Vidya Jonnagada, a resident of Tarnaka escaped the hardships of many of her neigbours who were stuck in their homes and flats without power, water and connectivity for several days due to the flood havoc caused by the incessant rains in October. “We had one advantage,” said Vidya. “We had set up a solar-powered backup for our entire complex, which proved a life-saver”. 

Tilak S. Gajendran, a resident of Nizampet too said the solar power backup enabled him to see through those rainy days even though the solar panels wasn’t very effective. “We were fortunate to have some power during the rains last year, though the ground floor of our house was flooded with three feet of water,” said Tilak.

A single 100-Watt Solar Panel can power several small devices ranging from cell phones, lights, fans, routers, laptops, mixers. “I always wondered if we could really power an entire house with solar power,” said Raju Mishra, a resident of Mehdipatnam. “Although I’ve not been able to power my indoor areas, all my garden lights run on solar power.”

Types of Solar Grids

“The main aim of a home-installed solar system is to help reduce your electricity bills and your carbon footprint,” says Sirisha Prabhala, a techie who has worked with Microsoft and Infosys. “But it can be expensive to set up a unit that will provide complete backup in case of power failure.”

There are three main types of solar power systems:

1. On-grid, also known as a grid-tie or grid-feed solar system, is the most used option. These systems do not need batteries and use either solar inverters or micro-inverters connected to the public electricity grid. Any excess solar power that one generates is exported to the grid. In exchange, a consumer is paid a feed-in-tariff (FiT) or given equivalent credits. When the solar system is not operating or one is using more electricity than the system is producing like in hot weather conditions, one can redeem the credits by importing or consuming electricity from the grid. An on-grid system can power all appliances including water pump, motor, lights, etc. These are the most cost-effective and simplest systems to install and are by far the most widely used by homes and businesses. However, on-grid solar systems are not able to generate electricity during low sun-light conditions.

• Off-grid, also known as a stand-alone power system (SAPS), is more for personal use as it is not connected to the grid and requires battery storage. This system can provide power for critical loads even when there is a power outage. These solar systems need to be designed to generate enough power throughout the year and have enough battery capacity to meet the home’s requirements, even in peak winter when there is generally much less sunlight. Off-grid systems are also much more expensive due to the high cost of batteries and off-grid inverters, but battery costs are coming down, creating a growing market for off-grid solar battery systems even in smaller cities and towns.

• Hybrid, grid-connected solar system with battery storage. Hybrid systems can both export excess electricity and store excess energy. Most hybrid solar systems with battery storage are able to automatically isolate from the grid (known as ‘islanding’) and continue to supply some power during a blackout. This is an expensive option and is generally not recommended for a residential setup.

Read more: Solar energy drive to make Shimla a ‘green’ city

How do they work?

All solar power systems work on the same basic principles. Solar panels convert sunlight into Direct Current (DC), which can be either stored in a battery or converted by a solar inverter into Alternating Current (AC), which can run home appliances. Depending on the type of system, excess solar energy can either be fed into the electricity grid for credits, or stored in-house in battery storage systems. 

“In an off-grid system, you own all the generated power,” explains Suchitra Akella, an ex-employee of HSBC, who has an on-grid solar system. “For example, if we pass on 200 units to the main grid and our usage is 150 units, they owe me 50 units or an equivalent amount of money. Currently, we generate around 240 units. Even if there is a power outage and we are not able to pass on any of our solar production, we get about six hours of power backup (depending on the size of batteries). If you’re off-grid, the advantage is that you don’t have to depend on external power supply, but you need huge batteries”. 

While designing the regulations for solar rooftop systems, governments make a provision for either one or both types of arrangements – Gross metering and Net metering. In India, ‘net metering’ was introduced as an initiative to make renewable energy more economical and accessible. Telangana state has an option for net metering. In this format, any excess electricity, which is generated by the solar system is sent to the electricity grid through an energy meter. Customers are allowed to offset their normal grid electricity consumption with power generated from their rooftop solar system and pay only for the balance consumed. The other option is ‘Gross metering’ where all solar energy is exported to the electricity grid. 

As per the Telangana State Electricity Regulatory Commission, for Net Metering, a single bi-directional meter is installed for recording of export and import of electricity according to the sanctioned load/contracted demand of the consumer with the DISCOM. Separate registers for export and import with the Meter Reading Instrument (MRI) downloading facility are maintained.

