Virtual net-metering under Delhi Solar Policy

To give access to the solar net metering facility for consumers who do not have a suitable roof for installing a solar system (e.g. residential consumers who live in apartments, consumers with shaded rooftops) there will be the facility of Virtual Net Metering. In Virtual Net Metering consumers can be beneficial owners of a part of a collectively owned solar system. All energy produced by a collectively owned solar system will be fed into the grid through an energy meter and the exported energy as recorded by that meter will be pro rata credited in the electricity bill of each participating consumer on the basis of beneficial ownership.

Collective ownership of solar plants may be established through societies, trusts or section 25 Companies or any other legal entity that safeguards the interests of participating consumers, including rights which are at par with the rights enjoyed by consumers who have solar net metering with a solar system installed on their own roof.

The State government shall work with DERC to approve and announce Virtual Net Metering for all consumers no later than 1 April 2017.

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Group net-metering under Delhi Solar Policy

To encourage solar plants on rooftops of buildings that cannot consume all of the energy generated locally, DISCOMS shall facilitate Group Net Metering, whereby surplus energy

exported to the grid from a solar plant in excess of 100 percent of imported energy at the location of the solar plant can be adjusted in any other (one or more) electricity service connection(s) of the consumer within the NCT of Delhi, provided these connections are in the same DISCOM territory. The purpose of this provision is to help maximize the utilization of rooftop space for solar energy generation for consumers with multiple buildings and service connections. At this time, Group Net Metering has been approved for all government buildings.

The State government shall work with DERC to approve and announce Group Net Metering for non-­‐government consumers, and remove the restriction on DISCOM territory for all consumers, no later than 1 April 2017. Until then, commercial/industrial and domestic consumers who wish to avail of Group Net Metering must make a written request to DERC, which shall review such requests in a timely manner on a case-­‐by-­‐case basis.

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Installation targets for rooftop solar in Delhi – 2,000MW by 2025

By August 2015, Delhi had installed 7 MW of rooftop solar capacity. To achieve its solar power generation targets, this Policy mandates solar installations—to be completed within 5 years— on all government-­‐owned rooftops. Since pricing parity hasn’t been achieved as yet in the domestic segment, except at the high end, solar adoption will be encouraged via a limited time generation-­‐based incentive.

This Policy has set aggressive, yet achievable, targets over the next ten years, outlined below. The State shall strive to achieve the objectives of the Policy and aim at implementing minimum targets, elaborated below, within the Operative Period:

Fiscal year New Solar Energy (MW) Cumulative Solar Energy (MW) Annual Growth (%) Percentage of peak grid load *1 Percentage of total electricity consumption *2
FY 16 30 35 700% 1% 0.15%
FY 17 84 119 240% 2% 0.56%
FY 18 193 312 162% 5% 1.43%
FY 19 294 606 94% 9% 2.66%
FY 20 385 991 63% 14% 4.16%
FY 21 285 1275 29% 17% 5.10%
FY 22 228 1503 18% 19% 5.73%
FY 23 187 1690 12% 20% 6.14%
FY 24 161 1850 10% 21% 6.40%
FY 25 145 1995 8% 21% 6.57%

*1 Based on 6 GW peak load in 2015 and a growth assumption of 5% per annum.

*2 Based on actual energy units consumed in Delhi (27,266 MU) in 2014-­‐15 and a growth assumption of 5% per annum.

 

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Nodal agency for rooftop solar in Delhi

Energy Efficiency and Renewable Energy Management Centre (EE&REM) is a sub-­‐division of the Department of Power, GNCTD, which shall act as the State Nodal Agency (SNA) for the purposes mentioned in this Policy and shall be responsible for the effective implementation of this Policy in consultation with the State Government, eligible consumers and entities, the Central Government, other States and other stakeholders.

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Technical challenges in grid-integration and net-metering in Delhi

Voltage fluctuation and imbalance

The solar energy generated by a PV system is dependent on the availability of sunlight. Power generated can vary drastically throughout the day, sometimes within seconds, because of, for example, cloud-cover and weather changes. This causes rapid voltage fluctuations that can hamper devices linked to the transmission network and can, in some cases, overheat and even melt the power lines. Inverters can be designed to regulate PV system voltage and provide for communication between the grid operator and the PV inverters. Such communication can allow for improved control of voltage fluctuations in the entire grid.

Further, voltage fluctuations can take place due to the improper functioning of an inverter and can be problematic if these fluctuations move outside specified values. Excessive under-voltage can cause “brownouts” characterized by the dimming of lights and inability to power some equipment. Excessive over-voltage can damage and decrease the life of electronic equipment. To avoid such scenarios, voltage fluctuations need to stay within specific limits[1], beyond which the PV system is required to automatically disconnect from the grid.

