Calculate Your Solar System Size
Enter your daily energy requirement and solar conditions.
What Is a Solar System Size Calculator?
A Solar System Size Calculator estimates the photovoltaic array capacity needed to produce a chosen amount of electrical energy each day. It uses energy consumption, available peak sun hours and an allowance for system losses.
The calculator can also estimate the number of solar panels required and provide a simple battery energy estimate when backup storage is being considered.
Solar System Size Formula
A common preliminary sizing method divides daily energy consumption by the effective solar production hours. System efficiency is included to account for real-world losses.
If efficiency is entered as a percentage, it must first be converted to decimal form. For example, 80% becomes 0.80.
How to Use the Solar System Size Calculator
- Enter your average daily electricity use.
- Enter the average peak sun hours available each day.
- Enter an estimated overall system efficiency.
- Enter the wattage rating of one solar panel.
- Optionally enter the number of battery backup days.
- Enter the intended usable battery percentage.
- Click Calculate Solar System Size.
The calculator estimates the required PV array size, number of panels, installed DC capacity, daily and annual energy production, and battery storage requirement.
Solar System Sizing Example
Suppose a property consumes 20 kWh of electricity each day. Assume five peak sun hours and an overall system efficiency of 80%.
20 ÷ 4
= 5 kW
A theoretical 5 kW solar array would therefore be required to generate about 20 kWh per day under those assumptions. The actual installed panel capacity may be slightly higher after rounding to whole panels.
How Many Solar Panels Do I Need?
Once the required array capacity is known, convert the system size to watts and divide it by the wattage of one solar panel.
Because only whole solar panels can be installed, the calculator rounds the result upward.
Example with 550-Watt Solar Panels
If the calculated system size is 5 kW and each solar panel is rated at 550 watts, the panel count is:
= 9.09
≈ 10 Panels
Ten 550-watt panels provide an installed DC array capacity of approximately 5.5 kW.
What Are Peak Sun Hours?
Peak sun hours are not simply the number of daylight hours. They represent the equivalent number of hours in which solar irradiance averages about the standardized peak level used for PV power ratings.
For preliminary sizing, higher peak sun hours generally mean a smaller array is required to produce the same amount of daily energy.
What Does Solar System Efficiency Mean?
Temperature Losses
Solar modules can produce less than their rated output when operating temperatures rise above standard test conditions.
Electrical Losses
Inverters, wiring and connections introduce conversion and resistive losses between the panels and usable AC energy.
Environmental Effects
Soiling, shading, orientation, weather variation and other site conditions can reduce actual production.
Estimated Daily and Annual Solar Production
Once the installed array size is known, estimated daily energy production can be calculated using peak sun hours and the system efficiency factor.
Annual Generation = Daily Generation × 365
These are simplified energy estimates. Seasonal weather, panel orientation, shading and site-specific solar resources can cause substantial variation throughout the year.
Solar Battery Size Formula
For a basic backup-energy estimate, multiply daily energy consumption by the number of desired backup days and adjust for the usable fraction of the battery.
For example, a 20 kWh daily load with one day of backup and 80% usable battery capacity would require approximately 25 kWh of nominal stored energy.
Common Solar System Size Examples
| Daily Usage | Peak Sun Hours | Efficiency | Estimated System |
|---|---|---|---|
| 8 kWh/day | 5 hours | 80% | 2.0 kW |
| 12 kWh/day | 5 hours | 80% | 3.0 kW |
| 20 kWh/day | 5 hours | 80% | 5.0 kW |
| 24 kWh/day | 5 hours | 80% | 6.0 kW |
| 32 kWh/day | 5 hours | 80% | 8.0 kW |
| 40 kWh/day | 5 hours | 80% | 10.0 kW |
Solar Panel Size vs Solar System Size
Solar panel size usually refers to the rated wattage of one module, such as 450 W or 550 W. Solar system size refers to the combined rated capacity of all modules in the array, usually expressed in kilowatts.
For example, ten 550-watt panels create a nominal DC array size of 5,500 watts, or 5.5 kW.
Factors That Affect the Actual Solar System Size
Roof Space
Available roof or ground area can limit the number and physical arrangement of solar modules.
Orientation & Tilt
Panel direction and tilt angle affect how much solar energy reaches the array during different times of the year.
Shading
Trees, buildings, rooftop objects and nearby structures can reduce solar production if they shade panels.
Grid-Tied vs Battery Solar Systems
A grid-tied system typically focuses on producing enough solar energy to offset part or all of a property's electricity consumption. Excess production may be exported depending on the applicable utility arrangement.
A battery-based system additionally requires storage sizing and inverter power analysis. Off-grid systems may require larger solar and battery capacity to provide adequate energy during poor weather and seasonal changes.
Frequently Asked Questions
How do I calculate the solar system size I need?
Divide your daily electricity consumption in kWh by peak sun hours multiplied by the expected system efficiency. The result is an estimated PV array size in kilowatts.
What size solar system is needed for 20 kWh per day?
At five peak sun hours and 80% system efficiency, 20 kWh per day requires an estimated 5 kW solar array before rounding to available panel sizes.
How many 550-watt panels make a 5 kW solar system?
Five kilowatts divided by 550 watts gives approximately 9.09 panels, so at least 10 whole 550-watt panels would be needed, producing about 5.5 kW of installed panel capacity.
What are peak sun hours?
Peak sun hours represent the equivalent number of hours of strong solar irradiance used to estimate daily solar energy production.
Why is system efficiency included?
Real solar systems experience losses from temperature, inverters, wiring, soiling, shading and other conditions, so the full panel rating is not converted into usable energy all the time.
How do I estimate solar battery capacity?
Multiply daily energy consumption by the desired backup days and divide by the usable battery fraction. Detailed battery design should also consider power and manufacturer limits.
Is this calculator suitable for final solar installation design?
It is intended for preliminary sizing. Final system design should use site-specific solar data, shading analysis, roof conditions, electrical requirements, equipment specifications, local rules and professional system design where required.