Do solar panels produce more in summer than winter

Summer power generation is usually 2-3 times that of winter. Although high temperatures slightly reduce panel efficiency by about 10%, the more than six hours of sunlight and better lighting angles in summer far exceed the two-three hours in winter, ensuring that summer is the peak revenue period of the year.

It is recommended to clean the panels regularly to ensure maximum light absorption.

Summer vs. Winter

Difference between summer and winter output

A 10 kW monocrystalline silicon PERC system can reach a daily average peak power of 9.2 kW in July, producing 58 kWh of electricity throughout the day, while the daily output of a system with the same specifications in January usually drops to 16 kWh, resulting in an output ratio of 3.6:1.

This 260% data fluctuation stems from the 23.5 degree change in the Earth's tilt, causing the effective irradiance in winter to attenuate from 1000 W/m² in summer to 450 W/m².

Within a 25-year operation cycle, the electricity production during the 6 months of summer typically accounts for 72% of the total generation share, while the contribution rate from November to February in winter is only around 14%.

Calculating with an electricity price of 0.12 USD/kWh, a single month in summer can generate 210 USD in revenue, while it shrinks to 58 USD in winter.

Is the day long enough?

In summer, the system can detect a startup current of 0.8A as early as 5:30 in the morning and will not cut off the output until 19:30 in the evening, with a total daily work cycle of 14 hours.

Limited by geographical latitude in winter, the system only reaches the inverter startup threshold of 200W/m² at 8:45 AM and shuts down at 16:15 PM because the irradiation intensity falls below 50W/m², shortening the actual working window by 46%.

This daily difference of 6.5 hours directly leads to a deficit of more than 120 Ah in the cumulative Coulomb charge of the PV array.

In regions at 40 degrees north latitude, the solar altitude angle at noon in summer is 73.5 degrees, while it is only 26.5 degrees in winter, increasing the transmission path of light through the atmosphere by 1.8 times and causing the photon flux density reaching the panel surface to drop by 55%.

Too hot is also not good

PV cells have a power temperature coefficient of -0.34%/°C, which means that for every 1°C increase in panel temperature, the output power is lost by 0.34 percentage points.

Under summer exposure, the internal silicon wafer temperature of a 550W module often rises to 70°C, which is 45°C higher than the Standard Test Conditions (STC) of 25°C, resulting in a mandatory reduction of real-time power by 15.3%, with the actual output being only 465W.

When the ambient temperature in winter is maintained at 0°C, since voltage is inversely proportional to temperature, the module's output voltage will reverse compensate by about 10%, causing the instantaneous conversion efficiency of a single module in January to increase from 20.5% in summer to 22.3%.

Although this 1.8% efficiency gain is very significant at the physical level, because the total radiation energy base in winter is only 35% of that in summer, this efficiency boost cannot reverse the downward trend in total production.

Sunlight hits at an angle

When the solar incidence angle deviates from the module normal by 60 degrees, according to the Cosine Law, the effective light-receiving area is reduced by 50%, which is the primary geometric reason for insufficient power generation in winter.

In summer, light enters the encapsulation glass almost perpendicularly at 90 degrees, keeping the reflectivity at an extremely low level of 2%, whereas the low-angle incidence in winter causes the reflectivity to surge to over 12%.

This means that, even on sunny days, in December, more than 10% of light energy bounces directly off the glass surface and cannot enter the silicon wafer.

By manually optimizing the tilt angle of fixed brackets from 20 degrees to 45 degrees, the incidence loss in winter can be reduced by 8%, thereby increasing the total monthly electricity generation in December and January by about 125 kWh.

Snow is blocking the light

A snow cover thicker than 3 cm will completely block 98% of short-wave radiation, causing the PV system output to drop to 0 W and enter a dormant state.

If there is 15% local shading on the roof, affected by the hot spot effect, the resistance of the shaded cell cells will skyrocket from 0.01 ohms, generating local high temperatures and consuming the current produced by the other 85% of normal cells.

Experiments show that an installation tilt of over 35 degrees allows 70% of the snow to slide off naturally within four hours after the temperature rises to 3°C, whereas a system with a small tilt of 15 degrees requires more than 48 hours for self-cleaning.

During months with frequent snowfall, snow that is not cleared in time can cause an additional loss of 25% to 40% in monthly revenue, extending the system's payback period by 1.2 years.

Temperature Paradox

Panels are also afraid of heat

At the site of a PV power station in July, the surface temperature of monocrystalline silicon modules often soars to between 65°C and 75°C, which is exactly 40°C to 50°C higher than the 25°C Standard Test Conditions.

Based on the calculation of the -0.35%/C power temperature coefficient for P-type PERC cells, this temperature difference will cause a mandatory fallback in real-time output power of 14% to 17.5%.

This means that a module rated at 550W may actually output only around 453W under intense exposure to high temperatures at 12:00 noon.

