Guide to Solar Panel Efficiency

What’s inside:

 

Solar panel efficiency is a top consideration when choosing a new photovoltaic system. Improving solar panel efficiency is a key in making solar energy a viable alternative to more polluting fossil fuels. Over the years, solar panel efficiency has jumped from 15 to 20% within a couple of short decades, with promise to expand. New and emerging technologies, such as perovskite material, hold promise to boost solar panel efficiency to 40%.

When choosing solar panels, efficiency rating is an important metric to determine how much power a panel will produce compared to other products.

Solar panel efficiency is based on two factors:

  • Photovoltaic cell (PV) efficiency, which results from cell design and materials.
  • Total panel efficiency, determined by cell configuration, design, and panel size.

Let’s start at the heart of the modern PV system: The cell.

What is solar cell efficiency?

When discussing solar cell efficiency, we mean the amount of sunlight that hits a solar panel and is converted into electricity. A solar panel is only as efficient as its weakest link: the cell. Cells, made of silicon, absorb photons and convert them to electricity. 

Not all photons are absorbed, however: Depending on the wavelength of light hitting the cell, some photons are reflected and others pass through while others are absorbed and produce heat. What’s left are able to separate electrons from the silicon, thus producing energy.

There’s also a theory-based upper bound of solar panel efficiency: 33.7% for a 1.34ev bandgap (typical of silicon) and 68% for a multi-layer cell capable of capturing everything. 

The age-old struggle of solar cell design is designing cells to maximize photon receptivity. Here are some factors that go into the equation.

Panel Material

Most of the cell efficiency has to do with the material, the purity of that material, and the spectra the layer(s) can capture.

The type of material (see below for a comparison of the different materials) plays a critical role in overall panel efficiency. The most efficient cells incorporate the purest silicon. Impurities can lead to recombination, which results from electrons recombining when they encounter an impurity or defect in the cell’s crystalline structure.

Panel/Module

On the panel/module side, there are a few other considerations:

  • Wiring and busing. Cells with multiple busbars and passivation help efficiently capture and transfer electricity.
  • Reflection. Minimizing the amount of light reflected off the cell is also an important factor affecting efficiency. Thus cells treated with anti-reflective coatings perform best.

What is solar panel efficiency?

Solar panel efficiency is measured under strictly controlled test conditions called standard test conditions (STC). STC is established by exposing a panel to a constant light source and temperature, measuring the current and voltage produced for different load resistances. STC accommodates a cell temperature of 25°C, 1000W/m2 irradiance, and air mass of 1.5. Efficiency is determined by the panel’s maximum power rating at STC divided by the panel’s area in meters.

Under STC, a one meter square, 15% efficient solar panel would produce 150 watts.

Overall average panel efficiency in the real world is a whole different story. Solar panel efficiency is measured at standard factory testing conditions, so real-world production may vary from what’s advertised. When the rubber meets the road, there’s a whole lot more to add to the efficiency cocktail:

  • Wiring and busing used to capture and transfer electricity
  • Reflection
  • Panel installation and placement
  • The region’s potential solar output
  • Panel age
  • Weather
  • Shade
  • Color of the roof and protective backsheeting

Why Solar Panel Efficiency Matters

Solar panel efficiency is an important consideration when choosing the right PV system. Just like fuel efficiency in a car, an efficient solar panel means less raw materials, a smaller footprint, and less required space for proper energy output. For some applications, highly efficient solar panels are the only option. If efficiency is too low, more panels will be required to fill the gap, wasting valuable space and money. If space is limited, solar panel efficiency is vitally important to ensure enough energy can be harnessed. This may be the case on smaller residential homes where roof area or bare ground is at a premium.

When looking for the perfect photovoltaic system, however, efficiency isn’t everything: On most homes there’s often more than enough space to install the number of solar panels required to suit energy needs, even when using less efficient panels. Consider the following:

  • The average U.S. Home has a 1,500 sq. ft. pitched roof and uses about 30 kWh of electricity a day.
  • The U.S. gets about 3-5 “sun-hours” a day, translating to 3-5 kWh of irradiance per square meter per day.
  • Even an “inefficient” panel, say 15%, captures .45-.75 kWh of energy per square meter per day when the sun is shining.
  • To supply the average household’s 30 kWh energy needs, a house requires 431-718 sq. ft. of solar installation, or about 20-40 panels.

Not every foot of a 1,500 sq. ft. roof is suitable for solar installation, but there’s likely ample space to install enough renewable energy capacity. Choosing a readily available, affordable, and efficient panel is an excellent choice for most applications. Polycrystalline panels have around 15% efficiency and are among the cheapest panels available, making them a viable choice for many installations. However, poly panels tend to have shorter lifespans than more efficient (and expensive) monocrystalline panels. So if longevity is another key factor for your next project, efficient panels win here.

Proper installation and placement of a PV system is the most important aspect of coaxing the most out of solar panels. Improper installation — unsuitable backsheeting, inadequate ancillary equipment, etc. — and placement can significantly impede solar panel performance.

Efficiency is a part of the grander litany of considerations when choosing to go solar. Other considerations included cost, value, warranty, and aesthetics.

