​In today era of advocating green energy, more and more people are installing solar energy and storage systems. A key part of the entire installation plan is determining how many solar panels a house requires, whether to include battery storage system, and what capacity that battery system should be. This process involves multiple complex factors and requires careful calculation and planning.

Understanding Household Energy Needs

Calculating the average daily electricity consumption of the house is the foundation of the entire planning process. You can find this by reviewing your electricity bills over the past few months, determining the total monthly consumption, and dividing by the number of days.
For example, if a household consumes 300 kWh per month, the daily average consumption would be around 10 kWh (300 kWh ÷ 30 days = 10 kWh/day).
This figure will serve as a crucial basis for all subsequent calculations.

Factors Related to Solar Panels

Panel Efficiency and Sunlight Conditions

The efficiency of solar panels directly impacts their ability to convert sunlight into electricity. Currently, most commercial solar panels have an efficiency rate between 20% and 25%. Let’s assume a panel with 20% efficiency.
Sunlight duration and intensity vary significantly across regions, so it’s important to check local solar resource data to determine the average effective sunlight hours per day.
For instance, if a certain location has an average of 4 effective sunlight hours per day, this becomes critical piece of information for calculating the required solar panel capacity.

Calculating the Number of Solar Panels Needed

Based on the household’s energy needs and local sunlight conditions, you can calculate the total required solar panel capacity.
If the household needs 10 kWh of energy per day and receives 4 hours of effective sunlight, the required system capacity would be:
10 kWh ÷ 4 hours = 2.5 kW.

If each solar panel has a rated power of 300W and actual output is 300W × 20% = 60W, then the required number of panels would be:
2.5 kW (2500W) ÷ 60W ≈ 42 panels.

Note that this is a rough estimate. Actual installation must also consider panel angle, system losses, connection configuration (series vs. parallel), and potential future increases in energy demand.

Determining Battery Storage Capacity and Efficiency

If you plan to add a battery storage system, its capacity should be determined based on daily electricity usage and the desired backup duration.
Assuming the goal is for the battery to supply one full day of electricity during times without sunlight, and the daily consumption is 10 kWh, a storage battery with 12 kWh capacity would be appropriate—factoring in depth of discharge and possible future increases in usage.

Battery efficiency should also be considered. Lithium battery charge/discharge efficiency typically ranges from 85% to 95%. Let’s assume an average efficiency of 90%.

Recalculating the Number of Solar Panels

Because of the battery’s charge/discharge efficiency, the solar panels must generate more energy than the battery’s rated capacity to fully charge it.
To fully charge a 12 kWh battery at 90% efficiency:
12 kWh ÷ 90% ≈ 13.33 kWh.

Given 4 hours of effective sunlight per day, the required system size is:
13.33 kWh ÷ 4 hours ≈ 3.33 kW.

Using solar panels with 60W of actual output, the number of panels needed is:
3.33 kW (3330W) ÷ 60W ≈ 56 panels.

Other Considerations

When installing a solar power system with battery storage, additional factors such as battery lifespan, maintenance costs, and compatibility with the solar panels and home electrical system must be considered.
A complete solar system also requires inverters, controllers, and other components to ensure stable and safe operation.

It is strongly recommended to consult professional engineers during the planning and installation phases. A detailed design based on your home’s structure, power usage, and local climate conditions will help maximize both the performance and economic benefits of the system.