Micro-Solar Sizing: Powering Your Farm Sensors Off-Grid 24/7

Author: Reynan M. Maglimolo | Project: Uni-Farm Hub

We have the cloud software running (DevLog #1) and the hardware components blueprinted (DevLog #2). But we face one final, very practical hurdle: Power.

Broiler houses are large, and tilapia ponds are often hundreds of meters away from the main electrical panel. Running long AC extension cords across a farm is not only a tripping hazard, but it is also highly dangerous in wet agricultural environments. The Uni-Farm Hub sensor nodes must be completely autonomous and off-grid.

Here is the exact math and architecture I am planning to use to keep these ESP32 microcontrollers running forever using nothing but the sun.

Step 1: Calculating the Daily Power Load

Before we buy a solar panel, we need to know exactly how much "fuel" the sensor node burns every day.

An ESP32 microcontroller with the Wi-Fi actively transmitting data draws roughly 100 milliamps (mA) of current. Because the climate in a broiler house is so sensitive, I want the sensor running 24 hours a day without going into deep sleep.

• 100mA x 24 hours = 2,400 mAh per day.

This is great news! A single, standard 18650 Lithium-Ion battery (the same ones used in laptops and power banks) generally holds about 2,500mAh to 3,000mAh of juice. This means a single battery can run the farm sensor for exactly one full day and night.

Step 2: Sizing the Micro-Solar Panel

Since the battery will be mostly empty by the next morning, we need a way to refill it during the day. This is where micro-solar comes in.

Here in the Philippines, we get intense, reliable sunlight. If we assume we get at least 4 to 5 hours of peak sunlight per day, we need a solar panel that can pump about 2,500mAh back into the battery within that time frame.

// The Solar Math
Target Output: 5 Volts
Required Current: ~500mA per hour of sunlight

5V * 0.5 Amps = 2.5 Watts

Based on this math, a tiny 5V, 3-Watt mini solar panel (which is roughly the size of a smartphone) will generate more than enough power to top off the 18650 battery by noon, ensuring the sensor stays online through the night.

The Final Wiring Architecture

You cannot connect a solar panel directly to a lithium battery, or the battery will overheat and catch fire. To bridge the gap, I will be using a TP4056 Charge Controller module. It costs less than ₱50 and acts as a safety valve, carefully trickling the solar power into the battery and preventing overcharging.

The final, fully autonomous Off-Grid blueprint looks like this:
3W Solar Panel ➔ TP4056 Controller ➔ 18650 Lithium Battery ➔ ESP32 Sensor Node.

What is the longest you have ever kept an IoT project running strictly on battery power? Let me know in the comments!