Rooftop solar for hotels and resorts in Cox's Bazar and Sylhet

Hotels run a load that never stops, on roofs that guests can see, in two of the harshest siting environments in the country. Where the panels can go, what the salt air does, and why solar is not back-up power.

A resort general manager can usually tell you two numbers without looking them up: the electricity bill in peak season and what the generator burned last month. Neither number is improved by a solar plant that was designed for a factory roof and dropped onto a hotel, because a hotel is a different load, a different roof and, on the coast, a different environment altogether.

A load that never stops, meeting a supply that does

Hotels run around the clock, but not evenly. Guest room air conditioning peaks in the afternoon and again overnight. Corridor and facade lighting, the restaurant and the banquet hall are evening loads. Laundry, kitchen preparation, housekeeping, pool filtration, water pumping and the office block are firmly daytime, and those are the loads a rooftop array will actually displace.

So the useful sizing question is not what the hotel consumes in a day. It is what the hotel consumes between roughly nine in the morning and four in the afternoon, on a low season weekday, when occupancy is at its worst. Size against that floor and the plant is consumed on site all year. Size against a full house in peak season and the plant spends the monsoon exporting units that are settled rather than avoided.

Two levers move that floor in the right direction, and both are free. Laundry can be scheduled into the middle of the day rather than run late at night for the night shift's convenience. Pool filtration and water pumping can be timed to the generation window instead of a timer somebody set at commissioning years ago. On a large property those two changes shift a surprising amount of load into daylight.

Where the panels can actually go

A hotel roof is the most contested piece of real estate on the property. Before any array is drawn, walk every roof with the chief engineer and mark what is already there and what is promised to somebody else.

• The main block roof often has a restaurant, a bar, a pool, a helipad or a plan for one. It also carries chillers, cooling towers, lift machine rooms, water tanks and the antenna farm. What is left is frequently a narrow perimeter that is not worth the crane time.
• Back of house is where the plant usually lands. The laundry block, the kitchen block, the staff quarters, the generator house, the store and the workshop have flat unloved roofs, no guest sightlines and, conveniently, the daytime load sitting directly underneath.
• Car park and driveway canopies cost more per kWp than a roof array but buy shade the property already wanted, and at a resort they are the one visible installation guests tend to approve of.
• Sightlines matter more than the engineer thinks. Check what the array looks like from the arrival drive, from the upper floor rooms that overlook the lower roofs, and from the beach or the lawn where the photographs are taken. Black framed modules, a set back from the parapet and a screen wall are cheap answers to a complaint that is otherwise permanent.
• Glare is a real objection. Modules reflect far less than plate glass, but a low tilt array facing a wing of rooms will still catch a late afternoon sun angle. Check the geometry before installation rather than after the first guest email.

What the coast does to the specification

Cox's Bazar, Kuakata, Saint Martin's and the rest of the coastal belt combine salt laden air, high humidity, driven rain and cyclone season wind. A specification written for a Dhaka rooftop will corrode there, and the failures are slow, ugly and expensive to reverse.

• Ask for salt mist corrosion tested modules. IEC 61701 is the test, and the certificate should be in the submittal, not described in a sales sheet. Some module warranties also carry an exclusion for installation within a stated distance of the coast unless the salt mist rating is met. Read that clause before you buy, because it is exactly the clause that will be quoted back at you in year eight.
• Hot dip galvanising, not painted steel. Structure galvanised to a recognised standard with the coating thickness stated, or an aluminium structure. Painted or pre galvanised light sections will bleed rust down a white hotel wall within two monsoons.
• Stainless fasteners, and the right grade. A4 stainless where the salt reaches, and no mixing of dissimilar metals at the clamp without an isolating washer. Galvanic corrosion at the module frame is the classic coastal failure.
• Wind uplift is a calculation, not an opinion. The basic wind speed for the site is taken from the national building code and the mounting structure is designed to it, including the uplift on the leading row and the corner zones. Ballast alone is rarely enough on an exposed coastal roof.
• Seal and drain the enclosures. Combiner boxes and inverter enclosures on the coast need the ingress rating to be genuine and the glands to be fitted properly. Humid salt air inside a box does more damage than rain on the outside.

Solar is not back-up power, and guests will find out

This is the conversation to have early, because the expectation is almost always wrong. A grid tied inverter is required to disconnect when the grid fails. It is an anti islanding protection function, it is not optional, and it means that during a load shedding event the array stops even at noon under a clear sky. A hotel that installs solar and still loses the lifts in a power cut has not been badly served. It has been correctly served and badly briefed.

There is a second interaction that catches properties which run a generator regularly. When the hotel is on the diesel set, an array feeding the same board can push the generator into reverse power, which its protection will not tolerate and which can damage the machine. The answer is a controller that either blocks the inverters or limits them to the measured on site load while the generator is running, and it has to be commissioned and tested with the generator, not assumed.

If the property genuinely needs solar backed reserve, it belongs on a defined list of circuits rather than the whole hotel: fire alarm and pumps, emergency and corridor lighting, one lift, the front desk and the servers, the cold rooms. That list is small, it is affordable, and it is the list guests and the fire inspector actually notice.

Hill sites and weak spurs in Sylhet

Resorts in the Sylhet hills and the tea belt have the opposite set of problems. Salt is not the issue. The issues are a long low tension spur from a distant transformer, voltage that swings enough to trip inverters on their own protection settings, tree lines that shade the array for part of the day and grow taller every year, rainfall that overwhelms a badly detailed roof, and site access that decides how big a delivery can reach the property at all.

Two things are worth doing at survey. Log the supply voltage for a full week before selecting inverters, so the grid protection window is set against measured conditions rather than a default. And survey the tree line for what it will be in ten years, not for the shadow on the day of the visit, because the resort will not cut the trees. They are the reason guests come.

Hill sites also make the earthing and lightning protection more than a formality. Exposed ridge positions, tall structures and a hospitality building full of guests is not a combination to leave to a token earth rod. Specify the earthing design, measure the resistance at commissioning and record it.

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