How to Specify Solar Street Lights in a Tender

Start from delivered light, not from wattage

“100 W solar street light” specifies an input, not a result. Two luminaires rated at the same power can differ by a factor of two in delivered lumens once optical efficiency, driver losses and lens design are taken into account, and the panel wattage that follows is a separate question again. The same applies to phrases such as “high quality”, “long life” and “maintenance free”: none of them can be tested, so each should be replaced by a number, a standard, a document or an inspection step. Write the requirement at the road surface instead:

• A lighting class for the road type — for example an M-class for a traffic route or a P-class for a footpath — with the class named for the standard the client uses locally, plus the average maintained illuminance and the uniformity ratio (Emin/Eavg) that go with it.
• The measurement basis: maintained lumens at 25,000 or 50,000 operating hours, at a stated ambient temperature, with the light distribution described by a photometric file rather than a marketing figure, and a requirement that the supplier hands over the photometric data (IES or LDT) and the lighting design made with the same luminaire, so the client’s consultant can re-run the calculation.

Files like these come from the manufacturer, so require the supplier to obtain them and to name the offered product in the bid.

Fix the geometry: height, spacing and overhang

The same luminaire on a 6 m pole and on a 9 m pole gives two completely different installations. State mounting height, spacing between poles, whether the pole is on one side, staggered or on both sides, and the root position on the carriageway, since a pole too far from the kerb wastes light and one too close can clash with services.

For a road lit to an M-class, a spacing-to-height ratio somewhere between 3:1 and 4:1 is a common starting point, but the correct figure comes from the lighting calculation, not from a rule. Solar projects often push the ratio wider to cut pole count, which raises both the luminaire output and the battery load per pole, so ask bidders to state the ratio they assumed. See pole height and spacing for the arithmetic.

Define the energy system: hours, dimming, autonomy

Three numbers drive every solar street light design, and all three must be in the tender:

• Daily lighting hours — the total hours the luminaire is on, driven by the astronomical clock or a fixed schedule, at a stated latitude or city.
• Dimming profile — the fraction of full output in each period of the night. A profile of 100% for four hours, 50% for four hours and 30% until dawn can cut nightly energy by more than half against full output all night, changing the panel and battery requirement completely.
• Autonomy days — the number of consecutive days of no useful charge the system must ride through while still giving the specified profile. Two to three days is common for main roads; five days or more appears in remote or high-reliability schemes. Autonomy without a stated solar resource assumption is meaningless, so require the assumed worst-month daily yield to be declared. See battery autonomy.

Battery chemistry, usable capacity and depth of discharge

Name the chemistry and, more importantly, the usable energy. A 100 Ah nameplate battery at a 50% depth of discharge gives 50 Ah of usable charge; at 80% it gives 80 Ah, and bidders who quote only nameplate capacity are quietly relying on the deeper figure. Specify the allowed depth of discharge and the end-of-life criterion, typically 70% or 80% of rated capacity. In hot climates the chemistry matters more than headline capacity — see LiFePO4 versus lead-acid.

Ingress, impact, electrical protection and temperature

These are the requirements that separate a five-year installation from a two-year one, and they are usually the first thing dropped from a cheap bid:

• Ingress protection for luminaire, battery compartment and controller, distinguishing the optical chamber from the driver and battery cavity. IP65 or IP66 for the light; battery enclosures often need more.
• Impact resistance (IK rating) for the luminaire and its diffuser.
• Surge protection: a stated surge immunity level for the driver and controller, plus any external surge device the site’s exposure requires, and the operating temperature range of every electronic component, not just the LED.

Mechanical and structural requirements

The pole is a structural element and should be specified as one. State the design wind speed and reference standard, the pole material and wall thickness, the taper, the anchor bolt arrangement, and who designs the foundation — the tender should say clearly whether that is the contractor or the equipment supplier. Specify hot-dip galvanizing with a minimum coating mass or thickness and the standard it is checked against, and require the coating to be measured on the finished item.

Documents and warranty: specify what you will receive

Test reports, certificates and design files are produced by the manufacturer, so list them as deliverables and require them before shipment: photometric test report and IES/LDT files from the testing laboratory, type-test reports for panel, battery and controller, a lighting calculation for each road type, GA and foundation drawings, an as-built wiring diagram, a commissioning record with the settings actually used.

Warranty should be split by component rather than given as one number: luminaire, panel, battery and pole usually carry different terms. State the start point (delivery, commissioning or handover), what is covered and who pays freight for a replacement — a warranty that excludes transport is worth less than it appears. A pre-shipment inspection clause is worth adding; see the inspection checklist.

How we can help

We are a China-based trading and project sourcing company, not a manufacturer. We review specifications and BOQs, match a product and configuration to your site conditions, source from qualified manufacturers, and manage quality through to pre-shipment inspection. If you are preparing a tender or specification and want a second opinion, contact us.