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load calculation solar system

To find out how much solar energy you need for a solar system, first figure out how much energy you use in a day (measured in watt-hours). Then, calculate the size of the solar panels and the battery you might need. This means you should write down all the appliances you have, how much power they use in watts, and how many hours you use them. After that, add up the watt-hours for each appliance.

Here’s a breakdown of the process:
1. Determine your daily energy consumption:
  • List all appliances:

    Make a list of all appliances you plan to power with the solar system, including lights, fans, TVs, refrigerators, etc. 

  • Determine wattage and usage hours:

    Find the wattage of each appliance and estimate how many hours per day you’ll be using them. 

  • Calculate watt-hours for each appliance:

    Multiply the wattage by the usage hours to get the watt-hours (Wh) for each appliance. 

  • Sum the watt-hours:

    Add up the watt-hours for all appliances to get your total daily watt-hours. 

2. Calculate solar panel capacity:
  • Consider peak sun hours:

    Peak sun hours vary by location and time of year. This represents the number of hours where the sun’s intensity is equivalent to its peak output. 

  • Account for system losses:

    Solar panels are not 100% efficient. A typical derating factor is 0.8 (or 80%) to account for losses due to temperature, shading, and other factors. 

  • Calculate required panel wattage:

    Divide your total daily watt-hours by the peak sun hours and the derating factor. 

    • Formula: (Total Daily Wh) / (Peak Sun Hours * 0.8) = Required Panel Wattage 
3. Calculate battery capacity (if needed for off-grid or backup power):
  • Determine backup time:

    Decide how many hours of backup power you need in case of cloudy days or power outages. 

  • Consider battery voltage:

    Batteries are typically 12V, 24V, or 48V. 

  • Calculate required battery capacity:

    Divide the total daily watt-hours by the battery voltage to get the required amp-hours (Ah). 

    • Formula: (Total Daily Wh) / (Battery Voltage) = Ah Required 
  • Factor in battery depth of discharge:

    Batteries should not be fully discharged. A typical depth of discharge is 50%, so you may need to double the required Ah. 

  • Consider temperature and other factors:

    Extreme temperatures can affect battery performance, so it’s best to consult with a professional or use a solar calculator that takes these factors into account. 

Example:

Let’s say your total daily watt-hours is 2000 Wh, you have 5 peak sun hours, and you are using a 12V battery system. 

  • Solar Panel Calculation:
    2000 Wh / (5 hours * 0.8) = 500 Watts. You would need 500 watts of solar panels.
  • Battery Calculation (assuming 50% depth of discharge):
    2000 Wh / 12V = 166.67 Ah. You would need a 333.34 Ah battery (166.67 * 2).
Tools and Resources:
  • Online solar calculators:
    Many websites offer solar calculators that can help you determine the appropriate system size based on your location and energy usage.
  • Professional solar installers:

    Consult with a qualified solar installer for accurate load calculations and system design. 

By following these steps and using the appropriate tools, you can accurately calculate the solar load and ensure your solar system is sized correctly to meet your energy needs.

Load Calculation for Solar System (Step-by-Step Guide)

To design the right solar system for your home/office, you need to calculate your total load (wattage) and daily energy consumption (kWh). Here’s how:

Step 1: List All Appliances

Appliance Power (Watts) Quantity Daily Usage (Hours) Total Watt-Hours/Day
LED Lights 10W 10 6 10 x 10 x 6 = 600Wh
Fan 80W 4 8 80 x 4 x 8 = 2,560Wh
Fridge (Inverter) 200W 1 24 (cycles) 200 x 1 x 8 ≈ 1,600Wh
AC (1 Ton) 1,200W 1 5 1,200 x 1 x 5 = 6,000Wh
TV (LED) 100W 1 4 100 x 1 x 4 = 400Wh
Total Daily Consumption ~11,160Wh (11.16kWh/day)

Step 2: Calculate Solar System Size

  • Daily Usage: 11.16 kWh

  • Sunlight Hours (Pakistan Avg.): 5–6 hours

  • System Size Required:

    11,160Wh5.5h=∗∗2,029W(2.03kW)∗∗

    → Recommended: 3kW–5kW system (accounts for inefficiencies & future expansion).

Step 3: Battery Backup (If Off-Grid/Hybrid)

  • Required Battery Capacity (Ah):

    11,160Wh48V(systemvoltage)=∗∗232Ah∗∗

    → Recommended: 2 x 200Ah Lithium Batteries (or 4 x 200Ah Lead-Acid).

Step 4: Inverter Sizing

  • Total Running Load:

    • AC (1,200W) + Fridge (200W) + Fans (320W) = 1,720W

    • Surge Requirement (for AC startup): 1,200W x 3 = 3,600W
      → Recommended Inverter: 5kW Hybrid Inverter (e.g., HISEL, Growatt).

Step 5: Solar Panels Needed

  • Total Wattage Required: 3kW–5kW

  • Panel Type: LONGi 550W

    5,000W550W≈∗∗9–10panels∗∗

Key Notes:

  1. On-Grid System: No battery needed (net metering covers excess).

  2. Hybrid/Off-Grid: Add 20–30% extra solar capacity for cloudy days.

  3. Efficiency Losses: Wiring, inverter, and temperature reduce output by ~15–20%.

Example Scenarios

Load (kWh/Day) Recommended System Battery (If Needed)
5–10 kWh 3kW Solar + 5kW Inverter 200Ah Lithium (2x)
10–20 kWh 5kW Solar + 8kW Inverter 400Ah Lithium (4x)
20+ kWh 10kW Solar + 10kW Inverter 600Ah+ Lithium

Need a customized load sheet? Share your appliance list!