How to Choose the Right Solar Panel Capacity

The single most common mistake we see at Tristar Green Energy Solutions is homeowners and business owners picking a solar system size based on a neighbour's recommendation or a salesperson's suggestion rather than on their own electricity consumption data. Go too small, and you leave savings on the table every single month. Go too large, and you export surplus power to TANGEDCO at the low APPC (Average Pooled Purchase Cost) rate -- a fraction of what you pay to buy that same unit. Either way, you lose money.

This guide walks you through the exact methodology our engineering team uses when sizing a rooftop solar system for any customer in Tamil Nadu. It starts not with your roof, but with your electricity bill.

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Why You Should Start With Your EB Bill, Not Your Roof Size

Most solar companies begin the conversation with "How much roof space do you have?" That is the wrong starting point. Your roof determines the upper limit of what you can install, but your electricity consumption determines what you should install.

A 2,000 sq ft terrace can fit a 15 kW system. But if your household only consumes 300 units a month, installing 15 kW would be a spectacular waste of capital. You would export thousands of units every year at roughly Rs 2.25 to Rs 3.00 per unit (the APPC rate in Tamil Nadu) while having paid for panels, inverter, and structure sized for five times your actual need.

The correct sequence is:

1. Find your average monthly electricity consumption from your TANGEDCO bill.
2. Convert that consumption into the required system capacity in kW.
3. Check whether your roof can physically accommodate that capacity.
4. Verify that TANGEDCO's sanctioned load and net metering rules permit that capacity.
5. Adjust up or down based on future load growth, budget, and roof constraints.

Let us work through each step.

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Step 1: How to Read Your TANGEDCO Bill to Find Monthly Consumption

Your TANGEDCO (Tamil Nadu Generation and Distribution Corporation) electricity bill contains all the data you need. Here is what to look for.

Units Consumed (kWh)

TANGEDCO issues bills on a bimonthly cycle for most domestic consumers. The bill will show "Units Consumed" or "Energy Charges" for the billing period. Since the bill covers two months, divide by two to get your approximate monthly consumption.

Better yet, collect your last six bills (covering 12 months). Add up all the units consumed across those six bills and divide by 12. This gives you a true average monthly consumption that accounts for seasonal variation -- summer months with air conditioning will be much higher than mild winter months.

For a detailed walkthrough on reading every line of your TANGEDCO bill, see our guide on understanding your TANGEDCO EB bill.

Sanctioned Load (kW or kVA)

This is the maximum load your electrical connection is approved to draw. For domestic consumers, it is typically 2 kW, 3 kW, 5 kW, or 10 kW. For commercial and industrial consumers, it can range from 10 kW to several hundred kW or more.

Sanctioned load matters because TANGEDCO's net metering rules tie the maximum allowable solar capacity to your sanctioned load. We will cover this in detail below.

Tariff Category

Your bill will indicate your tariff category:

• LT-1A: Domestic (subsidised, first 100 units free under the TN government scheme)
• LT-1B: Domestic (general)
• LT-2A: Non-domestic / Commercial (small)
• LT-2B: Non-domestic / Commercial (medium)
• LT-3: Cottage and tiny industries
• LT-4: Agricultural
• HT-1 to HT-4: High Tension industrial and commercial

Each category has different tariff rates, which directly affects your solar ROI. The higher your per-unit tariff, the faster your solar investment pays for itself.

Worked example: Suppose your last six bimonthly TANGEDCO bills show the following consumption: 700, 680, 900, 1100, 1050, 780 units. Your total annual consumption is 5,210 kWh. Your average monthly consumption is 5,210 / 12 = 434 kWh per month.

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Step 2: Converting Monthly Consumption to Required Solar Capacity (kW)

This is the core sizing formula. It uses three inputs: your monthly consumption, the average peak sun hours in your location, and a safety factor to account for real-world losses.

