KEY TAKEAWAY
The project conditions should determine the solar lighting configuration.
Neither solar nor grid-powered street lighting is universally cheaper. The comparison usually turns on four local variables: the distance from each pole to a usable connection point, the cost of trenching and reinstatement along that route, the price of a metered kilowatt-hour including fixed standing charges, and how often the storage battery has to be replaced. A defensible answer prices the same service on both sides, the same lighting class for the same hours over the same 10 to 20 year period, and states its assumptions instead of comparing a purchase price with a purchase price.
Compare a service, not a product
The most common mistake in this comparison is to put a solar luminaire price next to a conventional luminaire price. The two products do different amounts of work: one includes its own generation and storage, the other assumes a distribution network already exists or will be built. A comparison is only meaningful once both options are required to deliver the same lighting service.
Fix the functional unit first, then price each option against it. Everything downstream, including whether solar looks expensive or cheap, follows from these definitions.
- The same lighting class or target average lux, with the same uniformity criteria
- The same operating hours and dimming profile across the year
- The same road section, pole count and mounting geometry
- The same evaluation period, commonly 10 to 20 years for public lighting
- The same maintenance standard, including cleaning and fault-response times
- The same treatment of end-of-life: removal, recycling and residual value
Where the money actually sits
Both options carry costs the other does not. Listing them side by side usually shows immediately which variable will decide the case, and which lines are small enough to estimate roughly without changing the conclusion.
| Cost line | Grid-powered | Solar | Comment |
|---|---|---|---|
| Luminaire and pole | Lower per unit | Higher per unit (includes PV and storage) | The only line where grid is normally ahead |
| Trenching, ducting, cabling | Often the largest single item | Usually none between poles | Dominates on long runs and hard surfaces |
| Reinstatement of surfaces | Road, pavement and landscaping repair | None | Can rival the trenching cost in urban areas |
| Feeder pillar, protection, metering | Required | Not required | Includes design and inspection effort |
| Utility connection and standing charges | Application fee plus recurring charges | None | Recurring charges often persist regardless of use |
| Metered energy | Full consumption for the period | None | Sensitive to tariff escalation over 10-20 years |
| Battery replacement | None | Scheduled pack replacement | The main recurring solar cost |
| Panel cleaning and vegetation control | None | Periodic | Frequency depends on dust, salt and canopy growth |
| Fault finding and repair | Cable faults can be slow and disruptive | Faults are local to one pole | Solar failures rarely take out a whole street |
| Theft and vandalism exposure | Copper cable | Panels and batteries | Local risk profile decides which is worse |
Capital cost: the trenching question usually decides it
In most real comparisons, the deciding variable is not the luminaire at all. It is how many metres of trench the grid option needs and what a metre of trench costs in that surface, in that jurisdiction, with that reinstatement standard.
Distance to a usable connection point
Measure to a connection point with adequate capacity and a realistic route, not to the nearest visible cable. A connection that requires a transformer upgrade, a road crossing, a railway or watercourse crossing, or a wayleave over third-party land is materially more expensive than its map distance suggests.
The comparison changes shape with layout. A long, thin run of poles, a rural approach road, a perimeter fence line or an isolated car park all maximise the trenching disadvantage. A dense urban infill project next to existing infrastructure minimises it.
Cost per metre and reinstatement
Trenching rates vary enormously by surface and jurisdiction: soft ground, footway, asphalt carriageway and heritage paving are different projects. Reinstatement, traffic management, permits, night-work premiums and out-of-hours restrictions often add as much as the excavation itself.
Collect these as local rates rather than as national averages, because they are the input that most often reverses a conclusion reached with generic numbers.
Connection, metering and design fees
Grid schemes carry costs that are easy to omit at concept stage: utility application and connection fees, feeder pillars, protection devices, metering, electrical design, inspection and certification. Solar schemes carry their own: energy modelling for the location, structural checks for the larger wind area on the pole, and sometimes a larger foundation.
Neither list is optional. A comparison that includes one and omits the other is not a comparison of options; it is a comparison of paperwork completeness.
Operating cost: energy, charges and cleaning
Operating cost is where the two options diverge most predictably. A grid installation pays for every kilowatt-hour it consumes for the whole evaluation period, plus fixed charges that continue whether the lights are dimmed or not. A solar installation pays nothing for energy and instead pays for keeping its generation and storage healthy.
