Every solar question answered — basics to advanced

Solar energy is electricity generated directly from sunlight using photovoltaic (PV) cells. When light photons hit the silicon material inside a solar panel, they knock electrons loose — this flow of electrons is electricity. A single cell produces a tiny amount; panels are made of many cells wired together, and many panels are wired into an array.

The process: Sunlight → Solar panel (DC electricity generated) → Inverter (converts DC to AC) → Your home's wiring → Appliances use power. Excess power either feeds back to the grid (net metering) or charges a battery.

A unit of electricity is 1 kilowatt-hour (kWh). It is the amount of energy used when a 1,000-watt (1 kW) appliance runs for 1 hour — or a 100-watt bulb runs for 10 hours.

Your electricity bill charges you per unit consumed. In India, household tariffs range from roughly ₹3 to ₹10 per unit depending on state, DISCOM and consumption slab. The higher your slab, the more you pay per unit — which is exactly why solar saves more money for heavy consumers.

DC (Direct Current) is electricity that flows in one direction only, at a constant voltage. Batteries, solar panels, and electronics internally use DC. A phone charger, for instance, converts AC from your wall socket to DC for the battery.

AC (Alternating Current) is electricity that rapidly reverses direction — in India, it reverses 50 times per second (50 Hz). All home wiring, grid power, and most appliances are designed for AC.

Solar panels produce DC because of the physics of the photovoltaic effect — electrons flow in one direction when knocked free by photons. The inverter's job is to convert this DC into grid-compatible AC (230V, 50Hz in India) so your appliances can use it.

Why does this matter? A system without an inverter (or with a failed inverter) cannot power your home from solar — the raw panel output is unusable by normal appliances. Battery systems store DC, so a hybrid system converts DC → battery storage, and then battery DC → AC when needed.

Watt (W) and Kilowatt (kW) measure power — the rate at which energy is used or produced at a given moment. 1 kW = 1,000 W.

Kilowatt-hour (kWh) measures energy — the total amount of electricity consumed or produced over time. It is power × time.

Think of power as the speed of a car and energy as the total distance covered. Running a 2 kW geyser for 30 minutes uses 2 × 0.5 = 1 kWh (1 unit).

Monocrystalline (Mono) — Made from a single silicon crystal. Higher efficiency (18–23%), better performance in low light and high temperatures. More expensive but the best choice for limited roof space. Identifiable by uniform black cells.

Polycrystalline (Poly) — Made from multiple silicon crystals melted together. Lower efficiency (15–18%), cheaper. Blue-ish appearance. Good for large open areas where space is not a constraint.

TOPCon / HJT (premium) — Next-generation monocrystalline technologies. Efficiency up to 25%+. Lower temperature coefficient (degrades less in heat). Higher upfront cost but better long-term generation. Increasingly popular in Indian market.

Bifacial — Generates power from both sides. The rear captures reflected light from rooftops or ground (albedo effect). Can produce 5–15% more energy than standard panels in the right installation.

Thin-film — Flexible, lower efficiency, mainly used in building-integrated applications. Rare in residential India.

Panel efficiency is the percentage of sunlight hitting the panel that gets converted to electricity. A 20% efficient panel produces 20W per 100W of sunlight falling on each square metre of its surface.

Does higher efficiency mean a better panel? Not always — it means more watts per square metre. This matters if roof space is tight. If you have ample space, a lower-efficiency panel at a lower price can give the same total output at lower cost.

What matters more for long-term performance: temperature coefficient, degradation rate, manufacturer warranty, and actual local performance data.

Temperature coefficient — Panels lose power as they heat up. A coefficient of -0.35%/°C means a panel rated at 25°C loses 0.35% of its output for every degree above 25°C. On a 55°C rooftop in May, that is a 10.5% power loss. TOPCon and HJT panels have lower temperature coefficients (-0.25 to -0.30%), making them better suited for India's climate.

Solar panels are designed to last 25–30 years. They do not fail suddenly — they gradually degrade (produce slightly less power each year).

Standard warranty structure:
1. Product/workmanship warranty — 10–12 years coverage against manufacturing defects, delamination, cracking.
2. Performance/power output warranty — 25 years. Guarantees the panel will produce at least 80–83% of its rated power after 25 years. Premium panels (TOPCon) now offer 87–90% at 25 years.

