Four rooftop solar facts
- Silicon panels make DC electricity from daylight without a motor or mechanical drive.
- The inverter changes DC into grid-synchronised 230 V or 415 V AC for your building.
- A bi-directional meter records grid imports separately from surplus solar exports.
- Around southern Andhra Pradesh, 1 kW may average 4 to 4.5 units a day or 1,400 to 1,600 units a year, with roughly 80 to 100 sq ft of clear roof.
Your electricity bill reflects everything running in the house, from fans and the refrigerator to a summer air conditioner or water pump. A panel on the roof can cover part of that daytime demand. To judge whether the investment suits you, it helps to know where its electricity goes, what happens after sunset and what the meter records.
A standard grid-connected home system needs no large battery bank. The panels generate while there is light, and the grid supplies any shortfall. When generation exceeds the power being used at home, approved net metering records the export. The equipment is quiet, but its wiring, mounting and protection still need careful design.
This guide follows power from the silicon cell to your distribution board. It also explains the roof checks, daily generation pattern, meter readings and safety devices you should see in an installer proposal. Use those points to ask clear questions before agreeing to a system size.
The five parts of a rooftop system
Think of rooftop solar as five connected parts, each with a specific job. Panels make DC electricity. A structure holds them in a safe position. An inverter supplies AC power. Switchgear and cables protect and connect the circuits. A bi-directional meter accounts for power exchanged with the DISCOM.
1. Panels that make DC power
A photovoltaic module contains many connected silicon cells under protective glass. Incoming light releases charge carriers in the cells, producing direct current, or DC, without a motor or moving mechanism. Most current Indian proposals use Mono PERC or newer TOPCon modules. Compare the exact module's rating, dimensions and warranty rather than choosing by colour alone.
2. Frames that hold the array
Panels need a frame that secures them above the roof and leaves room for drainage and maintenance. Hot-dip galvanised iron or anodised aluminium are common materials. A south-facing layout in southern India often uses a tilt near 10° to 15°, adjusted for the roof. The structural design should account for local monsoon winds up to 150 km/h and protect terrace waterproofing at every fixing.
3. The inverter
Panels deliver DC, while most household loads use 230 V single-phase or 415 V three-phase AC. The inverter converts between them and follows the local grid's 50 Hz frequency, voltage and phase. Ask which inverter is specified, where it will be mounted and whether its input range suits the proposed panel strings.
4. Distribution boxes and cables
The DC distribution box, or DCDB, includes devices such as DC fuses and surge protection. The AC distribution box, or ACDB, contains breakers and AC surge protection before the supply reaches your main board. UV-resistant, double-insulated solar cable links the array and equipment. Cable routing, isolation labels and sound terminations deserve as much attention as panel wattage.
5. The import and export meter
Your DISCOM supplies and seals the bi-directional meter; APSPDCL is one example in southern Andhra Pradesh. It replaces a one-way meter and keeps separate readings for electricity imported from the grid and solar electricity exported to it. The billing treatment follows the applicable net-metering approval and tariff rules.
Service life: Silicon modules and string inverters have few moving parts, though some inverters use cooling fans. The panels quoted here have a 12-year product warranty and 30-year performance warranty. Keep the product certificate and installation record so you can claim the appropriate cover if a fault develops.
From daylight to electricity in your home
Follow one portion of daylight through the system. Each stage has a different task, and none can be skipped safely. This sequence also shows why a solar array can serve a load immediately, export extra power at noon and draw from the grid after dark.
Step 1: Light reaches silicon
Light arrives as photons and passes through the panel's anti-reflective glass. When a photon transfers enough energy in the silicon junction, it frees an electron. The resulting movement of charge is the photovoltaic effect. Cloudy light can still trigger it, although the available power is lower than under clear direct sun.
Step 2: Cell current enters the string
Fine metal busbars on each cell collect current and connect it into a circuit. Cells connected in series form a module, and several modules in series form a string. This raises the string's DC voltage to several hundred volts. The installer must select the panel count so that voltage remains inside the inverter's safe input range in local weather.
