Over the years, we have seen the standard monocrystalline and polycrystalline PV modules increase in wattage per square foot, but they are getting close to the maximum possible efficiency on these typical solar cells. But manufacturers aren’t giving up, there are a few new up and coming technologies that will continue the progress of PV efficiency.
Split cell technology uses the same solar material but cuts the cells in half. The new smaller solar cells have the same voltage as the original size cells, but they have half the amps. Putting 2 of these cells together gives you the same wattage as a single standard cell, but that wattage is a higher voltage and lower amperage.
Power loss on conductors like the busbars inside a PV module is caused by voltage drop which is amps multiplied by resistance. Less amps means less voltage drop which means less power loss on the internal conductors.
Voltage drop also causes heat build up so lower amps means the PV module is operating at lower temperatures, further increasing the efficiency. Overall, using split cell technology can increase solar panel power output by 5 to 8 watts per module. This lower operating temperature also increases the expected life span of the module as excessive heat leads to degradation.
N-type solar cells are not new, but they are gaining popularity in the industry which until recently has been dominated by the p-type solar cells. Solar cells are made by “doping” silicon with very small amounts of either Boron to make the silicon more positively charged (p-type) or Phosphorus to make the silicon more negatively charged (n-type).
The p-type solar cells are cheaper to make, but the n-type cells are more efficient. Adding to this, the Boron in the p-type cells causes an undesirable effect called Light Induced Degradation (LID). LID happens in the first few days and weeks that the p-type cell is exposed to sunlight and it can reduce its efficiency by 2%-3%. The n-type cells do not experience LID, so not only do they start at a higher efficiency than p-type and they maintain that efficiency over time.
Another advantage of n-type cells is they are not as sensitive to impurities in the silicon base so manufacturers of n-type cells can use lower quality silicon without impacting the efficiency. Currently n-type PV modules are still more expensive than p-type, but many people are willing to pay for the higher efficiency, so the n-type is gaining in market share.
Back contact (or rear contact) solar cells are another innovation coming to the forefront. A typical PV cell is made in a way that requires contacts to be on the front and back of the cell, with positive on one side and negative on the other. The problem is that the busbars on the front of the cell cover a small area of the cell so it does not get sunlight. These busbars are made as small as possible but still cause a loss in power production. Back contact PV cells are made so that all the conductors, positive and negative, can be on the back side of the cell leaving 100% of the front side exposed to sunlight. This results in a higher efficiency. While this not new technology, manufacturers are finding less expensive ways to do it, increasing its popularity.
Shingling is a new technique where a solar cell is cut into strips and layered in a shingled configuration with conductive adhesive. This allows the electricity to flow across the cells without busbars as conductors. This method of building a solar module eliminates the wasted space between the PV cells and the busbars on top of the PV cells. The overall effect is all the space inside the PV module frame is now active PV cells which increases module efficiency by 5% to 17%. Shingling also helps mitigate power loss when part of the PV module is shaded.
With all these new advancements beginning to hit the market, we can be assured that PV efficiencies will continue to rise a little bit every year just as they always have.