Solar panels have been around for what seems like forever. They also seem to be everywhere these days, from rooftops to pocket calculators. As you probably know, many people are going completely off-grid with their homes and businesses, all through the use of these fascinating devices.
So we know that solar panels work. The sun shines on them and then electricity comes out of the panel, which we can then use to watch TV, refrigerate our food, and have a hot shower. That’s pretty amazing, right? But how exactly does it work? Knowing how solar panel technology works is important if you want to use it, especially if you want to avoid getting ripped off. This is an area of rapid development, after all.
So in this article I’m going to talk about how these modern miracles take in all those rays and then somehow provide us with pure, homemade electricity at the other end. It’s a fascinating story that begins really at the start of the whole thing – by which I mean the Sun itself.
(Almost) Everything is Solar Powered
Before we get to solar panels in particular, let’s talk about solar energy as a whole. It’s a little crazy to think that we live on a massive dirty spaceship known as Earth, orbiting around a humongous ball of burning nuclear fire.
That ball of fire we call the Sun is a star – the same sort of star that we see billions and billions of in the night sky. In the center of a star the pressure is so great that the nuclei of atoms are pushed into contact with each other. This is not a comfortable situation for the typical atom, which means a whole lotta energy is released. This is known as nuclear fusion, which is a different process than we use in nuclear power stations.
The way stars work, they pump out energy for billions of years. In the case of our Sun, there’s about 5 billion years left on the clock. We don’t actually have that much time left, however, since at some point before that the fusion material will start to run out, making the Sun expand into a red giant, engulfing most of the solar system, including Earth. However, if you consider that human beings have only been around for about 200,000 years, there’s still plenty time left to do the things we want to.
While all of this is rather astounding to think about, what really amazes me is the fact that almost everything on Earth is already solar powered. How is this possible? It’s actually simple. Energy from the Sun drives every natural process on Earth. The food chain begins with plants. Plants convert solar energy into biomass. Herbivores eat plant matter and then are eaten by carnivores. Fossil fuels are also essentially stored solar energy too, although stored from millions of years ago.
I say that “almost” everything on Earth is solar powered, because we have found some creatures that live near volcanic vents. So that means they are powered by geothermal energy. That’s pretty rare, however.
So you see that almost all of our main energy sources, excluding nuclear, originally come from the Sun. Solar energy technology is therefore just a way to cut out all that inefficient intermediate stuff. It’s a return to the energy source we’re supposed to live off in the first place.
Photovoltaics: The Basics
Solar energy can be harvested in a number of ways, but if we want to convert it into electricity the only practical technology is something known as a photovoltaic cell. As the name suggests, this device takes light and then converts it into electricity. When someone talks about a solar panel, they are generally referring to photovoltaic cells.
It was back in 1876 that William Grylls Adams and Richard Evans Day made the discovery that some solid-state materials could take light and then turn it into electrical power. In that case, the material in question was selenium, which is not what we use today. Nonetheless, this discovery was thought of as world-changing even then. The only issue was that these selenium devices did not create electricity in any sort of usable quantities.
How is it even possible for light to become electricity? I can’t pretend to understand the fundamental physics of the process, but I have found some information to make it all more understandable.
First of all, it’s important to understand that light consists of particles called photons. Photons travel at, well, the speed of light. However, they also have mass, albeit a tiny amount. Electricity is nothing but the flow of electrons – subatomic particles that carry a negative charge. So what we want to do is use the photons to create a flow of electrons, which is exactly what a PV panel does.
The Structure of a Photovoltaic Cell
While the first PV cell was made from selenium, almost all modern cells use silicon. But since 2010, research has shown that selenium might actually be the better choice when it come to PV cells. For now however, PV panels you buy on the open market are going to incorporate silicon.
A PV cell consists of two silicon layers sandwiched together. Each layer is doped with a different material so that one layer has a positive charge and the other a negative charge. Because the two layers have such different charges, it causes an electric field to form where the plates meet.
When photons come in, they knock electrons free. These electrons are pushed out of the interface by the electric field, where they are shepherded towards metal plates and then to the wires; ready to enter a device or be stored in something like a battery.
Solar Panel Efficiency
Whenever we convert energy from one form to another, we lose some of the useful work that this energy can do as some goes to waste. For example, the total amount of energy in a liter of gasoline is not what you actually get out when you put it into your car. At every conversion stage a little bit of power is lost. The more efficient this process is, the less energy is wasted.