Step 3: The inverter prepares AC
Protected solar cable carries the string output to the inverter. Maximum Power Point Tracking, or MPPT, shifts the electrical operating point as light and cell temperature change. The inverter then makes AC at the grid's voltage, frequency and phase. Its datasheet and string design should be checked together, especially where parts of the roof face different directions.
Step 4: Your board supplies active loads
The inverter feeds AC into your main distribution board, the MCB box. Appliances already running in the home use the available local generation first, with the grid providing the balance. The system does not require you to switch a fan or refrigerator manually between sources during normal grid operation.
Step 5: Surplus exports or grid power enters
At noon, suppose a 3 kW plant is producing 2.8 kW and your home is using 800 W. Around 2.0 kW is then available for export through the meter. If two air conditioners lift demand to 3.5 kW while solar still supplies 2.8 kW, about 700 W comes from the grid. These are instant power examples; your bill records accumulated energy in kWh.
How net metering records your units
Net metering is important when your home uses less power than the panels make during the day. An approved bi-directional meter records that extra energy instead of requiring a battery to hold it. Later imports can be offset under the applicable billing rules. Check how your DISCOM treats carried-forward units, fixed charges and any settlement period.
After grid connection approval, the DISCOM replaces the ordinary meter with one that measures power in both directions. Look for separate import and export registers on the meter or bill. The difference is useful, but it is not the entire bill because fixed and other applicable charges can remain.
- Imported units: Power drawn from the DISCOM at night, under cloud or when appliances need more than solar provides.
- Exported units: Daytime surplus sent from your installation to the grid.
- Net billable units: The billing-cycle difference is
Total Import - Total Export, subject to current tariff rules and fixed charges.
If a month's reading shows 400 imported units and 350 exported units, the net energy is 50 units. You pay for those net units plus applicable fixed charges. If exports exceed imports, the surplus may be carried forward as credit for later monsoon or winter bills according to the current DISCOM rules. Ask your installer to show a sample bill for your tariff category.
For the process and tariff details, see our residential on-grid solar guidance. If you are comparing a normal grid-connected installation with battery options, the on-grid, off-grid and hybrid comparison explains what each one does during a cut.
Sanctioned load: Grid-connected capacity is generally limited by the sanctioned electrical load and local approval. If your bill shows a 2 kW load but your proposal is for 3 kW solar, ask the DISCOM about load enhancement before installation. Confirm the current rule for your connection and do not treat a sales drawing as permission to connect.
What generation looks like through the day
An array follows the sun rather than producing one fixed amount all day. Light angle, cloud, dust and panel temperature shape a daily curve. The periods below are a practical illustration for a southern Indian roof, not a guaranteed hour-by-hour forecast. A site model should also account for seasonal changes and local shade.
6:00 AM to 9:00 AM: Output begins
Soon after dawn, low-angle light reaches the cells. The inverter begins work once string voltage crosses its start threshold, commonly around 80 V to 120 V DC on the example equipment. Output rises gradually. It may cover small steady loads such as a refrigerator and standby devices before larger daytime demand begins.
9:00 AM to 1:00 PM: Strongest light
From about 9:00 AM to 1:00 PM, stronger sunlight can reach roughly 800 to 1,000 W/m² of irradiance. In the example, a 3 kW array may produce about 2.4 kW to 2.8 kW at a good moment. This is a useful time to run washing machines, borewell pumps or an electric water heater, subject to the load rating and available generation.
1:00 PM to 4:30 PM: Afternoon output
Between 1:00 PM and 4:30 PM, light can remain strong even as the terrace air reaches 40°C to 45°C. Hotter cells produce less voltage, so output may ease from the peak. Generation can still offset afternoon cooling loads. The actual pattern depends on roof ventilation, shade and the weather that day.
4:30 PM to 6:30 PM: Output falls
From roughly 4:30 PM to 6:30 PM, the lowering sun reduces generation. Grid imports rise as the inverter output falls. At dusk, a normal on-grid inverter shuts down and the home uses grid electricity. A battery-equipped hybrid system can instead draw on stored energy for designated backup loads.
