How to Calculate the Installed Capacity of Your Solar System

How to Calculate the Installed Capacity of Your Home Solar System

Switching to solar energy is an eco-friendly and financially sound decision. However, determining the accurate installation capacity for your home PV system can be challenging. This guide will walk you through the steps needed to calculate the ideal capacity for your PV system, ensuring that you optimise investment.

Step 1: Determine Your Energy Consumption

Before you embark on your solar journey, it’s crucial to understand your average energy consumption. You can find this information on your utility bill or by conducting an energy audit. The goal is to estimate the amount of energy you want your PV system to produce, aiming to cover a significant portion, if not all, of your household electricity needs. Don’t forget to evaluate any potential future electricity demands, such as additional air conditioning or the need to charge electric vehicles

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Average Monthly Energy Usage:  450 kWh Units

Provision for Future Electricity Demand increase:  +100 kWh Units

Total Required Energy per month:  550 kWh Units

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Step 2: Calculate the required system capacity

Sunlight availability varies by location and time of year. Research the number of sun hours your area receives to estimate how much solar energy your PV system can harness. You can find this data online or by consulting Hayleys Solar.

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Sun Hours in Your Area (per day): 3.8 hours

Estimated Daily Energy Generation per kWp: 3.8kWh Units

Required System Capacity:  550 kWh / 30 days /3.8kWh  = 4.82 kW Units

Recommended System Capacity:  5 kW Units

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Step 3: Calculate the Number of Panels

With the required system capacity determined, divide it by the capacity of each panel. For instance, if your calculated system capacity is 5kW and each panel has a capacity of 500W, you would need 10 panels. Make sure to consider the specifics of the panels you choose, which can affect the overall system configuration.

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Panel Capacity: 500W each

Number of Panels Needed:  5000W (5 kW) / 500W = 10 panels

Recommended Number of Panels:  10 panels

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Step 4: Assessing Your Roof Space

Measuring the available roof space is a crucial step in determining the potential capacity of your PV system. Begin by measuring the unshaded area on your roof where solar panels can be installed effectively. Unlike other regions, Sri Lanka, located close to the equator, enjoys efficient solar energy generation regardless of the panel direction. While the ideal panel orientation is typically south-facing, it’s important to consider the roof’s inclination, which can impact energy generation. In our country, the general rule of thumb for roof inclination is approximately 10 degrees, which ensures that most sunlight is captured.

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Size of a Single Panel Approx: 28 sq.ft

Installable Panel Quantity: 10 Panels

Required Roof Space: 28 * 10 = 280 sq.ft

Steps to Calculate

1. Determine the Power Consumption of the AC:

   • Look at the AC unit’s specifications to find out its power rating (in watts or kW).
   • Calculate the total energy needed to run the AC for the duration it will be used at night (in kilowatt-hours, kWh).

2. Calculate the Energy Requirement:

   • If the AC runs for 8 hours at night and consumes 1.5 kW, the total energy required is:
     $$\text{Energy Required} = \text{Power Consumption} \times \text{Hours of Operation}$$$$\text{Energy Required} = 1.5 \, \text{kW} \times 8 \, \text{hours} = 12 \, \text{kWh}$$

3. Determine Battery Storage Needs:

   • To store 12 kWh of energy, you need batteries with a combined capacity of at least 12 kWh. Considering efficiency losses, you might need batteries with a total capacity of around 15 kWh (assuming 80% efficiency).

4. Calculate Solar Panel Requirements:

   • The number of solar panels depends on the daily energy generation needed and the average peak sunlight hours.
   • If you need to generate 15 kWh to cover the AC and efficiency losses, and you have 5 peak sunlight hours per day, the required power generation capacity is:
     $$\text{Required Power} = \frac{\text{Energy Required}}{\text{Peak Sunlight Hours}}$$$$\text{Required Power} = \frac{15 \, \text{kWh}}{5 \, \text{hours}} = 3 \, \text{kW}$$

5. Determine the Number of Panels:

   • If each solar panel generates around 300 watts (0.3 kW), the number of panels needed is:
     $$\text{Number of Panels} = \frac{\text{Required Power}}{\text{Power per Panel}}$$$$\text{Number of Panels} = \frac{3 \, \text{kW}}{0.3 \, \text{kW/panel}} = 10 \, \text{panels}$$