When it comes to PV panels, the holy grail has always been to improve the efficiency. The first selenium cells barely made any electricity, but as the science has improved, more and more of the sunlight coming into the panel is leaving as electricity.
How efficient are modern solar panels? Not very, to be honest. However, thing have taken off by leaps and bounds as semiconductor technology improves. The world record for solar panel efficiency was set in 2014, with a measured efficiency of 46%. That’s with a special experimental panel that is definitely not for sale yet. Typically, panels that you’d buy off the shelf will have an efficiency rating of somewhere between 13 and 18 percent. Panels that exceed 20 percent are also creeping towards mainstream use.
How is efficiency measured? This number is actually the result of a standardized test condition based on 1000W of solar energy per square meter, cell temperatures of 25ºC, and an air mass of 1.5. The air mass number is important because the quality of the air acts as a buffer between the panel and the sunlight. Spacecraft that use solar energy don’t have to worry about this, because the vacuum of space lets the light through without any resistance. Likewise, if the panels get hotter than 25ºC, their efficiency drops.
So a panel with 20% of efficiency should deliver 200W under these standard conditions.
Why The Low Efficiency?
In practice, solar panels don’t ever perform at their rated efficiency. The first reason for this is pretty obvious. There are few places in the world where the environmental conditions match up to standard test conditions.
Even over the course of the day, how much power the panel produces will fluctuate. In England, for example, you might need twice as many panels to generate the same power as one would need in California or Australia. Hot and sunny conditions are best.
Deviations from standard test conditions tell us why a panel isn’t reaching its rated efficiency, but not why that rated efficiency is so low in the first place. The sun is putting a certain amount energy on the panel, but 80% of that power is going somewhere else.
It isn’t any one source of power loss that causes inefficiency. Instead it’s a list of factors which each eat up a chunk of the solar energy and wastes it. For starters, the panel surface itself has some degree of reflection. So some photons that hit the panel don’t pass through to the substrate; instead they are bounced away, never to be seen again.
Thanks to the internal structure of PV cells, some of the electronic components actually cast a bit of shade onto the cell itself.
It’s also important to know that light waves vary in frequency. This is why we see different colors of light. Some wavelengths are too energetic for the cell, which means extra energy gets converted to waste heat instead of electricity. Other wavelengths are weak, so they don’t make electricity at all. One of the ways researchers are working on the efficiency problem is to create PV cells or panels that are sensitive to more frequencies of light than at present.
The next source of power loss has to do with how electrical systems work. The materials we use to ferry electrons from one place to the next aren’t all equally good at doing it. When a material lets lots of electrons through we say that it is a good conductor. When it lets few electrons through we say it has high resistance. Copper is a great conductor, which is why we use if for wiring.
There are materials which provide better conductivity, but they are rare and expensive, at least in a large scale application such as solar panel production. In lab conditions we have even seen so-called superconductors. These materials offer zero resistance, but currently have to be cooled down to incredibly low temperatures to work.
Energy is lost thanks to electrical resistance in the solar panel’s components, which is then lost as heat. Some solar panel setups use active cooling to help keep their efficiency up, but of course any active cooling solution uses power too!
Just Getting Started
Solar panels have advanced incredibly since their invention, but not nearly as incredibly as technologies such as computer microprocessors. With all that time and energy put into them, we still can’t capture more than about a fifth of the solar energy that comes into the panel.
However, solar panels are now finally good enough to be practical. As more money is diverted from fossil fuels and people are incentivized to go solar, the rate of development should go up. There’s also a lot of energy synergy going around. The devices we need power for in the first place are becoming more power-efficient themselves. This means the average household doesn’t need as much electricity to begin with, since their appliances are now more effective.
Future PV cells and panels might look very different from the ones that we have today, especially when it comes to their internal structures and the sorts of materials we use. Material science and physics are adding new knowledge relative to solar technology all the time.
For now, however, every PV panel that you see for sale on the market works more or less as I have described it here. I’ll be looking at some of the more promising speculative solar power developments in another article.
Taking all the direct and related developments in solar panel technology into account, it’s clear that solar power is finally coming into its own, both in terms of usable power and affordability. Armed with a basic knowledge of how PVs work and realistic expectations, you now hopefully feel a little more confident when it comes to how solar tech works.