## Photovoltaic panels in practice lesson

The lesson was carried out by an electrical specialist ? teacher in Zespół Szkół Elektrycznych in Włocławek-  Jacek Kandyba. It is the first part of the vocational training classes prepared as a result of the availability of the equipment such as PV cells kit bought  in the Project ?Alternative Energy ? present and future energetic? for its realization.

The lesson took place on the 23rd May 2014. It lasted 90 minutes and was aimed at both Hungarian and Polish students during the stay of the Hungarian students in Poland.

Pointing at Maximum Power for PV

Summary

Student teams measure voltage and current in order to determine the power output of a photovoltaic (PV) panel. They change the resistance in a simple circuit connected to the panel to demonstrate the effects on voltage, current, and power output. After collecting data, they calculate power for each resistance setting, creating a graph of current vs. voltage, and indentifying the maximum power point.

Photovoltaic (PV) panels utilize a scientific technology that creates power from solar radiation. Because PV panels are expensive and their power production is limited by the amount of sunlight available, it is important for them to run as efficiently as possible. One way to improve PV panel efficiency is to adjust the resistance in the design of the electrical circuit to create a combination of voltage and current that results in the greatest power output. Engineers must understand how to control a basic circuit in order to design PV arrays that operate as efficiently as possible.

Pre-Req Knowledge

A basic understanding of an electrical circuit, including voltage, current, power and resistance.

Learning Objectives

After this activity, students should be able to:

• Measure the voltage and current of a photovoltaic (PV) electrical circuit.
• Explain how to calculate and maximize the DC power output of a PV system.

Materials List

Each group needs:

• PV panel 5Wp
• wires
• multimeters (voltmeter, ammeter) and light meter lux
• sunlight, or a lamp

Equations

Ohm's law:                               V=I*R

Electrical power equation:        P=V*I

Where :

V = potential difference (in volts V)

I = current (in amperes A)

R = resistance (in Ohms ?)

P = power (in watts W)

Definitions

 maximum power point (MPP): The point on a power (I-V) curve that has the highest value of the product of its corresponding voltage and current, or the highest power output.

Materials List

The experiment can be conducted either outdoors in sunlight, or indoors using a 500-watt incandescent lamp. Simply place the PV panel under the lamp. This lamp can become extremely hot! Be careful! While conducting the experiment, make sure nothing blocks the light from reaching the panel. Try not to modify the position or any other variables that might disrupt the results.

Circuit diagram for  measurement  PV panel

Figure 1. The electrical circuit configuration to measure voltage and current.

Experiment Procedure

• assemble the circuit (Figure 1)
• measure the illumination
• measure the voltage open circuit Voc
• measure the short-circuit current Isc
• change the resistance of the resistor decade box
• measure the voltage and current
• write the results in the table 1

Mono Solar panel PV specifications:

 Type - RS-M 5W Nominal Maximum Power(Pmax) 5W Optimum operating voltage (Vmpp) 12V Optimum operating current (Impp) 0.25A Open-circuit voltage (Voc) 21,9V Short-circuit current (Isc) 0.315A Power tolerance ?2% Maximum system voltage 1000V(IEC)/600V(UL) Maximum Serises Fuse Rating 15A NOCT 45 °c Temperature Coefficient  PMAX -0.43%/ °c Temperature Coefficient  Voc -0.34%/ °c Standard STCs: 1000 W/m2 solar irradiance, 1.5 Air Mass AM, temperature of 25oC.

Table 1: PV Panel Data Collection

 light intensity [lx]   ???????? Trial # Collected Data Calculated Resistance [W] Voltage [V] Current [A] Power [W] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Post-Experiment Assignment

• calculate power (voltage * current) for each reading and record it in the table.
• graph current and power vs. voltage on the graph provided

I=f(U)

Figure 2. Current and Voltage Curves

P=f(U)

Figure 3. Power Curves