You might have heard that solar panels aren’t efficient at converting the sun’s energy to electricity. That statement is frequently used by detractors to point out that solar technology doesn’t live up to its potential, and it’s a load of hogwash.
There’s a reason that solar is the fastest-growing new energy source, and millions of homeowners have installed solar panels. The technology is mature today and ready to power our homes and our grid.
That’s not to say there isn’t room for improvement. It’s true that the most efficient commercially-available solar panels can reliably convert about 24% of the sun’s energy. It’s also true that traditional silicon-based solar cells have a maximum theoretical efficiency of 30%; and two-thirds of the way there ain’t bad.
But new technologies can take us to 50% efficiency and beyond, and some are just a couple years off. Is it worth waiting for them before you install panels on your home? Let’s find out.
How solar panels work
To begin with, it helps to have a working knowledge of how modern silicon-based solar panels work. Thankfully, SaveOnEnergy.com has made a stunning infographic that explains the process in pictures better than I could in a thousand words.
Check it out:
What the infographic doesn’t show
What that wonderful explainer doesn’t show is that only between 20% and 24% of all solar energy can actually “zap loose” electrons and holes in the silicon. That’s partly because solar energy is emitted across the electromagnetic spectrum, but silicon can only convert visible light to electricity.
Energy from the sun is delivered to the earth in the form of photons. Each photon is like a little bundle of energy. Gamma photons are super-high energy, while radio photons have hardly any energy at all. Here’s our own little mini infographic to explain:
So you can increase efficiency in a silicon solar cell, but silicon alone can’t turn more of the EM spectrum into electricity.
The question is: what can?
How solar cells can get more efficient
There are a few ways scientists are using to make solar cells more efficient. Some of them involve capturing heat, some use new semiconductor materials, and some use layering of existing materials. None of them are quite ready for prime time, and they all have faults, but they all show promise. Time will tell whether one or more of them can overcome those faults.
Here’s a quick rule to remember: Increased solar cell efficiency is meaningless unless it can be done cheaply and the finished product can last a long time.
Here’s a quick run-down of some of the new technologies:
Solar technologies that convert heat to visible light
Nanotechnology has led to scientific breakthroughs in countless disciplines, and solar cell efficiency is no exception. The image above shows a nanophotonic crystal suspended above a solar cell.
- Technology: Nanophotonic Crystals
- Theoretical Efficiency: 60% or more
- Time to market: At least several years
- Drawbacks: Expensive an complicated to make, in very early development
The crystals work by taking in solar energy until they become superheated to 1,000 degrees Celsius. They’re made of carbon nanotubes that emit that stored heat as light.
The final component of the system is a special optical filter that allows light to pass through in the precise wavelength that matches the solar cell’s peak efficiency, and reflects the rest of the light back to the crystal to keep it heated.
As discussed above, this technology has the potential to double solar cell efficiency, but it’s in the very early stages. No one knows how well the crystals would survive 25 years of heating and cooling, or how long it will take for the the theoretical efficiency increases to be available commercially.
Don’t hold your breath on this one, folks. But definitely read more about it.
Using different solar cell materials to reduce cost
One way to circumvent the limitations of silicon is to eliminate it entirely. A new class of photovoltaic materials called perovskites might hold an answer to creating efficient solar cells cheaply.
- Technology: Perovskite Solar Cells
- Theoretical Efficiency: 25%-30%
- Time to market: 2+ years
- Drawbacks: The (current) best kinds are made with lead and degrade quickly
The reason perovskites are so interesting is because, unlike silicon, they don’t need to be painstakingly manufactured and purified. Preovskites can be applied to a backing material by simply applying a chemical solution with a printer. This technique could lead to efficiency levels close to silicon-based cells at a fraction of the cost.
But, oh yeah… the most useful perovskites we currently know about are chock full of toxic lead which can easily get into the environment and poison us. They’re also extremely unstable, and subject to damage from being exposed to water.
Scientists are working with perovskites that don’t contain lead (tin is in), and also trying to find ways to decrease susceptibility to moisture. If those barriers can be overcome, perovskite-based cells could end up being the industry standard in the next half-decade or so. If not, maybe there’s still a way to use perovskite in solar cells…
The promise of tandem solar cells
Silicon works best with certain wavelengths of light, and not well with others. One way to overcome this limitation is to add a microscopic layer of another material on top of the silicon to absorb some of the light that would otherwise be lost. Tandem solar cells do just that.
- Technology: Tandem Solar Cells
- Theoretical Efficiency: 40%+
- Time to market: 2+ years
- Drawbacks: Rely on complex manufacturing procedures and/or perovskites
Several different kinds of tandem cells exist. The picture above shows a new kind of solar “step cell” which is made by adding a layer of gallium arsenide phosphide to the top of a silicon-based solar cell. In the future, the cells will have the second layer grown on top of them then etched away to allow light to pass through, making the silicon layer look like a bottom step.
The technology to do this is at least a couple years away from being mature, though if it can produce the predicted efficiency of 35%, it will do so at a cost not much greater than that of traditional silicon cells. Read more about solar step cells.
Perocskite tandem solar cells
A second kind of tandem solar cell involves layering perovskite on top of silicon to ensure more absorption of solar energy. The drawbacks here are similar to perovskite-only cells: they degrade quickly and contain lead.
Theoretical efficiency is again in the 35% range, and production is about as far off. Combining a cheap layer of perovskite on top of a traditional cell could be attractive to current manufacturers, because it would mean they could compete with these other technologies without having to do much re-tooling.
Again, time will tell whether the limitations of perovskite can be overcome.
Multi-junction solar cells
This kind of solar cell involves adding additional silicon to a typical solar cell by a process called “direct wafer bonding.” It has already shown efficiency of 30.2% under lab conditions.
- Technology: Multi-junction Solar Cells
- Theoretical Efficiency: Over 30%
- Time to market: 1+ years
- Drawbacks: Relies on high-cost process
The cells in the picture above were made using a process that bonds a thin layer of special semiconductor material to a traditional solar cell, creating what scientists called a “monolithic device”.
The resulting cell has an efficiency higher than any traditional silicon-based cell can reach, but the process used to make it is costly. If the group that made the cells can find a way to make the process more streamlined and cost-effective, this could be an ideal way to use existing technologies to exceed 30% efficiency.
Are any of these new solar technologies worth the wait?
In our opinion, no.
Here and now we have solar panels that are cheaper than every before. Combined with incentives like the federal 30% tax credit, an investment in solar will provide savings that are better than the 25-year returns from the stock market in most places in the Unites States.
When presented with an opportunity like that, especially when the incentives and beneficial solar policies of today may be gone soon, it would be folly to suggest that waiting is the right move, given that you have the resources (cash, equity, or credit score) to go solar today.
Connect with one of our expert partner installers near you to get a custom solar quote for your home.
Last modified: February 21, 2017