By Vvon Engineering Team | Published | Updated
Evaluate tannery and ETP electrical loads, chemical exposure, module suitability and maintenance before choosing rooftop solar.
Solar EPC & street lighting RFQ checklist (TXT)
Tannery process emissions can expose rooftop equipment to a corrosive environment. Assess the actual chemicals, deposition, humidity and location before selecting modules, mounting, enclosures and electrical connections.
The good news is that the same plant has one of the better electrical load profiles in Bangladeshi industry for self-consuming solar, and it comes from the effluent treatment plant.
Tanning itself is intermittent. Drums turn for the soaking, liming, deliming, bating, pickling, tanning, retanning and dyeing stages, and between them the motors sit idle. Sammying, shaving, buffing, setting, toggling and spraying run on a batch rhythm. The boiler is usually gas or biomass, so the process heat is not electrical, and the plant's electrical demand swings with what is on the floor that day.
A captive effluent-treatment plant may provide a substantial recurring electrical load from blowers, pumps and other auxiliaries. The actual duty follows the treatment process and operating controls. Obtain logged demand and the treatment operator's permitted operating schedule.
Use the measured ETP and process loads in the self-consumption model, including shutdown and low-production conditions. Compare additional PV capacity against export settlement and cost rather than assuming that either zero export or maximum roof coverage is always optimal.
Units in the Savar estate that discharge to the central effluent treatment plant rather than running their own do not have that anchor, and their profile looks much more like a batch process factory. Size those against the measured process load, not against a generic industry figure.
This is worth setting out step by step, because the specification decisions follow directly from it.
| Process step | What it releases | What that attacks |
|---|---|---|
| Liming and unhairing with sulphide | Hydrogen sulphide, worst at drains, sumps and floor channels | Copper and silver: busbars, plated contacts, junction box internals, connector pins |
| Deliming with ammonium salts | Ammonia | Copper and brass fittings, and module encapsulants and frames that have not been tested for it |
| Pickling with salt and acid | Chlorides and acid mist | Stainless steel by pitting, zinc coatings, and aluminium under its coating |
| Chrome tanning, retanning and dyeing | Liquor mist and aerosol | Coatings generally, plus a film on glass that ordinary washing does not lift |
| Effluent treatment | Hydrogen sulphide and ammonia from tanks and sludge handling, continuously | All of the above, and worst within the footprint of the tanks |
Two consequences follow. The first is that the roof nearest the ETP is the harshest location on the site, and it is often the roof with the best solar access, because ETP buildings are low and unshaded. The second is that hydrogen sulphide attacks precisely the metals that carry current, which is why electrical enclosures and connectors matter more here than mounting steel does.
Corrosivity is a category, not an adjective, and there is a framework for it. ISO 9223 classifies atmospheric corrosivity, and ISO 12944 sets protective paint systems against those categories with a stated durability. A tannery roof, and particularly a roof near an ETP, must be classified from its actual exposure. Assess it, write the category into the specification, and specify the coating system and its durability class against the assessed category.
A corrosion test certificate does not override a warranty exclusion. Check the exact module's certificates and warranty, then obtain written confirmation of suitability for the assessed exposure before purchase.
Connectors deserve their own paragraph. The single most common origin of a rooftop DC failure anywhere is a pair of connectors from two different manufacturers mated together, because the contact geometry and the tolerances do not match and the joint runs hot. In a sulphide-bearing atmosphere the same joint tarnishes as well. Specify correctly matched, approved connector pairs, crimped with that manufacturer's tool, and have the commissioning engineer record the crimp checks.
DC combiner boxes and inverters should be at IP65 as a minimum, with pressure-equalisation breather elements rather than open drain holes, because an open drain in a hydrogen sulphide atmosphere is an invitation. Ask the inverter manufacturer for a written statement of the corrosion class the unit is rated for and whether conformal coating on the boards is standard or optional on that model. Several manufacturers offer a coated variant; it is not usually what gets quoted unless it is asked for.
Site the inverter room upwind of the ETP and away from drain vents, and give it filtered ventilation. If the room has to sit close to the process, a sealed and slightly pressurised room with filtered supply is worth the cost, and the filter change interval goes into the maintenance schedule.
Select earthing materials from the soil assessment, corrosion exposure and complete electrical design. Provide accessible inspection and test arrangements, with maintenance intervals agreed by the designer. Copper-bonded rods are not automatically suitable for every contaminated soil.
Walk a tannery roof and look at the fastener holes and the gutter lines. On many sheds the sheet is already rusting through at the washers and along the valleys, because the same atmosphere that attacks the array has had a head start on the roof.
Putting a twenty-five year array onto a sheet with a few years left is a false economy of the most expensive kind, because removing and refitting an array to re-sheet a roof costs a large share of what the array cost to install, and it happens at a time nobody has budgeted for. If the sheet will not outlast the array, replace it first. That decision belongs in the feasibility stage, where it can be compared honestly against the return, rather than being discovered on the survey after a price has been agreed.
Cleaning water quality matters more here than most people expect. Washing glass with hard or contaminated water leaves a mineral film that is harder to remove than the deposit it replaced, and on a site where the deposit already includes liquor aerosol, the two combine. Specify a low-dissolved-solids supply for the final rinse.
Many tannery units occupy plots or sheds they do not own. Where the site sits inside an industrial estate, the estate authority's permission is a separate document from the landlord's, and both come before the utility file. Get the owner's written no-objection covering the roof area, the plant capacity, the mounting method and the term, and get the estate's approval for anything that alters the building envelope.
On the utility side, confirm which distribution licensee actually issued your connection before filling in anything. Savar and the surrounding area are not served by a single utility, and the net metering file goes to the one whose name is on your bill, under SREDA's guidance. Check the sanctioned load at the same time, because the guidelines cap the plant against it and a tannery's sanctioned load is often lower than the connected load its owners quote from memory.
Consult the relevant edition and the documents for the exact equipment and site: IFC: environmental, health and safety guidance for tanning and leather finishing; JinkoSolar: model datasheets, certificates, installation manuals and warranties; SREDA: Net Metering Guidelines and current application documents.
Share your application, equipment requirements and procurement timeline. Our engineers can help clarify the configuration and scope for your enquiry.