In the U.S. in 2022, about 22% of our electricity came from renewable sources. Of that total, solar power accounted for just under 5%, but it’s growing fast. In 2022 the growth rate was 40% over 2021. Now with the Inflation Reduction Act offering tax credits of 30% through 2033, that growth will surely continue. Fortunately, almost all the materials in solar photovoltaic (PV) panels are abundant on planet earth. In fact, most of a solar panel is made from the most abundant materials on the planet—silica and aluminum.
By weight, a typical polycrystalline solar panel is composed of:
Sand, one of the earth’s most abundant natural resources, provides raw material for the glass and the silicon. Aluminum, used for the frame, is also abundant and is commonly recycled, so we won’t be running out of that. Copper, too, is one of the most plentiful resources and is used for the busbars that conduct the electricity between the silicon cells. Other metals used in solar panels are not as plentiful, but they’re used in minute quantities. Indium, gallium, selenium, and cadmium telluride, considered minor metals, are most often used in thin film panels. That leaves plastic, which we seem to have enough of, so far.
Silicon goes through a manufacturing process to create solar-grade silicon in the form of cylindrical ingots. The silicon ingots are then sliced into wafers less than 1mm thick, which are the pieces you see in a solar panel that absorb sunlight. The wafers are typically trimmed into square, rectangular, octagonal, or hexagonal shapes to fit more tightly together in the panel.
You’ll find three types of solar panels available: monocrystalline, polycrystalline, and thin-film panels. We’ll look at thin-film panels last.
Monocrystalline and polycrystalline solar panels look basically the same. They’re flat and dark rectangular panels with an aluminum frame and a glass top. The important distinction between them is in the silicon, which is monocrystalline silicon or polycrystalline silicon.
Monocrystalline solar panels are more expensive than polycrystalline and are also more efficient at converting sunlight into usable energy. At the moment we’re seeing mono panels that can reach just over 23% conversion efficiency for a 460 watt panel. Greater efficiency means more electricity generated and that means faster payback on your investment.
However, there is a cost/benefit ratio at work here, as the most efficient panels are more expensive. If you have plenty of roof area, or you’re using a ground mount, you may be better off just adding a few more lower-efficiency panels. It just depends on your situation, your budget, and your space.
But if you’re constrained on space, monocrystalline panels will provide more electricity in that space than an equivalent area of polycrystalline panels. That makes sense for small homes or on roofs that have dormers, for example. It also makes sense for use on RVs, as well, that are severely space constrained.
Greater efficiency also equates to the use of a higher grade of silicon with lower power loss over time. The acceptable industry standard has been around 1% per year of loss, so a 20-year-old panel that produces 80% of its rated wattage is considered acceptable. According to Clean Energy Reviews, “When calculated over the panel's 25 to 30-year life, many high-efficiency panels are guaranteed to still generate 90% or more of the original rated capacity.”
A further advantage for monocrystalline panels: they’re more efficient in warm weather conditions, and as we know, those conditions are becoming more prevalent.
Besides the silicon, monocrystalline and polycrystalline panels are essentially the same. They both use a rigid aluminum frame that serves to house and protect all the other parts, as well as provide a way to mount the panels.
A series of copper busbars and smaller fingers runs through the silicon cells. They connect all the cells together and distribute the electricity through the panel to the junction box. The more busbars a panel has, the more efficient it is at distributing the electricity generated by the silicon wafers. When you see “9BB” or the like, that’s what it refers to: 9 busbars.
Two layers of tough, clear plastic encapsulate the silicon cells, holding them all together, and a plastic back sheet or another sheet of glass protects the back side of the panel. The junction box is attached to the back of the panel, with the connection wires hanging out.
Another type of solar panel that’s becoming more popular is thin-film solar panels. These flexible panels can often just be rolled up for shipping and are great for travelers and campers. They’re made from amorphous silicon, not the crystalline type, or cadmium telluride, or copper indium gallium selenide. They’re flexible because the silicon layer is so thin and is applied to a flexible substrate like metal, plastic, or cloth.
At present, most are less efficient and more expensive than conventional rigid panels, and they also contain the minor metals I mentioned above, some of which are toxic and may be carcinogenic, such as cadmium. Because they’re less efficient, you might need more of them to meet your needs.
However, they’re very lightweight and so suitable for numerous uses where traditional rigid panels would be challenging. You can adhere them to curved surfaces such as a curved roof on your home or vehicle. Thin-film panels are adaptable for mobile uses, for example, for RVs and vanlifers, as well as for boats.
Another use for thin-film panels is building-integrated photovoltaics (BIPV). You can think of this as a Tesla roof, where the thin-film solar panels are integrated into the shingles, so you do not need the racking system for an array of monocrystalline panels. Thin-film panels can also be integrated into various facade and glazing treatments, making your entire building an electricity producer.
Thin-film technology is also undergoing rapid development and some panels already exceed the efficiency of the best monocrystalline panels, but at very high cost and at uncertain lifespan. Researchers have new, nontoxic and less-toxic materials in the pipeline, as well, such as perovskite and quantum dot photovoltaics.
All in all, solar panels are advancing rapidly and it will be fun to see what we have available in five years!