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How does Off-Grid & On-Grid System work

Solar power solutions are typically classified as On-Grid and Off-Grid.  The on-grid solution is connected to the Electricity Grid, so that the Load requirement can be fulfilled even during the Cloudy days.  And also, if there is excess of energy generated, then same may be deposited to Electricity Grid for later use.  The off-grid system can not deposit electricity.  Any of these power solutions can be implemented either as Capex or Opex.

 

Solar power plants are increasingly gaining popularity across a wide range of industrial, commercial and residential sectors due to relatively lower cost of investments and lesser complexities involved in setting up a plant. Several favorable government initiatives like tax benefits, subsidies and net metering policies are giving rise to a demand for rooftop solar projects in India.  With the support of these elements, power solutions for Rooftop Segment is also very successful and economical - Plant installations under ₹ 50,000* per KW within 30 days.

Typically 1 KWp of plant requires about 10 Sq Mt area.  Such power can then be used, either for captive consumption of the premises or can be fed into the grid and be adjusted in the electricity bill. Net metering regulations notified by respective State Electricity Regulatory Commissions (SERCs) provide a legal framework for such adjustment.

1) How does On-Grid Solar Plant work !

When sunlight falls on solar panels, they generate DC electricity. This electricity goes to Grid-Tie Inverter (GTI) where it gets converted into usable AC Electricity.  AC then enters the main power supply of the building, and powers all connected electrical load.

The On-Grid System is connected to the Electricity Grid, so that the Load requirement can be fulfilled even during day.  And also, if there is excess of energy generated, then same may be deposited to Electricity Grid for later use.

Another important thing that the grid-tie inverter does is to regulate the charge. The PV cells may make excessive DC but all that DC can’t be fed into your main supply as it may be too much to handle. Inverter regulates the voltage of DC that it gives to the main supply.

This system is designed for areas where power supply is always available most of the Day Time, or goes for 1-2 hours only.  Grid-Tie system is particularly good for establishments that function during the day, such as Schools and Offices, because they operate during the sunshine hours. They can generate and use all the electricity they need with grid-tie solar.

 

There are three major components of grid-tie solar installation: solar Panels, grid-tie solar Inverter and Net-Meter.

 

What happens to grid-tie solar system when it is cloudy/rainy ?

In the absence of sun, the solar panels won’t generate the quantity of power that you may need and that is why it is connected to the grid.  Remember, it is called grid-tie solar system for a reason. It will then work by taking from grid so that you enjoy non-stop power no matter what how it is like outside.

 

How Grid-tie Solar System Saves You Money ?

 

When PV solar panels are generating DC, and inverter is feeding to the main supply after converting it into AC, you are saving money because you are taking absolutely NOTHING from the grid.  You can literally see your electricity meter stop when there is sun.  As electricity keeps getting expensive, you are likely to recover the entire cost of solar system in just 3 years, as you are not paying much to the electricity company.

How Does the Net-Metering & Gross Metering process work !

Under net metering, electricity generated by the Solar Rooftop System is first utilized by the consumer to meet their internal/captive requirements. Excess electricity, if any, is exported to the grid. Subsequently, when the consumer imports power from the grid, the exports are adjusted against the imports, lowering the electricity bill.

 

A net meter (bi-directional meter) records the energy imported from the grid to meet the load and surplus energy exported to the grid after self-consumption. Both energy import and export are recorded in the net meter. The difference between export and import readings is the actual energy consumed/delivered.

Method of Billing Under Net Metering : The energy generated from Solar Rooftop System shall be adjusted against the consumption of energy from the DISCOM by an eligible developer/consumer every month. In case of groups/societies, the energy generated shall be prorated as per the installed capacity share indicated in the Agreement between the group/society and DISCOM. This computed energy share shall be adjusted against the consumption of energy for each consumer every month.

 

In case of excess generation (after energy adjustment) injected into DISCOM network in a billing month will be carried forward to the next month till every quarter end and settlement will take place on an Average Cost of Supply (ACOS) basis for net metering as determined by APERC from time to time

In case of Gross Metering, there are two different meters, one for Exporting the electricity, which is called as Gross Meter.  And, another meter is the usual meter which is generally not replaced.  So, when solar is installed under ross metering, then all the solar output is exported into Grid, irrespective of captive need.  The captive need is fulfilled by Grid, not by Solar.

2) How does Off-Grid Solar Plant work !

Unlinke, Grid Tie system where Power Backup is done in Grid, the Off-Grid System stores Electrical Power into the Battery Bank.

Stand-alone (or off the grid) PV systems are intended to operate independent of the electric utility. Since PV panels do not store energy and can generate electricity only during daylight hours, for continuous power flow they need to generate excess of the energy which has to be stored somewhere. Normally, this extra energy is accumulated in the batteries.  

 

If the off grid home has no other power source, both the PV array and the battery bank have to be significantly oversized by design to account for possibly several days of inclement weather. To reduce the size of the panels and the battery bank, solar systems for off-grid homes are often supplemented with wind turbines that can produce electricity at night and during cloudy periods. Fuel-powered electric gensets are also often used as an another auxiliary energy source that simplifies the isolated system's sizing.

3) How does Hybrid Solar Plant work !

Grid Interactive Rooftop SPV system with battery back up
 

In this configuration when the grid is available, consumer loads are fed from grid as well as from solar system with a priority to solar PV system.

SPV also feeds to the grid in case of surplus generation.

Battery and inverter cum charger are also present in the arrangement. The DC generated from solar is first converted to AC and then it is supplied to other equipment/grid.

When grid fails, automatic disconnection from the grid side takes place and solar gets connected to battery system and AC consumer load.