The Formula

System Size (kWp) = Monthly Consumption (kWh) / 30 days / Peak Sun Hours / System Efficiency

Or equivalently:

System Size (kWp) = Monthly Consumption (kWh) / (30 x Peak Sun Hours x System Efficiency)

Peak Sun Hours in Tamil Nadu

Peak sun hours (PSH) represent the number of hours per day during which solar irradiance averages 1,000 W/sq.m. Tamil Nadu is one of India's best states for solar energy. Here are location-specific PSH values:

City / Region	Average Peak Sun Hours (per day)
Coimbatore	5.5 - 5.8
Madurai	5.6 - 6.0
Tirunelveli	5.7 - 6.1
Salem	5.4 - 5.7
Trichy	5.5 - 5.8
Chennai	5.0 - 5.4
Erode	5.4 - 5.7
Tirupur	5.5 - 5.8

For Coimbatore, we use 5.6 hours as a conservative planning figure.

System Efficiency Factor

No solar system converts 100% of incident sunlight into usable electricity at the meter. Real-world losses include:

• Inverter efficiency loss: 3-5%
• Cable and wiring losses: 2-3%
• Soiling (dust, bird droppings): 3-5%
• Temperature derating: 5-8% (Tamil Nadu summers push panel temperatures well above 25 degrees Celsius STC rating)
• Module mismatch and degradation: 2-3%

Combined, these losses mean a typical rooftop system in Tamil Nadu operates at about 78-82% overall efficiency. We use 0.80 (80%) as the standard efficiency factor for planning.

Worked Example

Using our earlier example of 434 kWh per month, with Coimbatore PSH of 5.6 and efficiency of 0.80:

System Size = 434 / (30 x 5.6 x 0.80)
           = 434 / 134.4
           = 3.23 kWp

We would recommend rounding up to 3.5 kWp or 4 kWp depending on your budget and future consumption expectations. Use our solar ROI calculator to compare the financial returns of different system sizes, or try the interactive calculator on our website.

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Step 3: Roof Area Calculation

Now that you know the capacity you need, check whether your roof can accommodate it. The area required depends on the wattage of the panels you choose.

Panel Wattage to Roof Area Requirement

Panel Wattage	Panel Dimensions (approx.)	Area per Panel (sq ft)	Panels per kWp	Area per kWp (sq ft)
330W	6.5 ft x 3.3 ft	21.5	3.03	65
400W	6.9 ft x 3.5 ft	24.2	2.50	60
440W	7.1 ft x 3.6 ft	25.6	2.27	58
540W (Bifacial)	7.6 ft x 3.8 ft	28.9	1.85	54
580W (Bifacial)	7.8 ft x 3.9 ft	30.4	1.72	52

Important: These are panel areas only. You must also account for:

• Inter-row spacing: To avoid self-shading, rows need spacing of 1.5 to 2 times the panel height. This typically adds 30-40% more area.
• Walkway and maintenance access: Leave at least 2 feet of clearance around edges and between rows for cleaning and maintenance.
• Obstructions: Water tanks, staircase rooms, parapet walls, satellite dishes, and other rooftop structures reduce usable area.

Rule of thumb for Tamil Nadu flat rooftops: Budget approximately 100 sq ft of total roof area per kWp when using 400W-540W panels with proper inter-row spacing.

For our 3.5 kWp example, you would need approximately 350 sq ft of shadow-free, obstruction-free roof area.

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Common Sizing Mistakes (and How to Avoid Them)

Mistake 1: Oversizing Beyond Annual Consumption

Under TANGEDCO's net metering framework, excess units exported to the grid beyond your annual consumption are compensated at the APPC rate, which is approximately Rs 2.25 to Rs 3.00 per unit. Compare this to the Rs 6 to Rs 9 per unit you pay TANGEDCO for consumption at higher slab rates, and you can see why oversizing is financially destructive.

If you install a 10 kW system but only consume 500 units a month, your system will generate roughly 1,350 units per month. You will export 850 units every month, earning only Rs 1,900 to Rs 2,550 for power that cost you Rs 4,000 or more per month in EMI or capital cost amortisation.

Mistake 2: Undersizing to Save on Upfront Cost

Going too small is equally problematic. If you install 2 kW when your consumption warrants 4 kW, you continue paying TANGEDCO for the remaining 2 kW worth of consumption at the highest slab rates. The marginal ROI on each additional kW of solar is highest when it offsets your most expensive consumption slab.