Guidelines for Implementation of Net Metering Rooftop Solar PV Grid Interactive Systems 2020 can be viewed here.

In the case of Gross Metering, an eligible consumer has the option of choosing the gross metering at 11 kV and above at an average rate of rupees eight or as per the price from the Solar Power Purchase Agreements entered into by the Distribution Licensee and notified on their website;

What kind of setup is needed? 

Ten solar panels at a size of 365 watts per panel results in an on or off-grid solar system of around 3.65 kilowatts. “We have a 3.15kva on-grid system with a net metering system,” said Tilak. “It occupies a major portion of the roof. We also have a 0.5 Kva solar panel, which is connected to two batteries using a micro-hybrid inverter.” 

“Typical units for individual apartments/homes are 2KW, 3KW or 5 KW,” added Sirisha. “The government offers more subsidies on 2kW and 3kW units as compared to bigger units.”

Methuku Gurunath, a Physics lecturer in PAGE Junior College, Kompally explained that “to encourage domestic households, the Government is encouraging smaller rooftop units, which are less expensive. In Anantapur, Andhra Pradesh, large-scale units are installed in arid lands for commercial purposes.”

“The system size depends on the power consumption for each house/apartment,” said Radhika Choudary, Co-founder, Freyr Energy. “In general, a 3BHK house might need 2kW to 3kW system to offset the entire power bill. A 3kW system can generate 360 units of power every month and can result in a saving of approximately Rs. 2,500 every month.”

Read more: Solar rooftop connections: Why are city homes lagging?

The decision for the capacity is primarily driven by 

● Power consumption/past bills per month 

● Future projected consumption as the unit is set for 25 years and it cannot be increased

● Solar systems generating higher units need much more space 

“We typically need at least 80 sft of shadow-free area to put up solar rooftops for any location, be it residential, industrial or commercial,” said Radhika.

Tilak shared the solar panel measurements for his home systems: 

● On-grid – Length – 398cm * Width – 500cm 

● Off-grid – Length – 392cm * Width – 98cm 

How much area is available for SRT for residential purposes in the city? What is the level of implementation so far?

“India had set a target of 40GW of rooftop solar by 2022,” added Radhika. “However, we have achieved only around 10% of this target as on June 30, 2020. As on date, the residential space makes up to 13-14% of the total rooftop solar segment, so the potential for growth of rooftop segment is huge. In Hyderabad, market penetration is under one per cent today. However, solar water heaters are very common”.

 How much does it cost? 

Under Phase-II of Centre’s solar programme, Central Financial Assistance (CFA) for the residential sector has been fixed at 40% for RTS systems up to 3 kWp capacity and 20% for RTS system capacity beyond 3 kWp and upto 10 kWp.

“It cost us Rs. 2.2 lakhs but prices have come down a lot as compared to the time we had it installed,” said Tilak. A similar system today costs Rs. 1.5 lakhs with subsidy, though an off-grid is more expensive.

On a rough estimate, the price of 1 KW off-grid residential solar system costs around Rs. 80,000. For a 1kW solar power unit, the cost in the on-grid scheme is Rs. 70,000 after deducting the 30 per cent government subsidy on the benchmark or on the invoice price. 

“In residential rooftop solar panels, the excess power generated is sent to the grid and may be helpful in cutting down electricity bills,” said Telangana State Renewable Energy Development Corporation Limited (TSREDCO) General Manager Satya Vara Prasad. “The exported current will be deducted from the bill and the new amount will be displayed on the customer bill and in case the export is more than the import, then the additional units of power will be transferred to the next month’s bill.”

How much solar energy can be generated?

“Solar energy generated depends on factors like the orientation and tilt angle of the solar panels as well as the efficiency of the solar panel,” explained Sunil Rao, a techie. “We also have to account for losses due to dirt, shading, and temperature. Dirty panels block sunlight and reduce power output while shade from trees and buildings can reduce sunlight to the panels.” 

The amount of solar energy that can be produced depends primarily on three factors:

● Sunlight – Photovoltaic panels (PV) require light to produce energy. 

● Heat – More light and low heat produce best results.

● Installation of the solar panels – The direction of the panels relative to the sun’s path. 

Contrary to popular belief, solar panels can generate some amount of energy even during cloudy and overcast weather depending on how much light can pass through the clouds. Solar panels provide power to the solar charge controllers, which are used to recharge the batteries. When the batteries are fully charged, the charge controller maintains a trickle charge to hold the batteries at their full charge. 

