What increases the efficiency of a photovoltaic or solar cell and what happens to the efficiency of solar cells on cloudy days?
The efficiency of a solar cell is the (light) power abosrbed / (electrical) power delivered.
To increase the eficiency of a solar cell you must have a solar cell structure that absorbs most of the incoming light and transforms this light into electrical current. You can use multiple junction solar cells for example with the top material absorbing the most of the incoming light. The eficiency remains the same on a clody day when the insolation (the incoming light power) is reduced and thus the electrical power delivered is lower. From what I have read the best commercial solar cells have an efficiency of about 20%
Reflection—A cell's efficiency can be increased by minimizing the amount of light reflected away from the cell's surface. As, untreated silicon reflects more than 30% of incident light. Anti-reflection coatings and textured surfaces help decrease reflection. In addition to reflecting the performance of the solar cell itself, the efficiency depends on the spectrum and intensity of the incident sunlight and the temperature of the solar cell. Though most commercial panels have efficiencies from 15% to 20%, researchers have developed PV cells with efficiencies approaching 50%.As of 2022; the world record for solar cell efficiency is 47.1%, set in 2019 by multi-junction concentrator solar cells developed at National Renewable Energy Laboratory (NREL), Golden, Colorado, USA. This record was set in lab conditions, under extremely concentrated light.Expanding might involve modifying or adjusting part of the original system setup. For example, if the system has a string inverter and it doesn't have additional capacity, you will need to supplement or upgrade the inverter. If the system is a ground mount, you might need to add another racking system. The optimal temperature for solar panels is around 25°C (77°F). Solar panels perform best under moderate temperatures, as higher or lower temperatures can reduce efficiency. For every degree above 25°C, a solar panel's output can decrease by around 0.3% to 0.5%, affecting overall energy production. Photovoltaic modules are tested at a temperature of 25 degrees C (STC) – about 77 degrees F., and depending on their installed location, heat can reduce output efficiency by 10-25%. As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly.Solar cell performance decreases with increasing temperature, fundamentally owing to increased internal carrier recombination rates, caused by increased carrier concentrations. The operating temperature plays a key role in the photovoltaic conversion process. While solar panels still work even when the light is reflected or partially obstructed by clouds, their energy production capacity will be diminished. On average, solar panels will generate 10 to 25% of their normal power output on days with heavy cloud coverage. Photovoltaic panels can use direct or indirect sunlight to generate power, though they are most effective in direct sunlight. Solar panels will still work even when the light is reflected or partially blocked by clouds. Rain actually helps to keep your panels operating efficiently by washing away any dust or dirt. Since any form of light is suitable (even artificial light would work to some extent), solar panels do work on cloudy days, albeit not as productively. On cloudy days, solar panels absorb not only energy from the light spectrum we can see, but also different wavelengths that can pass through thick clouds. There are four main factors that contribute to normal degradation, all from natural causes: thermal cycling, damp heat, humidity freeze and ultraviolet (UV) exposure. Thermal cycling involves dramatic changes between extremes of hot and cold temperatures. This impacts the soldered connections within the panel.
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