Solar energy conversion relies on photovoltaic (PV) panels, which transform light energy from the sun into usable electricity. Efficiency is defined by the percentage of incident sunlight converted into electrical power, a rating determined under standardized laboratory conditions. Real-world efficiency, however, is heavily influenced by the quality of the light and the panel’s operating environment. Locations that consistently compromise these factors are where solar energy will be the least efficient.
Extreme Latitudes and Seasonal Variation
The most geographically intuitive areas of low efficiency are high-latitude regions, such as Northern Scandinavia, Alaska, or parts of Antarctica. These locations suffer from profound seasonal variation in solar availability. Winter months offer only a few hours of weak daylight, severely limiting the annual energy yield despite long summer days.
The low angle of the sun at high latitudes is another major contributor to inefficiency. When the sun is closer to the horizon, its light must travel through a significantly greater thickness of the Earth’s atmosphere to reach the panel’s surface. This extended path, often described as a high air mass, causes more solar radiation to be scattered and absorbed before reaching the PV cells. Consequently, the light intensity hitting the panel is substantially reduced compared to the direct sunlight received closer to the equator.
Persistent Atmospheric Obstruction
Regions characterized by persistent cloud cover, haze, or high humidity often experience reduced solar efficiency due to atmospheric obstruction. When sunlight passes through thick clouds or heavy smog, the direct beam of light is scattered, turning it into diffuse light. PV panels are much less efficient at converting this diffuse light compared to the intense, directional input of direct sunlight.
Coastal cities frequently affected by heavy fog or regions with prolonged monsoon seasons showcase this effect regardless of their latitude. The constant presence of atmospheric particles, such as water vapor or industrial aerosols, acts as a permanent, partial shield against incoming solar radiation. Airborne pollution containing dust and soot can also absorb solar radiation, with studies showing an efficiency reduction of up to 20% in some polluted regions.
Impact of High Ambient Temperatures
A factor causing significant efficiency loss is the presence of high ambient temperatures, common in hot, arid deserts like the Middle East or the Southwestern United States. PV panels are semiconductor devices, and their electrical performance decreases as their operating temperature increases. The standard testing condition for PV panels is 25°C (77°F). For every degree Celsius above this temperature, a panel’s efficiency typically declines by a measurable amount. This thermal loss, quantified by the temperature coefficient, generally ranges between a 0.3% and 0.5% decrease in power output per degree Celsius increase.
On a scorching day, a panel’s surface temperature can easily reach 60°C (140°F) or higher, resulting in a substantial drop in power generation. While a desert location may receive the greatest amount of raw sunlight, the intense heat causes a systemic reduction in the panel’s ability to convert that light into electricity. This makes the overall operation less efficient than in a cooler, sunny climate.
Localized Soiling and Air Quality
A highly impactful cause of inefficiency is the accumulation of material on the panel surface, a process known as soiling. This is particularly challenging in dry, arid, and dusty environments, or in areas with heavy bird populations. The layer of dust, sand, or grime blocks the light from reaching the PV cells, directly reducing light transmittance and causing a loss of power output.
In extremely dusty regions with infrequent rain, power losses due to soiling can range from 20% to 70% before cleaning. Major urban or industrial centers with poor air quality also experience a continuous deposition of fine particulate matter and smog residue. This industrial grime can permanently coat the panel. In cities with severe pollution, this surface accumulation alone can reduce power generation by 15% to 25% if not cleaned regularly.