Typical degradation: First year ~2%, then ~0.5% per year. So a 400W panel produces roughly 398W after year 1, and around 350W after 25 years.

What voids a warranty? Physical damage (hail, falling objects), improper installation, incorrect mounting angle causing sustained mechanical stress. Always get certified installers.

The inverter is the most important and most failure-prone component of a solar system. It performs three essential jobs:

1. DC to AC conversion — Converts the variable DC from panels (which changes with sunlight intensity) into stable 230V, 50Hz AC for your appliances and the grid.

2. Maximum Power Point Tracking (MPPT) — Panels have a "sweet spot" voltage at which they produce maximum power. MPPT is an algorithm that constantly adjusts the electrical load to keep the panels operating at this optimal point, even as sunlight, temperature and shading change throughout the day. Without MPPT, you could lose 20–30% of potential energy.

3. Grid synchronisation and safety — The inverter monitors the grid and synchronises its AC output precisely (voltage, frequency, phase) before feeding power. If the grid goes down, the inverter's anti-islanding protection immediately disconnects — this is critical for safety of DISCOM lineworkers.

String inverter (most common in India)
Multiple panels are connected in series (a "string") and wired to one central inverter. Simple, cost-effective, easy to maintain. The weakness: if one panel is shaded or fails, it drags down the entire string's output (like Christmas lights in series). Best for unshaded, uniform roofs.

Microinverter
One small inverter per panel. Each panel operates independently — shading or failure of one panel doesn't affect others. Excellent for partially shaded roofs or complex orientations. More expensive (3–4× the cost per watt). Monitoring per panel. Popular in premium residential installations.

Power optimiser + string inverter (DC optimiser)
A middle ground. A small DC-DC converter on each panel maximises each panel individually (like microinverter) but still feeds a single string inverter. Better shade tolerance than pure string, cheaper than microinverters.

Hybrid inverter (grid-tied with battery)
Manages solar panels, battery bank and grid simultaneously. Has two MPPT inputs — one for panels, one for battery charging. When solar > load, charges battery. When solar < load or at night, discharges battery. When battery is full and solar is excess, exports to grid. Required for any system with battery storage on a grid-tied connection.

Off-grid inverter
No grid connection. Entirely self-sufficient system with battery bank. Designed for remote locations with no DISCOM supply. Sized for worst-case solar generation (monsoon months). Higher overall cost.

Inverter efficiency is the percentage of DC power coming in from the panels that successfully gets converted to usable AC power. Modern string inverters are 96–98.5% efficient. Hybrid inverters handling battery charge/discharge cycles are typically 93–97%.

What is "European efficiency" vs "peak efficiency"?
Peak efficiency is the best-case number at ideal operating conditions. European efficiency (or "weighted efficiency") accounts for the fact that inverters operate at different power levels throughout the day — early morning and late afternoon they work at partial load. This weighted number is more realistic for estimating annual generation.

Factors that reduce inverter efficiency:
- Heat (inverters should be wall-mounted in shade, not direct sun)
- Operating far below rated capacity (0.5 kW input into a 5 kW inverter)
- DC cable losses from panels to inverter (keep cable runs short, use correct gauge)
- Poor DC/AC voltage matching

CEC/EU efficiency rating is what you should compare across brands, not peak efficiency.

Inverter sizing involves choosing the right inverter capacity relative to your total panel wattage.

DC:AC ratio (clipping ratio) — It is common to "oversize" the solar array relative to the inverter. A 1.1–1.3 DC:AC ratio means you might install 6.5 kW of panels on a 5 kW inverter. Why?

Panels almost never produce their rated output simultaneously (they need perfect sunlight, cool temperature, exact orientation). Peak production happens for only a few hours. Clipping (when panel output exceeds inverter capacity) occurs briefly during ideal conditions. The economic benefit of cheaper extra panels usually outweighs the small clipping loss.

String voltage limits — Each inverter has a maximum input voltage. Panels in series add their voltages. In cold mornings, panel voltage is at its highest (Voc). The string must not exceed the inverter's maximum DC input voltage — this is a safety and equipment protection requirement, not just efficiency.

