Solar vs Grid-Powered LED Street Light: 10-Point Comparison and Sizing Method
Short answer: Choose grid-powered LED where mains power is available, illuminance requirements are high and the road matters (arterials, sub-arterials, tunnel portals, junctions). Choose off-grid solar where there is no mains supply, trenching is expensive, or illuminance requirements are moderate (rural roads, campus and park paths, new district service roads, mountain scenic routes). The deciding factor is not unit price but power availability + illuminance class + consecutive rainy-day autonomy.
Figures below are common engineering ranges compiled from widely used standards such as CJJ 45 (urban road lighting design), GB/T 24460 (solar PV lighting installations) and GB/T 31832 (LED application requirements for urban road lighting). Always verify against local solar irradiation data, weather records and the project specification.
1. Ten-point comparison
Criterion
Off-grid solar street light
Grid-powered LED street light
Power source
PV array + battery, fully off-grid
Mains supply, requires connection and metering
Upfront cost per pole
Higher (array and battery dominate)
Lower (luminaire and pole dominate)
Cabling and civil works
No cable trenching; smaller foundation
Trenching, conduit, cable, handholes, distribution board
Installation time
Short; each pole is independent
Longer; subject to utility approval and utility diversions
Rainy-weather performance
Limited by configuration; risk of dimming or switch-off
Unaffected by weather
Luminous stability
Varies with battery state and controller strategy; decays in winter
Constant; dimmable on schedule
Maintenance
Battery is a consumable, typically replaced every few years; array needs cleaning
Mostly luminaire and driver; cable faults are harder to locate
Smart control
Per-pole autonomy; NB-IoT single-lamp control optional
Expressways, arterials, sub-arterials, important local roads
Life-cycle cost
No electricity bill, but battery replacement raises long-term cost
Ongoing electricity cost, but long system life
2. Decision flow: three steps
Step 1 — Power: Is there a supply within roughly 100 m of the pole position? Does connecting it require cutting the road surface or crossing existing utilities? When trenching and connection are expensive, solar wins.
Step 2 — Illuminance class: Determine road class and maintained average illuminance per CJJ 45. Arterials demand high illuminance and must not go dark — avoid off-grid solar there.
Step 3 — Sunshine and rain: Check annual irradiation hours and the longest recorded run of consecutive rainy days, then confirm whether the resulting array and battery sizes stay within budget.
3. Sizing: two practical formulas
3.1 PV array wattage
A common first-pass method is the "luminaire wattage multiplier":
Array (Wp) ≈ luminaire wattage (W) × operating hours per day × (3 to 4) ÷ local peak sun hours
Rule of thumb: in high-irradiation regions such as South China, array wattage is typically 3–4 times the luminaire wattage; take the upper bound — or more — at higher latitudes and in rainy climates.
Pole height
LED wattage
Reference PV array
Reference battery (LiFePO₄)
6 m
30–40 W
80–150 Wp
12.8 V / 30–50 Ah
7 m
40–60 W
120–200 Wp
12.8 V / 40–70 Ah
8 m
60–80 W
180–280 Wp
12.8 V / 60–100 Ah
3.2 Battery capacity
Battery (Ah) = luminaire wattage (W) × hours per day (h) × autonomy days ÷ system voltage (V) ÷ depth of discharge (DoD)
Hours per day: all-night operation 10–12 h; part-night (full output early, reduced later) 6–8 h
Autonomy days: commonly 3 days; 5 days or more in rainy regions, monsoon and typhoon areas
Depth of discharge: LiFePO₄ typically 0.8–0.9; gel lead-acid typically 0.5–0.6 (deep discharge sharply shortens lead-acid life)
Autonomy days are the main cost driver. Moving from 3 to 5 days pushes both array and battery up roughly one size class and raises unit cost noticeably. Agree the guaranteed autonomy days with the owner in the tender specification instead of guessing.
4. Battery: LiFePO₄ is now the mainstream choice
Type
Characteristics
Typical use
LiFePO₄
High energy density, long cycle life, deep discharge capable, light; suits integrated or in-pole designs
Default choice for new projects
Gel lead-acid
Low cost, better low-temperature tolerance, bulky, short cycle life, dislikes deep discharge
Tight budgets or cold regions
NMC lithium
Higher energy density, stricter thermal management requirements
Rarely used in outdoor street lighting
Install batteries in the pole base compartment or a buried waterproof enclosure, avoiding sections prone to standing water. In hot and humid regions, address condensation and heat dissipation inside the compartment.
5. Five common mistakes with solar street lights
Comparing LED wattage instead of lumens and distribution: two 40 W luminaires with different optics can differ by a factor of two in road illuminance. Specify lumens and the photometric curve.
Pointing the array in an arbitrary direction: in the northern hemisphere face it south (about 5–10° west of true south is often slightly better), with tilt set by latitude. Shading from trees, buildings or signage directly causes undercharging.
Trusting nameplate ratings: some low-cost products overstate array and battery figures. Verify charge current and discharge duration at acceptance testing.
Neglecting the controller: it handles charge/discharge management, over-discharge protection and time/photocell strategy; a part-night dimming strategy (for example 50% after midnight) significantly extends autonomy.
No cleaning regime: dust and bird droppings reduce generation year after year. Include array cleaning in periodic inspection.
6. Key points for grid-powered LED
Voltage drop: check end-of-circuit drop; long circuits need larger conductors or additional feed points.
Distribution and protection: residual-current and overload protection per circuit; locate the distribution board for maintainability and flood safety.
Earthing and surge protection: pole earthing resistance is commonly specified at ≤ 4 Ω (per project design); add SPDs on important routes.
Dimming strategy: part-night dimming saves substantial energy — specify dimmable drivers with 0–10 V, DALI or power-line carrier interfaces.
FAQ
Can solar street lights be used on urban arterials?
Generally not recommended. Arterials require high illuminance and reliability and must not go dark after consecutive rainy days. Use grid-powered LED there; solar suits local roads, rural roads, campuses and greenways.
How many consecutive rainy days can a solar street light survive?
It depends on the specified configuration: 3 days is common, while rainy regions and monsoon areas often specify 5 days or more. More autonomy means a larger array and battery and higher cost, so state the requirement explicitly in the tender documents.
What array and battery does a 60 W solar street light need?
As a first estimate, take array wattage at 3–4 times the luminaire wattage (roughly 180–280 Wp). Battery capacity = wattage × hours × autonomy days ÷ system voltage ÷ DoD; with all-night 10 h, 3-day autonomy, 12.8 V and DoD 0.85, expect roughly 60 Ah, then verify against local irradiation.
Which is cheaper overall, solar or grid?
Do not compare unit price alone. Solar avoids cables, trenching and electricity bills but carries higher initial configuration cost and periodic battery replacement. Grid luminaires are cheaper upfront but require electricity and cabling. Solar usually wins on remote routes with no supply and difficult trenching.
Do solar street lights get dimmer in winter?
They can. Shorter days reduce generation and low temperature reduces usable battery capacity. Size against the worst local month and use a sensible controller dimming strategy rather than simply increasing luminaire wattage.
What ingress and impact ratings are needed?
Luminaires typically IP65 or higher with IK08 or higher. Buried battery enclosures need dedicated waterproofing and drainage. Array frames and brackets must be checked against local wind load, with additional reinforcement in typhoon-prone coastal areas.
Zhongshan Haohong Lighting & Decoration Co., Ltd. · QIJIUJIU ｜ mjzh@hhlighting.cn
General technical reference only. Project-specific values must follow the design documents and local codes.