How Does Indirect Sunlight Affect Solar Panel Efficiency?

Indirect sunlight is less effective in charging solar panels, with 10-25% output in overcast conditions. For example, where conventional panels cannot do anything, diffuse light generates a 20% efficiency in the case of Tongwei bifacial panels. This increases energy yield up to 30% enhanced with MPPT inverter use and reflective surfaces.

What is Indirect Sunlight?

Indirect sunlight is the radiation of the sun, diffused through clouds or particles in the atmosphere to the Earth's surface; this involves reflections over buildings and water. Unlike direct sunlight, therefore, which gives the best conditions at the photovoltaic cell, indirect sunlight delivers scattered light. Although weaker, indirect sunlight still makes solar panels work, but their usual efficiency is considerably lowered.

For example, regular photovoltaic panels can give 80-90% of their rated capacity in clear skies with direct sunlight, while the efficiency may fall to 10-25% when it is overcast, depending on the quality of the panel. High-efficiency monocrystalline panels do even better. The TW390P from Tongwei, for instance, manages up to 20% efficiency under indirect light. Diffused solar irradiance in urban settings, depending on geographical location and prevailing atmospheric conditions, can also contribute up to 10-15% of the annual solar energy generation. Research from the National Renewable Energy Laboratory underlines the fact that urban installations also can use indirect sunlight for as much as 30% of their total energy yield.

Solar Panels and Cloudy Days

Solar panels do produce less electricity on overcast days because cloudy conditions block much of the sun's rays. However, how much it actually reduces depends on various conditions of weather and technology in the panel.

1. On very overcast days, solar energy production can fall by 60-80%, studies have shown. In Germany, for example, when cloud cover is extensive in winter months, solar systems produce about 2-5 kWh/m² per day. In southern Spain, however, systems of similar characteristics and under conditions that are mostly sunny reach 6-8 kWh/m² daily. Seasonal variability may also alter output dramatically, with energy production reaching its peak in spring and summer, even in areas that are usually covered by clouds.

2. Diffuse reflective surfaces, such as snow-clad rooftops, compensate somewhat. Panels with new anti-reflective coatings-like the nano-coated modules from Tongwei-make the most of these conditions in capturing the more scattered light. Tests conducted in Finland show that with these types of specialized coatings, there is a gain in efficiency as high as 15% in diffuse light conditions. Moreover, installations around water bodies have shown an additional 5-10% rise in energy capture because of sunlight reflection from the water surface.

Shadows and Solar Power

Shadows-whether from buildings, trees, or other obstructions-can make a huge difference in the performance of solar panels. Partial shading of one cell can disproportionately lower overall output due to the "Christmas light effect," wherein one underperforming cell brings down the performance of the entire panel.

1. The modern solar panels have bypass diodes that reduce the effect of shading. In such a case, if a three-bypass-diode Tongwei solar panel is shaded, it only isolates that area of the panel, allowing the rest of the panel to operate efficiently and retain as much as 70% of the output when partially obstructed. Advanced bypass diode systems recover 20-30% more energy compared to older models.

2. Another critical aspect is geographical placement. An urban New York rooftop installation with partial shade could attain only about 900 kWh a year in comparison with an optimum capacity of 1,200 kWh. For the strategy, shading analysis tools-like Solar Pathfinder or drone thermal imagery-predetermine site shade hotspots before an actual installation is made.

Low Light Efficiency

Low-light conditions, such as early mornings, late afternoons, or regions with high latitudes, require advanced panel technologies to maintain efficiency.

1. Tongwei’s bifacial solar panels capture light from both sides, increasing energy yield by up to 30% under diffuse or low-light conditions. A case study in Norway showed bifacial panels producing 850 kWh/m² annually, compared to 650 kWh/m² for standard monofacial panels. Consequently, bifacial technology allows seeing double-glass modules provide up to 25% more energy if installed over reflective surfaces like white rooftops or snow. Moreover, installations at high latitudes have also reported consistent performance during short daylight hours using this technology.