Carriers inside the silicon wafer move more vigorously at high temperatures, increasing the recombination rate by 12% and directly lowering the fill factor (FF) by about 3 to 5 percentage points.

On a summer day with an ambient temperature of 38°C, if the backplane ventilation gap is less than 10 cm, the heat accumulation inside the module will cause the conversion efficiency to drop from 21% to below 18.5%.

Important Data Quote:
Experimental data shows that for every 1°C increase in module temperature, the open-circuit voltage (Voc) will drop by about 0.12 V, and although the short-circuit current (Isc) has a slight increase of 0.05%, it completely fails to compensate for the drastic power loss of over 2.3% at the voltage end.

Cold is better

When the temperature in January drops to 0°C or even lower, the physical performance of PV modules enters a high-efficiency range because the band gap of the silicon wafer is more stable in a cold environment.

In a -5°C environment, the conversion efficiency of the module can reverse increase by about 10.5% compared to 25°C, making the instantaneous peak efficiency of a 10 kW system reach over 23%.

The cold air density in winter is 15% higher than in summer, which enhances the convective heat transfer efficiency of wind on the panel, keeping the module operating temperature only about 10°C higher than the ambient temperature.

Although the solar radiation intensity in winter may only be 400 W/m², far lower than the 1,000 W/m² in summer, under the same low-light conditions, low-temperature modules produce 8% more electricity per watt than high-temperature modules.

This negative temperature coefficient characteristic of 0.3% to 0.4% allows PV systems to show more stable voltage curves on sunny days in December than in August.

How voltage changes

Low temperatures in winter cause the DC input voltage of the inverter to rise by about 12% to 15%, which stems from an 8% reduction in the internal resistance of semiconductor materials in cold environments.

For a commercial system designed for a pressure of 1000 V, under extreme conditions of -20°C, the open-circuit voltage of the string might surge from 850 V to near 980 V, close to the equipment's withstand voltage limit of 1000 V.

The maximum power point tracking (MPPT) range of the inverter is usually between 200V and 850V; high summer temperatures cause the voltage to drop to around 550V, in the middle to low segment of the efficiency curve, with a conversion efficiency of about 97.2%.

In winter, with the voltage maintained in the golden range of 750 V, the inverter's conversion efficiency can stabilize above 98.5%.

This 1.3% efficiency difference can reduce heat energy loss by 6.5 kWh per day in a 50 kW distributed power station.

Important Data Quote:
The temperature coefficient of N-type TOPCon modules is only -0.29%/°C, which allows them to produce 3.2% more electricity at high temperatures of 70°C compared to P-type modules, increasing the internal rate of return (IRR) in hot regions by 0.8 percentage points.

Which is more efficient

A comprehensive comparison reveals that although summer has an ultra-long sunlight duration of 14 hours per day, the total energy loss due to temperature rise accounts for more than 18% of the theoretical output.

Although the sunlight duration in winter is shortened to 8 hours and the irradiation intensity is weakened by 50%, the system conversion efficiency (PR value) can usually reach 85% to 88%, much higher than the 75% to 78% in summer.

Taking a 1 kW experimental array as an example, every 1 kWh of output in summer requires consuming 1.25 kWh of solar radiation energy, whereas in winter, only 1.14 kWh is needed to produce the same amount of electricity.

Within a 25-year system life cycle, the probability of PID (Potential Induced Degradation) effects caused by high temperatures is 4 times higher in summer than in winter.

From June to August each year, the high-temperature and high-humidity environment will cause the light transmittance of the encapsulated EVA film to drop by about 0.1%, a non-reversible physical attenuation that is almost zero in winter.

Lifespan is affected

Long-term exposure to high-temperature environments above 60°C will accelerate the oxidation rate of the metallization layer between the PV ribbon and the cell, increasing contact resistance by 15% within 10 years.

Experiments show that for every 1,000 hours a module runs at 70°C, its power degradation rate will be 0.25 percentage points faster than at 25°C.

While the low-temperature environment in winter can effectively inhibit this thermal degradation process, extreme low temperatures below -15°C will shorten the aluminum alloy frame by about 0.5 mm, posing a pressure test of over 20 MPa on the tensile strength of the encapsulated silicone.

During seasonal transitions where temperature fluctuations exceed 50°C, the expansion rate of micro-cracks inside the cells will increase by 30%, leading to 2% more loss in output power by the 5th year than expected.

To extend the service life by 3 to 5 years, a module gap of more than 20 mm must be maintained during installation to use natural wind to reduce the panel's operating temperature by 3°C to 5°C.

Important Data Quote:
Modules encapsulated with double-sided glass lose 45% less mechanical strength at high temperatures than single-glass modules, maintaining 99.8% physical structural stability in a 75°C environment, effectively reducing the failure rate in summer.