Roof space, shade and system size
Before fixing a capacity, an engineer should inspect the roof and your consumption. The survey needs to cover structural strength, usable shade-free area and the path of the sun. It should also leave safe access to tanks, drains and the equipment. A neat panel arrangement on paper is only useful if it can be maintained on the real roof.
1. Map the shade
A tank, parapet, stair room or tree can shade part of a string. Because series-connected panels share current, a shaded section can limit the whole string's output. Map shadows from about 9:00 AM to 4:00 PM and consider how their positions change through all seasons of the year. Separate MPPT inputs or a changed layout may reduce the loss.
2. Estimate clear roof area
High-wattage monocrystalline modules around 540 Wp to 590 Wp need roughly 80 to 100 sq ft of shade-free roof per kW once access and spacing are allowed. Use the following rough examples to check a quotation. The final layout depends on panel dimensions, setbacks and obstacles; the unit figures are annual-average daily estimates, not daily promises.
- 2 kW: Allow about 160 to 200 sq ft and an annual-average 8 to 9 units per day.
- 3 kW: Allow about 240 to 300 sq ft and an annual-average 12 to 13.5 units per day.
- 5 kW: Allow about 400 to 500 sq ft and an annual-average 20 to 22.5 units per day.
- 10 kW: Allow about 800 to 1,000 sq ft and an annual-average 40 to 45 units per day.
3. Check direction and tilt
At this northern-hemisphere location, a south-facing array often collects strong annual sunlight. An initial tilt estimate for Tirupati, Srikalahasti and nearby districts is around 13° to 15°, close to local latitude. Your roof shape, row spacing and shade may justify another angle. Ask the engineer to show the orientation on the layout and explain any deviation.
Generation rule of thumb: In this part of Andhra Pradesh, allow roughly 4 to 4.5 units per kW per day averaged across the year, or about 1,400 to 1,600 units per kW annually. Actual output depends on shade, weather, equipment and cleaning. Compare the estimate with your last twelve months of use before sizing the plant.
Electrical protection on your roof
Solar equipment carries DC voltage on the roof and AC voltage near the building's main board. A safe installation needs suitable earthing, surge protection and a grid-disconnection function. Ask for a single-line diagram and protection list. The commissioning team should test and label the circuits before handing the system over.
Separate earthing paths
The example installation provides three separate earthing paths using suitable pits and conductive compound. They serve the module frame and DC side, the inverter and AC side, and the lightning protection system. The exact design must follow the approved site drawings and local conditions, including soil and roof construction.
- DC path: Earth the metal module frames and mounting structure.
- AC path: Earth the inverter enclosure and AC distribution box.
- Lightning path: Connect the roof-mounted Franklin arrester to its dedicated earth so a strike has a route to ground.
Automatic shutdown on grid loss
During a grid blackout or maintenance shutdown, DISCOM technicians may be working on street cables. A normal on-grid inverter must stop feeding those lines. Its anti-islanding protection detects the missing grid and disconnects, with example certified equipment specified to shut down within 20 milliseconds. It does not keep ordinary home sockets alive merely because sunlight remains on the panels.
A factory or commercial roof may need additional protection and load checks. Our commercial solar information and manufacturing plant guide cover the larger-site questions. Ask for protection coordination and an approved electrical drawing alongside the generation estimate.
Components, lifespans and cover
Use the component list below to read quotations line by line. It identifies the electrical job, example technology, possible service life and warranty associated with each item. These are different measures: an expected lifespan is not the same as a written product or performance guarantee. Request model numbers and certificates for everything supplied.
