How to Size PV Solar Systems? Utility-Scale To Residential

PV Solar Systems, What Are They?

Photovoltaic (PV) solar systems are a technology that converts sunlight into electric power.
The PV solar systems use solar panels to collect sunlight, and then convert the energy from the sunlight into electricity. They are versatile and can supply power to small installations or large energy grids. In addition, they can supply power to residential homes, commercial buildings, industrial sites & factories, or even utility-scale power networks for entire cities.

Major Components Of
PV Solar Systems

The major components of PV solar systems typically include:

Solar Panels: Devices that collect sunlight and convert it into direct current (DC) electricity.
Inverter: Converts DC electricity from the panels into alternating current (AC) electricity for use in homes or the grid.
Battery (optional): Stores electricity for later use when sunlight is not available.
Charge Controller: Regulates the flow of electricity to the battery to prevent overcharging or damage.
Mounting Structure: Holds the solar panels in place on roofs or the ground, often angled for maximum sunlight.
Cabling and Wiring: Connects all components and ensures safe electricity flow.
Monitoring System (optional): Tracks system performance and energy production.

Image source: electricaltechnology.org

What Does Sizing a PV Solar System Mean?

Sizing a PV solar system is to determine the amount of solar power that is necessary to meet your electricity demand.
This structured process (of PV solar system sizing) aligns solar energy generation with actual electricity demand and site conditions. It is not about guessing how many solar panels fit on a roof!

A well-sized system starts with one critical question: How much energy do you consume, and when do you consume it?
From there, the design accounts for real-world factors such as:

Load profiles and peak demand
Local solar irradiance and climate conditions
System losses, shading, and orientation
Available installation space and grid constraints

When done correctly, sizing ensures the system generates sufficient electricity without unnecessary oversizing, wasted investment, or underperformance.

A properly sized system can generate sufficient electricity for residential, commercial, or industrial applications:

Residential homes seeking energy independence
Commercial buildings optimizing operational costs
Industrial facilities managing high and continuous loads

How To Size A PV Solar System,
Step-by-step:

1. Determine Daily Energy Demand

How much electricity do you need, per day?
Typically, this is expressed in kilowatt-hour per day:

E(demand) = Average Daily Energy Demand [kWh/day]

Note!
The unit kilowatt-hour per day [kWh/day] is equivalent to the SI unit watt [W].

It is possible to determine the daily energy demand through:

Consulting utility bills for an existing site (for example, a home, an office, or a shopping mall)

Calculating the total energy used by all loads (electric appliances & devices) in the existing site:
- Energy [kWh] = Power [kW] x Time [h]

Note!
Power is typically available in the technical data sheets or instruction manuals of the electric appliances & devices.

2. Consider Energy Losses

In real-life PV solar systems, energy is lost at several stages. Solar panels rarely operate at their rated power due to:

Temperature
Dust
Shading
Inverters lose energy when converting DC power to AC power
Cables cause losses due to electrical resistance.
Batteries, if used, also lose energy during charging and discharging.

The system efficiency factor ( $\eta$ ) represents the generated energy that is usable, after accounting for the losses:

η = System efficiency factor

Typically, for PV solar systems, the system efficiency factor ( $\eta$ ) is approximately from 0.75 to 0.85 – this means that 75% to 85% of the generated energy is usable.

Now, it is possible to calculate the effective usable PV power, with the use of formulas such as:
- P(effective) [W] = P(PV) × η [W]

3. Determine Peak Sun Hours

It is important to determine how much sunlight is available, to size the PV solar system.

The peak sun hours is the number of hours per day that the system would operate at full rated power:
- H = Peak Sun Hours (h/day)

How to determine peak sun hours:

1. Understand your location
Peak sun hours depend on local climate, latitude, and seasonal variations.
For example, a sunny desert location will have far more peak sun hours than a cloudy northern city.

2. Use solar radiation data
You can find daily or monthly solar radiation data for most locations from sources like NASA, PVGIS, or local meteorological services.

3. Convert to peak sun hours
Solar radiation is usually given in kWh/m²/day.
Divide this by 1 kW/m² (standard test condition) to get the peak sun hours.

Example:
If your location receives 5.5 kWh/m²/day, then:
H = 5.5 kWh/m² ÷ 1 kW/m² = 5.5 peak sun hours/day

4. Calculate The Required PV Array Power

The required PV array power is the rated power of the solar panels that must be installed so that, over a typical day, they generate the required amount of energy.

