What actually degrades a rooftop solar plant in Bangladesh, how often to clean and with what water, how to read string-level data, and the scope an annual maintenance contract should contain before you sign it.
A well-maintained solar system in Bangladesh will generate electricity reliably for 25 to 30 years. A neglected system can lose 15 to 25% of its output within 3 to 5 years due to soiling, degraded connections and inverter issues. Bangladesh's climate, with high temperatures, high humidity, monsoon rain and dust from construction and industrial activity, creates specific maintenance problems that a structured O&M programme has to address directly.
Generic advice about dust misses what is happening on most industrial roofs here. Brick kiln and cement dust binds to glass and does not wash off with a light shower. Fine lint settles on arrays above RMG floors. Feed and grain dust coats panels at agro processing plants. Roadside sites in Dhaka, Gazipur and Narayanganj accumulate a greasy traffic film that behaves quite differently from loose dust and needs contact cleaning.
Monsoon adds two of its own. Rain splashing off the roof surface throws mud onto the lowest module row, so the bottom edge stays dirty while everything above it looks clean, and the affected cells drag down the whole string through their bypass diodes. And persistent damp encourages algae and moss growth along frame edges and in the gap between glass and frame, which holds moisture against the seal. Bird droppings are the other localised case: they are opaque rather than translucent, so a single dropping on one cell causes a hotspot rather than a small proportional loss.
In Bangladesh's industrial areas, dust and pollution can reduce panel output by 5 to 15% per month without cleaning. During the dry season, November to March, monthly cleaning is essential. During the monsoon, June to September, rain provides natural cleaning and monthly washing can be reduced to quarterly. Use soft brushes and clean water, never abrasive materials or detergents that can damage the anti-reflective coating.
Water quality matters more than most operators expect. Much of Bangladesh's tube-well water carries high iron and dissolved solids, and washing with it leaves an orange or chalky residue that scatters light as effectively as the dust you removed. If your supply is hard or iron-rich, use filtered or low-TDS water for the final rinse, or you will be cleaning the panels and dirtying them in the same operation.
| Task | Frequency | Who performs it |
|---|---|---|
| Panel cleaning (water wash) | Monthly (more in dry season) | O&M team or trained staff |
| Visual inspection (cracks, discolouration) | Monthly | O&M team |
| DC string voltage and current check | Quarterly | Qualified electrician |
| Inverter firmware update | Annually | Authorised service engineer |
| Inverter cooling fan cleaning | Every 6 months | Authorised service engineer |
| AC/DC surge protection device (SPD) test | Annually | Qualified electrician |
| Earthing resistance test | Annually | Qualified electrician |
| Thermal imaging (IR scan) of panels | Annually | Specialised O&M team |
| Performance ratio (PR) analysis | Monthly (via monitoring) | System owner / O&M team |
| Structural mounting inspection | Annually | Structural engineer |
All Vvon-installed solar systems include a cloud-based monitoring platform (Sungrow iSolarCloud, Huawei FusionSolar or SMA Sunny Portal) that shows real-time generation, daily and monthly totals, and performance alerts. Review your monitoring data weekly. A sudden drop in output from one string indicates a panel fault, shading issue or connection problem that needs immediate attention.
The useful comparison is between strings, not against a datasheet. Strings on the same roof see the same irradiance and the same weather, so they should track each other closely. Read it this way: if every string declines together, that is soiling or seasonal irradiance and it is a cleaning decision. If one string sits consistently below its neighbours, that is a fault, and the size of the gap points to the cause. A few per cent is usually a connector or a dirty bottom row; a step change of roughly a third is a bypass diode conducting across one substring; a string reading zero is an open circuit, a blown fuse or a tripped MPPT input. Plant-level monitoring cannot show you any of this, which is why string-level monitoring is worth specifying at purchase rather than retrofitting later.
An annual thermal scan finds the faults that monitoring hints at and the eye cannot see: individual hot cells from micro-cracks or shading, whole-substring heating where a bypass diode has failed, hot junction boxes, warm MC4 connectors on the DC side, and loose or corroded terminations in combiner boxes and at the inverter AC output. In Bangladesh's humidity, connector and termination heating is the most common finding, and it is also the one that eventually causes fires.
The scan has to be done under the right conditions to mean anything: at least 600 W per square metre of irradiance, low wind, and a clear sky, which in practice means a mid-morning slot on a dry-season day. A scan taken on an overcast afternoon will look reassuring and tell you nothing. Compare each year's scan against the commissioning baseline rather than assessing it in isolation, because what matters is what has changed.
Modules rarely fail. Inverters do, and in Bangladesh the reason is usually thermal and environmental rather than electrical. Dust drawn through cooling fans clogs filters and heat sinks, the unit derates in the afternoon heat precisely when generation peaks, and you lose the top of the curve without any alarm being raised. Clean or replace the filters and cooling fans on the manufacturer's schedule, keep the inverter room ventilated and out of direct sun, and check the derating history in the monitoring portal rather than assuming a lack of alarms means a lack of problems.
Humidity and salt-laden air near the coast attack control boards and terminals, so seal cable entries properly and inspect terminations annually. Keep firmware current through the authorised service engineer, and confirm before you buy that the make has spares held inside Bangladesh, because an inverter waiting weeks for an overseas part takes a proportional share of your plant offline for that entire period.
A shading study done at design stage is a snapshot. Roofs change. A neighbouring building adds two storeys, a water tank or antenna mast is relocated onto the roof, an exhaust stack is extended, trees grow into the morning sun path, and site staff install a new duct or cable tray across the array without telling anyone. Each one costs a string, permanently, and none of it triggers an alarm. Walk the roof once a year with the array layout in hand, look at the horizon in all four directions, and cut back vegetation at the boundary before it reaches panel height. Where a permanent obstruction has appeared, restringing the affected area so the shaded modules sit on their own MPPT input recovers most of the loss, which is a good reason to keep the as-built layout drawing accessible.
Most annual maintenance contracts on offer are a cleaning schedule with a service visit attached. Before you sign one, check it contains all of the following, and make the reporting obligation explicit rather than assumed.