Friday, May 1, 2015

Net metering in Solar Systems; On Grid and Off Grid system in Solar Power

What is Net Metering?
Net metering is the concept  used in Solar Power where discoms will allow Individuals and corporate's to feed power generated from Solar or any means to their grid . A net metering meter will be installed by Power distribution company(DISCOM) which measures power fed to grid and accordingly consumer will be charged or paid back. Alternatively, the meter, having the feature of recording both the import and export values.

Solar PV Power Generation:
Sunlight is converted to electricity directly when made to fall on solar photovoltaic (SPV) modules. This electricity generated is used for lighting and various other purposes. 

Grid connected roof top solar PV system: 
In recent years solar PV systems became viable and attractive.  Available roof-top area on the buildings can also be used for setting up solar PV power plants which will leads to no expenses for land requirements for solar panels installations.

The electricity generated from SPV systems can also be fed to the distribution or transmission grid after conditioning to suit grid integration. There are two types of configurations available for connecting the solar power generated from the system.
(1) On grid
(2) Off grid

In On grid System power generated from solar panels is directly synchronized with existing power source of discom in such a way that solar power generated get consumed in systems and power cost get reduced by power generated by solar system. let's simplify the same with an example:- Suppose there is plant having Three phase 100 KW power requirements now the plant installed 5 KW three phase Solar power panels now in On grid system power generated from solar system is directly get reduced from total power requirement means there will be 95 KW requirement from DISCOM and user have to pay for 95 KW instead of 100 KW. This type of activity is most popularly used worldwide.

Now lets discuss Off Grid system. In off grid power generated from Solar panels is stored in batteries and later on used whenever there is requirement. e.g. in morning power is stored in Batteries and later on this stored power is used for lighting and other purposes by taking the help of Inverters.

Usually On grid System is most preferred as there is no requirement of Batteries . Also efficiency of On grid system is more then Off grid system.

How does it work?
Based on available roof area solar PV panels will be installed on the roof of the building. The output of the panels (DC electricity) connect to the power conditioning unit / inverter which converts DC to AC. The inverter output will be connected to the control panel or distribution board of the building to utilise the power. The inverter synchronises with grid and also with any backup power source to produce smooth power to power the loads with preference of consuming solar power first. If the solar power is more than the load requirement, the excess power is automatically fed to the grid. For larger capacity systems connection through step up transformer and switch yard may be required to feed the power to grid. Operation and Maintenance Requirements: There are no moving parts in the system and it requires only minimal attention. Depending upon the dust level, the system requires periodic cleaning.


The grid connected roof top solar PV system would fulfil the partial / full power needs of large scale buildings. The following are some of the benefits of roof top SPV systems:
· Generation of environmentally clean energy.
· Consumer becomes generator for his own electricity requirements.
· Reduction in electricity consumption from the grid.
 · Reduction in diesel consumption wherever DG backup is provided.
· Feeding excess power to the grid.
a) Implementation of net metering facility shall be made applicable for the consumers having 3-phase supply service connection.
b) Protection system including its switch gear has to be certified by concerned DE/MRT Operation. Further, harmonic suppressive device has to be installed by such SPV generator to suppress the harmonics injection as harmonics is more in case of solar plants where conversion of DC to AC is taking place (Islanding protection requirements are enclosed).
c) The SPV generator shall provide the indication of solar PV plant at the injection point for easy identification to the operating personnel.
d) The SPV generator needs to get statutory approvals from appropriate authority (CEIG) for the connected equipment including its solar panels.
e) The proposed generator shall submit the prescribed application to the concerned DE/Opn.
f) The net meter / meter to be used for arriving net energy shall have the specifications prescribed.
g) Concerned DE/Opn and DE/MRT will issue a technical feasibility certificate and witness the synchronization of SPV plant with distribution network.
h) 0.2 class accuracy, tri-vector based energy meter, non ABT having the MRI downloading facility along with related accessories shall have to be installed by the SPV generator as per the specifications of APTRANSCO/APDISCOMS.

Alternatively, DISCOM may provide the metering arrangement after receiving entire estimated cost from such generator.
i) SPV generator needs to provide an insurance coverage of Rs.5.00 lakhs per annum to meet the expenditure that may be aroused due to electrocution in the event of failure of connected protective and switch gear.

 j) Spot billing is to be arranged by concerned ADE/Opn as per the billing period. DISCOM shall arrange to develop suitable software and incorporate in the billing instrument for such billing.