Standalone against centralised, battery chemistry in Bangladeshi heat, autonomy days, lux and pole spacing, and the foundation that actually fails in a monsoon wind. What to specify before a tender is awarded.
Walk a rural road two years after a solar street lighting scheme was commissioned and count the lit poles. In a lot of places the answer is under half. The panels are still there, the poles are still standing, and the lights do not come on. Almost none of that is a failure of solar technology. It is battery selection, autonomy sizing, foundation design and the absence of anybody whose job it is to replace a battery in year three.
Bangladesh has approximately 370,000+ km of roads, of which a significant portion, particularly in rural areas, industrial zones, and new developments, lacks reliable street lighting. Solar street lights are a genuinely good answer for those roads, because a self-contained unit needs no grid extension and no monthly bill. They are also the easiest category of solar equipment to buy badly, because everything that determines whether the light still works in year four is invisible at handover.
The first decision is whether each pole is its own power plant. In a standalone scheme, every pole carries a module, a battery, a controller and a luminaire. In a centralised scheme, one array and one battery bank at a single point feed conventional LED luminaires over an LV distribution cable, exactly as a grid-fed street lighting circuit would.
Standalone wins where the poles are scattered, the run is long, or trenching a cable is impractical. Its weakness is arithmetic: a hundred poles means a hundred batteries, each ageing in its own microclimate, each needing a ladder and a technician to replace. Centralised wins on a compact site, a factory estate, a housing project, a college campus, a market area, where one battery room can be ventilated, locked, monitored and serviced by one person. Where the site is dense enough to justify the cable, centralised systems tend to be alive far longer.
| Type | Description | Best for | Typical cost |
|---|---|---|---|
| All-in-one integrated | Panel, battery, LED, controller in one unit | Simple installations, quick deployment | BDT 15,000–35,000 |
| Split system (panel + pole) | Separate panel on top, battery in pole base | Higher power, longer autonomy | BDT 30,000–80,000 |
| Smart solar street light | Motion sensor, remote monitoring, dimming | Urban roads, security areas | BDT 50,000–1,50,000 |
| High-mast solar | Large panel + battery for 12m+ poles | Highways, industrial zones | BDT 2,00,000–5,00,000 |
Lithium iron phosphate (LiFePO4) is preferred over lead-acid for longer life (2,000+ cycles versus 500 cycles), and on a street light that difference compounds, because the unit cycles every single night whether anybody is watching or not. Lead-acid also punishes partial state of charge, which is exactly the state a street light battery lives in through the monsoon.
Chemistry is only half of it. Where you put the battery decides how long it lasts. A battery in the head of an all-in-one unit sits in the hottest place on the installation. A battery in the pole base sits in the wettest. The best arrangement in Bangladeshi conditions is a ventilated, lockable enclosure at the pole base raised clear of the highest local waterline, or a separate cabinet on a centralised scheme. Ask the supplier for the battery datasheet cycle life at a stated depth of discharge and a stated temperature. A cycle figure quoted without a temperature is not a specification.
Autonomy is the number of nights the unit runs with no useful charging. Set it from the longest run of overcast days the site actually sees in Sravan, not from an annual average. A dimming profile, full output until late evening and reduced output through the small hours, buys autonomy at almost no cost and is the single cheapest reliability improvement available on these schemes.
Lighting quality is specified at the road surface, not at the fixture. Ask for average maintained illuminance and uniformity across the carriageway, and for a photometric layout using the actual luminaire file at the actual mounting height and spacing. A row of bright pools with dark gaps between them is a failed design even when every individual light is working, and it is what you get when spacing is decided by where the poles were convenient rather than by the optic.
A conventional street light pole carries a small luminaire. A solar pole carries a module that behaves as a sail, mounted at the top, where its wind load produces the largest possible overturning moment. In a cyclone or a nor'wester it is almost never the pole section that fails. It is the foundation, or the base plate bolts. The wind resistance requirement of a minimum 120 km/h for Bangladesh's cyclone-prone coastal areas has to be carried through to the footing calculation, not left as a line in the luminaire datasheet.
Two site conditions matter more here than anywhere else. Soft delta soil has low bearing capacity, and it drops further when the monsoon saturates it, so a standard footing drawing copied from another project is not a design. Coastal salt attacks the galvanising, the base plate and the fasteners, so specify the coating and use stainless or well protected fixings on the coast. Also check the module tilt frame: a module clamped flat against a bracket that was cut on site is the joint that opens first.
The Local Government Engineering Department (LGED) and Roads and Highways Department (RHD) are the primary government agencies procuring solar street lights in Bangladesh. LGED has installed over 100,000 solar street lights in rural areas under various ADP projects. Municipalities (City Corporations, Pourashavas) also procure solar street lights for urban roads. Vvon Technologies has designed, supplied and installed solar street lighting for municipal and government clients across Bangladesh. The all-in-one and split-type units it supplies are listed as Solar Street Light, with IP65 rated LED luminaires, lithium battery storage and dusk-to-dawn automation.
In an e-GP tender the specification is the only defence a public buyer has against the cheapest compliant offer. Put the things that decide year-four survival into it explicitly: battery datasheet with cycle life at a stated depth of discharge and temperature, IP ratings backed by test reports rather than claims, a photometric layout for the actual pole spacing, a foundation design signed against the site soil, a named in-country party responsible for warranty service, a defined spares holding handed over with the works, and a maintenance contract priced as a separate BoQ item so it is visible and does not quietly disappear during evaluation.