Solar & Electronics Calc

V1.0
Ohm's Law / Power
V = IR, P = VI. Fill any two, get the rest.
Voltage (V)
Current (A)
Resistance (Ω)
Power (W)
Fill any two fields.
Load Profile
Average power for a duty-cycled device. Active for X seconds every Y minutes, sleeping in between. For always-on devices, set active time = cycle interval.
Supply Voltage (V)
Active Current (mA)
Sleep Current (mA)
Active Time (sec)
Cycle Interval (min)
Fill the fields above.
Battery Sizing
How big a battery for N hours without charging? Common: 18650 LiPo = 2500-3500mAh, LiPo pouch = 1000-10000mAh, lead-acid 12V = 7-100Ah.
Avg Load (mA)
Autonomy (hours)
Battery Voltage (V)
Min Charge (%) keep above
Fill the fields above.
Solar Panel Sizing
Minimum panel wattage to charge your battery and power the device. Peak Sun Hours (PSH) vary by location and season. Design for winter if you need year-round operation.
Daily Energy (mWh)
Peak Sun Hours
Controller Eff. (%)
Safety Margin (%)
Fill the fields above.
PSH reference (approx, fixed panel): Belgrade: 1.5 Dec, 3.5 Mar/Sep, 5.5 Jun. General: latitude 35-50°N similar pattern. TP4056 eff ≈ 80%, MPPT ≈ 90-95%.
Battery Life
How long will a battery last under a given load? Reverse of battery sizing.
Battery (mAh)
Avg Load (mA)
Usable Capacity (%)
Fill the fields above.
Voltage Divider
Vout = Vin × R2 / (R1 + R2). For reading battery voltage via ADC (ESP8266 max 1V, ESP32 max 3.3V). Fill any three.
Vin (V)
Vout (V)
R1 (kΩ)
R2 (kΩ)
Fill any three fields.
LED Resistor
R = (Vsupply - Vf) / If. Common Vf: Red 1.8V, Green 2.1V, Blue/White 3.2V. Typical If: 20mA (standard), 2mA (indicator).
Supply Voltage (V)
LED Forward V (V)
LED Current (mA)
Number of LEDs series
Fill the fields above.
Wire Voltage Drop
Voltage lost over a cable run. At low voltages (5V, 3.3V), even 1-2m of thin wire eats significant voltage. Uses copper resistivity.
Current (A)
Cable Length (m) one way
Wire Gauge (AWG)
Source Voltage (V)
Fill the fields above.
dBm / Watts
Convert between dBm and Watts. Useful for RF, WiFi, LoRa, cellular. 0 dBm = 1 mW, +20 dBm = 100 mW, +30 dBm = 1 W.
Power (dBm)
Enter dBm value.