- SOLAR
Solar Balance of System (BOS) Costs in India (2026)
Say two EPC quotes arrive for the same 1 MW ground-mount project. One comes in at Rs 32 per watt, the other at Rs 40.
Most buyers react the same way. They assume the cheaper one cut corners on the module, so they pull both datasheets. Same tier-1 panel on both. The natural conclusion is that the cheaper contractor is simply more efficient.
Usually, that's the wrong conclusion. Modules make up only about half of what a solar plant costs. The other half is the Balance of System, and that's where the gap between quotes almost always hides. It's also the part of the quote most buyers never ask to see itemised.
This guide walks through what BOS covers, what share of a typical Indian EPC price each piece takes up in 2026, and how to compare two quotes so you're looking at like for like.
What is Balance of System (BOS) in solar?
BOS is everything in a solar plant apart from the modules. That includes mounting structures, inverters, DC and AC cabling, switchgear, earthing and lightning protection, civil foundations, and the labour and commissioning that turn a pile of components into a working plant.
"Everything except the module" is a fair shorthand, but it's too loose for procurement. It helps to split BOS into three groups by what each one does:
Group | What's in it | What it does |
|---|---|---|
Power conversion | String or central inverters, transformers | Converts the DC power from the modules and steps it up |
Structural and electrical BOS | Mounting structures, DC/AC cabling, combiner boxes, ACDB/DCDB switchgear, earthing, lightning protection | Holds the array up and carries power safely to the grid connection point |
Civil and soft costs | Foundations, site preparation, SCADA and monitoring, engineering, DISCOM liaisoning, installation, commissioning | Turns purchased equipment into a working, grid-compliant plant |
None of this shows up under the module line on your quote. Put together, it usually comes to around half the total project cost, and sometimes more.
1 MW solar plant cost breakdown in India (2026)
Independent industry sources come up with a remarkably similar split for a standard 1 MW ground-mount plant built with tier-1, ALMM-compliant equipment. The ranges below reflect where they overlap.
Cost head | Share of total EPC cost | Indicative cost (1 MW, ~Rs 3.5–4 crore) |
|---|---|---|
Solar modules | 50–60% | Rs 1.75–2.1 crore |
Inverters | 10–15% | Rs 35–52 lakh |
Mounting structure | 7–10% | Rs 24–40 lakh |
DC/AC cabling, combiner boxes, general BOS | 6–8% | Rs 21–32 lakh |
Switchgear, metering, protection | 4–6% | Rs 14–24 lakh |
Civil work and foundations | 4–6% | Rs 14–24 lakh |
SCADA, monitoring, installation, commissioning, engineering | 8–13% | Rs 28–48 lakh |
A turnkey fixed-tilt plant of this kind costs roughly Rs 3.5 to 4 crore per MW in 2026, or about Rs 35 to 40 per watt. Go for a single-axis tracker and the figure climbs to around Rs 4 to 4.5 crore per MW, mostly because of the extra structural and mechanical work. Our mounting structure comparison covers that trade-off in more detail.
Why two solar EPC quotes can be so far apart
Here's what most buyers miss. A Rs 32 quote and a Rs 40 quote for the same capacity often aren't describing the same plant. The difference nearly always comes from choices on the BOS side.
Start with the mounting structure. Hot-dip galvanised steel costs noticeably more than lighter-gauge or pre-galvanised options, but it lasts decades longer in Indian soil and near the coast.
Cabling is the next one. Undersized DC cable saves money upfront and then quietly loses power to resistance for the life of the plant, eating into the generation the modules were meant to deliver.
Inverters matter too. A tier-1 string inverter with a properly worked-out DC/AC ratio costs more than a tier-2 unit, but you get a stronger warranty and better reliability over the years.
Then there's structure type. Fixed tilt versus a single-axis tracker can move the mounting line, and BOS as a whole, by a wide margin, regardless of which module you pick.
Finally, check what's actually in scope. DISCOM liaisoning, SCADA monitoring and full commissioning paperwork are sometimes included and sometimes billed later. That alone changes what "BOS" means in the number you've been given.
Put it in perspective. A Rs 2 per watt swing in module price moves a Rs 40 per watt plant by about 5 percent. The much bigger gaps between quotes come from the choices above, which is why the headline Rs/watt figure on its own tells you so little.
How to compare two solar EPC quotes properly
Don't anchor on the total. Ask each contractor for a line-item breakdown that maps to the cost table above, then check these five things before you look at price:
- Mounting structure material and coating (hot-dip galvanised or something lighter)
- Cable cross-section and the DC/AC ratio specified
- Inverter brand tier and warranty length
- Whether DISCOM liaisoning, SCADA and full commissioning documents are included in the price
- Whether the module is DCR or Non-DCR, and ALMM List-I and List-II compliant where your project needs it
Once you line these up, two quotes with the same module can still be 15 to 20 percent apart. And the cheaper one isn't automatically the better deal over the life of the plant.
The bottom line
The Rs/watt number on the front of an EPC quote hides more than it shows. Modules are only about half the cost, and BOS quietly makes up the rest. Most of the real difference between competing quotes comes down to structure grade, cable sizing, inverter tier and what's in scope, not the module brand on the cover page. Get the component-wise breakdown before you compare anything on price.
At Metalbook, we fabricate mounting structures and supply BOS materials to solar EPCs and developers across India. If you're reviewing a quote or specifying structural components for a project, our team can help you read the numbers properly.
