Solar Street Lights Design Guide: Key Calculations and Considerations

Comprehensive Guide to Designing Efficient Solar Street Lights

When designing solar street lights, multiple aspects must be considered through various calculation formulas to ensure the system’s efficiency, reliability, and cost-effectiveness. Below are detailed calculation formulas and their applications:

Solar Street Lights Average Road Illumination Calculation

Formula:

E = (Φ * N * U * K) / (S * W)

Parameter Explanation:

• E: Average road illumination (units: lux)
• Φ: Total luminous flux of the light source (units: lm)
• N: Streetlight arrangement value; take 2 for rectangular arrangement, 1 for single-side and staggered arrangements
• U: Utilization factor
• K: Maintenance factor
• S: Spacing between lamp poles (units: meters)
• W: Road width (units: meters)

Application Example:

Assume a city’s secondary road where the light source is an LED with a total luminous flux of 3000 lm, single-side arrangement, utilization factor of 0.7, maintenance factor of 0.8, lamp pole spacing of 30 meters, and road width of 10 meters. The average road illumination E is calculated as:

E = (3000 * 1 * 0.7 * 0.8) / (30 * 10) = 5.6 lux

Solar Street Lighting Solar Panel Power Calculation

Formula:

P = (Pload * Tuse) / (Tsunlight * η)

Parameter Explanation:

• P: Power of the solar panel (units: W)
• Pload: Load power (units: W)
• Tuse: Daily usage time (units: hours)
• Tsunlight: Local sunlight hours (units: hours)
• η: System efficiency (typically between 0.6 to 0.8)

Application Example:

Assume the load power is 30W, daily usage time is 8 hours, local sunlight hours are 3.42 hours, and system efficiency is 0.7. The solar panel power P is calculated as:

P = (30 * 8) / (3.42 * 0.7) ≈ 102.4 W

Solar Street Light Battery Capacity Calculation

Formula:

C = (Pload * Tuse * Drainy days) / (Vsystem * ηdischarge * 1.5)

Parameter Explanation:

• C: Battery capacity (units: Ah)
• Pload: Load power (units: W)
• Tuse: Daily usage time (units: hours)
• Drainy days: Continuous rainy days (units: days)
• Vsystem: System operating voltage (units: V)
• ηdischarge: Battery discharge efficiency (typically taken as 0.8)
• 1.5: Loss coefficient

Application Example:

Assume the load power is 30W, daily usage time is 8 hours, continuous rainy days are 3 days, system operating voltage is 12V, and battery discharge efficiency is 0.8. The battery capacity C is calculated as:

C = (30 * 8 * 3) / (12 * 0.8 * 1.5) ≈ 50 Ah

Solar Street Light Solar Panel Installation Angle

Formula:

θ = Latitude + 5°

Parameter Explanation:

• θ: Solar panel installation angle (units: degrees)
• Latitude: Geographical latitude of the installation site (units: degrees)

Application Example:

Assume a region located at latitude 24.48 degrees (like Xiamen); the solar panel installation angle θ is calculated as:

θ = 24.48° + 5° = 29.48°

Solar Lighting Wind Pressure on Solar Panel Surface

Formula:

P = (1/2) * ρ * V² * (1 + C)

Parameter Explanation:

• P: Wind pressure (units: N/m²)
• ρ: Air density (approximately 1.25 kg/m³ at room temperature)
• V: Wind speed perpendicular to the surface (units: m/s)
• C: Structural constant, varies with the shape of the structure, ranging from 0.3 to 1.0

Application Example:

Assume the maximum wind speed is 28.4 m/s, air density is 1.25 kg/m³, and the structural constant is 0.8. The wind pressure P on the solar panel surface is calculated as:

P = (1/2) * 1.25 * (28.4)² * (1 + 0.8) ≈ 1024.8 N/m²

Solar Street-Lights Working Voltage of Solar Panel Components

Formula:

UA = Uf + Ud + Ui

Parameter Explanation:

• UA: Output working voltage of the solar panel (units: V)
• Uf: Floating charge voltage of the battery component (units: V)
• Ud: Voltage drop caused by the blocking diode and line losses (units: V)
• Ui: Voltage drop caused by temperature rise (units: V)

Application Example:

Assume the floating charge voltage is 14V, voltage drop due to line losses is 1V, and voltage drop due to temperature rise is 1.5V. The output working voltage UA of the solar panel component is calculated as:

UA = 14 + 1 + 1.5 = 16.5 V

Street Lights Voltage Drop Due to Temperature Increase Calculation

Formula:

Ui = a * (T - 25) * Ua

Parameter Explanation:

• Ui: Voltage drop caused by temperature rise (units: V)
• a: Temperature coefficient of the solar panel component; 0.005 for monocrystalline and polycrystalline panels, 0.003 for amorphous silicon panels
• T: Maximum working temperature of the solar panel component (units: °C)
• Ua: Nominal working voltage of the solar panel component (units: V)

Application Example:

Assume a monocrystalline solar panel component is used, with a maximum working temperature of 60°C and a nominal working voltage of 17V. The voltage drop due to temperature rise Ui is calculated as:

Ui = 0.005 * (60 - 25) * 17 = 2.125 V

Optimization of Solar Panel Power

Formula:

PA = (Q * 365 * K) / ((1 - a * (T - 25)) * η)

Parameter Explanation:

• PA: Power of the solar panel component (units: W)
• Q: Daily electricity consumption (units: Wh)
• K: System efficiency
• a: Temperature coefficient
• T: Maximum working temperature of the solar panel component
• η: Safety factor (typically taken between 1.05 to 1.30)

Application Example:

Assume the daily electricity consumption is 240Wh, system efficiency is 0.7, temperature coefficient is 0.005, maximum working temperature is 60°C, and safety factor is 1.1. The power PA of the solar panel component is calculated as:

PA = (240 * 365 * 0.7) / ((1 - 0.005 * (60 - 25)) * 1.1) ≈ 73.2 W

Solar Street lamp Solar Panel Capacity Design

Formula:

Wp = (Q * 365) / ((1 - a * (T - 25)) * η * A)

Parameter Explanation:

• Wp: Capacity of the solar panel array (units: Wp)
• Q: Daily electricity consumption (units: Wh)
• a: Temperature coefficient
• T: Maximum working temperature of the solar panel component
• η: System efficiency
• A: Solar radiation on the inclined solar component (units: MJ/m²)

Application Example:

Assume the daily electricity consumption is 240Wh, temperature coefficient is 0.005, maximum working temperature is 60°C, system efficiency is 0.7, and solar radiation on the inclined solar component is 1.1 MJ/m². The solar panel array capacity Wp is calculated as:

Wp = (240 * 365) / ((1 - 0.005 * (60 - 25)) * 0.7 * 1.1) ≈ 132.4 Wp

Solar Lights Street Battery Capacity Design

Formula:

C = (D * Q * 1.5) / (U * η)

Parameter Explanation:

• C: Battery capacity (units: Ah)
• D: Longest period of no sunlight for daily electricity (units: days)
• Q: Daily electricity consumption (units: Wh)
• U: System operating voltage (units: V)
• η: System efficiency

Application Example:

Assume the longest period without sunlight is 3 days, daily electricity consumption is 240Wh, system operating voltage is 12V, and system efficiency is 0.8. The battery capacity C is calculated as:

C = (3 * 240 * 1.5) / (12 * 0.8) ≈ 90 Ah

By utilizing these detailed calculation formulas, the solar street light system can operate efficiently and reliably under various geographical and climatic conditions. The design must also consider factors like cost, aesthetics, and practical application to achieve optimal system performance.