Choosing the best solar panels for your home can seem like an impossible task, especially if you’re not technically minded. Thankfully, a competent, trusted solar installer can help enormously. In most cases, your chosen installer will guide you through your options and help you pick panels that meet your needs.
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If you’re going it alone, though, it pays to understand some basic information about solar panels and how they work. That way, you know what to look for (and what to ignore) when faced with a slew of technical information and marketing hyperbole from photovoltaic (PV) manufacturers.
A brief history of solar panels
The first photovoltaic (PV) cells were built in 1883 by American inventor Charles Fritts. He used selenium to make PVs, hoping to compete with Edison’s coal-fired power plants. Unfortunately, despite selenium’s conductivity under light, Fritts’ PVs were just 1% efficient, meaning 99% of the sun’s energy falling on a panel did not get turned into electricity.
Things improved dramatically in the 1950s, when researchers stumbled upon silicon as an alternative to selenium. This element, abundant in sand (and, therefore, cheap), acts as a semiconductor. Soon, researchers had a solar cell that was 4% efficient. By the 1960s, PV panels (solar panels) were efficient enough to power a research satellite orbiting Earth.
These days, solar panels average around 20% efficiency, depending on their type, location, and other factors. The range of efficiency is huge, though. Amorphous silicon-based solar cells are still only 6-11% efficient, while most commercially available poly- or multicrystalline Silicon (Si) solar cells clock in at around 14–19% efficiency. Even the best monocrystalline solar cells are just 22% or almost 23% efficient.
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Research-cells tend to be far more efficient than commercially available panels. They are also very expensive and, as such, are usually relegated to use in unmanned aerial vehicles and satellites. The most efficient research-cells typically originate at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and include solar cells up to around 47% efficient that rely on quantum lattices and six collectors comprising 140 layers of photoactive cells.
NREL regularly updates the Best Research-Cell Efficiency Chart with new advances in solar research-cell technology.
Why efficiency matters
The first solar cells, courtesy of Charles Fritts, were capable of converting just one-hundredth of the sun’s energy into electricity. In contrast, a high-tech research-cell can convert up to 47% of the sun’s energy falling on the cell into electricity.
Efficiency matters because given the same amount of sun exposure, a more efficient solar panel will produce more electricity. For example, under the same conditions, a panel that is 21% efficient will produce 50% more electricity than one that is 14% efficient.
If you’re short on space, efficiency is even more important, because you’ll need fewer efficient panels to create the same amount of electricity as larger inefficient panels.
More efficient panels tend to be more expensive, although efficiencies also tend to improve while costs decrease year on year. Some Chinese solar panel manufacturers (such as LonGi, Canadian Solar, and Trina Solar) are also producing more efficient (20% plus) panels that cost less per Watt than American-made panels from SunPower, LG, and Panasonic.
How to calculate solar panel efficiency
To calculate your solar panel’s efficiency, you’ll need the power output in watts and the size of your panel in square meters. Efficiency ratings are based on a 1,000 watt per square meter incident radiation flux.
As an example, let’s say you have a 350 W solar panel that measures 50 cm by 40 cm (2 square meters). Your panel has a power output of 2,000 w under standard testing conditions (1,000 w x 2 square meters).
Next you’ll divide the total wattage of your system (350 w) by how much wattage your panel’s square footage can produce, and then multiply by woo to get your efficiency percentage. In this case, this looks like:
350 watt power output/(1,000 watt per sq. m x 2 sq. m) x 100 = 17.5% efficiency.
It would be very strange to see a solar panel for sale without efficiency data, but if it is missing, you now know how to calculate it yourself.
It’s also worth noting that these efficiency calculations assume optimal conditions. If your solar panels are partially shaded, or regularly get covered in dust, dirt, bird poop, or other debris, the efficiency rating will be far lower.
Solar panels also have a temperature coefficient. This is a way of telling if the efficiency of the panel is seriously hampered by very hot or cold weather. Solar panels are generally designed to perform best at around 77 degrees Fahrenheit (25 degrees Celsius). For every degree above or below, the panel’s performance will decrease by the temperature coefficient.
Some panels are designed to perform better in very hot or cold weather. These panels will have a lower temperature coefficient (good brands include REC and Panasonic). You can also ask your local solar installer for guidance. If you live somewhere cold, with lots of snow, it’s also a good idea to locate your solar panels somewhere you (or service personnel) can easily reach to clear off snow.
Types of solar panels
There are three main types of solar panels currently available for homeowners. These are all silicon-based and comprise:
- Single crystal (monocrystalline) cell panels
- Polycrystalline cell panels
- Amorphous silicon (thin-film) panels.
Of the three, polycrystalline is the most common. This is because polycrystalline panels require less energy to manufacture, making them more affordable without compromising too much on efficiency.
Single crystal cell panels are more expensive than polycrystalline cell panels but are the most efficient of the three types, at around 15% efficiency. Polycrystalline panels are about 12% efficient and amorphous silicon is about 11% efficient.
Monocrystalline panels are made from solar cells created from silicon formed into bars and then cut into wafers. The cell edges are cut and rounded, which helps the cells produce more electricity. This process is both wasteful and time-consuming, hence the added cost. It is also what gives monocrystalline panels their recognizable appearance. These panels are black and uniform, have a higher output, tend to last longer, and are the most efficient.
SunPower, LG, and REC Solar make some of the most efficient panels. SunPower’s monocrystalline panels are up to 22.8% efficient, making them the highest efficiency solar panels currently available to homeowners. LG’s monocrystalline panels are up to 22% efficient, while REC Solar make panels up to 21.7% efficient. CSun and Panasonic also make very efficient monocrystalline solar panels that are up to 21.2% efficient.
