Solar panel installations have grown explosively all over the world in the last ten years.
The best part is their costs have dramatically plummeted by 99% over the last four decades, so there’s no better time than now to take advantage of clean solar energy for your home or business to lower the electricity bill.
According to 2018 data from International Renewable Energy Alliance, (IRENA), the United States is the world’s third-largest solar energy user behind China and Japan. The United Kingdom is in 7th place followed by Australia in 8th place.
As the decade comes to a close, the forecast for solar power has never looked brighter. In fact, industry experts predict the United States will double its solar installations from two million to four million by 2023.
Much of that growth will occur predictably in sunny California, but several other states are spearheading solar projects, too. Note from the graph below that three of the top five states leading in solar panel installations in 2019 were in the not-too-sunny Northeast United States.
Even the UK, with less sun than many parts of the U.S., had over one million solar panel installations in 2018, up by almost 2% (in terms of power generated) from the previous year.
Australia meanwhile hit the 2 million solar installation mark in 2018.
In light of this solar energy trend wherever you turn, accelerated by the urgency to stop burning fossil fuels and switch 100% to renewable energy as quickly as possible, maybe you’re thinking it’s time to jump onboard.
If so, welcome to the solar energy revolution!
One of the major concerns when you’re initially considering a solar panel installation for your home or business is choosing the best type of solar panel for you.
In this article, you’ll do a deep dive into the three main options for solar panels available today. These are:
- Thin film
The technologies underpinning all three of these types of solar panels have made significant improvements over time to meet your energy needs better.
We’ll also survey what’s up and coming in the solar energy world. This includes technologies like:
- Bifacial solar
- Concentrated PV (photovoltaic) cell
- Solar tiles
- Transparent solar panels
All of these innovations in solar energy are cutting edge and many, especially bifacials and CPVs, are commercially available in some regions and competitively priced. They hold a lot of promise to boost the green energy segment of the global energy consumption mix.
For example, bifacial solar modules are expected to increase tenfold in capacity by 2024 to 28,000 megawatts (MW)! For reference, the current national average of American homes powered by just one MW of solar is about 190.
In this article, we’ll first consider what all solar panels, both those in commercial production and those up-and-coming, have in common: solar cells enmeshed in a solar panel system.
What is a solar panel system?
A solar panel system is an inter-connected assembly, (often called an array), of photovoltaic (PV) solar cells that (1) capture energy emanating from the sun in the form of photons; and (2) transform that solar energy directly into electricity. The amount of electricity produced, as measured in volts or watts, varies according to the system and the type of solar cell.
Each individual solar panel (also called a module) in the array consists of a group of solar cells packaged together in a metal frame. There are typically 60, 72 or 96 solar cells in a single solar panel.
To convert the direct current (DC) electricity produced into the alternating current (AC) used in your home, every solar cell system contains an inverter. The inverter may be large and centralized.
Alternatively, some photovoltaic modules have an inverter already built-in. These are called AC modules. Wiring is much simpler with AC modules.
What are solar cells made of?
Solar cells today are mostly made of silicon, a chemical element with semiconducting properties. In most types of solar cells, silicon is in a crystal form.
Because 100% pure silicon crystal doesn’t transfer electric current, it is “doped” with very small amounts of “impurities”—usually phosphorus and boron—that do readily carry an electric current within the silicon crystal lattice.
The silicon doped with phosphorus is called N-type (for “negative” because it has a surplus of electrons).
Silicon doped with boron is referred to as P-type (for “positive” because it has a deficit of electrons).
When constructed with one N-type section next to one P-type in this manner, the solar cell is called single-junction, meaning it has only one p-n junction.
When doped silicon absorbs some of the sun’s energy, it dislodges some free electrons in the process. In the electric field of a solar panel system, the electrons are routed to flow in one direction, establishing an electric current.
The solar cell’s electric field causes voltage. The mathematical product of current and voltage is power—the power used to run your household appliances and heat or cool your home.
Other components of a solar cell include an anti-reflective coating, since silicon’s natural luster would cause sunlight to reflect off of it—which is not what should happen if you want to create electrical power.
The silicon crystals of the solar cells are grouped inside an electric field and then covered in glass to protect all components from weather.
What is solar cell efficiency?
