Rooftop Solar for New Town Homes: Sizing, Shadow-Free Zones and Net Metering Basics
We've had more clients bring up rooftop solar in the last two or three years than in the entire decade before that, and almost every one of those conversations in New Town starts with the same slightly deflated question, whether solar even makes sense on a plot that's increasingly hemmed in by taller apartment blocks going up on neighbouring plots, because the client has usually already heard from a neighbour or a solar vendor that shadow from a nearby high-rise killed half the panel output on someone else's installation. It's a fair worry and, in a rapidly densifying area like New Town where 3 to 5 katha independent house plots increasingly sit beside four and five storey apartment developments, it's one we take seriously at the very start of any solar conversation rather than after panels are already ordered, because the honest answer is that solar absolutely still works on most of these plots, but only if the roof gets read properly first rather than assuming any flat, sun-facing surface will do. This piece is meant as a practical primer specifically for that New Town situation, walking through how we actually find the usable roof area on a plot with neighbours pressing in on multiple sides, how we size a system against what a typical household actually consumes, and what the net metering process with the local discom actually involves once the panels are up.
Mapping Shadow-Free Zones on a Roof That Isn't Fully Open Anymore
The starting point on every rooftop solar assessment we do is a proper shadow study of the specific roof, not a generic assumption that "south facing roofs get good sun," because in a plot surrounded by taller construction, the shadow cast by a neighbouring four or five storey building can fall across a meaningful portion of even a well-oriented roof for several hours a day, and that shadow moves and changes length with the season, running longer in winter when the sun sits lower in the sky and shorter in summer. We map this using a combination of on-site observation across different times of day, ideally including at least one visit during winter months when shadows are at their longest and most limiting, and shadow projection based on the height and distance of neighbouring structures, which lets us plot out which zones of the roof stay genuinely shadow-free for the 5 to 6 hours of strong midday sun that panels need to perform well, and which zones are compromised for part or all of the day. On a typical New Town independent house plot with a building on the south or west boundary rising higher than the client's own roof, we've often found the shadow-free zone shrinks to the northern or eastern half of the roof, which runs counter to the textbook advice of always orienting panels south, and in those cases we design the array layout around the zone that's actually clear rather than chasing an ideal orientation that the site doesn't support. Even a partially shadowed roof usually still has a workable footprint, since most of these plots have 800 to 1,400 square feet of roof area to begin with, and a residential system typically only needs 300 to 500 square feet of unobstructed space, so the shadow study is about finding that pocket precisely rather than writing off the roof entirely.
Sizing the System Against What the Household Actually Uses, Not a Round Number
The second mistake we see clients heading toward, often nudged there by a vendor quoting a package size rather than a household's actual load, is sizing the solar system around a round number like 3 kW or 5 kW rather than working backward from the home's actual monthly consumption. We start every sizing conversation by asking for six to twelve months of past electricity bills, because a household's units-consumed figure, not its sanctioned load, is what tells us how large a system actually makes financial sense, and Kolkata homes vary more than people expect on this, a compact New Town apartment running mostly fans, lights, a couple of ACs used seasonally, and a refrigerator might sit around 250 to 350 units a month, while a larger independent house running multiple split ACs through the Kolkata summer, a geyser, and full-time appliances can run 600 units or considerably higher. As a rough planning figure, a well-oriented 1 kW rooftop solar system in the Kolkata region generates somewhere in the range of 100 to 130 units a month depending on season, shading, and panel orientation, so a household consuming around 400 units monthly is typically looking at a 3 to 4 kW system to offset a meaningful share of that consumption, while a larger household nearer 700 to 800 units monthly might reasonably consider 6 kW or more, always assuming the shadow-free roof area from the previous step can actually accommodate that panel count, since a 3 kW system needs roughly 300 square feet of panel area and that scales up close to linearly as the system grows. We'd always rather size a system slightly conservatively against a shadow-constrained roof and have a client genuinely happy with a smaller but fully-producing array, than oversize based on a vendor's package pricing and end up with panels in a partially shaded zone underperforming their rated output for years.