How to cool down faster

By optimizing the installation height from 0.5 meters to 1.5 meters, the air flow rate on the back of the panel can be increased by 2.5 times, thereby reducing the panel temperature at noon in summer by about 8°C.

This 8°C reduction in temperature can be directly converted into a 2.8% increase in real-time power generation; for a system with a total investment of 5000 USD, an additional 140 USD in electricity revenue can be recovered annually.

In high-latitude regions, utilizing the high reflectivity of the snow surface (Albedo up to over 0.8) can provide an additional 25% light gain for the back of bifacial modules, which is enough to offset the bracket stress burden caused by low temperatures.

In tropical regions, using frame materials with high thermal conductivity can improve heat dissipation efficiency by 5%, reducing the system's LCOE (Levelized Cost of Energy) by 0.005 USD/kWh.

Over an operation cycle of 300 months, this physical fine-tuning for temperature characteristics can increase the cumulative total power generation by about 12,000 kWh.

Maintenance and Optimization

Clean panels frequently

In the daily operation of a PV array, the accumulation of dust, bird droppings, or industrial dust on the panel surface will cause serious shading loss, resulting in a direct drop of about 15% to 25% in the system's photoelectric conversion efficiency.

According to experimental data, in arid regions with 60 consecutive days of no rain, the power drop caused by surface dirt on a 550W monocrystalline silicon module can reach more than 80W.

Using neutral deionized water with a pH of 7 for cleaning can avoid a 0.2% probability of glass surface corrosion; the labor cost for a single cleaning is between approximately 0.08 USD and 0.15 USD per kilowatt.

If the cleaning frequency is increased from once every six months to once per quarter, a 10 kW system can produce an additional 950 kWh of electricity annually, which, based on an electricity price of 0.12 USD/kWh, equates to an annual increase of 114 USD in cash revenue.

In areas where the dust concentration exceeds 50 μg/m³, using an automatic cleaning robot with a 99% cleaning rate can reduce the system's Levelized Cost of Energy (LCOE) by about 0.003 USD.

Calculate the tilt angle accurately

By manually or automatically adjusting the bracket tilt angle, the 47 degree change in the solar altitude angle due to the Earth's revolution can be significantly offset.

In regions at 35 degrees north latitude, the ideal installation tilt in summer is usually 20 degrees, while it needs to be adjusted to 50 degrees in winter to ensure that the light incidence angle remains within a deviation range of 5 degrees.

This seasonal adjustment can increase the instantaneous power generation in December by more than 15%, raising the daily output from 18 kWh to about 21 kWh.

For a home system with a total investment of 8000 USD, adding 500 USD to the budget for adjustable brackets can increase the cumulative total generation by 6.5% over a 25-year lifespan.

This physical fine-tuning increases the effective capture rate of photons on the silicon wafer surface by 120 W/m², directly raising the internal rate of return (IRR) of the system by 0.7 percentage points.

Over an operation period of 300 months, this optimization measure can reduce the ineffective running time of the inverter in low-power zones and extend the working life of power modules by about 18%.

Shovel away the snow

Snow cover thicker than 5 cm will completely block the module's reception of short-wave infrared rays, causing the system output power to drop to zero instantly.

Experiments show that an installation tilt of over 35 degrees allows 65% of the snow to slide off naturally under gravity within 3 hours after the ambient temperature rises to 2°C.

If the snow cover exceeds 48 hours, the hot spot temperature inside the cells due to current obstruction may rise to 85°C, causing a non-reversible yellowing of 0.5% in the EVA encapsulation film.

Using a professional soft-edged long-handle snow shovel to clear snow can increase the system's winter self-consumption rate by 20%, avoiding about 45 USD in annual electricity purchases from the grid.

For a 1 MW medium-sized commercial power station, timely snow removal means reducing downtime losses by 2400 USD per day, thereby shortening the payback period by 0.8 years.

Tighten the screws

PV bracket bolts will produce 0.1 mm scale metal thermal expansion and contraction displacement under severe temperature fluctuations ranging from 70°C in summer to -20°C in winter.

If the tightening torque is lower than 25 Nm, long-term physical vibrations will cause the contact resistance of MC4 connectors to increase from 0.5 milliohms to over 5 ohms, which will cause a 2% power loss on the DC side and pose a risk of fire.

Conducting a standardized torque inspection of 35 Nm on all connection points every two years can ensure that the voltage drop of the 10 AWG DC cable remains within the design range of 1%.

On the inverter side, cleaning the dust from the cooling fans every 12 months can reduce the operating temperature of the internal capacitors by 5°C, thereby extending their 10-year life expectancy by about 15%.

Replacing aged and failed bypass diodes (costing about 5 USD each) can prevent a single shaded cell from dragging down the total output of the entire string of 20 modules, recovering potential power losses of over 500 W.