MPPT input range — Inverters have a minimum and maximum voltage range within which MPPT works. Panels in your string must keep voltage within this window across all operating temperatures.

No — for most grid-connected homes in India, a battery is not necessary and significantly increases cost and complexity. Here is the logic:

Without a battery (on-grid system): When your solar produces more than you need, the excess goes to the grid and you get a credit (net metering). At night or cloudy days, you draw from the grid normally. The grid acts as your "virtual battery."

With a battery (hybrid system): You store excess solar in the battery and use it at night or during power cuts. You pay a significant premium — batteries can add ₹1–3 lakhs to a 3 kW system cost — and they have a finite lifespan (typically 5–10 years for the battery, even if panels last 25 years).

When does a battery make sense?
- Frequent and long power cuts (grid reliability < 20 hours/day)
- Very poor or no net metering policy in your state
- High time-of-use tariff differences (cheap off-peak, expensive peak) — not yet common in India
- Remote locations without grid access (off-grid systems)
- Critical loads that cannot tolerate any outage (medical, server rooms)

Lead-acid (flooded/sealed)
Oldest technology. Cheap upfront (₹6,000–12,000/kWh). Heavy. Requires ventilation (off-gasses hydrogen). Can only use 40–50% of rated capacity (depth of discharge limit). Short cycle life (300–500 full cycles = 2–4 years of daily use). Higher maintenance. Still used in off-grid applications where upfront cost dominates.

Lithium-ion (NMC/NCA)
Used in most premium home storage products (Tesla Powerwall equivalent, Luminous NX series, etc.). 80–90% usable capacity. 2,000–4,000+ cycle life. Lighter. No maintenance. Temperature sensitive — needs thermal management. Fire risk if damaged (thermal runaway). Cost: ₹18,000–25,000/kWh installed.

LiFePO4 (Lithium Iron Phosphate)
A specific lithium chemistry. Safer (no thermal runaway risk), longer cycle life (3,000–6,000 cycles), better temperature tolerance. Slightly lower energy density (heavier per kWh). The preferred chemistry for solar storage in India's climate. Cost: ₹15,000–22,000/kWh installed. Most reputable Indian inverter brands (Luminous, Su-Kam, Okaya) now use LiFePO4 for solar batteries.

Usable capacity vs rated capacity
Always ask for usable kWh, not rated kWh. A 10 kWh lithium battery at 90% DoD gives 9 kWh usable. A 10 kWh lead-acid at 50% DoD gives only 5 kWh usable.

Capacity (kWh or Ah) — Total energy a battery can store. 1 kWh = 1,000 watt-hours. For a 48V battery bank, capacity in Ah × voltage / 1000 = kWh. A 200Ah, 48V battery = 9.6 kWh rated capacity.

Depth of Discharge (DoD) — The fraction of capacity you can safely use without damaging the battery. A 10 kWh battery with 80% DoD limit gives 8 kWh usable per cycle. Exceeding DoD regularly kills the battery prematurely.

C-rate — The rate of charge or discharge relative to capacity. A 1C rate discharges a 10 kWh battery in 1 hour (10 kW draw). A 0.5C rate discharges it in 2 hours (5 kW draw). Most home batteries are designed for 0.5C–1C continuous discharge.

- Discharging too fast (>1C) reduces effective capacity and stresses cells
- Charging too fast overheats cells
- Most BMS (Battery Management Systems) enforce safe limits automatically

State of Charge (SoC) — Current charge level as a percentage. Your inverter display typically shows SoC. 100% = fully charged. The BMS prevents charging above ~95% and discharging below ~10–20% to protect cell life.

Net metering is a billing mechanism where your DISCOM measures both what you consume from the grid and what you export to the grid, and only charges you for the net difference.

How it works physically:
1. A bi-directional or two-meter system is installed at your premises
2. When solar > load → excess power flows out to the grid, export meter records it
3. When solar < load (night, cloudy) → you draw from grid, import meter records it
4. At billing cycle end → DISCOM charges you for (imports − exports)

Settlement types:
- Net metering (true net metering): 1 unit exported = 1 unit credit at the full retail tariff. Most beneficial for the consumer.
- Net billing / feed-in tariff: Exported units credited at a separate (usually lower) "export tariff." Less beneficial than true net metering.
- Gross metering: All solar generation goes to grid at export rate; you buy all consumption at retail rate. Rare for small systems; only makes sense if export rate > retail rate.