Mistake 3: Ignoring Seasonal Variation

A system sized for your January consumption (when ACs are off) will be woefully inadequate in May when ACs run 12 hours a day. Always size for your annual average, not your lowest month.

Mistake 4: Not Accounting for Future Load Growth

If you are planning to buy an electric vehicle, add air conditioning to more rooms, or install a water heater, factor that future consumption into your sizing now. Adding panels later is possible but more expensive per kW due to repeated mobilisation, potential inverter upgrades, and re-application for net metering approval.

Mistake 5: Forgetting Sanctioned Load Limits

Your solar capacity cannot exceed your sanctioned load under TANGEDCO's net metering rules. If your sanctioned load is 3 kW but your consumption warrants a 5 kW system, you must first apply to TANGEDCO for a sanctioned load increase before installing the larger system.

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Capacity Recommendations by Monthly Electricity Bill Slab

This table maps your current monthly TANGEDCO bill amount to a recommended solar system size. It assumes LT-1B domestic tariff rates as of 2025-26.

Monthly EB Bill (Rs)	Approx. Monthly Consumption (kWh)	Recommended System Size (kWp)	Estimated Monthly Savings (Rs)	Approx. System Cost (after subsidy)	Simple Payback (years)
500 - 1,000	100 - 180	1 - 1.5	400 - 800	Rs 30,000 - 50,000	4 - 5
1,000 - 2,000	180 - 320	1.5 - 2.5	800 - 1,600	Rs 50,000 - 1,00,000	4 - 5
2,000 - 3,500	320 - 500	2.5 - 4	1,600 - 2,800	Rs 1,00,000 - 1,80,000	4 - 5
3,500 - 5,000	500 - 700	4 - 5.5	2,800 - 4,000	Rs 1,80,000 - 2,80,000	4 - 5
5,000 - 8,000	700 - 1,100	5.5 - 8	4,000 - 6,500	Rs 2,80,000 - 4,50,000	4.5 - 5.5
8,000 - 15,000	1,100 - 2,000	8 - 15	6,500 - 12,000	Rs 4,50,000 - 9,00,000	5 - 6
15,000 - 30,000	2,000 - 4,500	15 - 35	12,000 - 25,000	Rs 7,00,000 - 20,00,000	4.5 - 6
30,000 - 50,000+	4,500 - 8,000+	35 - 65+	25,000 - 45,000+	Rs 20,00,000 - 40,00,000+	4 - 5.5

Notes: Subsidy under PM Surya Ghar applies to residential systems up to 3 kWp (Rs 78,000 subsidy) and partially up to 10 kWp. Commercial and industrial systems do not receive central subsidy but benefit from accelerated depreciation. Costs are approximate 2025-26 figures.

For a detailed breakdown of how these returns are calculated, see our step-by-step solar ROI calculator guide.

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ROI Comparison by System Capacity

System Capacity	Annual Generation (kWh)	Annual Savings (Rs, Residential)	System Cost (after subsidy)	Simple Payback	25-Year Net Savings
1 kWp	1,500	8,000 - 10,000	Rs 35,000 - 45,000	4 - 5 years	Rs 2,00,000+
2 kWp	3,000	16,000 - 20,000	Rs 70,000 - 90,000	4 - 5 years	Rs 4,00,000+
3 kWp	4,500	24,000 - 32,000	Rs 1,00,000 - 1,30,000	3.5 - 5 years	Rs 6,50,000+
5 kWp	7,500	40,000 - 55,000	Rs 2,20,000 - 2,80,000	4.5 - 5.5 years	Rs 10,00,000+
10 kWp	15,000	80,000 - 1,10,000	Rs 5,00,000 - 6,50,000	5 - 6 years	Rs 20,00,000+

Annual savings assume Tamil Nadu domestic tariff rates for 2025-26 and account for an annual tariff increase of 3-5%. Generation figures assume Coimbatore-region irradiance. Use our ROI calculator for a personalised estimate.

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Sanctioned Load Rules for TANGEDCO Net Metering

Understanding TANGEDCO's sanctioned load requirements is critical before finalising your system size. Here is a summary of the key rules.