How To Maximize Solar Panel Efficiency

It should be noted there’s a difference between setting max efficiency records and maintaining consistent performance in the real world. As stated above, a highly efficient panel may look good in a lab, but could lack the performance needed to operate consistently in practical applications.

If your chief goal is to maximize electrical output of your system, high-efficiency solar panels paired with optimizers and microinverters are the way to go. Another benefit of purchasing the most efficient system possible is the potential in revenue from net-metering.

There’s no such thing as a free lunch. Efficient solar panels come at a premium. If you’re tight on space, the premium is worth it (or may be your only option). For other configurations, a middle-road panel may suit the energy needs and budget restrictions.

But if a high-efficiency, top-of-the-line panel is in the books for your next project, there’s never been more or better options.

For more information, check out our Understanding PV Losses blog series, which covers these topics, and more, in detail.

The most efficient solar panels in 2021

Here’s a rundown of the top ten most efficient consumer solar panels available today, according to Clean Energy Reviews:

  • SunPower Maxeon 3, 22.6% efficient
  • LG Neon R, 22% efficient
  • REC Alpha, 21.7% efficient
  • FuturaSun FU M Zebra, 21.3% efficient
  • Panasonic EverVolt, 21.2% efficient
  • Trina Solar Vertex S, 21.1% efficient
  • Jinko Solar Tiger Pro 6RI3, 20.7% efficient
  • Longi Solar Hi-Mo 4, 20.6% efficient
  • Winaico WST-375MG, 20.6% efficient
  • Q cells Q.Peak DUO G9, 20.6% efficient

Cleaning and maintenance

Just like maintenance on a car, keeping a solar panel system clean and in good repair is essential to peak performance. Dust buildup over the course of a year can reduce output up to 4.4%, so if your system is in a particularly dry area where rain doesn’t regularly wash your panels naturally, manually cleaning them is a good idea. Even if you get regular rainfall, all panels should be regularly checked for pollen, bird droppings, leaves, ash, and other pollutants and residue. Wash panels gently with a hose first. If they’re still dirty, softly squeegee with mild soapy water to effect.

Avoid shaded areas

The key to unlocking a solar panel’s maximum efficiency is ensuring optimal daylight. Maximize your region’s potential solar output by getting those panels as much time in the sun and at the right angle as possible.

Unlock output potential with proper planning

Regardless of which solar panel is chosen, the majority of planning and resources should go into the best installation and placement possible. Aurora Solar’s sophisticated solar design software generates complete engineering designs and sales proposals with just an address and an electric bill.

When selecting the best PV system, installers should find the sweet spot between price and efficiency, and configure the system to take full advantage of the manufacturer’s STC efficiency.

Schedule a demo to see how Aurora can help you design more efficient PV systems.

The Most Efficient Types of Solar Panels

Four major solar panel types are available to the consumer market today, each with its own advantages, disadvantages, and cell configurations:

  • Monocrystalline cells have a single orientation crystal structure — they are one solid silicon crystal. Mono cells provide more space for electrons to flow, resulting in a smaller, more efficient panel. The downside is they tend to be more expensive.
  • Polycrystalline cells are constructed of many individual shards of silicon melted together. They have many different crystal orientations and are cheaper to make, but the grain boundaries between crystals lead to some inefficiencies. TL;DR: They’re not as efficient as mono cells, but have a lower price point.
  • Passivated emitter and rear cells reflect light back into the cell, thereby reducing the tendency of electrons to recombine. As a plus, they also absorb greater wavelengths of light.
  • Thin-film cells are thin enough to be flexible, making them ideal for small-scale or portable applications, but are not efficient enough for use in large-scale installations.

Cells can be further configured to maximize efficiency. We’ll go through the various solar cell types and efficiencies below, but first, a brief description of acronyms …

  • PERC (Passivation): A technology preventing the loss of energy from electrons and holes recombining.
  • MBB (Multiple busbars): Reduces current loss by shortening the length a current must flow across a cell wafer.
  • IBC (Interdigitated back contact): Energy conversion occurs on the back of the cell, allowing the entire front of the cell to absorb sunlight, offering higher efficiency, yield, and reliability.
  • HJT (Heterojunction): Panels that capture a wider spectra of light.

What is the most efficient solar panel?

Here are the various solar cell types ranked by efficiency:

  • Polycrystalline PERC, 16-17% efficiency
  • Monocrystalline PERC, 17-19% efficiency
  • Shingled monocrystalline, 18-20% efficiency 
  • Half-cut monocrystalline PERC, 18-20% efficiency
  • Half-cut monocrystalline PERC MBB, 19-20.5% efficiency
  • Shingled monocrystalline PERC, 19-20.5% efficiency
  • Half-cut MBB heterojunction, 20-22% efficiency
  • N-type IBC, 20-23% efficiency

Check out this chart to see how the maximum efficiencies by material type have changed over time.

Key Takeaways

  • The most efficient solar panels for the residential and commercial markets are around 23% efficient.
  • Solar panels may eventually reach 40% efficiency, but that doesn’t negate the benefits of installing the best solar panels today.
  • The most efficient solar panels are produced by SunPower (22.6%), LG (22%), and REC Solar (21.7%).
  • Aurora Solar provides seamless planning solutions for high-efficiency solar equipment.  

Ali McBride