Transmission of unwanted current into the grid

The current in the grid which is supplied for end-use is alternating current (AC). The current generated by the solar PV system is direct current (DC). This is stored into the battery system (if there is one), also in DC, and then converted into AC by the PV inverter, which in turn is either fed into the grid or consumed. There is a possibility that the PV inverter passes unwanted DC current into the AC driven network of the grid, which can lead to overheating of distribution power transformers, power losses or damages. This injection of DC power into the grid can be avoided by using an isolation transformer at the output of the inverter. An isolation transformer would block transmission of DC signals from one circuit to the other, but allow AC signals to pass. Coupled with an isolation transformer, inverters are able to feed electricity into the grid with a maximum permissible DC component of 1% in the AC current.

Electrical disturbance caused by non-linear loads

Electrical disturbance (the permanent modification of the voltage and current sinusoidal wave shapes), generating harmonics, is created by the presence of non-linear[2] components in an electrical system. Harmonics in the power grid can overload equipment, interfere with telephone circuits and broadcasting and lead to metering errors. Typically, total voltage harmonic distortion, individual harmonic distortion and total current harmonic distortion produced by a PV system should not be allowed to exceed 5%, 3% and 8% respectively, such that electrical disturbances do not affect the quality of power in the grid.

Unintentional islanding

Unintentional islanding occurs when a solar PV system continues to supply electricity to the grid in the event of a larger grid failure. This can cause safety issues for technicians and the general public as a power line that might be considered off is, in fact, still powered. Unintentional islanding is a well-known problem and, therefore, most inverters now possess anti-islanding features whereby PV systems are automatically disconnected from the grid in the event of a power outage. In addition to that, a manual disconnect switch could also be provided in the PV system to isolate the grid connection. Despite these measures, unintentional islanding remains a particular concern when PV and other systems without anti-islanding features, such as diesel generators, are connected to the same line section. These machines may mimic normal grid conditions, causing the PV inverters to stay online and create unintentional islanding. At the moment, there are no finalized solutions to this problem.

Reverse power flow and voltage fluctuations

High levels of PV penetration may cause reverse power flow. Reverse power flow occurs when in the case of weak or/and long networks, voltage rises when consumption at the consumer’s end is low and the power fed into the grid by the PV system is high. In such a case, voltage increase may cause the electricity to change direction and flow through the transformer to the higher voltage. This is can lead to heating up of the distribution transformer and transmission lines. Another problem can arise when the power generated by the large number PV systems reduces at once due to the inherent intermittent nature of solar. This sudden reduction in power can destabilize the grid.

[1] For step changes (which may occur repetitively) the limit stated by CEA is 1.5 %.[1] For occasional fluctuations other than step changes the maximum permissible limit is 3%. Further, the voltage imbalance or maximum deviation from phase voltage at 33kV and is not allowed to exceed 3%

[2] Linear loads are electrical loads where the voltage and current waveforms are sinusoidal. The current at any time is proportional to the voltage. Non-linear loads are electrical loads where current is not proportional to voltage. The nature of non-linear loads is to generate “harmonics” or distortion in the current waveform. Non-linear loads include computers or refrigerators.

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How rooftop solar works in Delhi?

This section deals with the overview of a solar PV system, working of a PV system, different components, their sizing and connections. Further, we have analysed relevance of storage in PV systems, the importance of net metering and the typical PV system sizes across different consumer segments.

Functioning of a PV system

A solar PV power plant converts sunlight into electricity. It does so without any moving parts (unless it has a tracking system) and without generating either noise or pollution. A solar PV system can be installed at any un-shaded location such as on rooftops of buildings, car parking sheds, empty land, or even on top of canals and roads. Typical system sizes range from 240 watts to 100 MW. There is very little difference in the technical design between small kW-sized plants (typically de-centralized, off-grid) and large, MW-sized plants (typically centralized, grid-connected). Solar plants can easily be scaled using independent, modular components such as PV modules, inverters and batteries. The rooftops of buildings would be ideal for the installation of solar PV in Delhi because of the high cost of land in the city. A typical rooftop solar PV system for a household is between 1-10kW. For larger buildings, such as offices or malls, it can reach 100 kW or more. Given Delhi’s average irradiation of 5-5.5 kWh/m2/day, a kW of installed solar PV can generate 4-4.5 kWh of power during daylight hours, equivalent to the amount of power needed for a refrigerator to run for a day.

A solar PV system consists of the following key components

  1. Solar PV array (group of modules)
  2. Solar inverter
  3. Battery
  4. Interconnecting devices (junction box, cables, distribution box)

The PV array consists of solar modules interconnected with each other. The modules convert the energy from sunlight, are held on structures made of galvanized iron, mild steel or aluminum and are inclined at a horizontal tilt, facing either south or east-west.

The modules are designed to generate current at either 12 or 24 volt. Inverter models can differ in their input voltage requirements in the range of 12 to 1,000 volt. A junction box connects the modules in series or parallel to achieve the optimum voltage required by the inverter.

Solar modules produce direct current (DC). Almost all electrical appliances in India, however, require alternating current (AC) to operate. The function of converting DC to AC is carried out by the inverter. In the case of a battery backup system, the inverter is also connected to the batteries and is responsible for managing the charging and discharging of the batteries.

The output point of the inverter is connected to the distribution box, which consists of a meter, fuse, a miniature circuit breaker (MCB), and load connections. Cables connect the solar modules, junction boxes, inverters and distribution boxes.

