How to Use This Calculator

Step 1 — Enter your project details

Choose your country and city or reference point. Enter your road width and lighting arrangement. If your city is not listed, explicitly choose a reference point in the same country; its data does not represent a survey of your project site.

Step 2 — Set your operating requirements

Choose your lighting level, operating template, nightly operating hours and backup nights. Use Advanced Engineering for a custom operating schedule or technical specifications. Economic, Normal and High Brightness are preliminary power bands, not road-lighting standard classes.

Step 3 — Review your results

Calculate and review the suggested pole height, LED power, solar panel and battery capacity. Explore relevant products, then copy your summary and paste it into the Message field on our contact form for an engineering review. Calculator inputs are not sent automatically.

What Your Results Mean

Pole height and LED power are shown per lamp. Solar panel, battery and energy values apply to one independent power system, with the number of lamp heads stated in the result. They are not totals for the entire road.

Wp is the solar array’s rated peak power at standard test conditions. Wh describes battery energy; read the stated nominal or usable capacity basis. Ah describes charge capacity and must be read with the battery voltage: Wh = Ah × V.

Daily energy balance only means the planning PV value has not been sized to a recovery-time target. Review the actual estimated recovery time in the energy details, or enter a recovery target in Advanced Engineering. Backup nights mean maintaining the selected operating plan without solar charging.

How to Size a Solar Street Lighting System

A solar street light must meet two connected requirements: deliver the specified lighting on the road and supply that lighting throughout the required operating period. A higher LED wattage does not establish road-lighting compliance, and a larger battery does not solve an undersized solar array.

1. Define the illuminated road width, arrangement and maintained lighting target.
2. Establish a preliminary mounting height, spacing and luminous-flux requirement.
3. Use actual luminaire input power and a documented dimming schedule to calculate daily energy.
4. Size the PV array using tilted-plane solar resource and a suitable design month.
5. Size usable battery energy for the required zero-charge autonomy.
6. Check the complete PV, battery, controller and LED-driver combination.

Recommended INLUX Solar Products are relevant options supported by known published parameters, not verified project configurations. Known failed requirements exclude a candidate. A specific configuration is labeled Verified only when every required engineering check passes with complete supporting evidence. Up to three relevant options are shown; if none can be supported, request an engineering review.

Solar Street Light Design Inputs

Enter the width of the area that must be illuminated. Road length is optional and is used for a preliminary pole count. Choose single-side, opposite-side, staggered or median double-arm lighting. For staggered lighting, the spacing input is the longitudinal distance between adjacent alternating positions, not the distance between poles on the same side.

Use the maintained lighting target from the project specification. Residential, rural and arterial road labels do not by themselves establish the appropriate illuminance or lighting class. Projects specified by road-surface luminance also need a luminance-based design; there is no universal conversion from lux to cd/m².

Quick Design uses 34 road-width and lighting-arrangement rules for preliminary pole height, then 51 height-and-lighting-level power entries across Economic, Normal and High Brightness. These are historical planning rules, not photometric or structural validation. Advanced Engineering supports a separate average-illuminance estimate, measured input power and component limits. Switching to Quick recalculates its pole height, power and operating template; review the values before calculating again.

LED Power and Lighting Requirements

Advanced Engineering uses this preliminary average-illuminance model. If actual input watts are supplied, energy sizing uses those watts. Quick Design instead uses the road-width, arrangement and lighting-level rules; its illustrative luminous flux uses 150 lm/W, not verified INLUX product efficacy:

Required lumens per head ≈ target maintained lux × illuminated width × repeat length ÷ (heads per repeat × utilization factor × maintenance factor).

Estimated electrical input power is required lumens divided by whole-luminaire efficacy in lm/W. Use flux and input power measured at the same operating point. LED-chip efficacy, driver efficiency and power factor are different quantities and cannot replace the finished luminaire’s measured efficacy.

This method estimates an average. It does not establish minimum illuminance, uniformity, glare, road-surface luminance or compliance with a lighting class. The optics, mounting geometry, road surfaces and surroundings must be evaluated using the actual photometric data.

Multi-Stage Dimming and Nightly Energy

Lighting energy (Wh/night) = sum of actual input power (W) × operating hours for every lighting stage. Add controller, communications, sensor and other auxiliary consumption over their actual daily operating periods.