Consumer Category	Maximum Solar Capacity Allowed	Net Metering Settlement
LT-1A / LT-1B (Domestic)	Up to 100% of sanctioned load, max 10 kWp	Annual net settlement; excess paid at APPC rate
LT-2A / LT-2B (Commercial)	Up to 100% of sanctioned load, max 500 kWp	Annual net settlement; excess paid at APPC rate
LT-3 (Cottage Industry)	Up to 100% of sanctioned load	Annual net settlement
HT-1 to HT-4 (Industrial)	Up to 100% of sanctioned/contracted demand	Net feed-in or net metering as applicable

Key points to remember:

• For residential consumers under PM Surya Ghar, the subsidy covers systems up to 3 kWp at the full rate. Systems between 3 kWp and 10 kWp receive a partial subsidy.
• If your sanctioned load is only 2 kW but you want a 5 kW system, you must apply for a sanctioned load enhancement first. This involves paperwork, possible wiring upgrades, and a processing fee.
• TANGEDCO's settlement period is 12 months. At the end of the settlement period, if you have net exported more energy than you imported, the excess is compensated at the APPC rate (approximately Rs 2.25-3.00/unit). This is why matching your system to your actual consumption is financially critical.

For a complete comparison of net metering versus net billing under the latest TNERC regulations, read our detailed guide on net metering vs net billing.

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Residential vs Commercial vs Industrial Sizing: Key Differences

The sizing formula is the same across all segments, but several practical factors differ significantly.

Residential Sizing (1 kW to 10 kW)

• Consumption pattern: Peaks in morning and evening; daytime consumption is relatively low when occupants are at work or school.
• Net metering benefit: High, because solar generates during the day and excess is banked against evening consumption.
• Subsidy availability: PM Surya Ghar subsidy of up to Rs 78,000 for systems up to 3 kWp. See our complete subsidy guide.
• Typical system: 3 kW to 5 kW for a 3BHK household with 1-2 ACs.
• System type: On-grid with net metering is almost always the best choice for homes.

Commercial Sizing (10 kW to 100 kW)

• Consumption pattern: Heavy daytime consumption (shops, offices, showrooms, hotels, hospitals). Solar generation aligns well with load.
• Self-consumption ratio: Typically 70-90%, much higher than residential. This means more direct savings and less reliance on net metering credits.
• No central subsidy: Commercial consumers do not get PM Surya Ghar subsidy but can claim accelerated depreciation (40%) under the Income Tax Act.
• Tariff advantage: Commercial tariff rates (Rs 7.50 to Rs 12+ per unit) are higher than domestic rates, making solar ROI faster despite the absence of subsidy.
• Typical system: 15 kW to 50 kW for a mid-sized office or showroom.

Industrial Sizing (100 kW to 1 MW+)

• Consumption pattern: Continuous, heavy base load with machinery running 8 to 24 hours per day.
• Self-consumption ratio: Very high (often 90%+) for single-shift operations. For multi-shift operations, daytime generation still offsets a substantial portion of the bill.
• HT tariff savings: HT industrial tariffs include demand charges and energy charges. Solar reduces both, leading to significant savings.
• Open access option: For systems above 1 MW, open access solar (off-site generation) may be more economical than rooftop.
• Typical system: 100 kW to 500 kW on factory rooftops; larger installations on ground-mounted structures within the premises.

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Future-Proofing Your Solar System

One of the most frequent regrets we hear from customers who installed solar two or three years ago is "I wish I had gone bigger." Here are the common future loads you should factor into your sizing today.

Electric Vehicle (EV) Charging

A typical electric car (such as the Tata Nexon EV or MG ZS EV) has a battery of 30-45 kWh. If you drive 40-50 km per day, you will need roughly 8-12 kWh of charging per day. That is an additional 240-360 kWh per month, equivalent to an extra 2-3 kW of solar capacity.

Even if you do not own an EV today, if you plan to purchase one in the next 3-5 years, add 2-3 kW to your solar system size now. The cost of adding this capacity later will be 20-30% higher due to re-engineering, re-permitting, and potential inverter replacement.