The capacity of the solar PV system depends on the amount of electricity (kWh) required per day by a consumer and the shadow and obstruction free space available on the rooftop. For example, a 2 kWp load operating for 10 hours requires a PV system of 5 kWp [1]. Further, 1 kWp of solar PV requires 10 sq. meters of shadow free area. Therefore, a 5 kWp system would require 50 sq. m. In addition, if the consumption occurs during non-sunshine hours (6:00 pm to 6:00 am) or in case the consumption is not uniformly sufficient throughout the day[2], batteries to store energy might be added.

Another factor, which affects the system design, is the timing of electricity consumption. For example, residential consumers in Delhi have a peak demand during the morning (6:00 am – 10:00 am) and evening (6:00 pm – 10:00 pm). These are not peak sunshine hours (10:00 am – 4:00 pm). Residential demand tends to be lower during the day as household members become engaged in daily activities, mostly outside the house (e.g. adults going to work and children going to school). Thus, the peak power production of a PV system does not match the peak demand of residential consumers in Delhi. For industrial and commercial consumers, on the other hand, solar generation coincides more closely with peak demand as most of these sites operate through the day.

Solar PV systems could be sized to not exceed the load demand during the day. If they are larger, and solar power is being generated that exceeds consumption at that point in time, wastage can be avoided by storing the excess power. Alternatively, excess power could be injected into the grid. In this case, metering would be required to measure energy transactions between the PV system and the grid. As shown in the graph above , 40% solar generation will be unused if there is no net metering.

Rooftop solar PV with storage

Storage in solar PV systems is required to provide stable backup power when the solar energy is not available (at night) or not adequate to meet the entire load demand. Solar energy is an intermittent source of power. The power generation can vary with a change in sunshine due to, for example, a sudden cloud cover. Batteries can be used to store solar power to safeguard against a short-term fall in solar power generation. Intermittency can also be avoided by connected the solar PV system to the grid. In this case the grid provides the extra energy at times of inadequate sunshine.

Another application of storage is to protect against grid outages. During an outage it is possible that solar generation is inadequate to meet the load demand (e.g. if it occurs outside sunshine hours). In such a case, the stored energy can be utilized to provide a stable output of power. If the grid condition is good and power outages are rare, batteries would probably be avoided as they add significantly to the system cost, adding 25%.[4] Batteries also need to be replaced every three to five years.[5] Since Delhi does not experience long power cuts, batteries need not be an essential part of the PV system. Storage might, however, be an attractive option for Delhi’s DISCOMs as it can be utilized to offset expensive peak load power[6].

Rooftop solar PV with net metering

There are two common ways in which owners of kW-scale rooftop solar PV plants can be compensated for feeding electricity into the grid: FiTs and net metering. For FiTs, solar power generated and fed into the grid is measured through a separate meter and then given a price (the FiT) through which the owner is compensated for the electricity generated. The advantage is, that the price for solar power and the amount of solar power generated can be determined independently. This method is useful where either the cost of solar power far exceeds the cost of grid power and/or where the generation of solar power far exceeds the on-site consumption needs. A risk is the potential for fraud through channeling non-solar power through the solar meter and thus inflating the amount of power for which the – usually high – solar FiT is paid. A household-level FiT is offered in, for example, Germany.

Under net metering, on the other hand, conventional electricity and solar electricity are traded at the same tariff. The billing in this case is based on the net energy imported (energy consumed minus energy generated and fed into the grid). In case more energy is generated than consumed, the utility can adjust the excess in a future billing period (this would be akin to “banking” the power), rather than giving a monetary compensation, as in the case of FiTs. However, over the long term, the amount of solar power that can be generated and monetized through net metering will be limited by the amount of power consumed, where, at most, the consumer can feed as much power back into the grid as he draws from the grid so that the electricity bill is “zero”. Net metering is popular in, for example, the USA and Japan

The Central Electricity Agency (CEA) has initiated steps to set standards and guidelines for the integration of solar PV systems in to the grid. A report on grid connectivity of solar PV is under formulation at the CEA. A draft is to be shared with the public for comments by end-June. The CEA’s move is based on its acknowledgement that decentralized solar PV can play a key role in bridging the country’s energy deficit and is set to take off now. During our interactions with senior officials at the CEA, we were told that “solar PV is the future for this country, and we have to make sure that there are standards and guidelines in place to support its integration with the grid”. Various metering arrangements covering grid interaction of a PV system with battery, without battery, with different load battery back-ups, with different load DG back-ups, and with DG and battery back-up combinations, have been laid down in the draft report. Delhi’s Electricity Regulatory Commission[8] (DERC) though has the final authority to determine the metering arrangements that would be applicable in the city.

