When will solar panels be more efficient?

When it comes to buying solar panels for your home, the first thing that manufacturers usually tout is the panel’s efficiency.

Solar panel efficiency refers to the amount of sunlight hitting the panel that gets converted into electricity. The intensity of sunlight can be expressed in watts - the same unit used to measure electrical power.

For example, if 1,000 watts of sunlight is shining on your solar panel and it generate 200 watts of electricity, the panel is 20% efficient.

Why is this figure important? For one, your roof has a limited amount of space, and you might not be able to generate as much electricity as you like in the space available. Another reason is that if you could generate more electricity with fewer panels, that’s always preferable: you’d need less equipment installed on your roof and less space needed for your array.

Solar panels have gotten better over time, but what are the prospects for future improvements?

A brief history of solar cells

Charles Fritts developed the first solar cell in 1883. It was based on selenium and was only about 0.5% efficient. This means that a theoretical solar panel developed in Fritts’s time that received 1,000 watts of sunlight would generate only 50 watts of electricity.

Today, the best home solar panels are around 22% efficient - 44 times better than Fritts’s early invention. For the average homeowner, this means you might need fewer than 20 solar panels to match the electricity needs of their home.

That’s pretty good, but it’s still quite a lot of surface area. Wouldn’t it be great to have an array on your roof that takes up very little space but still generates all the power you need? When - if ever - will this magical future happen?

What are the best solar cells available today?

It’s pretty common to hear about solar cell breakthroughs in the lab. Today, the best solar cells reach close to 50% efficiency. That’s an incredible improvement over the panels you might have sitting on your roof.

Unfortunately, don’t expect to find 50% efficient solar panels at your local Home Depot any time soon. There’s a big difference between a lab experiment or small-scale production and a product that can be made cheaply at massive scale around the globe. With millions of solar panels being cranked out every year, the reliable silicon solar cell will only be replaced by a technology that can be scaled up quickly in factories around the globe.

At the moment, the very best solar cell technology that’s commercially available reaches around 32% efficiency. These are cells that use techonology called triple-junction and quadruple-junction. They are designed to capture multiple wavelengths of sunlight - not just the visible sunlight you see with your eyes, but invisible infrared and ultraviolet light too.

You can buy these solar cells! They’re intended for use in space on satellites and space probes where limited weight and size is very, very critical. I have no idea what they cost, but if you’re thinking about building a robotic space probe, you can give Spectrolab a call.

I’m not building a solar-powered space probe. When I can expect improved technology I can use in my home?

If you can’t expect triple-junction solar panels to be installed on your roof anytime soon, when can homeowners expect better solar panels to be available to them?

In one sense, they already are. According to data from Berkeley Lab, the average efficiency of solar panels installed on homes in 2002 was 12.7%. In 2019 - the most recent data available - average efficiency had improved to 19.4%.

That’s more than a 50% improvement in less than two decades. There’s a variety of technologies responsible for this improvement, including monocrystalline silicon, heterojunction cells, passivated emitter rear cells, half-cut cells, bifacial solar panels, and more.

Not only have these technologies have helped to make solar cells better, but they’ve continued to drop in price too - truly a win-win.

So, what are the next technologies we can expect to continue this trend of better and cheaper solar panels over the next 10 or 20 years?

It’s hard to predict the future, but I think two technologies are worth watching: n-type cells and perovskites.

What is an n-type solar cell?

Most silicon solar cells are what’s known as p-type. This means that the silicon has positively-charged atoms - boron - added to its crystalline structure using a process known as doping to make it electrically conductive.

Nearly all commercial solar panels available up to this point have been p-type, but n-type cells are becoming available. Instead of being doped with positive ions, n-type cells are doped with negative ions - phosphorous.

One benefit of this newer technology is that n-type cells don’t suffer from light-induced degradation, a loss of efficiency that happens immediately after the solar panel is put into service. Eliminating LID losses is the main reason why n-type cells can have improved efficiency.

N-type cells alone doesn’t guarantee outstanding efficiency. For example, the REC N-Peak reaches just shy of 20% efficiency. That’s good, but still short of the best panels from LG and SunPower.

However, when combined with other improvements, n-type cells can help push solar panel efficiency higher than what’s currently available. We might start seeing some of these advancements hit the marketplace soon. For example, JinkoSolar last year announced an n-type monocrystalline cell that reached 24.79% efficiency.

According to the company press release, n-type cells along with other technologies like anti-reflection coatings will gradually start to make it into production.

What are perovskite solar cells?

A more exotic and promising technology is perovskite solar cells. In nature, perovskite is a mineral made of calcium titanium oxide that has a cubic structure. Perovskite solar technology doesn’t use this natural mineral, but it does have the same cubic structure.

Pervoskite solar cells (PSC) might be made of synthetic crystals based on inexpensive elements such as tin or lead. Pervoskite cells potentially have several big advantages, including low cost, high efficiency, and ease of manufacturing.

Pervoskite cells currently in the lab have hit around 25% efficiency, exceeding the best commercial silicon cells. While this isn’t a massive increase over current silicon cells, the technology has the potential to reach perhaps 31% efficiency.

Higher efficiency is great, but perhaps the biggest potential of perovskite cells is ease of manufacturing. Pervoskites might be produced using relatively simple manufacturing methods such as inkjet printing and screenprinting, bringing the cost of solar lower than is possible today.

What’s stopping pervoskites from hitting the market today? There are a number of obstacles to solve before the technology can make it into commercial products, but perhaps the biggest is the stability of the material.

Of the great advantages of solar panels made with silicon cells is that they can withstand decades of abuse. You can have them baking in the desert, freeze them in the Arctic, leave them in a monsoon or hurricane, but they’ll still continue to crank out electricity for decades.

Pervoskites aren’t that tough yet. They start to break down when exposed to moisture, oxygen, or ultraviolet light - conditions that conventional solar panels have no problem with. That’s a big obstacle: solar electricity is now one of the cheapest forms of electricity, but the economics of solar work because you can install a solar array and expect it to work with minimal maintenance for 25 years or more.

Commercialization of perovskite solar cells

In spite of the challenges, at least one company thinks it can bring a pervoskite-based solar panel to market soon. Oxford PV, a spin-off company of Oxford University, has developed a solar panel that combines conventional silicon cells with a layer of pervoskite to reach 30% efficiency - a huge improvement over current solar panels.

The company is aiming to bring a product to market as soon as 2022.

Other companies are working on this too. Most likely, the first pervoskite solar panels will use tandem technology, combining a layer of pervoskite with a mature technology such as silicon cell or thin-film solar.

Looking into the crystal ball: what new solar technologies can homeowners expect to see soon?

Oxford PV’s roadmap sounds promising, especially if the cost advantage is there, but there are a lot of questions that need to be answered before homeowners will be putting Oxford PV’s solar panels on their roofs anytime soon. In particular, homeowners will want to know whether pervoskite technology will be as durable as a silicon solar panel with a 25 year warranty. The main cost of a home solar installation isn’t in the panels - it’s other hardware and “soft costs” such as design, installation, and permitting. If your solar panels are cheap but fail after 5 years and need to be replaced, the labor cost would wipe away any savings gained from cheap solar.

Still, given the impressive progress we’ve seen in the past 20 years, I think you can count on seeing n-type cells, pervoskites, and other technologies helping to continue the trend of cheaper and better solar panels.