Will Winter, Fog, Smog Cut Your Rooftop Solar Savings? What Homeowners Need To Know

Winter can bring relief from scorching temperatures, but it may also bring an unexpected problem for households that have installed rooftop solar panels. Shorter days, weaker sunlight and persistent fog can reduce electricity generation just when homeowners are hoping to keep their power bills under control.

The impact can be particularly noticeable in northern India, where fog and pollution frequently limit sunlight during winter mornings. On days when sunlight struggles to reach solar panels, electricity generation can fall sharply.

However, winter does not necessarily mean solar panels become less efficient. Cooler temperatures can actually help panels perform better. The real challenge is the amount of sunlight available and how long it lasts.

How Much Does Solar Generation Fall In Winter?

The decline depends largely on where a solar system is installed and the weather conditions it faces. In Delhi-NCR and other parts of northern India, rooftop solar generation can experience substantial seasonal variations. On days when sunlight is severely restricted, generation may fall by up to 30 per cent, according to Rakesh Malhotra, Founder of Livguard (SAR Group).

"Yes, generation does dip in winter. Shorter days, lower sunlight intensity, fog and smog, and higher pollution levels all reduce the amount of sunlight reaching the panels," Malhotra told NDTV. He said the impact varies depending on the location, weather and air quality.

Vijay Menon, COO of Navitas Solar, however, points out that colder weather itself is not necessarily bad for solar panels.

Solar panels generate electricity by absorbing sunlight. Cooler temperatures can improve their efficiency under comparable sunlight conditions. Shorter daylight hours and fog, rather than low temperatures alone, are responsible for much of the seasonal variation. "Winter does not automatically mean a sharp drop in solar generation," Menon told NDTV.

According to him, solar generation depends on geographical location, weather patterns and the design of the installation. Clear winter days can still deliver useful electricity, even when the temperatures are low.

Why Winter Solar Generation Can Be Lower

Three factors can influence rooftop solar output during winter. 

Shorter daylight hours: Solar panels have fewer hours to generate electricity. The sun also follows a lower path across the sky in winter, affecting the amount of sunlight captured.

Fog and smog: Dense fog can significantly reduce sunlight reaching solar modules. Pollution and atmospheric haze can further restrict sunlight, particularly across northern India.

Changing weather conditions: Cloud cover and prolonged periods of poor visibility can reduce generation for several days. The impact depends on local weather and the duration of these conditions.

There is, however, a counterbalancing factor. Solar panels generally operate more efficiently in cooler temperatures than under extreme heat. Menon said properly designed systems can continue delivering useful electricity throughout winter. He added that solar installations should be evaluated on their annual generation potential rather than judged by a few cloudy days.

Does Lower Winter Electricity Demand Offset The Loss?

For households, the effect of lower solar generation depends on their electricity consumption. Air-conditioners are used less frequently during winter, potentially reducing electricity bills and partially offsetting the seasonal decline in solar output.

However, electricity consumption does not fall uniformly. Geysers, room heaters and other appliances can increase household power usage during colder months. Malhotra said the reduction in India's overall electricity demand during winter is relatively modest compared with the summer peak.

Menon said households could improve savings by using suitable appliances during daylight hours, allowing them to consume solar electricity directly instead of drawing power from the grid.

How To Get More Electricity From Rooftop Solar In Winter

Homeowners can take a few practical steps to improve solar generation throughout the year.

1. Get the installation design right: Panel orientation, tilt, spacing and shading can make a significant difference. The system should be designed around local sunlight conditions and the available rooftop space.

2. Keep solar panels clean: Dust accumulation can reduce electricity generation. Regular cleaning, following manufacturer guidelines, can help maintain performance.

3. Monitor electricity generation: Checking daily output helps homeowners identify unexpected drops. Persistent underperformance could indicate shading, dirt or equipment-related issues that require attention.

4. Invest in quality components: Malhotra said high-quality solar components, suitable inverters and storage solutions can help consumers make better use of the electricity generated.

Winter Is Not A Reason To Give Up On Solar

The seasonal decline in generation does not undermine the long-term benefits of rooftop solar. What matters is how well the system is designed for local conditions and how much electricity it generates over an entire year.

Menon said simulation tools can estimate monthly electricity generation using geographical coordinates, weather data, panel specifications and other installation parameters. These estimates help homeowners understand seasonal variations before investing in a system.

Malhotra, meanwhile, emphasised that proper system sizing, maintenance and storage can help households maximise the benefits of rooftop solar.