Why don't solar panels work in moonlight?

Moonlight has approximately 400,000 times less intensity than sunlight. While silicon solar cells technically respond to moonlight (it is reflected sunlight at the same wavelengths), the current generated is too tiny to charge a battery - approximately 0.001W for a 40W panel under full moon. Solar street light controllers use this principle - they measure panel voltage to determine 'day' vs 'night', and the very low panel output at night tells the controller to switch the light on.

Does the photovoltaic effect work differently in Indian sunlight versus German sunlight?

The photovoltaic effect itself is identical - it depends on photon wavelength and semiconductor properties, which are universal. The difference is irradiance: India receives 5.0–6.5 kWh/m²/day versus Germany's 2.5–3.5 kWh/m²/day. Indian solar panels produce 1.5–2× more energy per year from the same hardware. This is why India's solar economics are so compelling - the same panel that generates modest returns in Germany produces excellent returns in Nashik.

Can solar cells generate power from indoor artificial light?

Yes - some specialist solar cells (amorphous silicon type) are optimised for indoor light spectra and are used in calculators and indoor IoT sensors. Standard crystalline silicon solar panels used in street lights can also generate a small amount from indoor LED or fluorescent light - typically 1–5% of outdoor performance. This is not useful for charging a street light battery but is the principle behind solar garden lights that are charged under indoor bulb light.

What is the Photovoltaic Effect? - How Solar Panels Generate Electricity

The Photovoltaic Effect - Simply Explained

When a photon (a particle of light) strikes a semiconductor material (like silicon), it can transfer its energy to an electron in the material, knocking it free from its atom. If this happens near a p-n junction (a specially engineered boundary between two types of silicon), the freed electron is pushed in one direction by the built-in electric field of the junction, and a corresponding 'hole' (positive charge) moves in the opposite direction. This separation of charges creates a voltage difference - which drives current through an external circuit. Connect an LED and you have a solar-powered light.

P-Type and N-Type Silicon

Pure silicon is a poor conductor. To make it useful for solar cells, manufacturers deliberately add impurities - a process called doping. N-type silicon: doped with phosphorus (5 valence electrons) - has extra free electrons (negative charge carriers). P-type silicon: doped with boron (3 valence electrons) - has 'holes' (positive charge carriers). When N-type and P-type silicon are joined, electrons from the N side diffuse into the P side near the junction, creating a depletion region with a built-in electric field. When a photon knocks an electron free near this junction, the electric field sweeps the electron to the N side and the hole to the P side - creating current flow in an external circuit.

Why Solar Panels Lose Output in Heat

In hot conditions (like Nashik summers at 45°C+), there are more thermally excited electrons in the silicon - these create background 'noise' that slightly opposes the photovoltaic current. The result: panel voltage drops at high temperature (approximately -0.4%/°C above 25°C), reducing power output. This is why: Indian solar systems need oversized panels to compensate for summer heat losses. Ventilation behind the panel (air gap between panel and mounting surface) reduces panel temperature by 5–10°C and recovers some of the heat loss. MPPT controllers continuously adjust operating point to harvest maximum power even as temperature changes.

From Cell to Panel to Street Light System

A single silicon solar cell produces approximately 0.5–0.6V and 8–10A in full sunlight - about 5W per cell. To get useful voltage: cells are connected in series. A 36-cell series string gives approximately 18V - the standard for 12V charging systems. To get more current: strings are connected in parallel. A standard 40W solar panel for a street light contains 36 cells in a 4×9 arrangement, producing 18–20V open circuit and 2–2.5A short circuit current. The MPPT controller finds the exact combination of voltage and current from this panel that maximises the power harvested - the maximum power point on the I-V curve.