Banking (annual adjustment): Many states allow you to "bank" credits across months. Excess credits in summer (high generation) can offset deficits in monsoon (low generation). Most states do an annual settlement, paying out remaining credits at a lower rate at year end.

On-grid (no battery) system: Your system shuts down automatically. This is required by law and grid standards.

Why? If your inverter kept feeding power into the grid during a power cut, it would create "islanding" — an energised line that DISCOM workers assume is dead. A lineworker touching that wire could be electrocuted. Anti-islanding protection is a mandatory safety feature in every grid-tied inverter sold in India (IS 16169:2014 standard).

So during a power cut:
- Panels still generate sunlight-powered DC
- Inverter detects grid loss within milliseconds, disconnects, shuts output
- Your home has no power from solar or grid
- Any backup load you have runs on battery (if you have one)

With a hybrid inverter + battery: The system detects grid loss, disconnects from the grid, and switches to island mode — powering a defined "backup loads panel" from the battery + any available solar. The switchover typically takes 20–40 milliseconds (fast enough that most electronics don't notice).

Important: On-grid-only system = zero backup during power cut. Full stop.

This is the most bureaucratic part of going solar. The process varies by state and DISCOM but follows a general pattern:

Step 1: Feasibility application
Submit a technical application to your DISCOM with your proposed system size, location, single-line diagram and contractor details. DISCOM assesses your sanctioned load (contracted capacity) and transformer/feeder capacity. Most residential systems up to 10 kW get straightforward approval.

Step 2: DISCOM approval / rejection
If approved, you receive a feasibility letter specifying conditions (capacity limits, technical standards, approved contractor categories). Do not purchase equipment or start work before this.

Step 3: Installation by approved contractor
Install per the approved design. Use Tier 1 listed panels, BIS-certified inverter, proper earthing, AC/DC protection devices, labelling.

Step 4: Inspection and commissioning
DISCOM deputes an engineer to inspect your installation. They check earthing, protection devices, labelling, and that the installed capacity matches approval. Net meter is installed at this stage (or shortly after).

Step 5: Net metering agreement
Sign a net metering agreement with the DISCOM specifying the export tariff, settlement period, and banking terms.

Step 6: Commercial operation
DISCOM activates your net meter. You are now officially a "prosumer" — both producer and consumer.

Typical timeline: 3–8 weeks in states with functional portals (Gujarat, Maharashtra); 3–6 months in states with slower processes.

Step 1: Determine your monthly consumption
Look at your last 12 months of electricity bills. Note your monthly consumption in kWh (units). Identify your peak month. Use average monthly consumption as the baseline, but size to cover your highest demand months if budget allows.

Step 2: Calculate daily consumption
Monthly units ÷ 30 = daily consumption in kWh

Step 3: Account for peak solar hours (PSH)
India averages 4–5.5 peak solar hours depending on location (Rajasthan and Gujarat get 5.5+, Northeast India gets closer to 4). PSH is the equivalent hours per day of full-intensity sunlight.

Step 4: Apply system efficiency
Panels → Inverter → Wiring → Meter introduce losses. Assume 80% overall system efficiency (0.8 derating factor).

Formula: System size (kW) = Daily kWh ÷ (PSH × 0.8)

Step 5: Apply roof constraints
1 kW of panels requires approximately 8–10 square metres of shadow-free roof area.

A Peak Sun Hour (PSH) is not simply an hour of sunshine. It is a standardised unit equivalent to 1,000 W/m² (watts of solar radiation per square metre) sustained for one hour. This is the "standard test condition" intensity used to rate solar panels.

Real sunlight intensity varies from near-zero at dawn, peaks around solar noon, then decreases. You might have 12 hours of daylight but only 4–5 PSH because most of that light is less intense than the 1,000 W/m² benchmark.

Why PSH matters for sizing:
A 1 kW panel array (rated at 1,000 W/m² STC) in a location with 5 PSH generates approximately 5 kWh per day (before efficiency losses). In a location with 4 PSH, it generates only 4 kWh/day — 20% less.

