Rice mills run hard through Boro and Aman and idle between. How that duty cycle changes solar sizing, what a husking shed roof can carry, how the export credit absorbs the quiet months, and what to ask an EPC contractor.
A rice mill's electricity bill is not a flat line. Through Boro in April and May, and again through Aman in November and December, the husking machines, rubber roll shellers, whitening machines, polishers, elevators and paddy dryers run for 12 to 16 hours a day. Between those windows the same mill may be turning over at a fraction of that. Bangladesh is the world's third-largest rice producer, with over 35 million tonnes processed annually across approximately 15,000 mills, from small husking units to large automated complexes, and a great many of them, particularly in rural areas, still lean on diesel generators because the grid cannot be relied on. A solar design that treats the mill as a steady 12-month load will be sized wrong.
The peak is at least predictable, and it falls in the right months. Boro paddy arrives in April and May, Aman in November and December, and both windows sit at or near Bangladesh's best irradiance. A well-designed plant generates most when the mill needs most, which is a better match than most industrial loads here manage.
The complication is the dryer. Husking and whitening draw a fairly steady demand once the line is running, but dryer load rises with the moisture content of incoming paddy, which is why an Aman season in a wet year can push peak demand well above what the same mill drew in Boro. If load profiling happens to be done in a dry week, the dryer is under-represented and the plant is undersized against the one peak that matters.
| Mill type | Daily consumption | Monthly cost (grid) | Monthly cost (diesel) | Solar plant size |
|---|---|---|---|---|
| Small husking mill | 200-500 kWh/day | BDT 60,000-1,50,000 | BDT 1,20,000-3,00,000 | 50-100 kWp |
| Medium automated mill | 1,000-2,000 kWh/day | BDT 3,00,000-6,00,000 | BDT 6,00,000-12,00,000 | 200-400 kWp |
| Large milling complex | 3,000-5,000 kWh/day | BDT 9,00,000-15,00,000 | BDT 18,00,000-30,00,000 | 600-1,000 kWp |
Read the diesel column against the grid column. The same kWh costs roughly twice as much off a generator. That gap, not the grid bill, is usually where the return on a rice mill project comes from.
Two defensible ways to size a mill plant give different answers. Size to annual average consumption and the plant is self-consumed all year, but the seasonal peak still draws heavily from the grid or the generator. Size to the seasonal daytime load and the plant covers the expensive months, then exports through the quiet ones.
Under the Net Metering Guidelines 2025, administered through SREDA, the ceiling is 100% of your sanctioned load, or 80% of transformer capacity for medium-voltage consumers at 11 kV and above. That is a ceiling, not a target. Exported surplus is netted on the bill and carried forward; anything left at the financial year end on 30 June is settled at the prevailing BERC bulk-purchase rate, which is lower than the retail tariff you avoid by consuming your own generation. A unit used in the milling hall in May is worth more than the same unit exported in August.
For most mills with roof to spare, sizing towards the seasonal load gives the better economics: the months of near-total self-consumption are also the months of highest generation. The exception is a mill with a modest sanctioned load and a large roof, where the guideline ceiling binds before the roof does.
Most mills are corrugated metal sheet on light steel trusses, sometimes on timber in older husking units, spanning the milling hall and the attached godowns. The roof is rarely one plane. Mills grow by extension, so a single site can carry sheds of three different ages, three purlin spacings and three states of corrosion. Check purlin spacing and section before anyone quotes a mounting structure, and get the structural certificate signed: a missing or unsigned certificate is one of the more common reasons an application is sent back.
On corrugated sheet, clamp-based racking that grips the sheet profile avoids penetrating the roof. Where penetration is unavoidable, the fastener and sealing detail matter more than the racking brand: a mill roof leaking over a godown of milled rice is an expensive lesson. Shading usually comes from the site itself, so run the shadow analysis against silos, elevator head towers, dryer stacks and stacked paddy at the season's low sun angle, not at noon in June.
For mills where grid supply is unreliable, a hybrid system with battery storage is the sensible architecture. During the day the array powers the milling operation directly and the surplus charges the battery bank. When the grid fails, or after dark, the batteries and any remaining solar keep the critical machines running. Where the generator currently runs for a meaningful share of the milling day, this can reduce diesel consumption by 60 to 80%, with a payback of 3 to 4 years on the diesel savings alone.
A caution on battery sizing: a bank large enough to carry the whole milling line through a long outage is rarely worth the money. What is worth protecting is the equipment where an interruption costs a batch or a restart, meaning the dryer and its fans, the elevators, the control panels and the instrumentation. Agree that schedule with the mill manager, then size the battery to it.
Which utility you deal with depends on where the mill sits. A mill in a municipal area outside Dhaka normally goes to BPDB; a rural mill goes to BREB through the local Palli Bidyut Samity; mills in Rajshahi and Rangpur divisions fall under NESCO. The paperwork is much the same, but the queue and the inspection scheduling are not.