How Solar Power Works

The Photovoltaic Effect

Solar panels generate electricity through the photovoltaic (PV) effect, discovered by Edmond Becquerel in 1839. When photons from sunlight strike a silicon solar cell, they knock electrons loose from their atomic bonds. The cell's internal electric field — created by doping one layer with phosphorus (n-type) and the other with boron (p-type) — forces these free electrons to flow in one direction, producing direct current (DC) electricity.

A single silicon cell produces about 0.5–0.7 V. Solar panels connect 60 to 144 cells in series to reach working voltages of 30–50 V (for 12/24 V systems) or 35–55 V (for grid-tied panels). Panels wired in series multiply voltage; panels wired in parallel multiply current.

Key Panel Ratings

Every solar panel has a nameplate rating measured under Standard Test Conditions (STC): 1000 W/m² irradiance, 25°C cell temperature, AM 1.5 spectrum. Real-world output is typically 10–25% lower because cell temperatures on a rooftop easily exceed 50°C, and irradiance varies with weather, time, and season.

Parameter	What It Means	Typical Range
Pmax (Wp)	Maximum power output at STC	400–580 Wp
Vmp	Voltage at maximum power point	35–45 V
Imp	Current at maximum power point	10–14 A
Voc	Open circuit voltage (no load)	42–55 V
Isc	Short circuit current (max current)	11–15 A
Temp. coefficient (Pmax)	Power loss per °C above 25°C	−0.28 to −0.39 %/°C

The open circuit voltage (Voc) and short circuit current (Isc) define the outer boundaries of the panel's I-V curve. The maximum power point (MPP) sits at the knee of this curve — the exact voltage-current combination that extracts the most watts. This is where the charge controller's job begins.

The Charge Controller

Solar panels produce raw, variable DC. A charge controller sits between the panels and the battery, performing two critical functions: it tracks the maximum power point of the panels to extract peak energy, and it regulates the voltage and current flowing into the battery to prevent overcharging.

PWM vs MPPT

PWM (Pulse Width Modulation) controllers are essentially switches. They connect the panel directly to the battery and chop the connection on and off rapidly. The panel is forced to operate at the battery's voltage (say, 12.8 V) rather than its own optimal voltage (say, 38 V). This mismatch means a significant portion of the panel's potential power is simply wasted as heat. PWM controllers are cheap (₹500–2,000) but typically recover only 65–80% of available panel power.

MPPT (Maximum Power Point Tracking) controllers contain a DC-DC converter that transforms the panel's high-voltage, low-current output into the lower voltage and higher current the battery needs. The controller continuously sweeps the panel's I-V curve to find the voltage where power output peaks — the maximum power point — and locks onto it. As conditions change (clouds, temperature, time of day), the MPP shifts, and the controller tracks it. A well-designed MPPT controller recovers 95–99% of available panel power.

String vs Distributed MPPT

In a string inverter or string MPPT system, multiple panels are wired in series. The entire string shares one MPP tracker. If one panel is shaded, dirty, or degraded, it drags down the entire string's output — a phenomenon called the "Christmas light effect." The tracker finds the best compromise for the whole string, not the optimum for each panel.

In a distributed MPPT architecture — which is what Alloy Charge's SunXtractor uses — each panel (or small group of panels) gets its own dedicated MPPT controller. Every panel operates at its own optimal power point independently. Shading on one panel has zero effect on the others. This architecture also allows mixing panels of different wattages, orientations, and even brands in the same system.

The Battery

Batteries store the DC energy from the panels for use when the sun isn't shining — at night, during monsoon overcast, or during grid outages. The battery is the heart of any off-grid or hybrid solar system.

How a Battery Works

A battery stores energy through reversible electrochemical reactions. During charging, electrical energy drives ions from one electrode to the other through an electrolyte. During discharging, the ions flow back, releasing the stored energy as electricity. The chemistry of the electrodes and electrolyte determines the battery's voltage, capacity, cycle life, and safety characteristics.