India's PSH range:
- Rajasthan / Gujarat / Kutch: 5.5–6.0 PSH (best in India)
- Andhra / Telangana / Karnataka: 5.0–5.5 PSH
- Maharashtra / Madhya Pradesh: 4.5–5.0 PSH
- West Bengal / Assam / Northeast: 3.8–4.5 PSH
- Monsoon months reduce PSH by 20–40% in most locations

Shading is one of the most critical site assessment factors and is frequently underestimated. Even 5–10% shading can cause disproportionate output loss.

Why shading is so damaging in a standard string system:
Panels in series share the same current. The cell with the least illumination becomes the "bottleneck." It is similar to a chain — the weakest link limits the whole chain. A single leaf shadow on one cell of one panel can reduce the entire string's output by 30–50%.

Bypass diodes — Modern panels have 3 bypass diodes (one per cell group of ~20 cells). When one group is shaded, the bypass diode "short-circuits" that group, letting current flow around it. This limits the loss to one-third of the panel rather than the whole string. But it does not eliminate the loss.

Partial shading from trees, chimneys, water tanks, neighbouring buildings:
- Morning shading (east side obstruction): reduces generation in first 2 hours
- Afternoon shading (west side): reduces last 2 hours
- Overhead (north side tree in south-facing installation): reduces peak noon production

Solutions:
1. Physical removal or pruning (most cost-effective)
2. Panel reorientation to avoid shading zone
3. DC optimisers or microinverters — each panel independent, shade on one panel does not affect others
4. Shade analysis software (PVsyst, SketchUp + Helioscope) during site survey — insist on this before signing any contract

Simple payback period = Net system cost ÷ Annual savings

Annual savings = Annual generation (kWh) × Your average tariff (₹/kWh) × (1 − export percentage) + Export units × Export credit rate

The formula simplifies if you self-consume most of your generation and have good net metering:

Annual savings ≈ Annual generation × Your effective tariff

Example calculation:
- System: 3 kW, cost: ₹1,80,000
- Less PM Surya Ghar CFA: ₹78,000
- Net cost: ₹1,02,000
- Annual generation: 3 kW × 4.5 PSH × 365 × 0.8 efficiency = 3,942 kWh
- Your tariff: ₹8/kWh (including fixed charges impact)
- Annual savings: 3,942 × ₹8 = ₹31,536
- Payback: ₹1,02,000 ÷ ₹31,536 = 3.2 years

After payback, every year the system generates ~₹31,000 in savings for the remaining 21+ years of its life.

Many quotes show panel + inverter cost but omit the balance-of-system (BOS) and soft costs:

Hardware BOS:
- Mounting structure (GI/aluminium) — ₹8,000–20,000/kW depending on roof type and wind zone
- DC cables (6mm², UV-resistant) — ₹800–1,500/kW
- AC cables and conduit — ₹1,000–2,000/kW
- DC MCB, surge protection, array junction box — ₹3,000–6,000
- AC protection (RCBO, main switch) — ₹2,000–4,000
- Earthing system — ₹2,000–4,000 (critical, not optional)
- Net meter — Supplied by DISCOM, often at your cost ₹3,000–8,000

Soft costs:
- Installation labour — ₹8,000–15,000/kW
- DISCOM application and processing fees — ₹500–2,000
- Electrical drawings and documentation
- Commissioning inspection facilitation
- Monitoring system (optional, ₹3,000–8,000)

Ongoing annual costs:
- Panel cleaning: ₹1,000–3,000/year (or DIY with garden hose)
- Annual O&M contract (optional): 0.5–1% of project cost
- Inverter replacement: typically needed once in 25 years (~year 10–15), cost ₹25,000–60,000

Solar systems have no moving parts and are genuinely low-maintenance. Realistic annual maintenance:

Panel cleaning (most important maintenance task)
Dust, bird droppings, leaf litter and pollution accumulate on panels and block sunlight. In India's dust-prone regions, soiling can cause 3–8% generation loss without cleaning.
- Clean every 2–4 weeks in dusty season (November–April)
- Use soft cloth or gentle water spray — do not use detergents on glass
- Morning cleaning preferred (panels are cooler, no cleaning with cold water on hot glass)
- Cost: DIY is free; professional cleaning ₹500–1,500 per visit

Inverter checks (every 6 months)
- Check for error codes or warning lights on inverter display
- Ensure cooling vents are unobstructed (inverters heat up)
- Check DC and AC cable connections for corrosion (every 1–2 years)

Annual visual inspection
- Look for panel cracks, discolouration, delamination (look from below too)
- Check mounting clamps for tightness
- Inspect earthing connections for corrosion

Monitoring — Most modern inverters have WiFi-enabled monitoring apps. Check daily generation against expected output. A sudden 20%+ drop in generation is a signal something needs attention.