Polycrystalline panels are a mid-range option that marries efficiency with affordability. Instead of being made of a single silicon crystal, the cells in these panels comprise many fragments of silicon melted together. This process means electrons can’t move as freely, resulting in a less efficient panel with a shorter lifespan.
Aside from greater affordability, the main benefit of polycrystalline panels is that they’re made more sustainably. The wafers are created in square molds and don’t need to be cut at the corners. This means less waste and a faster, cheaper process overall.
Polycrystalline panels have a rectangular shape and are blue and speckled, thanks to the way sunlight reflects off the crystal fragments.
Amorphous thin-film solar panels
Most people are likely familiar with amorphous or thin-film solar technology thanks to the tiny solar cells in watches or calculators. The technology has improved over the decades, with far better efficiencies now and less degradation from sun exposure.
The cells in amorphous thin-film solar panels are flexible and approximately 350 times thinner than the wafers in mono- and polycrystalline panels. These panels are created from layers of semiconductor materials such as silicon, cadmium telluride, and copper iridium gallium selenide. Unlike in the crystalline panels made with solid silicon wafers, silicon in thin-film panels is non-crystalline.
Long rolls of amorphous thin-film or even spray-on amorphous silicon can even be used to create solar shingles or can be applied in places where more traditional, rigid solar panels won’t work (such as an awkwardly shaped roof).
When turned into panels, amorphous thin-film comprises a semi-conductor layer between transparent conducting layers, topped by glass to let sunlight through. These panels are a great option for homeowners who don’t like the look of standard solar panels or who have a peculiarly shaped roof.
Because thin-film panels are less efficient, at around 11%, you’ll need more of them, and more roof space, to create the same amount of electricity. These panels also have a shorter lifespan, degrading much more quickly compared to crystalline panels. Accordingly, these panels tend to have shorter warranties.
Solar shingles AKA a solar roof
Solar shingles are a relative newcomer to the solar scene. Designed to look like regular roof shingles, solar shingles can bring the benefits of solar power to homeowners constrained by homeowner associations or their own aesthetic predilections.
Solar shingles aren’t cheap, though. The average cost to install solar roof shingles on a single-story home is around $60,000 to $75,000. This is far higher than the cost of a standard solar array comprising crystalline panels. That said, solar shingles aren’t just solar panels; they’re also shingles. This means you’re essentially getting a new roof and rooftop solar all in one.
As such, solar shingles actually work out more cost-effective than rooftop solar arrays for most homeowners, assuming they’re also in the market for a new roof. These shingles offer durability and flexibility akin to regular shingles, but also create electricity from the sun. Each shingle can produce between 13 and 63 W.
Another key benefit to solar shingles is that they’re lightweight and easy to install. So, while they withstand rain, snow, and wind very well, it’s also easier and cheaper to replace a damaged shingle or two, compared to replacing a whole solar panel. You can also remove solar shingles quite easily and relocated them to a new home if you move.
The downsides of solar shingles include less efficiency compared to standard solar panels. Shingles need high sunlight exposure and a good slope to produce a decent amount of electricity. Shingles also have a shorter lifespan (around 20 years) than most regular solar panels (25 to 30 years), and it can be hard to track down a solar shingle installer in some areas.
How to choose the right solar panels for your home
One of the simplest calculations you can do to help inform your choice of solar panels is to work out the cost per watt. All you need is the price of the panel and its maximum power output as listed by the manufacturer. This figure is the maximum wattage under standard test conditions (usually 1,000 W per square meter of irradiance at 77 degrees Fahrenheit or 25 degrees Celsius).
Let’s say you’re interested in two panels, one costing $400 and one costing $200. The first is a 200 W panel and the second a 160 W panel. Of the two, the cheaper panel actually works out better value overall because the cost per watt is just $1.25, compared to $2.00 for the $400 panel.
Cost isn’t the only factor, of course. Other things to consider include manufacturers’ warranties, given that this is a good indication of the lifespan of a panel. Most modules these days come with a 25-year warranty. Anything less suggests an inferior quality panel that it’s likely best to avoid.
It’s also good to look at peak voltage for panels, especially if you live somewhere very hot and sunny. Under these conditions, PV modules with a peak voltage of 16.5 or less tend not to perform as well as those with a higher peak operating voltage. A good rule of thumb is to choose 12 volt panels that operate at 16.5 or higher or 24 volt panels that operate at 33 volts of higher.
Which kind of solar panel is best for homeowners?
Of the three main types of solar panels, most homeowners tend to choose polycrystalline panels. This is because they’re the most affordable and not that much less efficient than monocrystalline panels.
Where monocrystalline panels really shine, however, is for homeowners with a smaller roof or a partially shaded roof. These panels maximize electricity production in smaller spaces and can offer better returns for some projects. If you live in a state with generous SREC legislation, more efficient panels can also generate greater returns through Solar Renewable Energy Credits/Certificates.
Thin-film solar panels are rarely used for residential solar installations. Instead, these lightweight, low-profile panels can often be found on listed or heritage buildings or in commercial projects.
Solar shingles are increasing in popularity, with more installers now offering solar roofing options. If you’re due to upgrade your roof anyway, solar shingles are a great choice. Otherwise, you might consider installing just a few shingles in a particularly sunny spot on your roof. Then, if you move or decide to upgrade to a full solar roof, these shingles can move with you or get incorporated into the new roof.
In summary, the best solar panels for a home depend on the type of home, its location, the amount of roof space, and any aesthetic concerns. For most homeowners, a rooftop array comprising 15 to 20 polycrystalline panels will suffice to meet energy needs. This will take up about 25-35 square meters of roof space and assumes that the panels have a peak wattage of around 300 W.
As for brands, the most efficient solar panels, and arguably the best solar panels for a home, are made by SunPower, REC, and Panasonic.