Metered energy and tariff risk
Model the energy line with the actual profile rather than at full output all night. A staged profile of, for example, three hours at full output, two hours at 80 per cent and seven hours at 25 per cent consumes far less than twelve hours at 100 per cent, and both options benefit equally from that reduction.
Then test the result against tariff escalation. Over a 15 or 20 year horizon, a modest annual increase compounds into a large share of total cost, and it is the single assumption most likely to be disputed. Present the comparison at more than one escalation rate rather than defending a single forecast.
Cleaning and vegetation management
Solar adds two maintenance activities a grid scheme does not have: keeping the module surface reasonably clean, and keeping vegetation from growing into the solar window. Both are cheap individually and easy to forget in a budget.
Frequency is site-specific. Dusty roadsides, agricultural areas, coastal salt exposure and low panel tilts all soil faster. A steeper tilt and a rain-shedding installation reduce the cleaning interval, which is one reason panel tilt is a lifecycle decision and not only a yield decision.
The battery replacement cycle
Battery replacement is the recurring cost that makes solar comparable rather than automatically cheaper, and it is the line most often left out. Street lighting cycles its storage once per night, which is roughly 365 cycles per year, so cycle life converts into a service interval in a straightforward way.
Lithium iron phosphate (LiFePO4) packs of the type used across the Reluxlight street-light series are commonly rated in the region of a few thousand charge and discharge cycles before usable capacity falls toward roughly 80 per cent of nominal, with depth of discharge and operating temperature both strongly affecting the result. Treat any single cycle number with caution unless the supplier states the depth of discharge, the temperature and the end-of-capacity criterion behind it.
What is published for these products is the chemistry and pack size per model, from 12.8 V 30 Ah on the smallest all-in-two configuration up to 25.6 V 100 Ah on the 200 W split configuration, a BMS with overcharge, over-discharge and temperature protection, a working range of -25 to 65 degrees Celsius on the all-in-two and split series, and a warranty of three years as standard with a five-year project option. Those are the figures to build a replacement plan around, alongside the supplier's stated cycle rating for the specific pack supplied.
- Ask for the cycle rating with its depth of discharge, temperature and end-of-life definition
- Ask what the controller does to protect the pack at low state of charge and in high heat
- Confirm whether the pack is field-replaceable and whether it can be sourced separately later
- Budget the labour and access cost of replacement, not only the pack
- Confirm the recycling or take-back route before the first replacement is due
Plan replacement as a scheduled event
A planned pack change across a street during daylight, with a known part number and a stocked spare, is a routine maintenance visit. The same work as an emergency response to scattered failures across several winters costs far more per pole and generates the complaints that damage a programme's reputation.
Build the replacement into the operating budget from year one, in the same way a grid scheme budgets for driver and lamp replacement, and record the installation date and pack serial number per pole at commissioning so the schedule can be driven by data rather than by failure.
Design choices that lengthen the interval
Several decisions taken during specification have more influence on battery life than the purchase decision does.
- Oversizing the panel relative to the nightly load, so the pack spends less time deeply discharged
- Choosing a dimming profile that reduces nightly depth of discharge
- Keeping the enclosure out of prolonged direct sun and off heat-reflective surfaces
- Avoiding installations where the pack routinely sits at extremes of the rated temperature range
- Commissioning with a fully charged pack and not leaving stock discharged in storage
Risk, resilience and the factors that are not costs
Two options with similar modelled cost can carry very different risk. These factors rarely appear in a spreadsheet, but they are usually what a stakeholder actually asks about, so it is better to state them explicitly than to let them arrive as objections.
- Outage exposure: a solar pole keeps working during a grid outage; a cable fault can darken a whole street
- Cable theft: copper theft is a recurring cost in some regions and a strong argument for solar
- Equipment theft: panels and batteries are themselves targets, so anti-theft fixings and monitoring may be needed
- Tariff risk: grid schemes carry energy-price exposure for the whole period; solar does not
- Expansion: adding poles to a solar scheme does not require re-cabling or a capacity review
- Deployment speed: avoiding trenching and connection approvals often shortens programme time significantly
- Weather risk: solar performance depends on the local resource, so a cloudy winter climate needs a more conservative design
- Skills: solar maintenance needs different competencies from network maintenance, which affects who can service the asset
A worksheet you can fill in with local numbers
The framework below is deliberately unit-free. Insert local rates and the comparison becomes specific to the project rather than to a market average.