Rooftop solar PV system sizes

Commercial consumers in Delhi (type-1, type-2 and privately owned public and semi-public facilities) such as malls and office complexes have an average load requirement above 1 MW. But due to the presence of cooling towers, air conditioning units, ventilating shafts, boilers and tanks, limited rooftop space is available for solar. As per our analysis on rooftop potential in Chapter 1 of this report, type-1 consumers accounting for 25% of the total built commercial area include buildings such as office complexes and malls that have an average area upwards of 10,000 sq. meters. These buildings offer a solar suitable roof space of 20%, which is upwards of 2,000 sq. meters. This space can typically accommodate PV systems of sizes exceeding 200 kWp. Type 2 buildings, which account for 75% of the total built commercial area comprise of buildings that have an average size ranging from 4,000 sq. meters to 8,000 sq. meters. The solar suitable space offered by these buildings is 30% that amounts to solar suitable space ranging from 1,200 to 2,400 sq. meters. Type 2 buildings can typically accommodate a PV system ranging from 100-200 kWp. Privately owned facilities that account for 30% of the built area of public and semi-public facilities comprise of private hospitals and educational institutes. These buildings typically have a size upwards of 6,000 sq. meters, offering a solar suitable space of 40% or upwards of 2,400 sq. meters. This can accommodate PV systems of sizes exceeding 200 kWp.

Industrial consumers have fewer obstructions as compared to commercial rooftops. As per our analysis in Chapter 1 of this report, industrial consumers have 40% of roof space available for solar. The solar suitable space for type-1 buildings ranges from 120-1,200 sq. meters which can typically accommodate PV systems of sizes ranging from 10-100 kWp. Type-2 consumers are bigger industrial buildings that have an average area ranging from 3,000 sq. meters to 6,000 sq. meters. The solar suitable area of these buildings ranges from 1,200 sq. meters to 2,400 sq. meters that can typically accommodate PV system of sizes ranging from 100-200 kWp.

Residential consumers of category B, C and D have an average of 50 sq. meters shadow free space available for solar[9]. This is adequate for a solar PV system of 5 kWp. Category A on the other hand has 120 sq. meters available for solar. This is adequate for a solar PV system of 12 kWp.

Government buildings such as courts and office complexes have an average rooftop area of 6,000 sq. meters. The solar suitable space available on them is assumed to be 40% of the built area. This translates to 2,400 sq. meters, which can accommodate PV system of 200 kWp. Government owned public and semi-public facilities like hospitals and educational institutions also have an average building size of 6,000 sq. meters. The solar suitable space for all public and semi-public buildings is assumed to be 40%. The solar suitable roof space offered by such buildings is 2,400 sq. meters that can accommodate a solar system size of 200 kWp.

[1] The size of a solar PV system is usually higher than the operational load as solar has an average Capacity Utilization Factor (CUF) of 18% as compared to 80% for coal power plants. 1 kW of solar gives 4 kWhs at a CUF of 18%. So, For 20 kWhs of power, we would need a system of 5 kW.

[2] If loads have no fixed time of operation or might be operational over a couple of hours. For example there can be a 10 kW load being powered for just 2 hours a day. This would require a system of 5 kWp. A 5 kWp system cannot generate enough electricity to power a 10 kWp load at any time of the day; Hence we require batteries that store energy

[3] Energy consumption data mapped – based on a residential house with a load of connected load of10 kW and operating load of maximum 5 kW. Solar irradiation data of 02.08.2011, source NREL. Solar system size – 5 kWp

[4] 5 kWp system with battery costs INR 750,000 (115,384, USD 150,000) as compared to INR 600,000 (EUR 92,307 USD 120,000) for a non battery backup system. Storage has been calculated for 2.5 kW load for 7 hours.

[5] Refer to the section on “The Viability of Rooftop Solar PV” for further details

[6] Refer to section “Why solar makes sense for DISCOMS” for details.

[7] Source: Gujarat Energy Development Agency (GEDA)

[8] DERC regulates the operation of the power system and sets standards for the electricity industry (standards related to quality, continuity and reliability of service) in the NCT of Delhi.

[9] Refer to annexure for category wise details

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Computation for rooftop solar potential for government buildings in Delhi

This land area type includes areas belonging to the President’s Estate, the Parliament House, government courts (High Court, Supreme Court and the District Courts), integrated government office complexes and land allocated for undetermined government use. In our analysis, we considered unoccupied government land as built-up land based on an understanding that the city of Delhi will eventually be entirely built. Government buildings are commonly concrete structures with average plot sizes upwards of 6,000 sq. meters, which qualifies them for the analysis.

According to the DDA Master Plan 2021, all government buildings are subject to similar development controls hence we have used the cumulative land area figures provided by the DDA plans. The total land area designated for government use is around 47 sq. km[1] and 80% of the area i.e. 37.71 is assumed to be plotted for development. The total built area/rooftop area available for solar power installations is 30%[2]of the plotted land area, which is 11.3 sq. km. We further discount 10% of the area for structures that might be old and unable to bear the weight of solar installations. Thus, the total qualified rooftop is 10 sq. km. The solar suitable rooftop space offered by government buildings is assumed to be around 40%, which is fairly larger than other land area types, considering their rooftop space is commonly free from elevator shafts and cooling towers. Structurally these buildings are simple with very little shadowing.This amounts to a solar suitable rooftop space of to 4 sq. km.

