Have you ever seen black rooftop solar panels and wondered what makes them different from the typical blue-tinted arrays? Those sleek dark panels are made of monocrystalline silicon, while the blue panels contain polycrystalline silicon. There are important differences between both options in terms of cost and efficiency which we’ll discuss below.
Monocrystalline vs polycrystalline silicon solar panels
Both kinds of solar panels contain photovoltaic (PV) cells made of silicon that capture energy from the sun and transform it into electricity. But since they are manufactured via distinct processes, they differ in appearance and quality.
To mass produce polycrystalline (poly-Si) solar cells, over half a ton of silicon rocks are melted down in a crucible at a temperature of 2,450 degrees Fahrenheit. After three days of cooling in a rectangular mold, the material is ready to be sliced into paper-thin segments called wafers. Once metal conductors are applied and their surface is electrically charged, they are ready to form part of a PV panel. Poly-Si solar cells appear blue as a result of the way this particular material formulation reflects light.
The production of mono-Si cells follows a similar process, but a very interesting step is added during the melting process. A single seed crystal is introduced into the molten silicon. By pulling it upwards at a controlled rate while rotating it, the crystal grows into a large cylindrical ingot (a bar of pure metal). The ingot is atomically uniform and free of impurities, making the solar cells cut from this material more efficient. This technique is known as the Czochralski method of mono-Si growth and is used in the manufacturing of semiconductors as well.
Mono-Si panels offer better performance at a higher cost
While typical poly-Si solar panels promise electricity conversion efficiency of around 15% to 17%, mono-Si panels may offer 20% efficiency or more. The latter absorb more light thanks to their black-colored cells, and offer better performance in warm weather. If available space on your roof is limited, mono-Si solar panels can help you maximize the power you produce per square foot. Higher efficiency also helps offset the higher cost, which is something to keep in mind as you perform your system sizing calculations.
Poly-Si panels are more economical in homes where space is not a concern, but labor costs may be higher due to the fact that more panels ultimately need to be installed.
Poly-Si panels are more eco-friendly to manufacture
Since poly-Si solar cells are made in a mold, very little of the material goes to waste. The same cannot be said for mono-Si wafers, which are sliced from a cylindrical ingot and may be shaped into octagonal wafers in order to pack them more closely together in the panel. The discarded trimmings are not reused, which results in mono-Si panels being less eco-friendly.
Which technology will you choose?
By many accounts, mono-Si panels are chipping away at the market dominance of poly-Si systems. However, the choice remains yours to make based on aesthetic, economic and performance factors. No matter which solution you side with, generating your own solar electricity in the US is usually a wise choice that can quickly save you thousands of dollars in utility bills.
Sources:
https://www.pv-tech.org/mono-and-multi-production-5050-in-2018-but-mono-is-the-future/
https://www.pv-magazine.com/2018/09/13/low-demand-driving-consolidation/
https://pv-manufacturing.org/silicon-production/cz-monocrystalline-silicon-production/
https://www.greenmatch.co.uk/blog/2014/12/how-are-solar-panels-made
https://www.cedgreentech.com/article/monocrystalline-cells-vs-polycrystalline-cells-whats-difference
https://www.aurorasolar.com/blog/solar-panel-types-guide/
https://www.solarreviews.com/blog/black-or-blue-solar-panels-which-is-better-for-your-home
Photo by Kent Rebman on Unsplash