Step 1: Benchmark correctly
Solar generation is not constant. Compare against the same calendar period last year, or against a design estimate for that specific month (generation is 30–40% lower in July than in March for most of India).

Step 2: Check obvious physical causes
- Panel surface dirty? Clean and re-measure
- New shading source? New tree growth, new construction, satellite dish moved?
- Panel physically damaged or cracked?

Step 3: Check inverter monitoring
- Any fault codes? (Write down the code, look it up in the inverter manual)
- Is DC input voltage in the expected range? (Should be ~350–500V for a typical string)
- Is MPPT operating? (Most inverters show MPPT tracking status)

Step 4: String-level check (with multimeter)
- On a bright day, measure DC voltage at inverter input — should be in spec
- Check each string individually if you have a multi-string inverter

Step 5: Compare with nearby PV systems or irradiance data
- Weather services (solargis, Meteotest) provide historical irradiance data
- If irradiance was 20% below average for the month, 20% lower generation is expected

When to call a technician:
- Inverter showing persistent error codes not resolved by restart
- DC voltage outside spec
- Physical damage to panels
- Generation consistently 15%+ below expectations across 2–3 clear weeks

Every solar panel has a current-voltage (I-V) curve — the relationship between the voltage the panel is operating at and the current it produces. The power (P = V × I) varies across this curve and reaches a maximum at one specific operating point: the Maximum Power Point (MPP).

The MPP shifts constantly with changing irradiance and temperature. At high irradiance, the MPP moves to higher current. At higher temperature, it moves to lower voltage. MPPT is an electronic algorithm that continuously adjusts the inverter's input impedance to keep the panels operating at their current MPP.

How MPPT algorithms work (Perturb & Observe method):
1. Every 100–1000ms, the inverter slightly adjusts the operating voltage
2. It measures whether power increased or decreased
3. If power increased → continue in that direction
4. If power decreased → reverse direction
5. Repeat continuously

More sophisticated algorithms (Incremental Conductance, hill-climbing variations) converge faster and handle partially shaded I-V curves with multiple peaks better.

Why dual MPPT inputs matter:
Hybrid inverters and some premium string inverters have two independent MPPT trackers. This allows panels on different roof orientations (east-facing and west-facing strings, for example) to be optimised independently — each operates at its own MPP simultaneously.

These four electrical parameters define how a panel behaves:

Voc (Open Circuit Voltage) — The voltage when no current is flowing (terminals disconnected). Maximum voltage the panel can produce. Important for safety: never exceed inverter maximum input voltage. Rises in cold weather. Used for string voltage calculations.

Vmp (Voltage at Maximum Power) — The operating voltage at the Maximum Power Point. This is where the panel should ideally operate for maximum output. Typically 80–85% of Voc.

Isc (Short Circuit Current) — Current when terminals are short-circuited. Maximum current the panel can produce. Important for cable and protection device sizing.

Imp (Current at Maximum Power) — Operating current at the MPP. Typically 95–97% of Isc.

Temperature coefficients — Each parameter changes with temperature. For a typical mono panel:
- Voc decreases ~0.3%/°C above 25°C
- Isc increases ~0.05%/°C above 25°C (small increase)
- Pmax (power) decreases ~0.35–0.45%/°C above 25°C

String design: In a string of N panels in series, total string Voc = N × panel Voc. At the coldest likely temperature (say 5°C in December morning in Delhi), Voc is higher than at 25°C STC. This maximum cold-morning Voc must not exceed the inverter's maximum DC input voltage.

Active power (W/kW) — The real work-doing power. What your appliances consume. What your solar produces. What your electricity meter measures in kWh.