Public and semi-public facilities

Public and semi-public facilities include hospitals, education/research universities, colleges, social and cultural complexes, sports complexes, stadiums, police stations/headquarters, fire stations, disaster management centers, religious buildings, burial grounds and crematoriums. Such buildings qualified for our analysis as most facilities included in this category are large, well-built structures. In addition to that, government bodies administer many of these buildings and the government can play a direct role in ensuring that these facilities install rooftop solar installations.

We have used the cumulative figures provided by the DDA for this land area type because there are more than 200 of these facilities, which are very widely distributed across Delhi, and are hence immeasurable. Further, the development controls for such facilities are almost similar and hence cumulative figures can be used to derive near accurate estimates.

The total land area designated for public and semi-public facilities is around 81 sq. km[3]. Of this, 40% is discounted for trees, roads and other open spaces giving a plot areas of 48.81 sq. km. Of the plots, 30 % is built[4] giving a total built area/raw rooftop area of 14.64 sq. km. After discounting for unsuitable public facilities such as burial grounds, dairy farms, and religious buildings[5], the total built area for public and semi-public facilities is 13 sq. km. We further discount 10% of the area for structures that might be old and unable to bear the weight of solar installations (these include police stations and fire stations). This gives a qualified rooftop potential of around 11.86 sq. km.

Public and semi-public facilities can be government owned or privately owned. Accordingly, they pay different prices for electricity and their viability for solar differs[6]. We assume[7] that 70% of the facilities are government owned while 30% are private based on the fact that most public and semi-public buildings facilities are government aided. The qualified rooftop space is 8 sq. km for government owned facilities and 3 sq. km for privately owned facilities. Based on our analysis through Google Maps and site visits, the solar suitable rooftop space on all public facilities is around 40%. This takes into consideration that rooftops of most public facilities are occupied by water heating systems (mandatory as per government regulations), cooling towers and elevator shafts. Thus, solar suitable rooftop space is a total 4 sq. km: 3 sq. km for government owned and 1 sq. km for privately owned facilities.

Transport buildings

This land area type includes areas covered by airports, bus terminals/depots, railway stations, metro stations and transport movement infrastructure like train tracks. Train tracks have been excluded from the analysis. Metro stations also fall outside the purview of our analysis as these buildings are mostly made of metallic roof sheeting rather than concrete structures and thus are unfit to bear the weight of solar installations. Bus depots are large open areas for buses to be able to park and do not have any covered, concrete structures. Railway stations and airports are the only two sub heads that qualified for analysis.

Transportation facilities in Delhi that qualify for analysis are airports and railway stations. These are limited in number hence we used online mapping tools to measure their areas. These facilities occupy large stretches of land for movement, such as runways, railway platforms and parking, but possess only limited built area, which mainly comprises of ticketing and boarding areas. The total built area/raw rooftop area under this land area type is around 0.16 sq. km that offers a solar suitable roof top space of 0.032 sq. km. The solar suitable roof area is assumed to be 20 % of the total raw rooftop area as most transport facilities have roof sheeting and the little concrete space left is occupied by support services such as cooling towers, shafts and monitoring units.

[1] As per the Zonal Plans developed by the Delhi Development Authority

[2] 30% ground coverage is permissible for the government integrated office complexes and courts as per the DDA Master Plan 2021

[3] As per the Zonal Plans developed by the Delhi Development Authority

[4] 30% coverage rate is applicable to Public and semi public facilities as per the Delhi Master Plan 2021

[5] Discounting factor for irrelevant sub categories is assumed to be 10% as per Bridge to India analysis. These buuldings have been discounted as they have very little buitl space and a solar installation may not be really wanted by them

[6] Refer to Chapter 6 on “The viability of rooftop solar PV” for details

[7] Rough assumption is based on the knowledge that within certain categories – e.g. hospitals – there are more government buildings and than private buildings (from Eicher Delhi map)

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Computation of industrial solar potential in Delhi

The industrial area of Delhi mainly comprises of textile manufacturing units, electrical machinery manufacturing units and units that offer repair services. This area is characterized by robust concrete buildings and big plot sizes, making rooftops well qualified to bear the size and weight of solar installations.

For data related to this land area type, we used cumulative figures provided by DDA zonal plans because in industrial areas the building structures and their development controls are fairly homogenous. The total land area in Delhi that is designated for Industrial use is around 47 sq. km.[1] Out of this area, 60%[2] of the area is authorized for Industrial plot development is around 28 sq. km. The built area/ raw rooftop area available for solar rooftop installations is around 50%[3] of the total area available for plot development, which gives around 14 sq. km. We discount 10% of the area for structures that might be old and unable to bear the weight of solar installations. Our analysis further discounts 10% for mini-micro and very large industrial buildings (that fall under <10kW and >200kW tariff group). Mini-micro industries have been excluded, as they are too small to accommodate the size of solar installations that could meet their power needs. The number of large industries on the other hand is very small and hence such buildings are chosen to be kept out of the analysis. The total qualified rooftop area after discounts is 11.3 sq. km.

