Solar Panel Temperature

The main effect of temperature on solar panels is that it reduces the efficiency of the solar cells at converting solar energy (sunlight) into electricity. In other words, the chemical reactions that occur within the solar panels are more efficient at cooler temperatures than at hot temperatures. As a solar panel increases in temperature, the power output of the solar panel decreases. Generally, monocrystalline solar cells have a temperature coefficient of -0.5%/deg C. This means a mono solar panel will lose half of once percent of its power for every degree the temperature rises. Photovoltaic modules are tested at a temperature of 25 degrees C (STC) – about 77 degrees F., and depending on their installed location, heat can reduce output efficiency by 10-25%. As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly. In order to calculate the amount of power extracted from solar panel it is necessary to calculate the efficient of the solar panel. The efficiency of the solar cells various as the temperature so it is necessary to measure the temperature of the panel and then we can calculate the efficiency. To measure the temperature of solar panel we can use” MAX31865 Evaluation Kit” it has software GUI to monitor the temperature in real-time by connecting it to the personal Computer without using any additional MCU. This will be good evaluation kit to perform the temperature measurement on the solar panel to calculate the efficiency exactly.

List of parts required for project:
  1. MAX31865 Ev Kit.
  3. Connecting wires.
The schematic diagram to record data from the sensor and convert it to digital data using on-board 16-bit ADC in max31865 chip.

Figure 1: Schematic diagram for RTD connected to MAX31865 chip.

Figure 2: Schematic diagram for SPI-to-USB converter circuit.

Procedure to install GUI and connect hardware to PC:
The RTD sensor is connected to the MAX31865 Ev Kit, Follow the steps below to verify board operation:
1) Verify the two jumper wires (included) are properly secured in the terminal block in accordance with the 2-wire RTD Sensor Connector diagram on the PCB’s silkscreen.
2) Verify the 1kΩ resistor is properly secured in the terminal block connecting the RTDIN+ terminal to the RTDIN- terminal.
3) Set the EV kit hardware on a non-conductive surface that ensures that nothing on the PCB gets shorted to the workspace.
4) Prior to starting the GUI, connect the EV kit hardware to a PC using the supplied mini-USB cable, or equivalent. The POWER LED (D20) should be green and the COM LED (D21) should be red and slowly flash orange.
5) Windows should automatically begin installing the necessary device driver. The USB interface of the EV kit hardware is configured as a HID device and therefore does not require a unique/custom device driver. Once the driver installation is complete, a Windows message appears near the System Icon
menu indicating that the hardware is ready to use. Do not attempt to run the GUI prior to this message. If you try to run the GUI prior to this message, close the application and restart it once the driver installation is complete. On some versions of Windows, administrator privileges may be required to install the USB device.
6) Once the device driver installation is complete, visit to download the latest version of the EV kit software,
MAX31865EVKitSoftwareInstall.ZIP. Save the EV kit software to a temporary folder.
7) Open the .ZIP file and double click the .EXE file to run the installer. A message box stating “The publisher could not be verified. Are you sure you want to run this software?” may appear. If so, click Yes.
8) The installer GUI appears. Click Next and then Install. Once complete, click Close.
9) Go to Start >> All Programs. Look for the MAX31865EVKitSoftware folder and click on MAX31865EVKitSoftware.EXE inside the folder.
10) When the GUI appears, the text below the Maxim Integrated logo should indicate that the EV kit hardware is connected. The COM LED (D21) turns off and flashes red when communication occurs.

Figure : GUI of MAX31865 Ev Kit showing the hardware is connected.

Source code:
* MAX31865 Evaluation Kit program for Solar Panel Temperature measurement.
#include <SPI.h>
#include <MAX31865.h>
#define RTD_CS_PIN 10
MAX31865_RTD rtd( MAX31865_RTD::RTD_PT100, RTD_CS_PIN );
void setup()
Serial.begin( 115200 );
/* Initialize SPI communication. */
SPI.begin( );
SPI.setClockDivider( SPI_CLOCK_DIV16 );
SPI.setDataMode( SPI_MODE3 );
/* Allow the MAX31865 to warm up. */
delay( 100 );
rtd.configure( true, true, false, true, MAX31865_FAULT_DETECTION_NONE,
true, true, 0x0000, 0x7fff );
void loop()
rtd.read_all( );
if( rtd.status( ) == 0 )
double temperature = rtd.temperature( );
Serial.print( " T = ");
Serial.print( temperature, 1 );
Serial.println(" deg C" );
Serial.print( "RTD fault register: " );
Serial.print( rtd.status( ) );
Serial.print( ": " );
if( rtd.status( ) & MAX31865_FAULT_HIGH_THRESHOLD )
Serial.println( "RTD high threshold exceeded" );
else if( rtd.status( ) & MAX31865_FAULT_LOW_THRESHOLD )
Serial.println( "RTD low threshold exceeded" );
else if( rtd.status( ) & MAX31865_FAULT_REFIN )
Serial.println( "REFIN- > 0.85 x V_BIAS" );
else if( rtd.status( ) & MAX31865_FAULT_REFIN_FORCE )
Serial.println( "REFIN- < 0.85 x V_BIAS, FORCE- open" );
else if( rtd.status( ) & MAX31865_FAULT_RTDIN_FORCE )
Serial.println( "RTDIN- < 0.85 x V_BIAS, FORCE- open" );
else if( rtd.status( ) & MAX31865_FAULT_VOLTAGE )
Serial.println( "Overvoltage or Undervoltage fault occured");
Serial.println( "Fault exist; Please check connection" );
delay( 3000 );
The details of source code is in the following URL:

Initially connect the 2-wire RTD sensor to the RTD port by replacing the 1kohm resistor in the Evaluation Kit. Plug in the USB cable to the PC and evaluation kit then open the GUI software which shows the EV kit is connected. ON the conversion mode, VBIAS, set to 2-wire RTD connection if red bubble in fault status indicates their is open connection in the RTD sensor or in-appropriate sensor connected. If all is well then start to measure the data from the chosen environment. In our present project we are going to measure the Solar Panel Temperature which is useful to estimate the efficiency of solar energy. We placed the RTD temperature Sensor on solar panel and measure the temperature. The data shows the stable sun radiation time to generate solar power in the panel which helps to estimate solar energy extracted from sun radiation without heating the panel.

Data graph showing increase in temperature.

View attachment 189079
The detail working process in shown in the video:

Improvements required
  1. If multiple sensor are connected to the same kit for multiple recordings it would me more advantages to sense at different placed at a time.
  2. Buzzer is need to set to alarm for fault detection on the evaluation kit t protect it from damage.
  3. If WiFi connectivity is add to the evaluation kit then it is easy for the user to utilize the kit for remote accessing the data from the measuring environment.
  4. An android app for data sensing is need to be designed for smartphone will help to share the data and monitor in real-time
MAX31865 Ev Kit is helpful to measure the temperature of solar panel to estimate the lose of energy due to panel heating by sun radiation. The on-board features of converting the temperature to 16-bit ADC gives the accurate value of the temperature. The software GUI will show the real-time graph and can save the data for further analysis. This evaluation kit will be useful in the solar plant industry to know the status of the solar panel heating effect with the sun radiation.
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