cut holes in the passivation layer on the back for the metal contacts to enter.<\/p>\n

Passivation Makes Bottoms Shine<\/h2>\n

Helping electrons flow is not the only advantage of passivation.\u00a0 It also increases the amount of light reflected from the bottom of the cell.\u00a0 This is useful because if light missed hitting a silicon atom and knocking an electron free on its way in, reflection will give a second chance on the way out.<\/p>\n

Almost all solar cells have a reflective layer on the bottom3<\/a><\/sup> which is normally aluminium.\u00a0 But because the refractive index<\/a> of silicon is higher<\/a> than glass4<\/a><\/sup> the resulting reflectivity of around 89% isn’t as high as a normal aluminium backed glass mirror.\u00a0 But placing the passivated layer with a lower refractive index between the silicon and the aluminium can increase reflectivity close to the maximum possible of 98%.\u00a0 This gives a slight boost to the panel’s efficiency.<\/p>\n

Reflecting more light and reducing the amount absorbed by the back of the panel makes it a little bit cooler and this also results in a small increase in efficiency.<\/p>\n

Light Induced Degradation Can Be Worse Than Average<\/h2>\n

Light Induced Degradation, or LID, reduces the efficiency of P-type solar panels by around 3% after their first few days in the sun.\u00a0 To be clear, this is 3% and not 3 percentage points, which would be far worse5<\/a><\/sup>.\u00a0 In PERC panels LID can be worse than average, but it’s not nearly enough to cancel out the benefits of PERC.<\/p>\n

LID can be avoided by using N-type solar cells, but as they are more expensive than conventional P-type cells, costs will have to come down before there is a major shift to them.<\/p>\n

\"LID\"<\/p>\n

We’re In For A World Of PERC<\/h2>\n

PERC solar panels first appeared around 2012 but it took manufacturers several years to refine the process and bring down costs.\u00a0 Over the past year or two PERC panels have really taken off and perhaps one quarter of new panels produced are PERC.\u00a0 This may reach 50% in 2020.<\/p>\n

While manufacturers have become pretty good at making PERC panels, it is still possible there is room for improvement and we may see further cost decreases and efficiency improvements making PERC even more popular.\u00a0 But I wouldn’t expect huge improvements.\u00a0 After all, even though the process involves strange words and unseen forces, it’s not magic.<\/p>\n

It Doesn’t Matter Whether Or Not Your Panels Are PERC<\/h2>\n

While PERC makes panels more efficient and is becoming more popular, you don’t need to worry about whether or not your panels are PERC.\u00a0 So if a salesperson tries to convince you you have to have PERC you can tell her to go jump.\u00a0 Or maybe just smile and nod while ignoring her if you are feeling polite.<\/p>\n

There are important things you do need to worry about when it comes to selecting solar panels and the main ones are:<\/p>\n