The formula for calculating the required PV array power is:

P_{PV} = \frac{E_d}{H \times \eta}

Where:

P_PV = required PV array power (kW)
$E_d$ = daily energy demand (kWh/day)
$H$ = peak sun hours (h/day)
η = system efficiency (decimal)

5. Calculate The Number of PV Modules

Sizing PV modules means answering one simple question:
How many solar panels are necessary to produce the electricity a site needs over time?

This is the formula to calculate the number of PV modules necessary:

N = \frac{P_{mod}}{P_{PV}}

Where:

N = Number of PV modules
$P_{mod}$ = Rated power of one module (kW)
P_PV = Required PV array power (kW)

6. Organize Available Installation Space and Layout

To organize the available installation space and layout of a PV solar system, consider these factors:

Layout factors to consider	Details
Roof or Ground Area	• Measure total usable surface • Identify and exclude shaded areas • Ensure structural support for panel weight
Orientation	• Face panels true south (Northern Hemisphere) or true north (Southern Hemisphere) • Avoid obstructions that block sunlight
Tilt Angle	• Match tilt to site latitude for optimal year-round energy capture • Adjust for seasonal optimization if feasible
Panel Spacing	• Maintain spacing to prevent self-shading between rows • Allow airflow for cooling
Access for Maintenance	• Leave pathways for cleaning and inspection • Ensure safe access for repairs or component replacement
Safety and Compliance	• Follow local building codes and electrical regulations • Avoid hazards like overhangs or unstable ground

7. Size The Inverter

The inverter converts DC electricity, from the PV solar panels, into AC electricity, for your home or grid.
The size of the inverter must handle the maximum PV power. Too small, and it cannot run all loads; too large, and efficiency drops!

The inverter’s power must be 80–100% of P_PV power.
This is because AC power is lower than DC power, due to conversion losses.
For example, 4 kW of P_PV → 3.2–4 kW for inverter.

In addition, check the inverter’s voltage and current limits. Ensure AC output matches load or grid voltage/frequency for safe/reliable operation.

7. Size The Batery (Energy Storage)

Sizing a battery determines how much energy it should store to supply power when solar panels are not producing electricity, sunlight is low, etc.

1. Determine backup duration
Backup duration, or autonomy, is the number of days the battery should supply electricity without solar input. Typically, the backup duration can be:

Residential grid-tied systems: 1 to 2 days, enough for common outages.
Residential off-grid systems: 3 to 5 days, to handle periods of low sunlight.

2. Consider Depth of Discharge (DoD)
DoD is the percentage of battery capacity that can safely be used.
Batteries cannot be fully discharged without shortening lifespan. Fully discharging a battery can permanently reduce capacity and cycle life.

For example: 80% DoD means 80 percent of total capacity can be used while 20 percent remains to prevent damage
DoD values are in the battery manufacturer’s technical datasheet. Usually, under Depth of Discharge, usable capacity, or recommended discharge range values.
Typical values:
- Lithium-ion batteries 80-90% DoD
- Lead-acid batteries 40-50% DoD

3. Calculate required battery capacity

Use the formula:
$\text{Battery Capacity (kWh)} = \frac{\text{Daily Energy Consumption (kWh)} \times \text{Backup Days}}{\text{DoD}}$
For example: Daily consumption = 30 kWh, backup = 2 days, DoD = 80 percent
$\text{Battery Capacity} = \frac{30 \times 2}{0.8} = 75 \text{ kWh}$
Therefore,
Battery Capacity= 0.830 × 2 = 75 kWh

4. Select battery type and voltage

Total capacity and voltage configuration must meet energy needs, space, cost, and performance!

System voltage must match your inverter and load requirements. Common options are 12V, 24V, 48V
Battery chemistry should match the application, typically:
- Lithium-ion: Compact size + High DoD + Long life
- Lead-acid: Larger size + Lower DoD + Cheaper

8. Size The Solar Charge Controller

The The charge controller regulates PV current to the battery. It prevents overcharging and protects the battery.

1. Calculate minimum controller current
Use the formula:

$I_{CC} = \frac{P_{PV}}{V_{batt}}$ Where:

I_CC = Minimum charge controller current, in Amperes (A)
P_PV = total power of the PV array, in watts (W)
V_batt = nominal voltage of the battery bank, in Volts (V)

For example, if PV array 4 kW, battery 48 V , then:

$I_{CC} = \frac{4000}{48} = 83.3 \text{ A}$ 2. Add safety margin
Add 25% to handle variations and prevent overload!
For example: 83.3 × 1.25 ≈ 104 A required controller current

3. Match controller voltage
Make sure that the controller voltage matches the battery bank voltage. Note that common battery voltages are 12 V, 24 V, 48 V.

