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      Solar Panel Efficiency

      Solar panel efficiency is a measure of the amount of sunlight (irradiation) that falls on the surface of a solar panel and is converted into electricity. Due to the many advances in photovoltaic technology over recent years, the average panel conversion efficiency has increased from 15% to well over 21%. This large jump in efficiency resulted in the power rating of a standard-size panel increasing from 250W to over 400W.As explained in detail below, solar panel efficiency is determined by two main factors; the photovoltaic (PV) cell efficiency, based on the cell design and silicon type, and the total panel efficiency, based on the cell layout, configuration and panel size. Increasing the panel size can also increase efficiency due to creating a larger surface area to capture sunlight, with the most powerful solar panels now achieving up to 700W power ratings.

      Cell Efficiency

      Cell efficiency is determined by the cell structure and type of substrate used, which is generally either P-type or N-type silicon. Cell efficiency is calculated by what is known as the fill factor (FF), which is the maximum conversion efficiency of a PV cell at the optimum operating voltage and current. Note cell efficiency should not be confused with panel efficiency. The panel efficiency is always lower due to the internal cell gaps and frame structure included in the panel area. See further details below.The cell design plays a significant role in panel efficiency. Key features include the silicon type, busbar configuration, junction and passivation type (PERC). Panels built using high-cost IBC cells are currently the most efficient (21-23%) due to the high purity N-type silicon substrate and no losses from busbar shading.However, panels developed using the latest monocrystalline PERC cells, N-Type TOPcon, and advanced heterojunction (HJT) cells have achieved efficiency levels well above 21%. Ultra-high efficiency Tandem Perovskite cells are still in the development phase but are expected to become commercially viable within the next few years.

      Panel Efficiency

      Solar panel efficiency is measured under standard test conditions (STC) based on a cell temperature of 25°C, solar irradiance of 1000W/m2 and Air Mass of 1.5. The efficiency (%) of a panel is effectively calculated by dividing the maximum power rating, or Pmax (W) at STC, by the total panel area measured in square meters.Overall panel efficiency can be influenced by many factors, including; temperature, irradiance level, cell type, and interconnection of the cells. Surprisingly, even the colour of the protective back sheet can affect efficiency. A black back sheet might look more aesthetically pleasing, but it absorbs more heat resulting in higher cell temperature, which increases resistance, this in turn slightly reduces total conversion efficiency.Panels built using advanced ‘Interdigitated back contact’ or IBC cells are the most efficient, followed by heterojunction (HJT) cells, TOPcon cells, half-cut and multi-busbar monocrystalline PERC cells, shingled cells and finally 60-cell (4-5 busbar) mono cells. 60-cell poly or multi-crystalline panels are generally the least efficient and equally the lowest cost panels.

      Why Efficiency Matters

      The term efficiency is thrown around a lot but a slightly more efficient panel doesn’t always equate to a better quality panel. Many people consider efficiency to be the most important criterion when selecting a solar panel, but what matters most is the manufacturing quality which is related to real-world performance, reliability, manufacturers' service, and warranty conditions. Read more about selecting the best solar panels in Australia here.

      Cost Vs Efficiency

      All manufacturers produce a range of panels with different efficiency ratings depending on the silicon type used and whether they incorporate PERC, multi busbar or other cell technologies. Very efficient panels above 21% featuring N-type cells are generally much more expensive, so if cost is a major limitation it would be better suited to locations with limited mounting space, otherwise, you can pay a premium for the same power capacity which could be achieved by using 1 or 2 additional panels.However, high-efficiency panels using N-type cells will almost always outperform and outlast panels using P-type cells due to the lower rate of light-induced degradation or LID, so the extra cost is usually worth it in the long term.For Example, a high-efficiency 400W+ panel could cost $350 or more while a common 370W panel will typically cost closer to $185. This equates to roughly $0.50 per watt compared to $0.90 per watt. Although in the case of the leading manufacturers such as Sunpower, Panasonic and REC, the more expensive panels deliver higher performance with lower degradation rates and generally come with a longer manufacturer or product warranty period, so it’s often a wise investment.
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