| Equipment | Job in the system | Example specification | Planning lifespan | Written cover |
|---|---|---|---|---|
| PV modules | Make DC electricity when daylight reaches the silicon | Mono PERC or TOPCon; DCR model for subsidy | 30 years or more | 12-year product and 30-year performance |
| Solar inverter | Convert DC to 230 V or 415 V AC and track panel output | Pure sine-wave grid-tied string unit | About 12 to 15 years | 8 to 10 years by model |
| Mounting frame | Hold panels above the roof at the designed south-facing tilt | Hot-dip galvanised iron, 80+ microns, or aluminium | 30 years or more | Example structural cover of 10 to 15 years |
| DCDB and ACDB | Isolate circuits and limit surge or short-circuit damage | Type II surge devices, DC fuses and rated MCBs | About 15 to 20 years | Example product cover of 2 to 5 years |
| Bi-directional meter | Measure imported and exported units for billing | DISCOM-approved DLMS smart meter | 15 years or more | Cover follows the utility terms |
| Optional lithium battery | Store power for night use or isolated backup loads | Lithium iron phosphate, LiFePO4 | About 10 to 15 years | 10-year battery product warranty |
PM Surya Ghar support for homes
The Ministry of New and Renewable Energy supports eligible home installations through PM Surya Ghar: Muft Bijli Yojana. The published scheme implementation period runs through 31 March 2027, with applications through the national portal at pmsuryaghar.gov.in. Approval, product compliance and your own eligibility still have to be checked before you budget for assistance.
For a qualifying residential system, the current central assistance slabs are:
- 1 kW: Indicative assistance of ₹30,000 for an eligible home.
- 2 kW: Indicative assistance of ₹60,000 for an eligible home.
- 3 kW and above: Assistance is capped at ₹78,000 for an eligible home system.
The home system needs compliant DCR modules on the applicable ALMM list and installation through a registered vendor. Commercial and industrial customers do not receive this residential subsidy. Businesses may be able to use accelerated depreciation at 40% of written down value under section 33 of the Income-tax Act, 2025, with half the rate if used for less than 180 days in the purchase year. Confirm the current rate and your eligibility with your chartered accountant.
Policy check: Subsidy figures are indicative, and scheme, DISCOM and net-metering rules can change. Confirm eligibility, sanctioned load and the current process for your address during a site audit and on the official portal. Ray2Volt does not give tax or investment advice.
Common questions about rooftop solar
Do panels produce electricity on cloudy or rainy days?
Yes. Cells can use diffuse daylight that passes through clouds, so a monsoon day still produces some power. An example range is about 25% to 40% of clear-sky peak output, but cloud thickness and time of day vary greatly. On an on-grid system, the DISCOM supplies any shortfall.
What can a 3 kW system generate in Andhra Pradesh?
Use the local annual-average rule of roughly 4 to 4.5 units per kW per day. A 3 kW system therefore gives an indicative 12 to 13.5 units a day, or about 4,200 to 4,800 units a year. The actual daily reading changes with weather, shade and cleaning. A site audit should refine the estimate for your roof.
Will a normal rooftop system run through a power cut?
A standard on-grid system stops when the grid fails because anti-islanding protection prevents power reaching utility workers on the lines. If you need selected lights, fans or other loads during a cut, specify a hybrid inverter with a compatible battery and isolated backup circuit. Ask which loads the backup can carry and for how long.
How much clear roof does a home system need?
Allow around 80 to 100 sq ft of clear roof per kW for modern Mono PERC or TOPCon modules. On that rule, 3 kW needs roughly 240 to 300 sq ft. Keep space for access and check tank, parapet and tree shade at different times before treating the full terrace area as usable.
Which warranties cover a residential installation?
The panel cover quoted here is 12 years for product faults and 30 years for performance. Inverter product cover is 8 to 10 years depending on model. A lithium-ion battery carries 10 years of product cover, and Ray2Volt includes 5 years of free service on workmanship and balance of system. Read each certificate for its claim terms.
Ray2Volt Solar Private Limited
We design, install, and service rooftop solar for homes and businesses across Tirupati district and Andhra Pradesh, from PM Surya Ghar residential systems to commercial and industrial plants. Every enquiry starts with a free power audit.
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Ray2Volt can inspect your roof and bills, estimate generation and help with an eligible PM Surya Ghar application. Start with a free power audit.