A measure of how well solar panels absorb sunlight and convert it to electrical energy is called efficiency. Light travels in different wavelengths of varying energy levels across the bands of the electromagnetic spectrum, and not all is absorbed by a solar panel. Measured in electron volts (eV), the typical band gap energy which can be absorbed and transformed by a solar panel into electricity is about 1.1 eV.
Photons hitting the panel with more energy than that (and there are lots of them) represent an energy loss.
Using different materials in solar panels with a low band gap would increase the number of photons absorbed, and, consequently, the current. But, it would also reduce the voltage of the panel. Since power equals current multiplied by voltage, there’s a trade-off between material selection and electric field strength in solar panel development.
Research shows that the optimal band gap of a material is between 1 and 1.6 eV.
Besides the material of a solar panel resulting in some energy loss, there is the problem of the internal resistance of a material (called series resistance).
Silicon, as a semiconductor, doesn’t conduct electrical current as well as metals. Its series resistance, in fact, is rather high. This translates into yet another source of high energy loss.
To correct for this, some panels are covered with a metal grid to allow the electrons to move more easily in the electric field, complete the circuit and create electrical power for your home.
But, the downside of this superimposing grid is that it blocks some of the PV cell surface from absorbing photons! A thinner grid covering would minimize this loss, but the thinness itself would contribute significant resistance and result in more energy loss.
Takeaway: There are several reasons why solar cells aren’t highly efficient. Ongoing research is based on finding materials that are more efficient, at reduced cost and are aesthetically pleasing.
Solar Trivia: The highest efficiency ever recorded for a PV panel to date (developed in 2006) was about 41%!
This was a U.S.-funded effort for power in space exploration. At the time, the Department of Energy believed the system would be scaled commercially, eventually reaching a solar panel cost of a mere $3/watt, producing energy at $0.8–0.10 per kilowatt/hour (kWh).
Incidentally, in 2019, the solar price per watt (PPW) is approximately $3–$4. In some areas, it may be as low as $2.50!
The cost of a kilowatt-hour of solar energy derived from a rooftop solar array is about $0.06–$0.08 cents (versus $0.09–$0.13 for coal or natural gas-derived energy).
Take-Home Message: These super low rates for solar renewable energy is extremely competitive with fossil fuel energy today.
Unfortunately, a 41% degree of energy efficiency is still not common for residential or commercial solar systems. However, some of the work done in labs looks promising.
Besides achieving higher efficiencies, experimental work on solar panels also focuses on lower costs and a more pleasing appearance.
3 major types of solar panels on the market today
Depending on your energy needs, budget, cosmetic preference and space allotment, it’s important to weigh the advantages and disadvantages of your three options in solar panels for your home or business.
Two of these solar panel types consist of single-junction solar cells. Theoretically, their maximum efficiency is about 33%. The highest efficiency achieved to date with single-junction cells is about 22%.
The thin-film solar panel may be single- or multi-junction depending on its material(s). Multi-junction solar cells are made of different materials, each of which best captures photons of varying wavelengths. In this manner, more sunlight can be converted to electric energy.
Monocrystalline solar panels
Constructed from a single silicon crystal that’s been sliced into wafers, monocrystalline solar panels contain rows and columns of these wafers. Since the silicone crystal (also called an ingot) is cylindrical, slicing them into wafers causes them to have rounded edges.
Polycrystalline solar panels
Polycrystalline (also referred to as multi-crystalline) solar panels have solar cells containing multiple crystalline fragments of silicon. The fragments may be the left-over pieces from monocrystalline solar production. They are arranged in an irregular manner. Then they’re melted together and formed into solid blocks before being cut into wafers. Each wafer is more rectangular than its monocrystalline counterparts.
Thin-film solar panels
Called second-generation solar cells, thin-film solar panels can be made of a variety of materials including:
- Amorphous silicon (no crystal lattice)
- Gallium arsenide
- Copper indium gallium selenide (CIGS)
- Cadmium telluride (CdTe)
Each wafer of a thin-film cell is super-skinny compared to the other types, making it flexible. They may be applied by an adhesive directly to a surface (like your roof, boat, or RV), or set up into durable frames (rack) much like the other common types of solar panels.