For example, an assumed 80 W input for five hours followed by an assumed 40 W input for seven hours consumes 680 Wh per night. A separate 1 W auxiliary load operating for 24 hours adds 24 Wh, giving 704 Wh/day at the load input. The 40 W state is an explicit input-power assumption; a 50% dimming command does not necessarily produce 50% input power.

When two heads share one battery and PV array, include both heads in that system’s energy total. If they have independent supplies, size each supply separately. Motion-sensor savings and reduced rainy-day lighting should not silently replace the required service schedule.

Solar Panel Sizing

Choose a city or an available reference point in the same country. The tool shows the selected reference, daily solar value and adopted month; Solar data details contains the source, statistical period, coordinates, panel angles and retrieval date. INLUX reference solar data uses saved, traceable monthly PVGIS data where available. Historical Excel indices with unconfirmed units and provenance are not used for sizing.

Checked reference coordinates can support a PVGIS monthly lookup. A saved valid reference may remain available if a refresh fails, with the fallback identified. When no validated solar value is available, choose another reference in the same country or enter sourced POA data in Advanced solar settings. Lighting and battery estimates remain available without a PV result. No national average or missing monthly values are invented.

Minimum PV capacity (Wp) = daily internal battery-energy depletion ÷ (design-month POA peak sun hours × PV-to-charge efficiency × internal charging efficiency).

Peak sun hours here represent daily irradiation on the proposed panel plane, expressed as equivalent hours at 1 kW/m². They are not the number of daylight hours. PVGIS monthly irradiation totals are divided by calendar days before the calculator forms monthly daily averages. The source, period, tilt and azimuth remain available in Solar data details. The month with the largest energy requirement relative to resource is used; with a constant load, this is the lowest-resource month.

The design month is the month with the greatest energy requirement relative to available solar resource. With a constant daily load, this is normally the lowest-resource month. Annual average irradiation should not be substituted without identifying the resulting limitation. If the lookup fails or coverage is unavailable, enter a sourced design-month POA value manually.

Include recovery as a separate requirement. An array that just balances a normal day may take a long time to recharge a depleted battery. If the required deficit must be recovered in a specified number of design days while lighting continues each night, the array must supply both the normal daily load and the additional recharge energy.

Battery Capacity and Autonomy

Required nominal battery energy (Wh) = autonomy nights × daily internal energy depletion ÷ (usable DoD × temperature capacity factor × end-of-life capacity factor).

Battery capacity (Ah) = nominal energy (Wh) ÷ nominal battery voltage (V). Ah values cannot be compared fairly without the voltage. Theoretical zero-charge autonomy is usable energy divided by the daily energy requirement at the same electrical boundary.

The capacity basis matters. If a supplied usable-Wh figure already includes depth of discharge, temperature, aging and internal discharge losses, do not apply those reductions again. The Advanced controls distinguish nominal stored energy, usable stored energy and usable energy delivered at the battery terminals. A real available capacity is needed to evaluate the proposed battery’s autonomy.

Three, four and five nights of backup scale with the declared daily service energy. Monthly average generation does not establish the likelihood of surviving a particular sequence of cloudy days. Battery chemistry, charging temperature, discharge rate, BMS limits and cutoff settings require separate confirmation.

Solar Controller Selection

A controller cannot be selected from panel wattage alone. Check cold-weather PV open-circuit voltage, the hot and cold maximum-power voltage range, short-circuit and operating input currents, the allowed array power, charging current and battery voltage window. Charging settings must respect the battery and BMS limits after temperature derating.

Also verify the LED driver’s input range, constant-current output and supported LED-string voltage. MPPT buck, buck-boost and PWM arrangements have different compatibility requirements. Missing electrical data produces REQUIRES VERIFICATION, even if the preliminary PV and battery energy totals appear sufficient.

Pole Height and Spacing

Pole height and spacing are preliminary layout variables. Quick Design suggests height from road width and lighting arrangement, then LED power from that height and the chosen lighting level. The default 24 m spacing is a separate planning assumption, not an optimized lighting layout. Use Advanced Engineering to enter a documented layout and validate it with the selected optics.

For a straight road with poles at both ends, the preliminary number of stations is ceiling(road length ÷ maximum station spacing) + 1. Opposite-side arrangements have two poles per station; a median double-arm arrangement has one pole with two heads. End effects, intersections and obstructions may change the final layout.