Additional Air Conditioning

Each 1.5-ton inverter AC running 8 hours per day consumes roughly 120-150 kWh per month. If you plan to add ACs to bedrooms or a new floor, add approximately 1 kW of solar capacity per AC.

Water Heater (Heat Pump or Electric Geyser)

An electric storage geyser used for 30 minutes twice daily adds about 60-90 kWh per month. A heat pump water heater is more efficient at 20-30 kWh per month for the same usage.

Home Office or New Business

If you or a family member is likely to work from home full-time (with desktop computer, monitor, printer, additional lighting and cooling), budget an extra 80-120 kWh per month.

Additional Floor or Extension

If your house plan includes a future first or second floor, the electrical load of that floor should be estimated and included in the solar sizing.

Our recommendation: If budget permits, oversize your system by 15-20% beyond current consumption to accommodate organic load growth. However, do not exceed your sanctioned load or oversize to the point where you become a net annual exporter.

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What to Do If Roof Space Is Limited

Not every rooftop in Tamil Nadu is a vast, shadow-free terrace. Many urban homes in Coimbatore, Chennai, and Madurai have limited usable roof area due to water tanks, staircase rooms, adjacent buildings causing shade, or simply a small plot size. Here are strategies to maximise generation from a constrained roof.

Use High-Efficiency Panels

Standard 400W panels require about 60 sq ft per kWp. High-efficiency 540W or 580W bifacial panels require only 52-54 sq ft per kWp. That is a 10-15% space saving. For a 5 kW system, this means needing 260 sq ft instead of 300 sq ft -- a meaningful difference on a compact rooftop.

The trade-off is cost: high-efficiency panels carry a 10-20% price premium. But on space-constrained roofs, the additional generation per square foot often justifies the premium.

Install Micro-Inverters Instead of String Inverters

In a traditional string inverter system, panels are wired in series. If one panel is shaded, the entire string's output drops. On a rooftop with partial shading from water tanks or adjacent structures, this can reduce generation by 20-40%.

Micro-inverters are installed on each individual panel and allow every panel to operate independently. A shaded panel loses only its own output without dragging down the others. On shaded rooftops, micro-inverters can recover 15-25% of generation that would otherwise be lost, effectively increasing the usable capacity of your limited roof.

Optimise Panel Layout

An experienced solar engineer can design panel layouts that maximise the number of panels on an irregular or obstructed roof. This includes:

• Using portrait and landscape orientations strategically
• Placing panels at different tilt angles on different sections of the roof
• Splitting the array across multiple roof sections (east-facing and west-facing, for example) with separate MPPT strings
• Using smaller panel formats (e.g., half-cut cells in compact frames) for tight spaces

Consider a Ground-Mounted System

If you have open land on your property (garden, parking area, backyard), a ground-mounted system can supplement or replace rooftop panels. Ground-mounted structures are more expensive per kW but can be oriented and tilted optimally, and they avoid rooftop shading issues entirely.

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Phase-Wise Installation Strategy

If your ideal system size exceeds your current budget or your immediate consumption needs, a phased approach can be practical and financially sound.

Phase 1: Cover Your Base Load

Install enough capacity to offset your non-AC, non-seasonal base consumption. For most 3BHK homes in Tamil Nadu, this is 2-3 kW. This phase has the fastest ROI because it offsets units at the highest slab rate.

Phase 2: Add Capacity for Seasonal and Growing Loads

After 1-2 years, if your consumption has grown (new AC, EV, additional family members), add another 1-3 kW. By this point, your Phase 1 system has proven itself, you understand your actual generation patterns, and you can size Phase 2 with precision.

Phase 3: Future Expansion

Add capacity for major life changes -- an additional floor, a home business, or EV charging infrastructure.

Practical considerations for phased installation:

• Ensure your initial inverter is oversized or expandable. For example, install a 5 kW hybrid inverter in Phase 1 even if you only connect 3 kW of panels initially. This avoids replacing the inverter later.
• Use a panel make and model that is likely to remain available in 2-3 years, or at least choose a mounting structure that can accommodate different panel dimensions.
• Each phase requires a fresh net metering application and TANGEDCO inspection, which adds 2-4 weeks of processing time.
• Combining phases may be more cost-effective if you can secure financing. The per-kW installation cost decreases with system size due to fixed costs (scaffolding, logistics, documentation) being spread across more capacity.