Industrial buildings can be categorized into two types, those with 10-100 kW of electricity consumption that we will call type-1 and those with 100-200 kW of electricity consumption that we will call type-2. The two types of consumers pay different electricity prices which can impact the financial suitability of solar power for them[4].

We roughly assume that 50% of the buildings are type-1 and 50% are type-2 consumers due to lack of information, but assuming that higher number of small industrial buildings will offset the smaller number of large-sized industrial buildings. The qualified rooftop area available for type-1 and type-2 consumers is 5.6 sq. km for each type.

Based on our analysis of samples[5] through Google Maps and site visits, plot sizes in industrial areas commonly exceed 400 sq. meters, with roof space occupied by boilers, cooling units and shafts. None the less, there is significant unoccupied/unobstructed rooftop space sufficient for solar rooftop installations. Accommodating for such obstructions, the solar suitable rooftop space for both type-1 and type-2 consumers is around 40% of their respective qualified rooftop area (6.3 sq. km each). This gives solar suitable rooftop space of 2.26 sq. km for type-1 and type-2 consumers each, or a total of 4.5 sq. km for industrial consumers. Some of the key industrial areas in Delhi are Okhla Industrial area, Badli Industrial area and Wazirpur Industrial area.

[1] As per the Zonal plans developed by the Delhi Development Authority

[2] As per Industry Zone Guidelines in the Delhi Master Plan 2021

[3] As per the developmental controls specified in the Master Plan 2021, 50 % is the ground coverage rate pertains to plot sizes of more than 400 sq. meters. Our analysis assumes that on an average, plot sizes in industrial areas exceed 400 sq. meters

[4] Refer to Chapter 6 “The viability of rooftop solar PV” for details

[5] Samples included industrial buildings in Wazirpur, Badli and Naraina industrial area.

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Computation of commercial solar potential in Delhi

This land area type includes retail shopping centers, commercial centers, wholesale markets, warehouses, oil depots and cold storages. Standalone convenience stores that are integrated into the residential areas are included in the land area type ‘Residential’.

To determine the solar suitable rooftop space offered by commercial buildings we have used cumulative figures provided by the DDA Zonal Plans for reasons similar to that of public and semi-public facilities. The development controls for this land area type are different for different sub heads. Ground coverage rate is 25% for district centers, community centers and city centers, 30% for hotels and 40% for local shopping centers as per the development controls in the Delhi Master Plan 2021. Average ground coverage rate taken for the analysis is 30% as a reasonable number. The total land area designated for commercial use is around 45.59 sq. km[1], which offers a built area/rooftop area of around 13.6 sq. km. We assume that 10% of this area belongs to small-sized shops and commercial buildings. Such buildings have an area less than 400 sq meters and offer very little solar suitable roof space (less than 15%). In addition to that, the structures of these buildings are typically weak. These small buildings are hence discounted from our analysis, as they will not be able to accommodate the size or bear the weight of the solar installations[2]. We further discount 10% for old commercial buildings from the remaining area of commercial buildings to get the total qualified rooftop area of 11 sq. km for our analysis.

After discounting, commercial consumers are classified into two types: those with an electricity consumption of 100-200 kW that we will call type-1 consumers and those with a consumption greater than 200 kW that we will call type-2 consumers. Type-1 and type-2 consumers pay different tariffs, which impacts the financial suitability of solar power for them[3].

Type-1 consumers (medium-sized) account for 75% of the qualified rooftop area i.e. 8.2. sq km. They include buildings such as commercial complexes and shopping areas that have an average area ranging from 2,000-4,000 sq m. Type-2 consumers (large-sized), which account for 25% of the total built area i.e. 2.7 sq. km, comprise of buildings such as shopping malls and hotels that have an average size upwards of 4,000 sq meters. Thus, the total qualified rooftop area for commercial consumers is 11 sq. km.

As per our analysis of commercial buildings using Google Maps, their rooftops are cluttered with cooling towers, ventilating shafts and water heating systems and tanks, reducing the solar suitable roof space. Type-1 consumers have solar suitable rooftop space that is 30% of their qualified rooftop area (8 sq. km) giving a total of 2.4 sq. km. Type-2 consumers have solar suitable rooftop space that is 20% of their qualified rooftop area (2.7 sq. km) giving a total of 0.6 sq. km. Thus, the total solar suitable rooftop space for commercial consumers is 3 sq. km. The % of solar suitable space for commercial consumers has been determined after analyzing sample commercial areas such as Promenade Mall and Nehru place. The solar suitable area is smaller for larger than medium-sized commercial buildings because these larger buildings tend to have an unsuitable architecture or elevated structures ,such as domes and glass panels.

[1] As per the Zonal Plans developed by the Delhi Development Authority

[2] The 400 sq m cut off for small commercial buildings is double the cut off point for residential buildings 200 sq m as rooftops of commercial buildings are typically more cluttered (e.g. with cooling towers) than the rooftops of residences.

