Formulas commonly used in solar street light design

Average Road Illuminance Calculation
Solar Panel Power Calculation
Battery Capacity Calculation
Solar Panel Installation Angle
Wind Pressure on Solar Panels
Component Operating Voltage Correction (Temperature Effect)
Voltage Drop Compensation Due to Temperature
Solar Panel Capacity Optimization Design

1. Average Road Illuminance Calculation.

Formula:
Eavg = (N × Φ × U × K) / A

Parameter Description:

N: Number of fixtures
Φ: Total luminous flux per lamp (lm)
U: Utilization factor (0.4-0.6)
K: Maintenance factor (0.7-0.8)
A: Road area (m2) = Road width × Lamp spacing

Example:

6m wide road, lamp spacing 30m, using 10,000 lm LED, one-sided lighting:
Eavg ≈ (1 × 10,000 × 0.5 × 0.75) / (6 × 30) ≈ 20.8 lx

2. Solar Panel Power Calculation .

Formula:
Ppv = Qday / (Hpeak × ηsys)

Parameter Description:

Qday = PLED × Twork (Daily energy consumption, Wh)
Hpeak: Local annual average peak sunlight hours (check meteorological data, e.g., Beijing 4.5h)
ηsys: System efficiency (0.6-0.75, including line losses, controller losses)

Example:
Load power 80W, daily operation 10h, Shanghai Hpeak=3.8h:
Ppv ≈ (80 × 10) / (3.8 × 0.65) ≈ 324 W

3. Battery Capacity Calculation.

Formula:
C = (Qday × D) / (DOD × ηbat × Vsys)

Parameter Description:

D: Number of consecutive cloudy days (usually 3-5 days)
DOD: Depth of discharge (0.5 for lead-acid batteries, 0.8 for lithium batteries)
ηbat: Charge/discharge efficiency (0.85-0.95)
Vsys: System voltage (12V/24V)

Example:
Daily consumption 800Wh, 24V system, 3 days backup, lithium battery:
C ≈ (800 × 3) / (0.8 × 0.9 × 24) ≈ 138.9 Ah → Choose 150Ah battery

4. Solar Panel Installation Angle

Formula:
θ = φ + (5° to 15°)

Parameter Description:

φ: Local geographical latitude
Winter optimization: latitude +10°~15°, summer optimization: latitude -5°

Example:
latitude 32°, fixed bracket tilt angle set at 37° (32°+5°) to improve winter power generation.

5. Wind Pressure on Solar Panels

Formula:
F = 0.61 × v2 × A

Parameter Description:

v: Maximum wind speed (m/s)
A: Wind-facing area of the photovoltaic panel (m2)

Example:
Panel area 2m2, design wind speed 30m/s:
F = 0.61 × (30)2 × 2 = 1098 N

Need to verify the wind resistance of the lamp pole and foundation.

6. Component Operating Voltage Correction (Temperature Effect)

Formula:
Vmp = Vmp(STC) × [1 + α × (T – 25)]

Parameter Description:

α: Temperature coefficient (approximately -0.35%/°C for monocrystalline silicon)
T: Actual operating temperature (°C)

Example:
Nominal component voltage 18V, operating temperature 60°:
Vmp ≈ 18 × [1 – 0.0035 × (60-25)] ≈ 15.3 V

7. Voltage Drop Compensation Due to Temperature

Formula:
ΔV = Nseries × α × ΔT × Vmp(STC)

Example:
3 series-connected components, each Vmp=30V, temperature difference 35°:
ΔV ≈ 3 × (-0.0035) × 35 × 30 ≈ -11V
Need to adjust the MPPT voltage range.

8. Solar Panel Capacity Optimization Design

Empirical Formula:
Ppv(opt) = 1.2 × Ppv

Consider shadowing, dust loss (efficiency reduction of 10-20%)

When paralleling multiple components, increase bypass diodes to reduce hotspot effects.

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Formulas commonly used in solar street light design