Net Metering arrangements for Roof top Solar PV Systems

Most of the Indian cities, towns and villages have nearly 250 to 300 days of sunny days and thus roof top solar PV system can be a very attractive option. The Jawaharlal Nehru National Solar Mission (JNNSM) with the goal to encourage roof top solar PV systems in India has implemented a separate scheme known as “Roof top PV and Small Scale Solar Generation Program”. 

In my opinion, Roof top solar PV systems are going to witness appreciable capacity expansion particularly on the residential and commercial buildings in India and can be seen as a significant business opportunity.

Types and Models of Roof top PV systems:

The roof top solar PV system can be:
1. A grid interactive system or,
2. A stand-alone system. 

In grid interactive system, the DC power produced is converted to AC power, and after due conditioning this power is fed to the captive loads of the premise. The excess power is injected to the utility grid through 11 kV or LT lines, depending on the size of the solar PV system. When sufficient solar PV power is not available, the loads are fed from the grid supply. 

Although the grid interactive solar PV system is not supposed to have a battery pack, but to enhance the reliability a minimum battery backup of 1 hour is technically recommended. There is some minimum capacity constraints ( 1 kWp) below which the system can not be grid interactive.    

In the stand-alone Roof top Solar PV system, the electrical energy produced by the solar modules are fed to the battery bank through a charge controller. A suitable inverter is connected to the battery which converts the DC output of the battery (or the Solar PV) into AC of specified voltage and frequency to run the electrical appliances of the premises. This system is not connected to the utility grid and hence excess electrical energy produced by the solar PV cannot be exported to the grid and similarly if extra energy, in excess of solar PV output, is required cannot be imported from the utility mains. Thus, such a system requires fine balancing of generation, demand and storage capacity.  

Different arrangements of Roof top solar PV system:

Two different arrangements of Roof top solar PV system do exist. They are:

1.      Self owned roof top solar PV system, and

2.      Third party owned roof top solar PV system.

In the self owned arrangement, the roof top owner or the premise owner installs the solar PV system, either of its own or with the aid of a system supplier. The power produced is first used to feed the captive loads within the premise and the excess power is fed to the grid.

The third party roof top solar PV system can be an attractive and viable model particularly for residential sector in India and seems to be a good business and job provider. In this model a developer or intermediate agency called the “third party” design, install and lease out the solar PV system to interested roof top owners who in turn pay them a monthly rent. 

This model offers some great advantages; 
(i) the roof top owner does not have to invest for the PV system, and
(ii) does not have to bear the brunt of the technological risks involved in a fast changing solar PV business.

Net Metering arrangement:

In both the above mentioned roof top solar PV models, the feeding of excess energy to the grid or the drawal from the grid in case of insufficient solar power generation is through a net metering arrangement. 

Two meters have to be installed at the premise and will replace the existing meter. One, the solar energy meter to record the energy produced by the PV system and other the net meter, a bi-directional meter, to record the import/export of energy by the consumer from/to grid. The point of solar power injection may be in between the load and the bi-directional meter. These meters are supposed to have the MRI and AMR facility and should adhere to the standards specified by the CEA regulations. Figure 1 shows a net meter installed for a 2 kW grid tie Roof Top Solar PV system in Bhopal, India.

Fig. 1: A Net Meter installed for a 2 kW Grid-tie Roof Top Solar PV system in Bhopal, India.

The net energy (kWh) injected to the grid during a billing month/period is supposed to be carried forward. At the end of the financial year any net energy credits which is yet not adjusted is paid to the owner of the premise/consumer by the distribution company. To promote the scheme, certain states have waived off the wheeling charge, cross subsidy surcharge and other similar charges/levy for a period of 5 years.  

If the cost of solar energy and the grid energy is kept the same, there may not be any significant financial benefit to the residential consumers, although the commercial consumer paying at a much higher grid tariff may get benefited. To get more, the residential premise owners have to install a much larger PV system. 

Policy on roof top solar PV systems of certain states in India has put a cap on the solar generation which is about 90 % of the annual energy drawal. In the net metered solar PV arrangement the roof top owner  can also avail the available subsidy (currently 30 %) from the Ministry of new and Renewable Energy (MNRE) for which he or she has to approach the state nodal agency.

Under-estimated small Off-grid Roof top solar PV systems to be re-examined

The utility scale solar PV projects have grown up significantly in India over the last 5 years. Focus is shifting on roof top (RT) solar PV systems, as is evident in the Jawaharlal Nehru National Solar Mission (JNNSM). Under the mission 40,000 MW of RT solar PV systems are to be installed by 2022.  In the light of falling prices of solar PV modules, both off-grid as well as grid connected roof top solar PV systems seem to be a viable and workable solution in addressing nation’s energy and environmental issues.

Potential of Roof Top Solar PV systems:

As per the 2011 census, over 140 million houses in India has proper roof top spaces that can accommodate up-to 3 kW of solar PV system. I am talking of residential houses not about the commercial buildings, shopping malls, educational institutions etc. RT solar PV systems can be vital in rural areas. Even a 300 W roof top Solar PV system on each of these 140 million houses will tremendously add to the Renewable Energy portfolio. 

Issues with Grid connected Solar PV systems, which are yet to be streamlined:

Looking into the extent of execution of solar PV systems in India, the weightage seems to be primarily on the grid connected RT solar PV systems, particularly on the government establishments and buildings. The rising electricity tariff has already given RT solar PV the much required niche and made it viable even without the support of any subsidy. 

Lack of clarity  on rules and regulations, technical and safety issues, power quality, metering and bill related issues pose tiresome proposition to both utility and owners of grid connected RT solar PV system. This is true particularly in the state of Madhya Pradesh, where the net metering has just started. Even the Discom officials are unaware of the procedures. Apart from that a grid connected RT solar PV system needs the approval of two government bodies i.e. the Urja Vikas Nigam and the related Distribution Company to get it installed; which as we know a time consuming and tiring exercise.

Potentials of Small scale Off-grid solar PV system needs to be Re-evaluated:

Small scale off-grid solar PV system is seen as underdog. In my opinion, such PV system has a huge potential in this country, provided the awareness is created. A properly worked out small RT off-grid solar PV system on affordable initial capital may lead to better utilization of unused roof top space. These RT solar PV systems can be seen as a sustainable remedy to frequent power cuts and peak power shortage. It’s better to promote small off-grid solar PV systems of say 200-300 W on every possible roof top. It hardly needs 25 square feet of space and can be arranged in a variety of fashion (refer fig1).

Fig.1: Small scale Off-grid Roof top Solar PV system of 300 W

Such small off-grid solar PV systems are capable of energizing the essential light and fans, TV and computer requirement of a three room house. The initial cost is also affordable, say around 40,000 INR with battery back-up, even less than 25,000 INR when an existing battery-inverter set is converted into a solar PV-battery-inverter system. There is no need to go for cheap popular gimmick as subsidy etc, provided the common mass is made aware. Such small solar PV systems are easy to install, and budget friendly.

Even a 20-25% of the residential energy requirements is fulfilled by these small but effective RT solar PV systems, it may be seen as a boon. A solar PV system is more worthy if the self-consumption is about 50% or more. The same energy can be routed to industries or commercial establishments and that too at a better tariff.