[3] Refer to chapter 6 “Viability for commercial consumers” for further details

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Computation of rooftop solar potential in Delhi

The residential area in Delhi is heterogeneous in nature and reflects the city’s rapid, often uncontrolled growth. There are different types of buildings, ranging from individual houses, apartments, residential complexes, unauthorized colonies, Jhugi Jhompri (JJ) clusters[1] to slums. Further, these housing settlements have different socio-economic characteristics and development controls. The cumulative figure of the residential area, provided by the DDA, does not include qualitative information about the constituent housing structures and occupants. However, such information is essential to understand the suitability for solar in different residential colonies/areas. Thus, rather than using the land area figures provided by the DDA, we use a bottom up approach in order to analyze this land area type in detail. Using Google Maps, we first determined the area measurements of individual colonies that qualified for solar rooftop installations. Colonies that had sufficient solar suitable rooftop space, concrete constructions and occupants that could afford solar installation were qualified for analysis. We then summed up the individual figures to reach the total land area for the residences.

While pursuing the bottom-up approach, we found that information about the entire residential area in the city was available in three sections (as per the municipality governing the areas) – Residential colonies under the jurisdiction of the Municipal Corporation of Delhi (MCD), residential area under the jurisdiction of the New Delhi Municipal Council (NDMC) and residential area maintained by the Delhi Cantonment Board (Delhi Cantt.). The colonies under the MCD are categorized from A to H, as per the circle rate [2] applicable to each colony. Circle rates are indicative of the economic standing of the colonies, which further provides a sense of the income level of the occupants, the quality of constructions, the type of housing and the average plot sizes. We excluded low income colonies as they are unsuitable for solar installations[3]. This categorization provided us with tangible figures and a comprehensive list of colonies to work with. For residential areas under the NDMC, we have used cumulative figures from the DDA zonal plans. This is because the NDMC area largely has government owned colonies that have large rooftops, similar rooftop structures, with no ownership rights for the occupants. In the case of the residential colonies under the Delhi Cantonment area too we have considered all the colonies as they are government owned and have the same characteristics as colonies in the NDMC area. For these colonies, we have mapped and analyzed all of them using online mapping tools because the area of the cantonment is relatively small and hence measurable. The bottom-up approach enabled us to understand the residential area in Delhi with a fair amount of accuracy in order to reach a representative figure for the solar suitable rooftop space available in Delhi’s residences. We have assumed that 20% of the total area can be discounted for having old rooftops, unable to support solar installations. This discount factor is higher than what we have considered for other categories (20% vs. 10%) because we assume that a larger proportion of residential buildings are on average older than buildings in the other categories. After this, the solar suitable rooftop space for Delhi’s residences was assumed to be around 20% of the total rooftop area. This is because water tanks, ventilating shafts, drying clothes and storage units occupy most of the area on a residential rooftop leaving limited unoccupied/unobstructed space.

Table A2: Solar suitable areas by jurisdictions

Residential areas as per municipalities governing them Total built area/raw rooftop area (sq. km) Total qualified area after 20% discount for old rooftops (sq. km) Solar suitable roof top area

(sq. km)

Area under the MCD 79.2 63.32 12.6
Area under the NDMC 8.6 6.9 1.4
Area under the Delhi Cant. 5.3 4.3 0.85
TOTAL 93.1 74.5 14.90

 

Residential colonies under the jurisdiction of the MCD:

Colony category Average plot size (Sq. m) Solar suitable area available Income level Principal type of housing Quality of Qualification
          Construction  
A 900 180 High Individual houses Good
B 400 80 Medium to high Individual houses and apartments Good
C 200-600 40-120 Low to medium Individual houses and apartments Average
D 250 50 Low to medium Residential complexes, apartments and individual houses Average
E 100-250 20-50 Low to medium Individual houses and apartments Low
F 150 30 Low Individual houses and apartments Poor
G 100 20 Low Individual houses and apartments Poor
H 50-100 10 -20 Low Individual houses and apartments

 

The total residential area under the jurisdiction of the MCD is classified into 8 categories, A to H. The basis for such classification is the circle rate applicable to each colony, where colonies under category A have the maximum circle rate and those under category G have the minimum circle rate. This categorization indicates the economic standings of the colonies. The economic standing further provides a sense of the income level of the occupants, the quality of constructions, the type of housing and the average size of plots. For example, a colony in category A, such as Sunder Nagar, would commonly have rich inhabitants that live in large-sized individual bungalows. We have used this categorization as a framework to assess the suitability of colonies to instate rooftop solar power installations.

In the analysis, we have considered 10 sample colonies from each category to determine the income levels of occupants, quality of constructions, type of housing and average size of pots. After analyzing these factors, we selected categories that indicate the suitability to install solar rooftop PV. Then, using Google Maps, we mapped these sample colonies to determine the average area of a colony in a particular category. The average area was further used to compute the total raw rooftop area/ built area available for solar in a particular category. The solar suitable rooftop space was then computed as 20% of the total rooftop area.

Table A3: Assessment of colonies under the jurisdiction of the MCD

Colonies under the categories F , G and H are excluded from our analysis, as they were unsuitable for solar power generation. Using Google Maps and site visits, we found that the houses in these colonies have small plot sizes offering a solar suitable rooftop space of 20-30 sq. meters, which barely meets the minimum space[4] required for rooftop installation. The poor quality of constructions in such colonies will not be able to endure the weight of rooftop solar installations without significant structural improvements. Further, inhabitants of these colonies, belonging to low-income groups, will not be able to afford the upfront investment costs associated with solar installations. Some key colonies from these categories are Majnu Ka Tila, Shakarpur, Nathu Pura and Zakir Nagar.