Reactive power (VAR/kVAR) — Power that oscillates between source and inductive/capacitive loads (motors, transformers, compressors) without doing useful work. Does not appear on a standard residential energy meter but causes real current to flow in cables, increasing losses and heating.

Apparent power (VA/kVA) — The vector sum of active and reactive power. What cables and transformers must be sized to carry.

Power factor (PF) = Active power ÷ Apparent power. Ranges 0–1. Unity PF = 100% efficient use of current. A 0.8 PF means you need 25% more cable capacity to deliver the same useful power.

Why it matters for solar:
- Grid-tied inverters in India must operate at near-unity power factor (PF ≥ 0.97 per CEA standards) to avoid introducing reactive power into the grid
- Modern inverters can provide reactive power support — operating at slightly leading or lagging PF to stabilise local grid voltage
- For commercial/industrial consumers billed on kVA demand (not just kWh), solar generation that improves power factor can significantly reduce demand charges
- Low power factor from industrial loads (AC motors, welding machines) reduces the benefit of solar — fixing PF correction capacitors first often has a better ROI

Panels:
- IEC 61215 (crystalline silicon) or IEC 61646 (thin-film) — international design qualification standard
- IEC 61730 — module safety qualification
- BIS certification (IS 14286) — Bureau of Indian Standards certification, required for subsidy eligibility
- ALMM list (Approved List of Models and Manufacturers) maintained by MNRE — panels must be on this list to qualify for government subsidies and public sector projects

Inverters:
- IEC 62109-1/2 — safety of power converters for PV systems
- CEA (Technical Standards for Connectivity) 2013 — compliance required for grid connection in India
- IS 16169:2014 — Indian standard for grid-connected PV inverters, includes anti-islanding requirements
- BIS / MNRE approved inverter list — required for scheme eligibility

Installation standards:
- CEA Guidelines 2010 — for roof-top grid-connected systems
- IS 3043 — Code of practice for earthing (critical)
- IS 732 — Electrical wiring code

Ask your installer for compliance declarations for each component. Keep copies — you need them for DISCOM applications and subsidy claims.

Yes, and this is an increasingly common use case. There are two main approaches:

1. Common area solar (simplest)
Solar installed on terrace/common roof to power common area loads — lifts, corridor lighting, water pumps, garden lighting, security systems. This is straightforward and treated like a single commercial/residential consumer by the DISCOM. Savings directly reduce the society's maintenance bill.

2. Individual flat net metering (complex)
Each flat wants its own solar and net metering benefit. Complications:
- Multiple consumers sharing one distribution transformer
- Individual metering for each flat's solar generation
- Who owns the roof? Common area or individual flat?
- DISCOM capacity constraints — feeding multiple residential net meters from one premise

PM Surya Ghar for RWAs:
The scheme has specific provisions for Residential Welfare Associations. Check the official portal for the current RWA/group housing pathway — it has evolved since the scheme's 2024 launch.

Practical path for most housing societies today:
1. Start with common area solar — immediately beneficial, no flat-level complexity
2. Once running, evaluate individual flat solar based on DISCOM willingness and roof ownership clarity
3. Consult a solar aggregator who specialises in housing society projects — they handle the DISCOM paperwork

ALMM stands for Approved List of Models and Manufacturers, maintained by the Ministry of New and Renewable Energy (MNRE).

The ALMM list was created to ensure quality and prevent import of substandard or dumped solar equipment into India. It lists specific panel models and manufacturers that meet Indian quality standards (IEC certification, BIS, manufacturing norms).

Why it matters:
1. Subsidy eligibility — For PM Surya Ghar CFA and other government schemes, the panels installed must be from the ALMM list. Installing non-listed panels means your subsidy claim will be rejected.
2. Government / PSU projects — All government solar installations must use ALMM-listed panels by policy.
3. Private installations — Technically no legal requirement for ALMM in private, non-subsidised installations, but quality assurance benefit remains.

How to use ALMM:
- The list is available on the MNRE website
- Search by manufacturer name to verify a specific model
- The list is updated periodically — always check before purchasing
- Your installer should confirm ALMM compliance — get it in writing in the purchase order

Important: The ALMM list also applies to certain inverter specifications for government schemes. The MNRE has been expanding ALMM coverage to include balance-of-system components.