Pole and foundation design must consider the project wind loads, fixture and panel weight, effective wind area, mounting angles, materials, wall thickness, connections and ground conditions. Road width alone does not demonstrate structural adequacy.

Worked Example — Advanced Engineering

This example explains the Advanced Engineering model. It is not the Quick Design default or a verified INLUX product configuration.

Illustrative assumptions, not an INLUX product configuration: an 8 m illuminated width, single-side 24 m spacing, 20 maintained lux, utilization factor 0.4, maintenance factor 0.8 and whole-luminaire efficacy 150 lm/W. The preliminary calculation gives 12,000 lm and 80 W per head. A 400 m straight road with both endpoints included gives 18 stations and approximately 23.53 m actual spacing.

Use the 704 Wh/day load example above. Assume distribution efficiency 0.97, internal discharge efficiency 0.95, PV-to-charge efficiency 0.75, charging efficiency 0.95, usable DoD 0.8, temperature factor 0.9 and aging factor 0.8. Internal battery depletion is approximately 763.97 Wh/day. These factors require project validation.

At an assumed design-month resource of 3.5 peak sun hours per day, the steady-state PV minimum is approximately 306.35 Wp. Recovering the three-night deficit in three design days, while continuing nightly operation, increases the calculated target to approximately 612.71 Wp. These are calculation thresholds, not confirmed standard product sizes. Select an available configuration above the unrounded requirement and then verify its electrical and physical compatibility.

Common Sizing Mistakes

• Choosing LED wattage from road width without checking photometry.
• Using annual-average solar irradiation as the worst-month value.
• Treating brightness percentage as measured electrical input power.
• Comparing battery Ah without its voltage or capacity basis.
• Counting the same driver, controller or battery loss twice.
• Assuming a long backup claim preserves the full requested lighting schedule.
• Ignoring recharge time after an autonomy event.
• Combining a series’ largest panel and battery into an undocumented configuration.

Frequently Asked Questions

How many watts does a solar street light need?

The requirement depends on the lighting target, road geometry, optics, mounting height, spacing and actual luminaire efficacy. Quick Design suggests a power band from road width, arrangement and lighting level. Advanced Engineering estimates power from an average-illuminance model or uses supplied actual input watts. The selected luminaire must then be checked photometrically.

Can a larger battery compensate for a small solar panel?

A larger usable battery can increase temporary backup. It cannot sustain a persistent daily energy deficit. The PV array must support the normal service load and the chosen recovery requirement.

Why does the calculator sometimes show no verified product match?

Verified Configuration requires complete evidence for the specific configuration and all required engineering conditions. Missing controller or battery data can prevent this status. Separately, Recommended INLUX Solar Products may show relevant options supported by known parameters. These are not engineering approval; series limits do not establish a combined panel-and-battery configuration.

Can I calculate without a PVGIS connection?

Yes. A valid saved monthly reference can be used when available. Alternatively, enter a sourced daily POA value with its time basis in Advanced solar settings; an annual reference is labeled preliminary and is not treated as design-month data. If solar data is unavailable, the tool can still estimate lighting load and battery requirements; the PV result remains unavailable until a valid resource input is supplied.

Does this replace DIALux or a structural calculation?

No. It provides preliminary energy sizing and documented electrical checks. Final lighting distribution, uniformity, glare, poles and foundations require the appropriate project-specific engineering work.

Related Tools and Engineering Guides

• Solar Street Light ROI Calculator — compare cost and return assumptions separately from engineering sizing.
• Solar Street Light Product Selector — shortlist product families from basic application requirements.
• Lumens to Watts Calculator — explore the relationship between luminous flux and electrical input.
• Watts to Amps Calculator — convert power to current with the appropriate electrical assumptions.
• Solar Street Light Engineering Guides — supporting design and application information.

Inlux Solar Product Options and Engineering Support

Review INLUX’s JAGUAR All-in-Two, FALCON All-in-Two and APOLLO Split product options. These links are reference options, not a statement that a particular configuration meets the estimate above.

For a configuration review, copy the calculation summary and share the project location, road geometry, lighting specification and operating schedule with INLUX. Include available IES files, component requirements and site constraints. Request engineering validation or return to the Engineering Calculators Hub.