Similarly, colonies under category E did not qualify for our analysis, as most houses in these colonies are low quality constructions. The plot sizes in this category are bigger than those in category F, G and H but are still fairly small and may not offer sufficient rooftop space suitable for solar installations. Some key colonies in this category are Paharganj, Yusuf Sarai and Inderpuri.

Colonies under category D are densely populated with residential complexes being the principal type of housing. Some key colonies in this category are Mayur Vihar, Paschim Vihar and Rajouri Garden. The residential society as a whole usually owns the rooftop space in such complexes. This may create problems when obtaining permissions to mount rooftop solar installations but may also make the solar installations affordable, as costs would be divided among a larger group of individuals. The roof space of such residential complexes is usually occupied by support services such as water tanks, shafts and other amenities that are instated for the entire building, leaving less unoccupied space. Despite such issues, with an average plot size of around 250 sq. meters offering a solar suitable roof space of 50 sq. meters and concrete building structures, this category qualified for our analysis. The built area/ raw rooftop area available in colonies in category D is around 48.92 sq. km.

Colonies under category C, with fairly big plot sizes and good quality constructions, are also suitable for rooftop installations. The solar suitable roof space available is around 40 to 120 sq. meters and occupants largely belong to medium income groups. Constituent colonies in this category commonly have a mix of individual houses and apartments/flats. Some key colonies in this category are Lajpat Nagar, Punjabi Bagh and Civil Lines. The total built area/rooftop area offered by colonies in this category is around 16.87 sq. km.

Finally, Categories A and B are the most appropriate fit for solar rooftop installations. Colonies in these categories have solar suitable rooftop of up to 180 sq. meters, 18 times of what is required. In addition to that, the houses in these colonies are well-constructed individual houses. The wealthiest population of Delhi inhabits these colonies and is probably in a position to afford such installations by itself. Some key colonies in these categories are Friends Colony, Sunder Nagar and West End. The total built area/ raw rooftop area of colonies in this category is around 13.38 sq. km. The total built area of residential colonies under the jurisdiction of the MCD is around 79.2 sq. km.

Residential area under the jurisdiction of the NDMC[5]

Residential area under the NDMC mainly comprises of either government housing areas or affluent residential properties of Delhi. Some key colonies under this category are Bapa Nagar, Golf links and Kaka Nagar. Through Google Maps, we found that the plot sizes within these colonies is 500-1000 sq. meters offering sufficient solar suitable rooftop space. The housing area under the NDMC comprises of well-maintained concrete buildings. All Colonies in this category are largely similar to colonies in category A of the MCD and are hence considered to have qualified for our analysis. Housing in the area maintained by the NDMC falls in the DDA zone ‘D’. The DDA plans provided the best numbers to use considering that the area under the NDMC is too large for actual mapping and the fact that most constituent colonies are similar in terms of size and structure and hence are subject to similar developmental controls.

Residential area maintained by the Delhi Cantonment[6]

The Delhi Cantonment houses the Indian army Headquarters, the army golf course, military housing such as residential complexes and flats, army hospitals and public schools. All buildings within this area are well-built structures maintained by the Delhi Cantonment Board with plot sizes of around 250-500 sq. meters. We consider all buildings within this area to be qualified to bear solar installations as they offer solar suitable roof space of around 50-100 sq. meters and have structures that can endure solar rooftop installations (checked through Google Maps and site visits). In order to determine the residential area of the Cantonment area or the area covered by military housing, we mapped the constituent colonies using Google Maps. We excluded the army hopital and mess from the mapping exercise to avoid double counting them as they might be included under the land area type ‘pubic and semi public facilities’ as per the Delhi Master Plan. Manual online mapping provided a more representative figure and was used it specifically for the Delhi Cantonment, as its area is relatively small and realistically measureable. Some key colonies inside the Delhi Cantonment area are Chitral lines, Kabul Lines and Asmara Lines.

[1] JJ clusters are households of poorly built congested tenements with inadequate infrastructure and lacking in proper sanitation and drinking water facilities. Unlike slums, these are illegal settlements.

[2] Circle Rate is the minimum rate per sq. meter area on which stamp duty has to be paid by the purchaser. This rate is decided by the government authorities for valuation of land in a particular area.

[3] Refer to Table A2 “Assessment of colonies under the jurisdiction of the MCD” for details

[4] Minimum unobstructed space required for a 1kW rooftop PV installation is 10 sq. meters as per ‘RENI- Renewables Insight, Energy Industry Guides’

[5] NDMC or the New Delhi Municipal Council is one of the local governing bodies in Delhi that administers and maintains around 3% of Delhi’s area. The government of India owns about 80% of the buildings under the jurisdiction of the NDMC.

[6] Cantonment was the permanent military station in British India.

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