How to Size a Solar Panel and Battery for a Solar-Powered Embedded System

A practical guide to matching solar panel size and battery capacity based on charging current, battery C-rate, available sunlight, and application energy requirements, with practical examples using SUNMOD03PU.

10/9/2026

SUNMOD03PU integrated into an embedded solar system with a solar panel, 12 V battery, optional UART interface.
SUNMOD03PU integrated into an embedded solar system with a solar panel, 12 V battery, optional UART interface.

Selecting the right solar panel and battery is one of the key design decisions in a solar-powered embedded system. The panel must provide enough charging current to recover the energy consumed by the system, while the charging rate must remain suitable for the selected battery.

Lower charging currents can contribute to longer battery life, depending on the battery chemistry and manufacturer specifications. At the same time, higher charging currents allow more energy to be restored during the available sunlight period.

In this article, we look at practical panel and battery combinations based on charging current, battery capacity, C-rate, and approximately 5 hours of effective peak sunlight per day. We consider Flooded, AGM/VRLA, GEL, and LiFePO₄ batteries, using SUNMOD03PU as a practical example.

The recommendations are intended as a starting point for system design and tuning. In all cases, the battery manufacturer’s specified maximum charging current and voltage limits must be observed.

Understanding C-rate and Daily Battery Recovery

C-rate describes charging current relative to battery capacity. For example, charging a 10 Ah battery at 1 A corresponds to 0.1C, while charging it at 2 A corresponds to 0.2C.

Assuming approximately 5 hours of effective peak sunlight per day, a charging current of 0.1C could theoretically restore about 50% of the battery’s nominal capacity per day. Similarly, 0.2C and 0.3C correspond to approximately 100% and 150%.

These are theoretical values. Actual energy recovery can be considerably lower due to solar irradiance, panel orientation, temperature, charging losses, battery characteristics, and power consumed by the system itself.

Systems with relatively low daily energy consumption may therefore use a lower C-rate and smaller panel, while systems requiring faster recovery or operating under less favorable solar conditions may benefit from higher available charging current.

Flooded, AGM/VRLA, and GEL Battery Sizing

The following recommendations provide approximate battery capacities for different solar panel sizes and charging C-rates. The values are intended as design references and assume approximately 5 hours of effective peak sunlight per day.

LiFePO₄ Battery Pack Sizing

For LiFePO₄ battery packs with a built-in BMS, higher charging C-rates may be supported compared with lead-acid batteries. The following recommendations provide approximate battery capacities based on 0.3C, 0.5C, and 1C charging rates. The values assume approximately 5 hours of effective peak sunlight per day and should be treated as design references. The battery manufacturer’s specified maximum charging current and voltage limits must always be observed.

Practical Example with SUNMOD03PU

A 50 W solar panel providing approximately 2.8 A of charging current combined with a 12 V / 18 Ah battery corresponds to a maximum charging rate of approximately 0.16C under ideal sunlight conditions.

Learn More About SUNMOD03PU

Explore specifications, features, and integration details.

View SUNMOD03PU →

Evaluate SUNMOD03PU

Get started with SUNMOD-EVK for configuration, testing, and integration.

Explore SUNMOD-EVK →

The information in this article is provided for general engineering guidance. Please review our Disclaimer before applying these recommendations to your design.