Key Battery Metrics

Metric	What It Means
Nominal Voltage	The system voltage — typically 12 V, 24 V, or 48 V. Higher voltage systems carry the same power with less current, allowing thinner cables and lower losses.
Capacity (Ah / kWh)	How much energy the battery can store. 100 Ah at 48 V = 4.8 kWh. Usable capacity depends on depth of discharge.
Depth of Discharge (DoD)	How much of the stored energy you can actually use. Lead-acid: 50%. LFP: 80–95%. Going deeper shortens battery life.
Cycle Life	Number of charge-discharge cycles before the battery degrades to 80% of original capacity. Lead-acid: 500–1,500 cycles. LFP: 4,000–6,000 cycles.
C-Rate	Charge/discharge speed relative to capacity. 1C means a 100 Ah battery is charged at 100 A (fully charged in 1 hour). LFP handles higher C-rates than lead-acid.
Round-Trip Efficiency	Energy out vs energy in. LFP: 90–95%. Lead-acid: 75–80%. Every percentage point lost is solar energy wasted.

The Inverter

Batteries and panels produce DC. Most household appliances — lights, fans, refrigerators, TVs, washing machines — need AC (alternating current) at 230 V, 50 Hz in India. The inverter performs this conversion.

How Inversion Works

The inverter uses semiconductor switches (MOSFETs or IGBTs) to rapidly alternate the direction of current flow, creating an alternating waveform from DC input. A pure sine wave inverter produces a smooth sinusoidal output identical to grid power. This matters because motors, compressors, and sensitive electronics depend on a clean sine wave — a "modified sine wave" (actually a stepped square wave) causes motors to overheat, fans to buzz, and electronics to malfunction.

Key Inverter Specifications

Spec	What It Means
Continuous Power (W)	The sustained load the inverter can deliver indefinitely. A 5000 W inverter runs 5000 W of appliances continuously.
Surge / Peak Power	Short-duration overload capacity for motor startup surges. Compressors and pumps draw 3–7× their running power for the first 50–200 ms. A good inverter handles 2× its continuous rating for several seconds.
Input Voltage Range	The DC voltage window the inverter accepts. A 48 V inverter typically works from 40–60 V DC. Wider range means better compatibility with different battery states.
Efficiency	Power out vs power in. Modern inverters run at 93–97% efficiency at rated load. Efficiency drops at very light loads (under 10% of rated capacity).
THD (Total Harmonic Distortion)	How "clean" the output sine wave is. Under 3% THD is excellent. Grid power itself typically runs 3–5% THD.
Transfer Time	For inverters with grid/generator changeover: how fast they switch between power sources. Under 10 ms keeps computers and refrigerators running without interruption.

The Complete Signal Chain

Putting it all together, a complete off-grid solar system follows this path:

1. Solar Panels convert sunlight into DC electricity at 30–50 V per panel.
2. MPPT Charge Controller tracks each panel's optimal power point, converts the voltage to match the battery bank, and manages the charging process — bulk, absorption, and float stages.
3. Battery Bank stores the DC energy. A 48 V LFP bank of 200 Ah provides 9.6 kWh of storage, with approximately 8.6 kWh usable at 90% DoD.
4. Inverter converts 48 V DC to 230 V AC pure sine wave, powering your home's appliances through your existing wiring.
5. Monitoring System tracks energy production, consumption, battery state-of-charge, and system health in real-time via a dashboard accessible on your phone or computer.

On-Grid, Off-Grid, and Hybrid

The signal chain above describes an off-grid system — completely independent of the electricity grid. But solar systems come in three topologies:

On-Grid (Grid-Tied): Panels connect through a grid-tied inverter directly to the grid. No batteries. Excess power is exported and credited through net metering. When the grid goes down, the system shuts off — this is a safety requirement called anti-islanding. You save on electricity bills but have zero backup.

Off-Grid: Panels, charge controllers, batteries, and an inverter form a self-contained power plant. No grid connection at all. Common for farmhouses, remote properties, and locations with no grid access or unreliable supply.

Hybrid: Combines both approaches. The system prioritises solar, stores excess in batteries, and uses the grid as a backup. Can also export surplus to the grid. Provides both savings and backup, but adds complexity and cost.