Solar lighting suits a lot of parking properties. It does not suit all of them, and the difference is usually visible from a site walk rather than from a proposal.

Knowing which sites do not work matters more than knowing which do, because a solar system installed on an unsuitable site does not fail immediately. It underperforms slowly, in the season when the lighting matters most.

Obstruction

The first and most common disqualifier is shade. Mature tree canopy over the parking area, a taller building on the southern side, or a structure that shadows the lot through the middle of the day all reduce generation below what the system was sized for.

Partial shade is worse than it looks, because generation does not fall in proportion to the shaded area. A pole shaded for three hours a day is not generating seventy-five percent of its rated output.

Some of this is fixable. Tree trimming, or moving a pole location by twenty feet, can turn an unsuitable position into a workable one. That is a site question, and it is answered by looking rather than by mapping.

Pole Condition

A retrofit array bands onto an existing pole, which is most of the cost saving. It also means the existing pole has to be sound and has to carry the additional load.

Older poles, poles with corrosion at the base, and poles already at their wind loading limit are all candidates for replacement rather than retrofit. Once a pole is being replaced, part of the retrofit economics disappears, and the comparison against a conventional installation shifts.

Wind loading is worth naming specifically. An array adds surface area to a pole, which adds load in high wind. In markets with severe weather, the pole's rating and the array's effective projected area both need checking before anything is banded to anything.

Lighting Requirements the Site Cannot Support

Some properties need more light than a pole-mounted array can generate. A large lot with a high illuminance requirement, a site with a lease or an insurance condition specifying a light level, or a property where an existing lighting design has already been approved to a standard all set a floor.

Where that floor is above what the available roof of the pole can produce, solar either does not meet the requirement or requires so many poles that the arithmetic stops working.

Sites Where Power Is Already Close

This one gets missed because it argues against the interesting answer. A property with spare service capacity and a panel near the proposed pole locations may simply be cheaper to light conventionally.

The case for solar is strongest where the civil work is expensive: long trench runs, pavement to cut, a service at capacity, a utility with a long interconnection queue. Where none of those apply, the case is weaker, and a recommendation that ignores this is not a recommendation.

Where the Answer Is Neither

A grid-tied hybrid sits between the two. The system draws from the panel where power is available and from stored solar the rest of the time, which reduces the utility cost without requiring full autonomy, and keeps the lights running when the grid does not.

It suits properties with partial capacity, or with an outage history, or where the lighting supports something that cannot go dark. It costs more than a straight retrofit and less than a full service upgrade.

Why Saying No Matters

A supplier who sells lighting has a reason to find a way to make any site work. A supplier who sells nothing does not.

The value of a site assessment is not that it produces a proposal. It is that it produces an answer, and on some properties the answer is that the existing lighting should be repaired, or that a conventional circuit is cheaper, or that the lot should be left alone until something else changes.

That answer costs nothing to receive and saves a project that was never going to work.