Aim of the Experiment
To plot the I-V (current-voltage) and P-V (power-voltage) characteristics of a solar photovoltaic (PV) panel and to determine short-circuit current (I_sc), open-circuit voltage (V_oc), maximum power point (P_max), and fill factor (FF).
Apparatus Required
- Solar PV panel (monocrystalline or polycrystalline)
- Variable resistance / electronic load (rheostat)
- Ammeter (DC, 0–5A)
- Voltmeter (DC, 0–25V)
- Pyranometer (for solar irradiance measurement)
- Connecting wires and light source (or outdoor sunlight)
Theory
A solar PV cell converts solar radiation into electrical energy using the photovoltaic effect. The I-V characteristic of a solar cell is described by the ideal diode equation:
I = I_ph − I_0 [exp(qV/nkT) − 1]
Where: I_ph = photocurrent (A), I_0 = diode saturation current (A), q = electron charge (1.6 × 10⁻¹⁹ C), n = ideality factor, k = Boltzmann constant, T = temperature (K).
Fill Factor: FF = P_max / (V_oc × I_sc) = (V_mp × I_mp) / (V_oc × I_sc)
Efficiency: η = P_max / (G × A_panel) × 100%
Where G is solar irradiance (W/m²) and A_panel is panel area (m²). A higher fill factor (typically 0.70–0.85 for good panels) indicates lower internal losses.
Procedure
- Connect the solar panel to the variable load resistor with ammeter in series and voltmeter in parallel.
- Expose the panel to sunlight or a constant light source. Note the solar irradiance G (W/m²) using a pyranometer.
- Start with maximum load resistance (open circuit limit) and record V_oc (current ≈ 0).
- Gradually reduce the resistance in steps and record corresponding voltage (V) and current (I) values.
- Continue until load resistance reaches minimum (short circuit limit) and record I_sc (voltage ≈ 0).
- Plot I vs. V to get the I-V curve. Plot P = I × V vs. V to get the P-V curve.
- Identify V_mp and I_mp at the maximum power point (peak of P-V curve).
- Calculate fill factor FF and efficiency η.
Observation Table
| Sr. No. | Resistance Ω | Voltage V (V) | Current I (A) | Power P (W) |
|---|---|---|---|---|
| 1 | ∞ (OC) | 0 | 0 | |
| 2 | ||||
| 3 | ||||
| 4 | ||||
| 5 | 0 (SC) | 0 | 0 |
Result
V_oc = _______ V | I_sc = _______ A | P_max = _______ W at V_mp = _______ V, I_mp = _______ A | Fill Factor FF = _______ | Efficiency η = _______%. The I-V and P-V characteristics are plotted and the maximum power point is identified.
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View Engineering Lab Equipment →Request a QuoteSolar Cell I-V Characteristics, Detailed Theory and Calculations
Equivalent Circuit of a Solar Cell
A solar cell is modelled as a current source (I_ph = photocurrent, proportional to irradiance) in parallel with a diode (representing the p-n junction recombination current) and two resistances: shunt resistance R_sh (representing leakage current paths) and series resistance R_s (representing contact and bulk resistance).
Cell current equation: I = I_ph – I₀[exp(q(V + IR_s)/nkT) – 1] – (V + IR_s)/R_sh
where I₀ = dark saturation current, q = electron charge (1.6×10⁻¹⁹ C), n = ideality factor (1–2), k = Boltzmann constant (1.38×10⁻²³ J/K), T = temperature (K)
Key Parameters from I-V Curve
| Parameter | Symbol | Location on I-V Curve | Typical Value (Si cell) |
|---|---|---|---|
| Short-circuit current | I_sc | V = 0 axis intercept | 5–10 A/m² per mW/cm² |
| Open-circuit voltage | V_oc | I = 0 axis intercept | 0.55–0.65 V |
| Maximum power point current | I_mp | At maximum P = IV | ≈ 0.9 × I_sc |
| Maximum power point voltage | V_mp | At maximum P = IV | ≈ 0.8 × V_oc |
| Maximum power | P_max | I_mp × V_mp | P_max area on curve |
Fill Factor and Efficiency Calculations
Fill Factor (FF) = P_max / (V_oc × I_sc) = (V_mp × I_mp) / (V_oc × I_sc)
FF indicates how “rectangular” the I-V curve is. High quality cells: FF = 0.75–0.85; degraded cells: FF < 0.70
Efficiency η = P_max / (G × A_cell) × 100%
where G = solar irradiance (W/m²), A_cell = cell area (m²)
Effect of Irradiance and Temperature
- Increasing irradiance: I_sc increases linearly; V_oc increases slightly (logarithmic); efficiency approximately constant
- Increasing temperature: V_oc decreases (approx. -2 mV/°C for Si); I_sc increases slightly; net effect: efficiency decreases (approx. -0.4% per °C for Si)
- Practical implication: Solar panels rated at STC (1000 W/m², 25°C) perform worse in hot climates, temperature correction is essential for real-world energy yield calculations
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