How to Enhance Solar Power Generation in Low Light | 3 Innovations

Low-light power generation relies on three major innovations: Perovskite cells break through 30% efficiency, bifacial modules utilize ground reflection to increase production by up to 25%, and AI power optimizers accurately capture dim light while reducing losses.

Perovskite Tandem Solar Cells

Two Layers Working Together

Traditional monocrystalline silicon cells have only one layer of "light-catching net". Due to the Shockley-Queisser limit, their theoretical photoelectric conversion efficiency upper limit is locked at 29.4%.

Perovskite tandem technology stacks a perovskite thin film with a thickness of only 500 to 1,000 nm on top of a silicon bottom cell, physically splitting the original single energy absorption bandwidth.

The top perovskite material has a tunable bandgap of 1.5 to 1.8 electron volts (eV), specifically intercepting high-energy short-wave photons in the 300 to 800 nm band, while the bottom monocrystalline silicon (bandgap 1.1 eV) is responsible for receiving the 800 to 1,200 nm long-wave infrared light that penetrates through.

· The efficiency of small-area tandem cells of 2 cm² in the laboratory has already surpassed 33.9%, which is 7.4 percentage points higher than the 26.5% theoretical limit of mainstream TopCon cells.

· Tandem modules with a 2-terminal (2-Terminal) structure require only one set of inverter systems, reducing cable material expenditure by 15% and circuit installation man-hours by 10% compared to 4-terminal structures.

· The light absorption coefficient of the perovskite layer is more than 10 times higher than that of monocrystalline silicon, which means only 1 μm thickness of perovskite can achieve the same light absorption capacity as a 180 μm thick silicon wafer, reducing raw material consumption by 99%.

A More Diverse Light Diet

Ordinary cells encounter rainy days or low-light environments before sunset, where the photon energy distribution shifts toward the infrared band, causing the voltage of standard cells to drop rapidly from 0.7 V to below 0.5 V.

Tandem cells precisely control the bandgap near 1.65 eV by adjusting the composition ratio of bromine (Br) and iodine (I) in the perovskite layer, allowing them to maintain an open-circuit voltage above 1.1 V even at low light intensities of 100 W/㎡ to 200 W/㎡.

· On heavily hazy days with PM2.5 concentrations exceeding 150, blue and green light are significantly scattered. The capture efficiency of tandem cells for scattered light is 18% to 22% higher than that of single-layer silicon cells.

· Since the temperature coefficient of perovskite is only -0.01%/℃ while monocrystalline silicon is as high as -0.35%/℃, when the backsheet temperature reaches 75 ℃ in summer, the power attenuation of tandem modules is over 4.5% less than that of ordinary modules.

· This "spectral segmentation" technology reduces the thermal energy loss of photons by 30%, decreasing the temperature rise inside the cell by 2 ℃ to 5 ℃, which indirectly extends the service life of encapsulation materials by 3 to 5 years.

Power Even on Cloudy Days

In regions with poor solar resources like Northern Europe or areas with continuous rain, the average annual sunshine duration may be less than 1,100 hours.

The cumulative annual power generation of modules using tandem technology in these areas is typically 15.6% to 20.2% higher than that of traditional PERC modules.

This is because tandem cells maintain over 85% of peak efficiency during early morning and late evening when the solar incident angle is greater than 60 degrees, while the conversion efficiency of traditional cells at these times usually plummets by more than 40%.

· By applying a 100 nm thick anti-reflective coating to the module surface, photon reflectance is reduced from 5% to 1.2%, providing an additional 35 W/㎡ of effective power between 6:00 and 8:00 in the morning.

· Even in extreme cases where cloud cover causes irradiance to drop to 10% of the standard value, a 20 kW tandem system can still output about 1.5 kW to 2.2 kW of power, enough to maintain the 24-hour standby power consumption of basic household appliances.

· This continuous output capability allows the configured capacity of the system's energy storage cell to be reduced by 15%, saving the procurement budget for lead-acid or lithium batteries by 3,000 to 8,000 yuan.

Longer Lifespan

Early perovskite materials were extremely sensitive to moisture and oxygen. In a damp-heat test at 85 ℃, the efficiency of unencapsulated cells would drop by 50% within 200 hours.

Current industrial solutions have enabled modules to pass the 2000-hour damp-heat aging test under the IEC61215 standard by introducing polymer encapsulation technology and interface modification of the hole transport layer.

Mass-produced tandem modules can now promise a power guarantee of 20 to 25 years, with the annual attenuation rate controlled between 0.55% and 0.6%.

· The alumina water barrier layer prepared using atomic layer deposition (ALD) technology has a water vapor transmission rate (WVTR) below 10^-6 g/m²/day, ensuring that the cell efficiency is not lower than 90% of the initial value after working for 10,000 hours in an 85% humidity environment.

· The defect density inside the perovskite layer has been reduced from 10^17/cm³ to 10^15/cm³, which increases the carrier diffusion length from 100 nm to over 3 μm, significantly reducing the internal charge recombination speed.