Total cost of ownership = capital cost + (annual operating cost x evaluation period) + planned replacements + end-of-life cost - residual value. Run it twice, once per option, using identical assumptions for lighting level, hours, period and maintenance standard.
- Pole count, road length and metres of trench the grid option requires
- Local trenching and reinstatement rate per metre, by surface type
- Connection fee, feeder pillar, protection, metering and design cost
- Tariff per kilowatt-hour, fixed standing charges and an escalation assumption
- Nightly energy consumption from the agreed dimming profile
- Battery pack cost, expected replacement interval and replacement labour
- Cleaning and vegetation visits per year for the solar option
- Expected fault rate and response cost for each option
- Evaluation period, discount rate if the organisation uses one, and end-of-life cost
When each option usually wins
Patterns recur often enough to be useful as a first screen, provided they are then tested with local numbers rather than trusted on their own.
- Solar is usually favoured where no usable connection exists nearby, where trenching is expensive or disruptive, on long thin runs and perimeters, where copper theft or grid unreliability is common, and where deployment speed matters
- Grid is usually favoured where a suitable connection is already adjacent, on high-output continuous-class roads with strict all-night requirements, in dense urban sections with short cable runs, and where heavy shading or a very poor winter solar resource makes storage sizing uneconomic
- It is close, and worth modelling carefully, on mixed schemes, phased renewals, sites with partial shading and projects with strong sustainability or resilience objectives on top of cost
- A mixed programme is often the correct answer: grid where the network is already present, solar on the extensions, car parks, footpaths and perimeter sections where cabling would dominate the budget
How to run the comparison without wasting a month
A useful comparison can be produced quickly if the data collection is scoped before the modelling starts. Gather the site facts, ask both supply chains the same questions, and keep the assumption list visible in the output so reviewers argue about inputs rather than about conclusions.
For the solar option, that means asking for the energy configuration behind the proposal rather than only a model number: the assumed peak sun hours and month, the dimming profile, the depth of discharge, the backup-night behaviour and the battery cycle rating. For the grid option, it means a route survey and a written connection cost rather than an assumed proximity. With both in hand, the arithmetic is the easy part.
FREQUENTLY ASKED QUESTIONS
Questions buyers ask before configuration
Is solar street lighting cheaper than grid-powered street lighting?
It depends mostly on avoided civil works. Solar removes trenching, cabling, reinstatement, connection fees and metered energy, but adds a higher unit cost and a scheduled battery replacement. Where poles are far from a usable connection or trenching is expensive, solar frequently wins over a 10 to 20 year period; where a connection is already adjacent and the road requires high output all night, grid often remains cheaper.
How often do solar street light batteries need replacing?
Street lighting cycles the pack roughly 365 times a year, so the interval follows from the cycle rating. LiFePO4 packs of this type are commonly rated in the region of a few thousand cycles before capacity falls toward about 80 per cent of nominal, but the figure depends heavily on depth of discharge and temperature. Ask the supplier to state the depth of discharge, temperature and end-of-life criterion behind any number, and treat replacement as a scheduled maintenance event rather than a failure.
What is usually left out of a solar versus grid comparison?
On the grid side: reinstatement, traffic management, permits, connection fees, metering, standing charges and tariff escalation. On the solar side: battery replacement with its access labour, panel cleaning, vegetation management and the structural implications of the panel's wind area. A comparison that omits either list is not decision-grade.
Does dimming change the comparison?
It reduces energy on both sides, so it rarely flips the result on its own, but it changes the solar system's size. A staged or motion-based profile lowers the nightly load, which allows a smaller battery and panel for the same lighting service and reduces depth of discharge, which tends to extend the replacement interval. The profile therefore belongs in the model, not in a footnote.
Can solar and grid lighting be mixed on one project?
Yes, and it is often the most economical outcome. Use the existing network where it is already present and short cable runs are cheap, and use solar for extensions, car parks, footpaths, perimeters and isolated sections where trenching would dominate the budget. Specifying one luminaire appearance and one colour temperature across both keeps the street scene consistent.
What data should be collected before modelling?
Pole count and road length, distance and route to a connection point with adequate capacity, local trenching and reinstatement rates by surface, connection and metering fees, tariff and standing charges with an escalation assumption, the agreed lighting class and dimming profile, and for the solar option the assumed peak sun hours, depth of discharge, backup-night behaviour and battery cycle rating.