Give me that sun: Efficiency and world’s most efficient solar panels in 2023

Half-cut cell design. Engineers split solar cells with a laser, making them two times smaller. The resistance inside a cell decreases, the electrical losses fall and you get more current. Half-cut design was introduced by REC in 2014 in its TwinPeak panel. Half-cut cell panels are 3–4% more productive than modules with standard cells.

Heterojunction technology. Engineers enclose a solar cell in ultra-thin layers of silicon. Not only does it slightly increase efficiency, it allows the panel to retain high production levels at high temperatures. In particular, Panasonic and REC use this technology, which makes their panels exceptional in hot areas.

Multi busbars technology. Busbars are thin ribbons of copper that connect solar cells and conduct the current between them. The problem with traditional busbars is that these ribbons shade the cell slightly. That’s why engineers started using thin wires instead and improved the efficiency by increasing the active surface of a panel. Trina Solar is the pioneer of multi busbars technology.

IBC cells. Interdigitated back contact cells have contacts on their backside and they don’t get in the way of solar production at all. That’s the signature technology of SunPower, although other brands try it out as well. Unfortunately, this design increases the manufacturing costs which reflects in Sunpower prices.

N-type cells. P-solar cells are the most widespread type, but N-type cells have become more and more popular in recent years. They are more efficient and lose less power in the first year of operation. Trina Solar experiments with n-type cells a lot: for instance, it tries to lower manufacturing costs by increasing the size of a wafer.

Most brands are fine with using only a few of these innovations in their modules. Implementing all of them at once drives the manufacturing expenses way up. So while LG and Sunpower did win in our solar panel efficiency comparison table, the cost of this victory is high.

Even if your panel is packed with the latest innovations, its production levels may be brought down by real-world factors:

Location and sun hours. Some areas just have more sunlight throughout the day than others, therefore the irradiance of panels in these sunny places is higher on average. Even if your panels aren’t all that efficient, they will harvest more solar energy in Los Angeles than our Top-5 modules would do somewhere in Alaska.

Weather conditions and shading. Bad weather brings the performance of solar panels down by 10–40%, depending on the model and thickness of the clouds. Shading is much more problematic, since cells in most panels are connected in series. If one cell doesn’t get any sunlight, it brings the production of the whole row. Solar panels by Canadian Solar and Q CELLS remain efficient even in low-light conditions.

Positioning and angle. Solar panels in the northern hemisphere and in the USA in particular should be facing south. It’s not always the option, but picking west or east makes panels 15% less productive. The angle of panels should be equal to your latitude or just set between 30 and 45 degrees — its impact on overall efficiency is relatively minor.

Temperature. The best weather for solar panels is cold and sunny. When it gets too hot, the panels start to lose efficiency. This is what the temperature coefficient shows — how much output the panel loses for each degree after 25 °C at which it is tested. Usually, the coefficient varies between −0.3%/°C and −0.5/°C.

Let’s set an example. The Aptos Solar 365 W panel has a temperature coefficient of −0.36%/°C. The solar panel’s temperature is always higher than the air ambient temperature. On a sunny day Aptos module heats up to 44 °C, which is marked as Nominal Operating Cell Temperature (NOCT) in the datasheet. Let’s see how much output it provides in these circumstances:

365 W − (44 °C − 25 °C) × (365 W / 100 x 0.36%) = 365 W − 24.89 W ≈ 340 W

REC and Panasonic engineers use heterojunction cell technology that gives their panels lower temperature coefficients — around −0.25%/°C.

Time of year. This one is pretty straightforward — there is just less sunlight in the winter and fall compared to spring and summer. The irradiance falls and so does the efficiency. In June-July panels generate about 50% more energy than in December-January.

Let’s round up our explanation of efficiency concept by learning how to calculate the conversion rate of a solar panel.

Efficiency = [Power output / (Area of panel x solar irradiance)] x 100%

Power output can be easily found in the solar panel spec sheet. Area of panel means the whole area of a panel, not just its active surface. In the past there were brands that increased the efficiency numbers of their panels on paper by not including the frame in calculations (not fair!). Standard solar irradiance in lab conditions is 1000 W/m² which is roughly equivalent to a sunny day.

Let’s do the math ourselves. Imagine we have a Q CELLS Q.PEAK DUO G6+ panel which gives 350W output and is 68.5​ x 40.5​ inches in size (or 1740 × 1030 mm). Therefore the area of a panel is 1.7922 m². Let’s calculate the efficiency:

[350W / (1.7922m² x 1000W/m²)] x 100% = 19.52%

Did we do it right? According to the datasheet, the efficiency of a 350W module is indeed equal or greater than 19.5%.

Ok, but what does having a highly efficient panel mean in practice? Let’s say, we have two panels of the identical size. One of them is polycrystalline and has 14% efficiency. The other one is monocrystalline and has a 21% conversion rate or 50% more than the first one. Since panels are the same size, the power output of a monocrystalline panel should be 50% greater and it should provide you 50% more energy in kWh. Here the comparison of solar panels efficiency shows massive difference which is multiplied by the number of panels that you have.

But what if we have two panels of the same power output but with slightly different efficiencies? Well, they are going to provide just the same amount of energy, but the more efficient panel is going to be slightly smaller.

If space is not a constraint for you, then efficiency is not the most important metric to look out for. Keep in mind, however, that a typical residential system consists of 15–35 panels: the bigger the system, the more significant the panel size becomes. Having efficient panels is especially important in a mobile installation. On a boat or on an RV, you might have room for only a couple of modules.

Here’s the bottom line: while it’s easy to compare solar panels efficiency, by itself it becomes a deciding factor only in specific situations, such as high energy needs combined with lack of space. Otherwise, we suggest paying more attention to power output of a panel, price and warranties.