· After ultraviolet (UV) irradiation tests simulating 20 years of sun exposure, the yellowing index of the improved organic-inorganic hybrid perovskite material increased by only 1.5, and the light transmittance loss was controlled within 0.8%.

Bifacial Technology

Both Sides Can Generate Power

Ordinary monofacial modules have an opaque aluminum alloy base plate on the back, while bifacial modules use transparent glass or transparent backsheets. Combined with bifacial cells (such as TopCon or HJT), they allow both front and back sides to generate current.

Numerical Values that Cannot Be Ignored: Current mainstream TopCon cells typically have a bifaciality between 80% and 85%, which means if the front can generate 100 watts, the back can generate 80 to 85 watts under the same light conditions.

During early morning and twilight, when the solar angle is very low, the front light-receiving area decreases, but the scattered light in the atmosphere becomes more active. The back contribution rate of bifacial modules will soar from the conventional 10% to over 25%.

For modules using 182 mm or 210 mm large-size silicon wafers, the front power of a single module has reached 580 W to 700 W. With the extra boost from the back, the actual output power can often easily exceed 750 W.

This high power output allows the inverter's over-provisioning ratio to increase from 1.1 to 1.3 or even 1.5, significantly lowering the power conversion cost per watt.

Ground Conditions Matter

The amount of power generated by bifacial modules largely depends on what kind of surface you install them on, which is known in the industry as "Albedo".

Since the back side absorbs light reflected from the ground, the color and material of the ground become variables determining the gain.

· If it is ordinary dark soil or grass, the albedo is usually only 10% to 20%, and the back gain is about 5% to 8%.

· If switched to a grey-white cement floor, the albedo can reach 30% to 40%, and the power generation gain will steadily rise to around 12%.

· The most ideal scenario is white sand or snow-covered polar regions, where the albedo can reach 70% to 90%. In this case, the extra power generation from the back can even exceed 30% of the total front output.

In actual calculations, if the module height from the ground is increased from 0.5 meters to 1 meter, the light-receiving uniformity of the back increases by 15%, effectively avoiding the "hot spot effect" caused by bracket shadows.

This extra current brought by the ground environment allows the system to generate 15% to 20% more total power over the same 25-year life cycle.

Raise the Brackets

If the modules are close to the ground, the light intensity on the back will decrease by over 40% because the space is too narrow.

According to field operation data, maintaining the lowest point height of the module between 0.8 meters and 1.2 meters is the most cost-effective solution, as it ensures the back can receive 360-degree scattered light.

Installation Data Watershed: If the module tilt angle is 2 to 5 degrees more than the local latitude, although the front power generation will slightly drop by 1%, the ground reflection light path received by the back will be optimized, and the total gain can instead increase by 3%.

The structure of the bracket is also critical. If a traditional crossbeam bracket blocks the exact center of the module's back, it will create a shadow band about 10 cm wide, causing the current in that series circuit to drop by 5% to 10%.

In scenarios using trackers (Tracker), bifacial modules combined with intelligent algorithms can automatically find the angle where the sum of energy from both front and back is the greatest, which can produce 15% to 25% more power than fixed brackets.

Tougher Structure

To protect the cells on the back, bifacial modules generally adopt a 2.0 mm + 2.0 mm double-glass encapsulation mode.

This design of two layers of tempered glass sandwiching the cells significantly enhances the mechanical strength of the module, allowing the front to withstand a snow load of up to 5400 Pa and the back to withstand a wind pressure of 2400 Pa.

Since glass is more wear-resistant and corrosion-resistant than plastic backsheets, these modules have extremely low attenuation rates in coastal salt spray areas or high-temperature and high-humidity environments.

· Ordinary monofacial modules have an annual attenuation rate of about 0.7%, while double-glass bifacial modules can lower it to 0.45% to 0.5%.

· Since there is no risk of water permeability from backsheet materials, these modules basically say goodbye to the PID (Potential Induced Degradation) phenomenon, and the internal charge loss rate is reduced by over 95%.

· Although the weight of the module is about 20% more than monofacial modules, usually between 28 and 32 kg, it comes with a power guarantee period of up to 30 years, which is a full 5 years more effective working time than traditional modules.

This thick encapsulation is not just for wind and rain protection; it also reduces the working temperature of the cells by 1 ℃ to 2 ℃.

Don't underestimate those two degrees. For silicon-based cells, for every 1 ℃ rise in temperature, the power drops by 0.35%. In the long run, this is another power gain of about 1.5%.

Luminescent Solar Concentrators

Power from the Edges

Luminescent solar concentrator plates do not require silicon wafers to cover the entire surface like traditional solar panels.

It typically uses a transparent polymer plate (such as PMMA acrylic or polycarbonate) with a thickness between 3 mm and 12 mm, with fluorescent molecules or quantum dots uniformly incorporated inside the plate at concentrations of 100 ppm to 500 ppm.