9. Cables & Wires

In addition, it is necessary to size organize cables & wires in a PV solar system.
The cabling and wiring systems connect all the PV system components and ensure safe, efficient electricity flow. Proper sizing of cables & wires prevents power losses, overheating, and potential hazards.

How to size cabling & wiring systems:

1. Calculate current
Determine the maximum current that will flow through each cable segment based on PV array and battery specifications.

2. Select cable size
Choose a cable with the correct cross-section to handle the current safely while minimizing voltage drop.

3. Consider voltage drop
Keep voltage loss within safe limits, typically below 3 percent for system efficiency.

4. Protect with fuses and breakers
Ensure each circuit has proper protection for safety and compliance.

5. Organize layout
Route cables neatly, avoid sharp bends, and keep them secure from mechanical damage and weather exposure.

Types Of PV Solar Systems:
Residential, Commercial, Industrial, & Utility-Scale

1. Residential PV Solar Systems

Residential PV solar systems are sized for households, where energy use is relatively low, predictable, and limited by roof space, so small arrays and optional batteries are sufficient.

Features for Residential PV Systems	Details
Size	• Small (1–10 kW)
Purpose	• Meet household energy needs • Optional battery storage
Where to Install	• Roof • Consider size • Avoid shading • Check orientation • Consider aesthetics
How It’s Designed	• Based on daily energy use • Rooftop area limits • Available sunlight • Simple safety margins and inverter/battery sizing
Tips / Key Points	• Focus on simplicity • Keep costs low • Easy to install

2. Commercial & Industrial PV Solar Systems

Commercial and industrial PV solar systems have higher and more variable energy demands, longer operating hours, and sometimes storage needs, so they require larger arrays, multiple inverters, and optimized layouts.

2.1 Commercial PV Solar Systems

Features for Commerical Systems	Details
Size	• Medium (10–500 kW)
Purpose	• Offset business energy costs • May include partial net metering
Where to Install	• Roof area • Parking lot canopy • Sometimes ground-mounted
How It’s Designed	• Based on building energy consumption profiles • Peak demand • Available space • Multiple inverters may be needed
Tips / Key Points	• Optimize energy across operating hours • Consider multiple meters • Focus on cost savings and efficiency

2.2 Industrial PV Solar Systems

Features for Industrial Systems	Details
Size	• Large (500 kW – several MW)
Purpose	• Support heavy loads • Power process operations • Reduce demand charges
Where to Install	• Often ground-mounted • Rooftop on large warehouses
How It’s Designed	• Align PV production with high energy-use periods • May integrate with storage and energy management systems • Inverters are modular for flexibility
Tips / Key Points	• Focus on reliability • Integrate with production schedules • Consider peak shaving to reduce costs

Note!
Peak shaving is a strategy to reduce the highest electricity demand (peak load) that a building experiences during the day.
Electricity costs are often higher during peak hours because utilities charge more when demand is high. Peak shaving uses on-site generation (for example, PV solar systems), batteries, or other energy storage to supply power during these peak periods, instead of drawing from the grid. This lowers electricity bills, reduces strain on the grid, and can extend equipment life.

3. Utility-Scale PV Solar Systems

Utility-scale PV solar systems are designed to supply electricity directly to the grid, requiring very large land areas, high-capacity inverters, and careful design to maximize efficiency and meet regulatory standards.

Features for Utility-Scale Systems	Details
Size	• Very large (MW to GW)
Purpose	• Feed electricity directly into the grid
Where to Install	• Large open land areas • Minimal shading
How It’s Designed	• Optimize land use • Minimize losses • Consider grid interconnection limits • Single or multiple high-capacity inverters
Tips / Key Points	• Focus on system efficiency • Minimize cost per kWh • Ensure grid compliance • Plan for long-term operation and maintenance

Conclusion

Sizing a PV solar system is a balance between energy needs, system losses, and the sunlight available. By using clear calculations and realistic assumptions, you can design a system that is both efficient and cost-effective.
The same principles apply whether you are planning a residential rooftop system, a commercial installation, or a larger utility-scale project, giving you a strong foundation for any solar project.
Getting the sizing right ensures your system produces enough energy to meet daily demand without overpaying for unused capacity. It helps prevent underperformance during cloudy days and allows you to plan for future upgrades with confidence.
When designed thoughtfully, a properly sized solar PV system can lower your energy bills, increase your independence from the grid, and contribute to long-term sustainability goals. With the right approach, solar energy becomes a reliable, smart, and impactful investment.