Calculator Small Solar

Small Solar System Calculator

Use this calculator to estimate the key components needed for a small off-grid solar power system, such as for an RV, cabin, or small shed.

Total Watt-hours consumed by all your devices in a typical day. (e.g., 10W LED light for 5 hours = 50 Wh)

The average number of effective sunlight hours your location receives per day. This varies by season and geography.

The voltage of your battery bank and system (e.g., 12V, 24V).

Account for losses from wiring, temperature, inverter, etc. (typically 15-30%).

How many days your battery bank should power the system without any sun (for off-grid systems).

The maximum percentage of battery capacity you plan to use. (e.g., 50% for lead-acid, 80-100% for LiFePO4).

The highest wattage drawn by all appliances running simultaneously at any given moment.

Understanding Your Small Solar System Needs

A small solar system can provide independent power for various applications, from charging devices in an RV or camper to powering lights and small appliances in an off-grid cabin, shed, or even for emergency backup. Designing an efficient and reliable small solar setup requires careful consideration of your energy consumption and environmental factors. This calculator helps you estimate the core components: solar panels, battery bank, charge controller, and inverter.

How to Use the Small Solar System Calculator

To get accurate estimates, you'll need to provide some key information about your energy needs and location:

1. Daily Energy Consumption (Wh/day)

This is the most critical input. It represents the total amount of energy your devices will consume in a 24-hour period. To calculate this, list all the electrical devices you plan to power, their wattage, and how many hours per day each will run. Multiply the wattage by the hours for each device, then sum them up.

• Example:
  • LED Lights: 20 Watts * 4 hours/day = 80 Wh
  • Laptop: 60 Watts * 3 hours/day = 180 Wh
  • Phone Charging: 10 Watts * 2 hours/day = 20 Wh
  • Small Fan: 15 Watts * 5 hours/day = 75 Wh
  • Total Daily Energy Consumption: 355 Wh/day

2. Average Peak Sun Hours (hours/day)

Peak sun hours (also known as "full sun hours") represent the equivalent number of hours per day when solar irradiance averages 1,000 watts per square meter. This value varies significantly based on your geographic location, time of year, and local weather patterns. You can find average peak sun hour data for your specific location online (e.g., from NREL or local weather resources). For example, a sunny region might have 5-7 peak sun hours, while a cloudier region might have 3-4.

3. System Voltage (V)

Small solar systems typically operate at 12V or 24V. The system voltage affects the current flowing through your wires and components. Higher voltage systems (e.g., 24V) are generally more efficient for larger power demands as they reduce current, allowing for thinner wires and less power loss. For very small systems, 12V is common.

4. System Inefficiency Factor (%)

No solar system is 100% efficient. Energy is lost at various stages due to factors like:

• Temperature: Solar panels produce less power in very hot conditions.
• Wiring Losses: Resistance in cables causes some energy to dissipate as heat.
• Inverter Efficiency: Inverters convert DC power from batteries to AC power for appliances, and this conversion isn't perfectly efficient (typically 85-95%).
• Battery Efficiency: Batteries lose some energy during charging and discharging cycles.
• Dust/Shading: Dirt on panels or partial shading reduces output.

A typical inefficiency factor ranges from 15% to 30%. Using 20% is a reasonable starting point for most small systems.

5. Days of Autonomy (days)

This input is crucial for off-grid systems. It determines how many days your battery bank can supply power without any sunlight (e.g., during cloudy weather or if you're away from your solar panels). For critical systems, you might want 3-5 days of autonomy, while for less critical applications, 1-2 days might suffice.

6. Battery Max Depth of Discharge (DoD %)

The Depth of Discharge (DoD) refers to the percentage of the battery's capacity that has been discharged. Regularly discharging batteries too deeply can significantly shorten their lifespan. Different battery chemistries have different recommended maximum DoD:

• Lead-Acid Batteries (Flooded, AGM, Gel): Typically 50% DoD is recommended for optimal lifespan. Discharging beyond this can severely degrade the battery.
• Lithium Iron Phosphate (LiFePO4) Batteries: Can safely be discharged to 80-100% DoD, offering more usable capacity for their rated size.

7. Peak Appliance Load (W)

This is the maximum wattage that all your appliances will draw simultaneously at any given moment. This value is critical for sizing your inverter. For example, if you plan to run a 60W laptop and a 15W fan at the same time, your peak load would be 75W. Always add a safety margin to this number.

Understanding the Results

The calculator provides estimates for the following key components:

Minimum Solar Panel Wattage (Wp)

This is the total rated power (in Watts-peak) of the solar panels you'll need to generate enough energy to meet your daily consumption, accounting for system losses and average sun hours. You might choose to install slightly more wattage for faster charging or to compensate for less-than-ideal conditions.

Minimum Battery Bank Capacity (Ah)

This is the total Ampere-hour capacity your battery bank needs to store enough energy to cover your daily consumption for the specified days of autonomy, considering your system voltage and maximum depth of discharge. Remember that Ah capacity is specific to the system voltage (e.g., a 100Ah 12V battery stores 1200Wh).

Minimum Charge Controller Current (A)

The charge controller regulates the power flowing from your solar panels to your battery bank, preventing overcharging. Its current rating must be sufficient to handle the maximum current produced by your solar panels. The calculator includes a 25% safety factor as recommended by electrical codes.

Minimum Inverter Size (W)

The inverter converts the DC power from your batteries into AC power that most standard household appliances use. Its wattage rating must be greater than your peak appliance load to handle all devices running simultaneously. A 25% safety factor is included to ensure it can handle surge currents when appliances like refrigerators or power tools start up.

Important Considerations

• Expandability: Consider if you might want to add more devices or panels in the future. It's often wise to slightly oversize components like the charge controller or inverter.
• Battery Type: The choice between lead-acid and lithium-ion (LiFePO4) batteries significantly impacts cost, lifespan, weight, and usable capacity.
• Wiring: Proper wire sizing is crucial to prevent power loss and ensure safety. Consult electrical charts based on current, distance, and voltage.
• Safety: Always include fuses or circuit breakers at appropriate points in your system to protect components from overcurrent.
• Professional Advice: For larger or more complex systems, consult with a qualified solar professional.