What Net Metering Actually Involves With the Local Discom
Once sizing and roof placement are settled, the process that trips up more homeowners than the physical installation itself is net metering, the mechanism that lets a household export surplus solar generation back to the grid during sunny hours and draw grid power back at night, with the discom (in most of the New Town and greater Kolkata area, that's the West Bengal State Electricity Distribution Company, or in parts of Salt Lake and central areas, CESC) netting the two against each other on the monthly bill. The broad sequence, which does vary somewhat depending on which discom's territory the plot falls in, generally runs through an application to the discom for net metering approval before or alongside installation, a technical feasibility check of the existing connection and sanctioned load, installation of the solar system by an empanelled vendor along with a bidirectional meter that can record both import and export, an inspection and commissioning sign-off from the discom once installation is complete, and finally the connection going live with billing that reflects net units consumed rather than gross import. West Bengal's residential net metering framework, in line with the broader national policy direction, generally allows rooftop solar capacity sized up to the household's sanctioned connection load, which is one more reason accurate sizing against real consumption matters early, since oversizing beyond what the sanctioned load supports can complicate the net metering approval itself. We'd strongly encourage anyone starting this process to confirm the specific documentation and empanelled vendor list with their discom directly before committing to a system size or installer, since the exact requirements and subsidy schemes available do shift from year to year and are genuinely worth verifying fresh rather than relying on advice, including ours, that may be a cycle or two out of date by the time you're ready to install.
Fitting the Array Into the Roof Without It Taking Over Every Other Use
A rooftop that's carrying a solar array still usually needs to do other jobs too, water tanks, a solar water heater if the household has one, drying space, occasional terrace use, and we design the panel layout to respect that rather than letting the array sprawl across the entire usable roof simply because the space is technically available. In practice this means we mount panels on a raised tilted frame rather than flush to the roof, which both improves generation by getting the tilt angle closer to optimal for our latitude and leaves usable floor space underneath and around the array for other roof functions, and we coordinate panel placement early with anything else headed for that same roof, since a solar water heater tank and its collector panels have their own load and orientation needs that are worth planning on the same drawing rather than as a later addition; we've written more specifically about that side of rooftop planning in fitting a solar water heater into a New Town terrace without giving up usable outdoor space. And because a home that's already minimised its electric lighting load through good daylighting design needs a proportionally smaller solar array to cover its remaining consumption, it's worth reading the sizing conversation above alongside our piece on zoning LED lighting circuits against daylight so artificial light only runs where the sun doesn't reach, since the two decisions genuinely affect each other's numbers.
A Note for Anyone Building New Rather Than Retrofitting
If you're at the design stage of a new independent house in New Town rather than retrofitting solar onto an existing roof, there's a real advantage in deciding the array's rough footprint and orientation before the roof slab and parapet detailing are finalised, since we can then route conduit for the DC and AC wiring inside the structure during construction rather than as exposed surface conduit added later, and we can also make sure the roof's structural design accounts for the panel mounting frame's load from the outset rather than needing a retrofit check. Sustainability choices at this stage tend to cluster together in our experience, and clients who are thinking hard about solar are often asking us the same week about the building envelope itself, a question we've addressed separately in local clay brick versus fly ash block and which is actually the greener choice for Bengal construction, since the embodied energy of the walls going up matters just as much to a genuinely sustainable house as the energy the roof generates once it's built. We touch on this kind of forward planning as part of our broader residential architecture process, and it's a conversation worth having at the same stage as roof form and terrace layout decisions rather than after the design is locked.
When the Roof in Question Is a Commercial One
Everything above is written around a residential rooftop, but we get a version of this same sizing and placement conversation on commercial projects too, and the load profile changes the calculation considerably, since a restaurant or commercial kitchen carries exhaust systems, refrigeration, and ventilation equipment that draw far more consistently through the day than a typical home does, a subject we've covered in detail in commercial kitchen ventilation design for Kolkata restaurants and what architects must plan for. Where a commercial client is running that kind of equipment load, solar sizing has to work backward from hourly demand curves rather than a monthly average the way we've described for homes here, and rooftop space is often further constrained by exhaust ductwork, chiller units, and fire safety clearances that a residential roof simply doesn't have to accommodate.
Getting Your Own Roof Read Properly
Every New Town roof we've assessed for solar has its own specific mix of orientation, neighbouring shadow, and structural capacity, which is exactly why we don't think a generic package size or a drone-photo estimate from a vendor who's never walked the actual roof is good enough for a decision this size, and a proper shadow study across the seasons combined with sizing against your real consumption numbers is what separates a solar installation that quietly pays for itself over years from one that underperforms because it was placed and sized without anyone checking the specifics first. If you're considering rooftop solar for a home in New Town, Rajarhat, Salt Lake, or anywhere across greater Kolkata and want a proper site-specific read on your roof before committing to a system size, get in touch with our studio and we'll walk the roof with you, map where the sun genuinely reaches across the seasons, and work out a system sized to what your household actually uses.