What it shows
An Arduino measures a small panel's voltage through a divider and its current through an INA219 sensor while a load resistor draws power, and logs both with light level and time to an SD card. The data shows how output changes with sun angle, cloud and panel temperature.
The science
The INA219 measures the voltage across a tiny shunt resistor in series with the load and reports current and bus voltage over I2C with good precision. Power is their product. The panel output follows the light falling on it, so an LDR reading beside the panel shows the correlation. Panels also lose output as they heat, about 0.4 percent per degree, which a comparison of midday readings with temperature can reveal. Logging with a real clock allows plots against time of day.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno clone and USB cable
- An INA219 current and voltage sensor module
- A 6 V, 1 to 2 W solar panel
- A 10 Ω, 5 W resistor as the load
- A micro SD module and card, and a DS3231 clock
- An LDR with a 10 kΩ resistor and a DHT11 for air temperature
- A 5 V power bank
Safety
For this project: Low voltage only. The load resistor gets warm in full sun; mount it on a metal clip away from plastic.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Wire the INA219 on A4 and A5; connect the panel positive to Vin+, Vin- to the load resistor, and the resistor back to panel negative.
Wire the SD module on SPI pins with CS on 10, the DS3231 on the I2C bus, the LDR divider to A0 and the DHT11 to pin 2.
Run the INA219 example and confirm sensible volts and milliamps in shade and sun.
Write the logging sketch: every 30 seconds, write time, volts, milliamps, milliwatts, LDR and temperature to a CSV line.
Place the panel flat on a rooftop or balcony with the electronics in a shaded box, and log a full day.
Repeat on a second day with the panel tilted towards the south at your latitude angle.
Open both files in a spreadsheet and plot power against time, and power against the LDR reading.
Compute the total watt-hours for each day by summing power times interval.
Note any dip in power at midday with high temperature even when light is highest.
What you should see
Two days of logged data with plots showing the daily power curve, the near-linear link between light and current, and more energy from the tilted panel.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1How does the INA219 measure current?
By the tiny voltage drop across a known shunt resistor, converted with a precise amplifier and ADC.
2Why does the panel voltage barely change but current changes a lot with light?
A solar cell is a current source driven by photons; its open voltage depends mostly on the cell material.
3Why tilt the panel?
A tilt equal to the latitude faces the panel more squarely to the sun on average over the year.
4Why does heat reduce output?
Higher temperature lowers the cell voltage faster than it raises current, so power falls.
Take it further
Sweep the load with several resistor values to plot the panel's I-V curve and find its maximum power point.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.