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About half the incoming solar energy is absorbed by water and land; the rest is reradiated back into space. Earth continuously receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by the atmosphere, oceans and land masses.

First used in about 1890, the word has two parts: photo, derived from the Greek word for light, and volt, relating to electricity pioneer Alessandro Volta. So, photovoltaics could literally be translated as light-electricity. And that’s what photovoltaic (PV) materials and devices do — they convert light energy into electrical energy (Photoelectric Effect), as discovered by renowned physicist Albert Einstein

PV rooftop is PV Module placed on top of roofs of commercial, Industrial, institutional, PV farm or residential buildings. They capture the light energy emitted by the sun and convert it into electrical energy. This setup is also known as PV rooftop system.

PV System can be broadly divided in to the following three categories

1. Stand Alone (off Grid) PV System
2. Grid Connected (On Grid) PV System
3. Hybrid System.

Stand alone (Off grid) system means the PV system does not connected to the utility grid and therefore requires energy storage system. This is appealing because you are 100% self-sustaining your energy use. An off-grid system is ideal for locations where grid connections are not accessible, such as cottages and remote home locations, or for anyone craving greater energy independence
However, there are disadvantages because off-grid systems require you to purchase backup battery which can be expensive, bulky, and not very environmentally friendly which defeats the purpose of going solar.

Grid Connected PV System is an electricity generating power plant that is connected to the local utility grid. It is designed to produce more power than the consumer uses during day. The surpluspower fed to the utility grid. This is what 95% residential homes will use because utility grid works as an energy storage system and it is possible through the net metering system.
If you are producing surplus energy with PV system, the excess energy is store in the grid in the form of Electrical unit (kWH) allowing you to build credit that you can cash out at the end of the fiscal year.

Being grid tide is beneficial because you don’t need to buy an expensive battery backup system to store any excess energy. They typically benefits 15 or more years of profits on grid connected PV system.

Pros of a Grid Connected PV System

• Zero Electricity Bill
• Maintenance free
• Passive income generation

Cons of a Grid Connected PV System

• Your grid Connected PV system will automatically shut off when the grid goes down, and will also automatically turn back on when power is restored.
• You’re not completely independent from the grid

Hybrid systems combine both the concept of off grid and on grid together for an easy “plug and play” solution. The goal with hybrid systems is to help reduce your peak energy consumption during the day. With more utilities shifting to an on demand pricing framework (means you pay more when energy is in higher demand), the cost efficiency of solar + batteries starts to make sense.

The amount of electricity generated by a rooftop solar PV plant depends on the location, orientation of the roof, panel efficiency, and ambient temperature.

As a rule of thumb, a 1 kWp plant will generate about 4 kWh (units) of electricity a day on average in a year

There are two methods for calculating needed kw system.

1st Method From the Electricity bill Amount

Check the electricity bill amount and as thumb rules divided it with 6 Rs.
whatever amount will come again it is dived by 60 because in residential electricity bill have 2 months then again divided by 4 because as our system will generate 4 unit per kW.

Example
Customer bill is 7000/-rs
7000/6 (Rs) = 1166.66 units for 60 days
1166.66/60 (Days) = 19.44 units per day
19.44/4 (Thumb Rule Unit) = 4.86 kw system need.
So we can suggest 5 kw to the customer

2nd Method From the Electrical Unit Consumption

From the electricity bill you can take units which is printed on the electricity bill.

Three row are appear for six months units

Apr – May = 1296
June – July = 1204
Aug – Sept. = 998
Total of above unit is 3498

Now get the average of above unit
3498/3 = 1166
1166 units for 60 days
1166/60 = 19.43 units per day

Now as thumb rules 1 kwp system will generate 4 units

19.43/4 = 4.85 kW system need
So we can suggest 5 kw to the customer

The area required by a rooftop PV plant depends on the extent of shade-free space available and solar panel efficiency. A solar PV system typically requires 100 (70) square feet (about 10 (7) sq.m) of shade free roof area per kW of capacity at current crystalline panel efficiency levels.

Example

If i need to install a 5 kw system then according to thumb rules I need a 500 (350) square feet shadow free area or 50 (35) sq meter shadow free area.

On grid rooftop solar plants can not generate power during a power failure.

There are various solar policies that incentives on rooftop solar in India.

Central Government or MNRE gives a subsidy on total capital cost.Subsidy criteria are up to 10 kW only above 10 kW there is no provision for subsidy.

For residential in Gujarat

• 1 to 3 kW -40% subsidy
• 3 to 10 kW 20 % subsidy
• For group housing society or common meter have 20 % flat subsidy
  Net meter – Surplus power – Grid – 2.25 per Unit Incentive

A rooftop solar PV system primarily comprises of Solar PV Modules (panels), Inverters, Cables, DCDB, ACDB, Isolation Switch, Earthing rod, Lighting arrester, Chemical bag, Plaster Bag, Conduit PVC Pipe and Mounting Structures. From Discom side they will provide Bidirectional meter and solar meter.

A PV module is an assembly of photo-voltaic cells mounted in a framework for
installation. Photo-voltaic cells use sunlight as a source of energy and generate direct current electricity.

A PV inverter is a device that converts variable Direct Current (DC) power output of a photovoltaic (PV) module Power into alternating current (AC) Power at desire output voltage and frequency.

It is control the dc power from PV module and having necessary surge protection devices to protect PV module string and PV inverter from any type of damage.

It receives AC Power from PV Inverter and directs it to AC Loads through distribution board. ACDB includes necessary surge protection device and circuit breaker , LED lights and terminal to protect PV Inverter from any type of damage and heavy voltage.

The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of low resistance wire is known as the electrical earthing.
The electrical earthing is done by connecting the non-current carrying part of the equipment or neutral of supply system to the ground.

The device which is used for the protection of the equipment at the PV
Power Plant against travelling waves, such type of device is called
lightning arrester or surge diverter.
Lightning arrester diverts the abnormals high voltage to the ground
without affecting the continuity of supply.

In India principally there are two major Business Model

1. Capex Model – capital expenditures are provided by the rooftop owner
2. Resco Model – capital expenditures are covered by third party

Capex Model

CAPEX mode is the most common business model for solar deployment in India. In this model the consumer purchases the solar system, by making 100% of the payment upfront or financing the system, often through a bank.

Resco Model

Under this model, a RESCO developer finances, installs, operates and maintains therooftop solar power plant. The developer signs an agreement with the rooftop owner .The rooftop owners may consume the electricity generated, for which they have to pay apre-decided tariff to RESCO developer on a monthly basis for the tenure of the agreement.
Based on the consumption choice and requirement, the model is further divided into two types – Rooftop Leasing and Power Purchase Agreement (PPA).

• Latest Electricity Bill
• Latest Property Tax bill/Index-2/sell deed
• Aadhar Card
• Customer Passport Size Photo
• Pan Card
• Customer Mobile Number
• Capacity of Solar rooftop system

• Purchase Order
• Latest Electricity Bill
• Customer Passport Size Photo
• Feasibility letter on letter head of organization
• Authorization Letter
• Pan card of Authorized Person
• Aadhar Card of Authorization Person
• Registration of organization letter (GST, MSME, Udhoygaadhar)
• Pan Card of Organization
• MOM /AOA/Partnership deed of organization
• Pollution related certificate
• Back power information