15 kW solar system — size, output and cost

What this size typically covers

A 15 kW array suits a site consuming in the region of 1800 units a month. That figure comes from a planning assumption of roughly four peak-sun-hours a day in Punjab, derated for temperature, soiling and inverter losses — about 120 units per kW per month.

It is a planning figure, not a guarantee. Real output varies with orientation, tilt, shading, module and inverter selection, ambient temperature, and how well the system is maintained.

Roof area

Approximately 1500 square feet of usable, unshaded area. Assess area honestly: parapet shadows, water tanks, stairwell blocks, and buildings to the south all reduce what is genuinely usable, and a layout that ignores them underperforms from day one.

How many modules is that

Roughly twenty-seven modules at around 500-550 W each. An array of this size usually needs a designed mounting structure rather than a catalogue frame, particularly on a flat RCC roof where ballast, wind loading and the roof’s own capacity all have to be considered together.

What a 15 kW system typically runs

Commercial territory: an office floor, a retail unit, a small factory, a school block, a clinic, or a large home with substantial cooling load. It carries lighting, cooling, refrigeration, computing and light machinery through a working day.

At this size, matching generation to the working pattern matters more than the headline capacity. A site that runs six days a week uses far more of what it generates than one that runs five, and that difference shows up in the return long before the equipment choice does.

Supply and phase

Three-phase, in practice. Load balance across phases, protection discrimination, and the condition and capacity of the LT panel all become design questions, and starting currents from motor loads have to be accounted for rather than assumed away.

This is where the electrical engineering work usually determines the schedule. If the board needs replacing or the earthing needs correcting, that happens before generation is connected — not because of a preference, but because adding a source to a weak installation is how a small fault becomes a large one.

With or without a battery

Grid-tied with net metering covers most commercial cases, because the load and the generation already coincide.

Storage enters the conversation when an outage costs money by the hour — a production line, a cold store, a server room. Those are essential-load problems with a specific answer, and they are designed as such: a defined backup board, a battery sized against that schedule, and a changeover arrangement that behaves predictably. See hybrid and off-grid.

Summer, winter and the shape of the year

Output is not constant across the year, and neither is consumption. Generation is highest in the long, clear days before and after the monsoon, and lowest in the short days of winter and under the dust and cloud of the wettest weeks. In this region the summer months combine the highest consumption with strong generation — which is why solar addresses a summer bill more directly than a winter one.

Two consequences worth planning around: a system sized against a summer bill alone will be larger than the year needs, and one sized against a winter bill will disappoint in June. We size against twelve months where the data exists, and say which way we are erring where it does not.

What determines the cost

We do not publish a price for this size, because a credible number depends on things that are only known after a site visit:

• Roof type and the mounting structure it requires
• Distance and route from array to inverter to distribution board
• Condition of the existing electrical installation
• Module and inverter selection
• Whether net metering is included
• Whether battery backup is part of the scope

Market-indicative ranges circulate widely online. They are not our prices, and repeating them here would imply a quotation we cannot stand behind.

If this size is not right

• Around 1,200 units a month: 10 kW.
• Above roughly 2,500 units, or with significant three-phase machinery: 25 kW.
• For a commercial site, bring twelve months of bills rather than one — seasonal spread changes the sizing more than any single month does. The sizing estimator is the starting point.

Next step

Use the sizing estimator to get an indicative size from your own bill or consumption. An engineer verifies the load and the site before any proposal.