When sunlight with wavelengths between 350 nm and 600 nm shines on the plate surface, these fluorescent substances absorb photons and re-emit them at longer wavelengths (such as 650 nm to 850 nm).

Since the refractive index of the polymer plate is usually around 1.49, according to the principle of total internal reflection, about 75% to 82% of the re-emitted light is "locked" inside the plate, bouncing back and forth like in an optical fiber, and finally all converging at the side edges, which are only a few millimeters thick.

We attach narrow strips of high-efficiency solar cells (such as triple-junction gallium arsenide cells, with efficiency up to over 40%) with widths of only 5 mm to 10 mm to these sides.

This structure allows the geometric concentration ratio (the ratio of the light-receiving area to the light-emitting area) to reach 10 times or even 50 times.

This means you only need 2% to 10% of the original expensive silicon wafer area to collect the light energy from the entire glass surface.

Under standard light of 1,000 W/㎡, although the optical efficiency of this concentrator is only 6% to 10%, it cuts the usage of expensive semiconductor materials by more than 90%, reducing the equipment investment cost per watt by 40% to 60%.

Advanced Coatings

The performance of LSC depends entirely on the "Stokes Shift" of the fluorescent coating.

If the shift is too small, the light emitted will be reabsorbed by other fluorescent molecules when bouncing in the plate, causing over 30% energy loss.

The industry now commonly uses non-toxic quantum dots such as CuInS2/ZnS, which can pull the shift to over 150 nm, reducing the effective re-absorption loss to below 5%.

The quantum yield (QY) of these quantum dots can reach over 95%, ensuring that for every photon that goes in, one comes out, with almost no waste.

To deal with light of different wavelengths, researchers also develop "double-layer sandwich" structures. The top layer uses materials that absorb blue-violet light, and the bottom layer uses materials that absorb green-yellow light.

Through this double-layer stacking, the system's coverage of the solar spectrum has increased from 40% for a single layer to 65%.

Under this configuration, even on a heavily cloudy day with a light intensity of only 150 W/㎡, the output current density at the edge of the plate can still be maintained between 15 mA/cm² and 22 mA/cm².

This segmented absorption design reduces thermal loss by 25%. Even if the plate works continuously at a high temperature of 50 ℃, the power drop ratio is controlled within 0.2%/℃.

No Stopping on Cloudy Days

The strongest point of LSC is its extremely high sensitivity to scattered light (diffuse light).

When the cloud layer is thick and direct light is less than 10%, the power generation of ordinary monocrystalline silicon plates will drop by more than 80% because they rely heavily on the incident angle of light.

But LSC is like a "photon sponge"; it can absorb scattered light from all directions with a full 180-degree field of view.

Measured data show that when irradiance drops to 200 W/㎡, the optical efficiency retention of LSC is as high as 88%, while traditional modules usually have less than 20% output.

This characteristic makes it highly competitive in regions above 50 degrees north latitude, where it is rainy all year round.

In areas where the average annual radiation per square meter is only 1,000 kWh, installing 10 square meters of LSC windows can generate 150 to 220 kWh of electricity per year.

In contrast, fixed monocrystalline silicon plates of the same area often have an actual annual power generation benefit about 35% lower than LSC due to limited installation angles in urban buildings where shadows frequently occur.

Since light is transmitted inside the plate, even if 20% of the surface area is blocked by tree shade, the photons captured by the remaining 80% of the area can still flow smoothly to the cell strips at the edges.

This immunity to partial shading makes its system stability more than 2 times higher than traditional series systems in complex light environments like city streets.

Glass Becomes Cell

By adjusting the concentration of fluorescent molecules, we can control the light transmittance of glass between 30% and 85%, fully meeting the lighting needs of offices or residences.

A standard 1.2 m by 1.8 m LSC glass window can produce 30 to 55 watts of electricity per hour while maintaining 70% transparency.

This part of the electricity can be directly used for LED lighting (power about 10 W-15 W) and computer monitors in the office, achieving self-sufficiency in local electricity consumption.

· Heat Insulation Benefit: Fluorescent molecules absorb most ultraviolet rays (over 99%) and some infrared rays, which reduces indoor heat gain by 20% to 30%.

· Air Conditioning Savings: Since windows block heat, the load on air conditioning in summer can be reduced by around 15%, saving an extra 12 to 25 yuan in electricity bills per square meter of glass each year.

· Installation Convenience: Its weight is only about 15 kg/㎡, which is 25% lighter than double-glass modules of the same specifications. Existing window frame structures can be installed directly without additional reinforcement.

This "power generation + heat insulation + lighting" three-in-one function significantly shortens the overall payback period of LSC.

Although the initial cost per square meter is 80 to 150 yuan more expensive than ordinary tempered glass, considering the saved electricity bills and government subsidies for green buildings (usually between 10% and 20%), the increased cost can usually be recovered within 4 to 6 years.