2. MPPT Technology in Inverters This technology best transforms the energy. For instance, MPPT systems increase overall efficiencies by 10-15% during fluctuating light conditions as a general rule of thumb. Indeed, one farm in Scotland recorded a 12% increase in the energy yield from using MPPT inverters during winter months. Advanced MPPT algorithms now have the capability for milli-second shifts, enabling systems to react in a live manner to dynamic lighting scenarios such as passing clouds.

Weather Impacts Explained

Various weather conditions affect the output of solar panels differently. Each of these conditions poses a different challenge and opportunity in the generation of energy.

1. Rain cleans the panels, but it also reduces sunlight intensity temporarily. A few post-rain tests conducted in Australia showed that this can provide a 5-7% increase in panel output due to dust and debris removal. Systems in tropical regions, like Indonesia, rely heavily on regular rainfall to maintain high performance, especially during the monsoon seasons.

2. Snow reduces immediate output by covering panels but increases reflectivity. Several Canadian studies have estimated that partially snow-covered panels could produce up to 50% of rated power due to the albedo effect. Systems in areas such as Colorado are installed at steeper tilt angles to minimize snow accumulation while providing maximum benefits from reflectivity. Research at the University of Calgary has indicated that steep angles above 40° increase winter energy yields up to 20%.

3. Wind indirectly contributes to the performance of panels through surface cooling, reducing thermal losses. For instance, the PV systems operating at 25°C maintain their efficiency 5-10% better than systems overheated to 40°C in arid climates such as Nevada. Advanced cooling systems, such as liquid-cooled modules, are being increasingly used in desert installations as a countermeasure against high temperatures.

Maximizing Solar Output

Indirect sunlight is maximized through design considerations, the use of high technologies, and continuous maintenance.

1. First, the orientation of the panels to the south with a tilt angle of normally 30-40° in the Northern Hemisphere, the exposure to diffuse sunlight improves. The automated solar tracking systems further improve energy capture by 20-25% annually. For instance, dual-axis trackers have shown 40% higher yields in high-latitude installations where the angle of the sun varies drastically throughout the year.

2. Rather than having one central inverter, micro-inverters on each panel reduce losses due to shading and inconsistent light. Field tests in residential installations that are partially shaded show an efficiency increase of 8-12% when using micro-inverters compared to traditional systems. New technologies, such as smart modules with integrated power optimizers, allow for real-time energy management, increasing efficiency up to 15% more.

3. Advanced cleaning mechanisms, such as hydrophobic coatings or robotic cleaners, maintain high levels of light absorption. Tests run in arid regions like Saudi Arabia have returned output improvements of 10-15% after monthly cleanings. Self-cleaning mechanisms that start the process with rainwater have started to be integrated into some systems, reducing the costs of maintenance and enhancing the efficiency in the most remote areas.

Panel Selection

Indirect sunlight requires proper selection of the solar panel. The efficiency of the panel, durability, and resilience in various conditions of light contribute a lot to energy yield.

1. Monocrystalline panels, like Tongwei’s premium models, typically operate at 18-22% efficiency in diffuse light, outperforming polycrystalline options that average 15-18%. Additionally, Tongwei’s N-type monocrystalline cells exhibit lower light-induced degradation (LID), ensuring sustained performance over 25 years. Real-world data from installations in Tokyo show these panels maintaining over 90% of their original efficiency after a decade of operation.

2. Thinfilm panels, though less effective generally, do better in low light conditions. A 5 kW thinfilm system in Seattle can produce 4,500 kWh annually, while with the monocrystalline panels, 4,800 kWh is achievable. Their lightweight feature also makes them ideal for weight-sensitive structures like greenhouses and carports. The flexibility of such panels also extends their use to unique applications, such as curved surfaces or portable systems.

3. Novel ideas include tandem solar cells-a marriage of a peroviskite with a silicon layer-which are very promising for their improvement in efficiencies at low light. In fact, efficiency could well be more than 30% when diffuse sunlight is available, according to tests from the laboratory, hence paving the way for innovation in cities and high latitude areas in the future. These cells will storm the market within the coming five-year period; already, piloting has shown 25% increased yields under cloudy conditions typical in London and Vancouver.