Photovoltaic (PV) devices – the topic of my senior thesis and today’s blog. As if the 65 pages I wrote during my last year of college weren’t enough, I am back for more because these are near and dear to my heart. Lucky for both of us, this will be significantly shorter. Anyways, you are probably more familiar with the colloquial name – solar panel. While the names aren’t exactly interchangeable, solar cells are photovoltaic devices, which are strung together (electrically) to make a solar panel – the magical power generating device you know, love, and might even have glued on the roof of your house.
What’s a photovoltaic device?
Okay, so it’s not actually magic and they probably aren’t glued, but what is magical though, is that for the very first time ever (since I began blogging for Megger), I genuinely feel like I could answer this question with my own, genuine knowledge. For your sake though, I am using research, as I always do. You’re welcome.
So, back to the question at hand. Photovoltaic devices use sunlight to generate electricity, thanks to semiconductors. There are a lot of different kinds of PV devices, but let’s just talk about it in the most simple, generic form. As mentioned, a semiconductor, such as silicon, is the main player in a photovoltaic cell. Inside a PV cell, you’ll find two semiconductor layers – one positive and one negative – achieved by “doping” each individual layer with another element (like phosphorous or boron) to achieve the desired charge. When sunlight particles (or photons) hit the surface of the solar cell, electrons shoot off the semiconductor. This electron will then jump into the electric field, created by the positive and negative semiconducting layers, and flow through the solar cell – generating an electric current.
Once those electrons are flowing, metal plates catch those electrons (in the form of electricity) and output direct current (DC). If you aren’t familiar with DC electricity, then you’ll need to read this blog first, to get a better understanding. Obviously, a solo photovoltaic cell isn’t going to produce enough energy to do anything special. You’ll need about 60 cells, wired together in a panel, to garner any significant level of power. On top of that, you’ll usually be installing multiple, if not hundreds or even thousands of panels, so the electricity output increases significantly, at that point. Make sense?
Oh, I mentioned it outputs direct current, which is great, but a solar inverter is required to convert that to alternating current, so it can be used in your home or office or wherever you’ve installed these sweet solar panels.
What can go wrong?
Well, there are a lot of obvious factors involved in the success of your solar panel system. For instance, if there is no sunlight, you are going to struggle to produce electricity – of course – and likely struggle with various low power issues. Temperature can also affect the functionality of solar panels, so that’s something to consider.
However, we are going to focus on the electronic issues that may arise, which likely comes as no surprise, since this is an electrical testing blog. So, let’s start with inverters, which we mentioned above. These convert the solar panel’s DC output into useable AC output, which is wonderful. Before we talk about what could go wrong, let’s briefly chat about your various inverter options.
Okay, don’t make this too complicated. This is very simple, everyone. A string inverter is designed to operate with single series strings of a solar panel – converting DC output from each individual string into AC power. Whereas, a central inverter converts DC output from all of your solar panel into a single AC output. Simple, yes? There’s also a micro inverter, which is designed to convert DC output from each individual panel into AC.
Now that we’ve got that covered, let’s make it even more confusing. On top of those categories of inverters, we also have stand-alone, grid-tie, and battery backup inverters. Excellent. Now is probably a good time to mention batteries; we are going to talk about them in more depth in a second, but for now, just know that they exist in certain photovoltaic systems. Anyways, stand-alone inverters draw DC from batteries, which are charged by the solar cells, while grid-tie inverters take the AC output and match it to the utility’s phase. These inverters are also designed to shut down automatically in the event of a power outage – keeping linemen safe on the job. Finally, battery backup inverters take DC from batteries, as the stand-alone inverters do, but they export excess energy back to the utility grid and provide AC energy to loads in the event of an outage.
If you are dealing with zero power output – a common solar issue – it is likely due to a faulty inverter.
As promised, let’s chat about batteries. Thanks to everyday electronics, we are all familiar with batteries already. In a solar power system, batteries may (or may not) play a role. When used, batteries can provide a form of energy storage, so power can remain on even on the cloudiest of days. However, batteries must be able to handle the heat that comes with the continuous charging and discharging. There is no ideal battery for solar use, so you must assess your individual solar needs when choosing a battery and consider its capacity, chemical composition, maintenance, and life span.
Since solar systems are attached to the electric grid, various power quality problems will arise too. For both the solar site and the utility, at large, troubleshooting power quality issues is an important part of maintaining a solar power system.
But wait. What are power quality issues?
There’s no doubt that the sun will always rise in the east and set in the west, but when it comes to solar power, the sun is rather unreliable. Since the weather, location, and time-of-day can heavily alter the input of sunlight, the output of a solar panel is constantly fluctuating. As the output is sent through an inverter to convert from DC to AC power, a variety of power quality issues can creep to the surface, including voltage, unbalance, transients, harmonics, and power reversals.
In the interest of your time (and sanity), we are going to wait until next week to venture into the specifics of those power quality phenomena because I think we’ve shoved more than enough solar knowledge at you today. For now, just know that excessive heating, premature motor or lighting failure, and damage to electronics can all be the result of power quality issues across solar equipment. And if you’re really desperate to learn more about power quality, you can check out my first-ever blog, my debut to the blogging world – Small, but Mighty. Go give that a read and let me know what you think.
-Meredith Kenton // Digital Marketing Assistant // Valley Forge, PA