Northern Illinois University
Virtual Renewable Energy Laboratory
College of Engineering and Engineering Technology

Solar cells can be divided into three groups based on raw material. Solar cells have an efficiency of about 10%.

1. Monocrystalline
   Highly pure silicon melt is used to grow mono-crystals in the form of round silicon blocks. A mono-crystal’s lattice has an entirely homogeneous structure. The silicon block is sawed into wafers each 200 to 300 μm thick.
2. Polycrystalline
   Highly pure silicon melt is also used as the initial material for polycrystalline cells. These cells are manufactured through controlled cooling of the silicon melt in square-shaped moulds. During cooling, the crystals arrange themselves in an irregular pattern resulting in an iridescent surface typical of polycrystalline solar cells.
3. Thin-film
   
   1. Amorphous silicon cell
      To manufacture amorphous solar cells, silicon is vapour-deposited on a carrier, e.g. glass. The vapour-deposited silicon layer has a thickness of 0.5 to 2 μm.
   2. Copper-indium-diselenide cell (CIS).
   3. Gallium-arsenide (GaAs).

A PV model can be expressed by the equivalent circuit shown in Figure 1.

Figure 1. Equivalent circuit of a PV model

Operational nominal and standard conditions for PV are shown in Table 1.

Nominal Condidtion	Standard Condition
Irradiance = 800 W/m2	Irradiance = 1000 W/m2
Ambient temperature = 20℃	Cell temperature = 25℃
Wind speed = 1 m/s

Open-circuit voltage of a solar cell
The open-circuit voltage V_OC is the maximum voltage available from a solar cell.As the cell temperature increases, V_OC decreases. V_OC is measured using a volt meter connected across the solar cell when no load is connected, shown in Figure 2.

Figure 2. Measuring open-circuit voltage

Short-circuit current of a PV cell
The short-circuit current I_SC is the maximum current a solar cell can supply. I_SC is directly proportional to the irradiance. If irradiance increases, I_SC will increase. If irradiance decreases, ISC will decrease. For example, if irradiance is cut in half, I_SC will drop by half. The current is measured using an ammeter connected directly across the solar cell, shown in Figure 3

Figure 3. Measuring short-circuit current

1. Measuring open-circuit voltage of solar cells
2. Measuring short-circuit current of solar cells

• Solar Cells
• Voltage Meter
• Current Meter

1. Connect a voltmeter to a solar cell with no load connected to it. Set the irradiance to 1000 W/m², and temperature to 25℃. Record the open-circuit voltage V_OC. Vary the cell temperature from 20 ℃ to 40 ℃ with the interval of 5 ℃ and keep the irradiance at 1000 W/m². Record the open-circuit voltage and short-circuit current with different temperature in Table 1. Click on the button “Export table to CSV file” to save the data to an Excel file. How does V_OC vary when the temperature increases?


Table 1 V_OC and I_SC with the temperature variations



2. Connect an ammeter to a solar cell directly. Set the irradiance to 1000 W/m², and temperature to 25℃. Measure the short-circuit current I_SC. Vary the irradiance from 800 W/m² to 1200 W/m² with the interval of 100 W/m², and keep the temperature constant at 25 ℃. Record the open-circuit voltage and short-circuit current with different irradiance in Table 2. Click on the button “Export table to CSV file” to save the data to an Excel file.How does I_SC vary when the irradiance increases?


Table 2 V_OC and I_SC with the irradiance variations

1. Fill out Table 1 with experimental data. How does V_OC and I_SC vary when the temperature increases?
2. Fill out Table 2 with experimental data. How does V_OC and I_SC vary when irradiance increases?