Solar quotations in Bangladesh are difficult to compare because vendors itemise them differently — sometimes deliberately. Two quotes for "5 kW rooftop solar" can differ by 40% and both be honest, because they are not describing the same system.

Here is how to read one properly.

Start with the three numbers that decide payback

Everything else is detail. Payback is determined by:

  1. Cost per installed watt-peak (Tk/Wp) — total quoted price divided by array capacity in Wp. This normalises quotes of different sizes into one comparable figure.
  2. Expected annual yield (kWh/kWp/year) — how much energy each installed watt actually produces where you are. Across most of Bangladesh this lands between 1,300 and 1,500 kWh per kWp per year for a well-oriented, unshaded array.
  3. Your effective tariff (Tk/kWh) — what you currently pay, including any slab escalation. Residential slab tariffs mean the marginal rate you avoid is usually higher than your average rate. Use the marginal one.

Payback in years is roughly:

(Cost per Wp × 1000) ÷ (Annual yield per kWp × Effective tariff)

If a vendor cannot give you numbers two and three with a straight face, that tells you something.

What should be itemised

A quotation you can actually evaluate separates:

  • Modules — make, model, wattage, quantity, efficiency, and the warranty split between product and performance
  • Inverter — make, model, rating, MPPT count, efficiency, warranty term
  • Mounting structure — material and finish (hot-dip galvanised, aluminium, or painted MS — these are not equivalent, and painted MS will not survive twenty-five years on a Dhaka roof)
  • DC and AC cabling, protection — DC isolators, SPDs, AC breaker, earthing
  • Civil work — foundations, ballast, waterproofing at penetrations
  • Monitoring
  • Labour, commissioning, documentation
  • Net-metering application handling — included or extra
  • Warranty and O&M terms — what is covered, by whom, for how long, and what voids it

A single-line quote reading "5 kW solar system — Tk X" is not a quotation. It is a number.

The line items that hide real differences

Mounting structure. The cheapest way to win a quote is to specify painted mild steel instead of hot-dip galvanised. It looks identical on day one and starts failing in year four. The structure has to outlive the panels; on a coastal or industrial site this is not a marginal consideration.

Inverter warranty. Five years and ten years are both common. The inverter is the component most likely to need replacement inside the system's life, so this term has real financial weight — often more than a small difference in panel price.

Cable sizing. Undersized DC cable is invisible, passes inspection, and quietly costs you yield for twenty-five years through resistive loss. Check that conductor cross-sections are stated.

Whose warranty is it? A manufacturer's warranty you must claim yourself, from abroad, is not the same product as an installer-backed warranty with local service. Ask who you call in year six.

Sizing: match consumption, not roof area

The most common expensive mistake is buying capacity you cannot use.

Pull twelve months of bills and find your monthly kWh. Divide by 30 for a daily average. Divide that by your expected daily yield per kWp (roughly 3.6–4.1 kWh/kWp/day in Bangladesh) and you have the array size that matches your consumption.

Then check it against the net-metering ceiling of 70% of sanctioned load, and take the lower figure.

Going larger only makes sense if you expect consumption to grow — a new AC, an EV, an expanded production line — or if you are genuinely comfortable accumulating export credit you may not fully use.

Questions worth asking every vendor

  • What annual yield are you projecting, and from what irradiance data?
  • Is the mounting structure hot-dip galvanised?
  • What is the inverter warranty term, and who services it in Bangladesh?
  • Is net-metering documentation included in this price?
  • What does your O&M contract cover after year one?
  • Can I see a system you commissioned three or more years ago?

The last question is the most useful one. Anyone can install. Fewer can show you something still performing after three monsoons.

We provide itemised quotations with a projected generation curve and a payback model before any commitment. Request one.