A 1,000 m rural road. Two ways to light it: solar street lights, or conventional lights connected to the grid. Most quotes compare only the lamp price — which is exactly why so many projects end up with the wrong answer.
This guide opens both bills completely: what is paid once, what is paid every year, and what is quietly paid again five years later.
The short answer: distance to a usable power source
Solar and grid-connected street lighting are not competitors; they are complements. One measurement decides most cases — how far the nearest usable power point is from the furthest pole.
- Under 50 m, with an existing distribution box: grid-connected is usually cheaper overall. The lamps last longer, output is stable, and consecutive rainy days are irrelevant.
- Over 100 m, or crossing farmland, a river or a mountain: solar wins clearly. You delete the cable, the trench and the transformer upgrade — the three items that dominate a grid quote.
- 50–100 m: it genuinely depends on cable size, road surface (asphalt, concrete, unpaved) and how hard the trench is to dig. Ask for both options priced.
What each option actually includes
| Item | Solar street light | Grid-connected street light |
|---|---|---|
| Pole and luminaire | Supplied as one set with panel, battery and controller | Pole plus LED luminaire |
| Cable | Not required | Required; copper cable priced per metre |
| Trench and backfill | Not required | Required, including road surface reinstatement |
| Distribution box | Not required | Required; several if the road has many circuits |
| Transformer upgrade | Not required | Often required; slow and expensive to arrange |
| Installation time | Short — each pole is independent | Longer — cabling, conduit, inspection |
| Electricity bill | Zero | Continuous, proportional to power and hours |
| Battery replacement | Every 4–6 years (main future cost) | None |
The essential trade is this: a solar system converts the money you would spend on cable, civil works and distribution into money spent on panels and batteries. The longer the road and the further the power source, the stronger that trade becomes.
Upfront cost: the half of a grid quote that is easy to miss
Comparing luminaire prices is the classic error. In a grid-connected project the pole and luminaire are often only about half the total; the rest is cable, trenching, backfill, distribution boxes and transformer capacity.
On a 1,000 m road with 30 poles, trenching and reinstatement alone can account for 30–50% of the civil budget — and it is the item most often left out when the two options are compared side by side.
Running cost: the electricity formula
Grid lighting produces a predictable annual bill:
Annual cost = lamp power (kW) × hours per night × 365 × tariff × number of lamps
Worked example — 30 poles of 60 W LED, 10 hours per night, USD 0.10 per kWh:
- One lamp per night: 60 W × 10 h = 0.6 kWh
- One lamp per year: 0.6 × 365 ≈ 219 kWh
- Thirty lamps per year: 219 × 30 × 0.10 ≈ USD 657 per year
Solar is zero here. But it is not free — the same money reappears as battery replacement, which is why it belongs in the comparison from the start.
The cost nobody budgets: battery replacement
A LiFePO4 battery is typically rated above 2,000 cycles; in real service it is replaced every 4–6 years. That replacement is a hard cost, usually 25–40% of the original set price, and it must be in the budget rather than dismissed as "install and forget".
Maintenance: different work, similar effort
Grid-connected: luminaire failures and cable faults — rodent damage, accidental excavation, insulation ageing. Buried cable faults are slow to locate.
Solar: dust on the panel (cleaning once or twice a year restores output), branch shading, controller failure, battery ageing. Each pole is independent, so one failure does not darken the road — but faults must be found pole by pole.
Neither is dramatically cheaper to maintain. Grid is easier on luminaire life; solar is easier on power interruptions and cable damage.
Payback: usually 3–6 years
Payback is driven by the electricity tariff you avoid and the cable and civil works you delete. Long roads, high tariffs and distant power points shorten it. Always include the 4–6 year battery replacement in the calculation — leaving it out flatters solar by a wide margin.
Six-point decision checklist
- Distance to power: more than 100 m to the furthest pole? Lean solar.
- Can the road be opened? Concrete, asphalt or a finished plaza? Trenching is expensive — lean solar.
- Sunshine hours: below about 1,200 hours per year, the solar array must be oversized and the economics weaken.
- Longest rainy spell: over 7 consecutive days means designing for 7–10 days of autonomy, which raises cost.
- Stability required: trunk roads with CCTV or signal coordination are better served by grid power.
- Who maintains it? Remote roads with no maintenance team suit independent solar poles.
Four ways the numbers get wrong
1. Lamp price only. Cable trenching and surface reinstatement are 30–50% of a grid project and are routinely omitted.
2. Solar quoted as maintenance-free. The battery is a scheduled replacement; a quote that hides it is not a cheaper quote.
3. Three days of autonomy in a seven-day climate. Under-sized batteries are the single most common cause of complaints about solar street lighting.
4. Shading ignored. A panel shaded by trees or a building loses output sharply. The site must be checked before the configuration is fixed.