For a full overview of what the installation process involves, read our solar installation process guide.

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The Impact of Roof Orientation and Shading

Orientation (Azimuth)

In Tamil Nadu (latitude approximately 10 to 13 degrees North), the ideal panel orientation is true south at a tilt of 10 to 15 degrees. Here is how other orientations compare:

• South-facing: 100% of maximum yield (baseline)
• Southeast or Southwest facing: 95-98% of south-facing yield
• East or West facing: 80-85% of south-facing yield
• North-facing: 60-70% yield; rarely economically viable

For a flat RCC rooftop (the most common type in Tamil Nadu), panels are mounted on aluminium structures at 10 to 12 degrees tilt facing south. This provides excellent year-round performance and allows natural rain-cleaning of the panels.

Shading Analysis

Even partial shading of a single panel can reduce the output of an entire string by 20-50% in systems without power optimisers or micro-inverters. Before finalising your system size, conduct a thorough shade analysis:

• Identify all shading sources: water tanks, staircase structures, adjacent buildings, trees, temple gopurams, cell towers
• Map shading patterns across seasons (a structure causing no shade in summer may heavily shade panels in winter when the sun angle is lower)
• Design strings to avoid mixing shaded and unshaded panels on the same MPPT input
• Consider micro-inverters for partially shaded sections

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On-Grid vs Hybrid: Choosing the Right System Type

Your choice of system type affects both sizing and cost.

On-Grid (Grid-Tied with Net Metering)

This is the most common and cost-effective option for Tamil Nadu customers with reliable grid supply. All generated solar power either serves your loads or is exported to TANGEDCO for credit. No batteries are involved, keeping costs low and ROI fast.

Best for: Homes and businesses in urban and semi-urban areas with fewer than 2-3 hours of power cuts per day.

Hybrid (On-Grid + Battery Backup)

A hybrid system includes battery storage to provide power during grid outages. This adds Rs 40,000 to Rs 70,000 per kWh of battery capacity (lithium LFP) to your system cost.

To size the battery, determine your critical load and backup duration:

Battery Capacity (kWh) = Critical Load (kW) x Backup Hours / Depth of Discharge (0.80 for LFP)

Example: 1.5 kW critical load (lights, fans, fridge, WiFi router) for 4 hours:

Battery = 1.5 x 4 / 0.80 = 7.5 kWh

Best for: Areas with frequent or extended power cuts; homes with medical equipment; businesses where downtime has a direct revenue impact.

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Putting It All Together: A Complete Sizing Walkthrough

Let us work through a realistic example from start to finish.

Scenario: Mr. Ramesh in Coimbatore has a 3BHK independent house with a 1,500 sq ft flat RCC terrace. He has two 1.5-ton inverter ACs, a water heater, and is planning to buy an EV next year. His sanctioned load is 5 kW. His last 12 months of TANGEDCO consumption averages 620 kWh per month. His average bimonthly bill is approximately Rs 5,800.

Step 1 -- Determine current consumption: 620 kWh per month.

Step 2 -- Factor in future loads: EV charging will add approximately 300 kWh per month. Total projected consumption: 920 kWh per month.

Step 3 -- Apply sizing formula:

System Size = 920 / (30 x 5.6 x 0.80)
           = 920 / 134.4
           = 6.85 kWp

Round up to 7 kWp.

Step 4 -- Check sanctioned load: Mr. Ramesh's sanctioned load is 5 kW. He needs to apply for an increase to at least 7 kW before installing a 7 kW system under net metering.

Step 5 -- Check roof area: At 100 sq ft per kWp, a 7 kW system needs approximately 700 sq ft. His 1,500 sq ft terrace has a staircase room (100 sq ft) and water tank area (50 sq ft), leaving about 1,350 sq ft of usable area. More than sufficient.

Step 6 -- Choose system type: Mr. Ramesh lives in Coimbatore city with minimal power cuts. An on-grid system with net metering is the best fit.

