Solar PV System Sizing and Load Analysis for Residential and Commercial Applications

Proper sizing of a solar PV system is critical to ensuring it meets the energy demands of the intended application — whether for a small home or a large commercial facility. Over-sizing results in unnecessary capital expenditure, while under-sizing leads to insufficient power and system inefficiencies.

This guide provides a step-by-step technical framework for load analysis, system sizing, component selection, and performance forecasting, using real-world examples and calculations tailored for both residential and commercial projects.

1. Why Load  Analysis Is Important

Load analysis is the foundation of PV system sizing. It determines:

• How much energy is consumed daily and monthly

• What the peak power demand is

• When the demand occurs (day/night)

• Seasonal load variations

This ensures the PV system is designed to match the demand curve as closely as possible.

2. Step-by-Step Load Analysis

🔹 Step 1: List Electrical Appliances

Create a table with:

• Appliance name

• Rated power (W)

• Quantity

• Daily usage hours

Example – Residential Load Profile:

Appliance	Power (W)	Quantity	Hours/day	Total Energy (Wh/day)
LED Bulbs	10	10	5	10 × 10 × 5 = 500
Refrigerator	150	1	10	150 × 1 × 10 = 1500
Ceiling Fan	75	4	8	75 × 4 × 8 = 2400
Television	100	1	4	100 × 1 × 4 = 400
Laptop	60	2	6	60 × 2 × 6 = 720
Total				5520 Wh/day

This is the daily energy demand (5.52 kWh).

🔹 Step 2: Estimate Monthly and Annual Energy Demand

Multiply daily demand by 30 or 365:

$$\text{Monthly Demand} = 5.52 \times 30 = 165.6\ \text{kWh}$$ $$\text{Annual Demand} = 5.52 \times 365 = 2014.8\ \text{kWh}$$

🔹 Step 3: Consider Load Factor and Demand Profile

For commercial setups, define:

• Load Factor:

  $$\text{Load Factor} = \frac{\text{Avg. Load (kW)}}{\text{Peak Load (kW)}}$$

Higher load factors (0.6–0.9) indicate efficient usage.

3. Sizing the Solar PV System

To size the system accurately, we need to factor in:

• Peak Sun Hours (PSH): Solar irradiation hours (kWh/m²/day)

• System Losses: Typically 20% for inverter, wiring, soiling, etc.

🔹 Step 1: Calculate PV Array Size

Formula:

$$\text{Required PV Size (kW)} = \frac{\text{Daily Energy Demand (kWh)}}{\text{PSH} \times (1 - \text{Losses})}$$

Assumptions:

• PSH = 5 hours/day

• Losses = 20% → (1 - 0.2 = 0.8)

• Daily demand = 5.52 kWh

$$\text{PV Size} = \frac{5.52}{5 \times 0.8} = \frac{5.52}{4} = 1.38\ \text{kW}$$

Recommended System: 1.5 kW solar PV system for residential case

🔹 Step 2: Choose Number of Panels

Using 375 W panels:

$$\text{Number of Panels} = \frac{1500}{375} = 4 \text{ panels}$$

🔹 Step 3: Battery Sizing (Optional for Hybrid/Off-grid)

Assume 1 day autonomy, DoD = 80%, inverter efficiency = 90%

$$\text{Battery Capacity} = \frac{5.52}{0.8 \times 0.9} \approx 7.65\ \text{kWh}$$

Choose: 8 kWh Li-ion battery bank

4. Sizing for Commercial Applications

Let’s consider a small commercial office with:

Load Description	Load (kW)	Operating Hours/day	Energy (kWh/day)
Lighting (LED)	2.0	10	20
AC Units (3 Nos)	6.0	8	48
Computers (20 Nos)	1.5	8	12
Servers	0.8	24	19.2
Printers, Others	1.0	4	4
Total	—	—	103.2 kWh

Assuming:

• PSH = 5 hours/day

• System Loss = 20%

$$\text{PV Size} = \frac{103.2}{5 \times 0.8} = 25.8\ \text{kW}$$

Commercial System: Recommend 26–30 kW system

5. Inverter Sizing

For grid-tied:

• Inverter size ≈ 80–110% of PV size

• For 1.5 kW system → use 1.5–2 kW inverter

For off-grid:

• Inverter must handle peak loads (motors, compressors)

Tip: Add 25–30% margin above peak load.

6. Tilt and Orientation Consideration

• Tilt Angle = Latitude of location (±10°)

• Orientation = True South (Northern Hemisphere) / True North (Southern Hemisphere)

Proper tilt and orientation increase annual yield by 10–25%.

7. Performance Ratio (PR) and Energy Yield

Performance Ratio (PR):

$$PR = \frac{\text{Actual Energy Output}}{\text{Ideal Output}}$$

Annual Yield Estimate:

$$\text{Annual Energy (kWh)} = \text{PV Size (kW)} \times PSH \times 365 \times PR$$

For 1.5 kW system, PSH = 5, PR = 0.8

$$1.5 \times 5 \times 365 \times 0.8 = 2190\ \text{kWh/year}$$

Enough to cover the 2014.8 kWh annual demand

8. Final System Components Checklist

Component	Residential	Commercial
Solar Panels	375 W × 4	375 W × 70
Inverter	1.5–2 kW	30–35 kW
Battery (opt.)	8 kWh	30–50 kWh
Mounting	Rooftop	Rooftop/Ground
EMS/Monitoring	Optional	Essential

FAQs

Q1: What if my area has cloudy weather?
A: Use lower PSH values (e.g., 3–4 hrs/day) and consider increasing system size by 25–40%.

Q2: Can I run my entire home on solar?
A: Yes, if sized correctly with battery backup or grid-tie for reliability.

Q3: Do solar panels work during power cuts?
A: Only if you have a battery or hybrid inverter. Grid-tied inverters shut off during outages.

Q4: How often should I clean my solar panels?
A: Every 3–6 months or sooner if in dusty environments. Dirt can reduce output by up to 20%.

Q5: What tools can I use for PV sizing?
A: PVsyst, NREL PVWatts, HOMER Pro, or online calculators from solar manufacturers.

Conclusion

Solar PV system sizing is a balance of technical precision, load dynamics, and economic efficiency. Whether for a home or a business, a detailed load analysis and careful component selection will ensure optimal performance, long-term savings, and sustainability. Use local irradiance data and real-time usage profiles to fine-tune your system.