Factors that affect your solar panel efficiency

Fast read

The quantity and size of solar cells used to make a solar panel affect its size and power production. Over the past two decades, solar panels have grown dramatically in size, with the most current iteration being 87% larger than older models.

The wattage has also increased due to the increase in size, with contemporary panels delivering 400 watts instead of 175 watts for earlier generations.

The bigger size of the panels is responsible for the remaining 59% of this increase, leaving only 41% to technical advancements. The type of technology employed in the solar cells can also affect the size and production of solar panels, with monocrystalline technology frequently resulting in more effective panels.

What determines solar panels’ size and output?

Right now, many of the residential solar panels for sale are around 400 Watts, and a bit less than 20 years ago, a panel was 167 or 175W. So one would assume that given the wattage now more than double the original wattage, many unique inventions were added to solar technology to achieve such a remarkable wattage increase.

From 175W to 400W is a significant difference in power class. It’s a stunning 128% more substantial output number. So how did this 128% higher number get achieved? Did we see remarkable technological inventions that will lead to similar improvements in the following decades?

And by the way – we urgently will need stunning inventions in panel technology if residential solar is to carry significant weight in the energy transition. This is because many residential roofs are not big enough to support a solar system size needed to generate the electricity required for the home’s consumption and the electricity used by these families’ electric cars of the future. A more efficient solar panel would solve this problem.

Interestingly, only about 41% of the wattage increase between the various generations is due to technical improvements, and the remaining 59 % is due to a simple trick. This trick is called – increasing the panel size. Unfortunately, the 400-watt panels of today are a staggering 87% bigger than the early generations, so a lot of the power class increases are not an improvement at all.

If the original 175W panels were rebuilt to the size of today’s panels, they would have a power class of about 330W. So only the remaining 70W improvements are technological innovations. So how did we get there?

solar panels with sun shining on them
Solar panels have increased in size and efficiency through generations of development

2005 – Generation 1

Two key factors directly influence the size and output of a solar panel,  the number of solar cells in the unit and the size of the solar cells. These two factors have been the basis for the changes in solar panels over the past two decades.

If we go back to 2005 and travel to where we are now, we have seen several changes in solar panels regarding the technology and the size and numbers of the individual cells within the panel. So overall, one can identify three or four different generations in this timeframe.

So in 2005, we started with a relatively small panel of about 80 centimetres wide and about 1.5 to 1.6 meters high. These panels weigh about 14 to 15 kilograms. Because of their size and weight, they were pretty easy to handle. As they developed, the maximum power you got out of those was initially 175 Watts and 190 Watts due to improvements in cell treatment and input materials.

The individual cells in those panels were relatively small, usually around the five-inch mark, and there were 72 of them in each, and they were square.  

2010 – Generation 2

Then, around 2010 to 2012, we moved to a new generation of panels and transitioned to a larger cell. The larger cell was about six and a quarter inches, around 16 centimetres in height and width, and the number of cells was reduced to 60. 

So this new design had 60 cell panels, which got bigger in height from about 1.5m to 1.65. However, because the cells were more comprehensive, we also widened the board from 80cm to about 1m. So they also became heavier, from 15kg to 18 – 19 kilos.

While the initial generation of panels often had monocrystalline technology in the cells, to save costs, the cheaper produced polysilicon was often used as the critical technology in panels from a decade ago. 

We started with about 250 watts in this panel version and later moved back to the more efficient mono-silicon version. This change allowed the efficiency to go as far as about 330 340 watts, and this period from about 2010 to 2019 was also a time of panel research and innovation. 

2020 – Generation 3

The next generation, the current batch that drove the wattage from 330W to 400W, is primarily due to the subsequent increase in size rather than many innovative developments.

The trick is that the cells have become more prominent again, and so have the panels. Unfortunately, this made the panels even heavier. Also, they are not 60 cells as they were with the second generation, but they’ve been cut in half to reduce the resistance, leading to 120 cell models. These changes, such as half-cut cells, have increased efficiency a little (approximately 18% to 20%), as the smaller half-cut cells have a lower resistance, leading to the 400W power class.

Some manufacturers have added two rows of half-cut cells; these panels can go up to 440W and have 144 cells. In terms of cell technology, we stayed with the more efficient monocrystalline.

two installers working on roof
Half-cut solar panels increase efficiency in energy production compared to typical panels, an example of gradual development in solar

2022 – Generation  4 

To increase efficiency further, there has been some development in the monocrystalline technology, whereby the original P-type cells have been improved to N-type cells, a monocrystalline form, while more expensive to produce, has increased the efficiency of panels by another margin. 

So does a solar panel’s size affect its output? All we have done is make the cells and the panels bigger and add some gradual and minor technological improvements, like increasing the number of busbars, cutting the cells in half,  passivation techniques, and interconnections (gapless technology), therefore resulting in improved electron flow and giving small efficiency increases.

While the weight of panels per m2 might not have increased, the new panels being so much bigger, are consequently heavier, and one has to feel for the solar panel installers. In 2005 they had to carry panels weighing 15 kg, and now they have to get  22 and 23kg up the ladder. Being larger means, especially in windy conditions  – it’s like taming a large, heavy sail on the roof.

Many installers say that this change made their work so much more challenging for a single person, and in many instances, two installers are required to carry the panels safely on modern roofs. 

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