Step 7 -- Estimate cost and ROI: A 7 kW on-grid system costs approximately Rs 3,50,000 to Rs 4,20,000 before subsidy. With the PM Surya Ghar subsidy (Rs 78,000 for first 3 kW + Rs 30,000 for next 4 kW at partial rate), his net cost is approximately Rs 2,80,000 to Rs 3,40,000. Monthly savings of Rs 5,000 to Rs 7,000 give a payback period of approximately 4 to 5 years.

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FAQ

How many solar panels do I need for a 3 kW system?

It depends on the wattage of each panel. With 400W panels, you need 8 panels (8 x 400W = 3,200W, rounded to 3.2 kWp). With 540W panels, you need 6 panels (6 x 540W = 3,240W). Higher-wattage panels mean fewer panels and less roof area, but they cost slightly more per unit. For most residential installations in Tamil Nadu, 400W to 540W panels offer the best balance of efficiency, cost, and availability.

Can I install more solar capacity than my sanctioned load?

Under TANGEDCO's net metering rules, your solar system capacity cannot exceed your sanctioned load for the connection. If your sanctioned load is 3 kW but you want a 5 kW system, you must first apply to TANGEDCO for a sanctioned load increase. The process involves submitting an application, possible wiring inspection, and a fee. Plan for 2-4 weeks of processing time. Your solar installer (including us at Tristar Green Energy Solutions) can assist with this paperwork.

What happens to excess solar power I export to the grid?

Under TANGEDCO's net metering scheme, excess units exported during the day are credited against units consumed from the grid at night or on cloudy days. At the end of the 12-month settlement period, if you have exported more than you imported, TANGEDCO compensates you at the APPC rate (approximately Rs 2.25 to Rs 3.00 per unit). Since this is far less than the Rs 6 to Rs 9 per unit you pay for grid power, it is financially better to size your system to match -- not exceed -- your annual consumption. Learn more in our net metering vs net billing guide.

Is it better to install solar panels in phases or all at once?

Installing everything at once is almost always cheaper per kW because you avoid duplicate mobilisation costs, multiple net metering applications, and potential inverter replacement. However, if your budget is limited, a phased approach makes sense -- start with 2-3 kW to offset your highest-slab consumption, then expand in 1-2 years. The key is to plan ahead: install an inverter sized for your eventual total capacity, and choose a mounting structure that can accommodate additional panels.

How do I know if my roof gets enough sunlight for solar?

Most flat RCC rooftops in Tamil Nadu receive excellent sunlight. The primary concern is shading, not sunlight availability. If your roof is shaded by taller adjacent buildings, large trees, or water tanks for more than 2-3 hours during the peak generation window (9 AM to 3 PM), your generation will be reduced. At Tristar Green Energy Solutions, we conduct a free site assessment that includes shade analysis using satellite imagery and, for larger systems, drone-based surveys. Contact us to schedule your assessment.

What is the minimum and maximum solar system size for homes in Tamil Nadu?

The practical minimum for a grid-tied residential system is 1 kWp, which generates approximately 120-130 units per month in Tamil Nadu. The maximum under TANGEDCO net metering rules for residential consumers is 10 kWp or your sanctioned load, whichever is lower. For the PM Surya Ghar subsidy scheme, the full subsidy of Rs 78,000 applies to systems up to 3 kWp. Systems above 3 kWp and up to 10 kWp receive a reduced per-kW subsidy.

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Next Steps

Choosing the right solar capacity is the single most important decision in your solar journey. Too small and you continue overpaying TANGEDCO. Too large and you subsidise the grid at a loss. The right size maximises your savings and pays for itself in 4-5 years.

At Tristar Green Energy Solutions, our engineers provide a free detailed site assessment and system sizing report for every prospective customer in Coimbatore and across Tamil Nadu. We analyse your last 12 months of TANGEDCO bills, conduct shade analysis of your rooftop, verify your sanctioned load and net metering eligibility, and present you with a precise system size recommendation accompanied by a full 25-year financial projection -- before you spend a single rupee.

Ready to find your ideal system size? Use our online solar calculator for an instant estimate, or contact us to schedule a free in-person site assessment.