Here’s a summary table of the three most common solar panel types:
(If you’re using a mobile device, please swipe left and right to view the full-size table.)
|Solar Panel Type||Material||Efficiency||Cost||Appearance|
|Monocrystalline||Pure, single silicon crystal||High (18% or slightly higher)||Highest||Black or dark blue cells with rounded corners|
|Polycrystalline||Silicon fragments||Medium (15-17%)||High||Blue rectangular cells|
|Thin-Film||Various||Low (11%, but may attain 15%)||Lowest||Black or blue uniform surface|
4 Solar panel innovations
The overarching goals of research and development into solar panels are to:
- Increase efficiency
- Lower cost of materials
- Increase longevity of solar systems
- Heighten aesthetic appearance
Although some of the following solar technologies are commercially available only in certain areas right now, here’s a glimpse of what you can look forward to everywhere as the renewable energy revolution advances.
Solar Panel Purchasing Tip: When you begin getting estimates for your rooftop or backyard solar array, always inquire about the local availability of these newer technologies. You just may get lucky!
Bifacial solar technology
“Two-faced” solar panels are able to generate electric current through photon contact with both sides of solar cells.
As sunlight hits the top of a solar panel, activating some PV cells, it continues on and passes through the panel. Then some of it is reflected back off the surface underneath the panel (like a roof). Those reflected rays expose the bottom solar cells to further photon activation.
Bifacials may be either monocrystalline or polycrystalline.
Concentrated PV technology (CPV)
One of the most avant-garde solar panel technologies uses lenses or curved mirrors to direct sunlight into a specific point, thereby concentrating it on a small, multi-junction solar cell.
Essentially, CPV reduces the energy loss by sunlight diffusion over a large surface. As a result, efficiency is greatly improved, even more than what a monocrystalline solar cell will deliver.
Right now, CPV is expensive because of added components like solar trackers and cooling mechanisms.
Solar tile technology
In 2016, Elon Musk of Tesla announced the concept of a solar roof equipped with solar tiles (also called solar slates or solar shingles). The solar tiles function like traditional solar panels. They may be constructed of thin-film material or monocrystalline silicon.
Right now, solar tiles are slightly less efficient than conventional monocrystalline solar cells.
However, this solar panel system has no supporting rack that traditional solar panels are placed in, and so considered more visually appealing than the common setup. Solar tiles are installed like conventional asphalt shingles and span the entire roof surface.
Tesla estimates that their solar roof costs about $22/sq. ft. while others calculate a price tag of $35/sq. ft. To put this in context today, to cover an average-sized home with solar shingles, it may cost upwards of $45K or more.
Transparent solar panels
Discovered by MIT researchers, transparent solar panels capture only the wavelengths of light that our eyes can’t see (near-infrared and ultraviolet) while allowing visible light to pass through.
So, everything in theory—from mobile phones to laptops to windows—could have a transparent solar panel on its surface, producing electricity, but you’d never know it!
Here is a schematic diagram of a transparent solar cell—low-cost to boot—taken from the MIT source linked in this section.
Currently, efficiencies for transparent solar panels are on the low end, but researchers see 11% or more very likely in the near future. Note, however, that if these cells cover all of the windows of a huge skyscraper, for example, even a 5% efficiency could easily defray 25% of the total cost of the power needs of the building.
Another significant advantage of transparent solar panels over conventional solar arrays is that they don’t need vast expanses of land or water (like traditional solar farms do) to operate.
First commercial applications (for cell phones) are expected in a few years.
Imagine how transformative the widespread use of transparent solar panels for windows (solar windows) in urban locations will be! Achieving this milestone in solar energy innovation will definitely tilt the global energy consumption pattern in favor of renewable energy from the sun.
Key takeaways on types of solar panels
Solar panel installations have grown in popularity and efficiency while decreasing in price due to the green, clean energy revolution. Now is a perfect time to invest in a solar panel system.
The most common types of solar panels for home use are composed of monocrystalline, polycrystalline or thin-film solar cells. They vary in efficiency and cost. Monocrystalline panels are the most expensive and most efficient. The least expensive, but typically least efficient, are thin-film solar panels.
Polycrystalline solar cells usually have moderate efficiencies and reasonable costs.
There is a large body of active R&D into new solar technologies. Among the most promising—already in the marketplace in some areas or projected to be in the next few years—are bifacial solar, CPV, solar tiles, and transparent solar panels. comment