Do solar systems work when the grid is down? 

“On days when there is limited sunshine, your solar panels will not be able to produce as much power as your home needs,” said Richa Mehta, a resident of Kondapur. “At night, your system will not be able to produce any energy at all.” Even with batteries, solar panels will not be able to provide one’s home with electricity during a power outage, unless the home system is equipped with large energy storage or the consumer opts for an off-grid system. 

“You need a lot of panels to run a home on solar power alone,” said Tilak. “For a normal house or villa, the limit is 5 Kva as per government guidelines. This is sufficient for most small household appliances, but may not be enough  to run air conditioners”. 

It takes approximately two months for getting approval for on-grid systems whereas installation can be completed in one month.

As per the Telangana State Renewable Energy Development Corporation Ltd. (TSREDCO), a domestic independent house has an eligibility of 1 kWp to 10 kWp. To register for an on-grid application for claiming subsidy, a technical feasibility report from the concerned electricity distribution companies (DISCOM) is mandatory.

“Telangana has 51 recognised developers and by paying the prescribed fee to the suppliers, one can easily install the solar rooftops at residential places,” Prasad added. “Telangana has 51 recognised developers and by paying the prescribed fee to the suppliers, one can easily install the solar rooftops at residential places,” Prasad added. Other eligibility criteria can be viewed here.

As per the subsidy scheme for 25 MW announced by TSREDCO, 125 cr has been allocated for the residential sector, out of which about 70% is earmarked for Hyderabad-Secunderabad.

Limitations of solar energy systems

As a rule of thumb, it is recommended that unless a consumer experiences a power outage of more than 1 hr every day, they should go for an on-grid system. Some constraints in setting up solar systems are location and sunlight availability, space for installation, reliability and efficiency, expensive energy storage costs, high initial cost, and aesthetics. 

“An on-grid system is a good option for long-term usage and sustainability,” said Suchitra. “We got our panels installed at a 7’ height. Under them, we planted shade-loving plants. We also use the space for compost storing, etc for our terrace garden. In our neighbourhood, one resident has raised the panel installation to 10’ height, so they’ve a lot of sun but cleaning of panels may be difficult if you raise it too high.”

“Generally, it is recommended to clean once in 3 months but in the last 2 years i did only twice,” said Gurunath, who lives in a triplex in Nizampet. “Our solar panels are erected at 15ft height from the roof, so panels are 50ft above ground level. I use my borewell (5hp motor) hose pipe to clean the panels. Otherwise, we can use a 0.5 hp motor connected from an overhead tank.”

Is it worth it? 

“We’ve been wanting to have a solar panel since we moved to our house six years ago,” said Suchitra. “We installed it over a year ago. It seemed like a lot of expense and we finished installation in the beginning of. Now, despite using two air conditioners, etc we paid only Rs. 1,000 per month last summer while our earlier bills were around Rs. 7,000.”

“Ours is a 5.2kw solar unit,” said Gurunath. “For a family of 6, whose average consumption per month is 400 units, I recommend a 3kw unit which comes at around Rs. 1 lakh due to current subsidies. Two years back, it cost us Rs. 2.5 lakh for a 5.2kw installation. In addition, we are also having a 200 ltr capacity solar water heater, which I don’t recommend at all. Because cost of installation of a 200 ltr solar water geyser, (unit price plus installation) is around Rs. 50,000. For this price we can get a 1.5kw solar power panel unit and by spending another Rs. 50,000, we can install a 3kw solar power. The problem with a solar water geyser is that we cannot use it for two months in winter season. We also cannot use hot water whenever we want as it heats up water only from 11am to 4pm. Also, a minimum of 20 litres of water will get wasted as a solar unit is set up far from our bathroom”.

“Interestingly, a solar rooftop gives much better value as a product when compared to solar heaters,” added Radhika. “SRTs can be connected to any load and they reduce a customers’ power bill substantially (upto 80-90%) while giving a payback of 3 to 4 years”.

“I charge my electric scooter from my solar power storage,” added Tilak. “All you need is a 15 amp plug to charge your scooter. The running cost of my scooter is 20 paise per km as compared to Rs. 6 per km for petrol scooters. If the majority of Indians who have the financial means and live in an Independent house install solar panels, we can save a lot of power for the country.” 

Several households in Hyderabad have now turned into power producers. Gated communities are increasingly adopting solar energy systems. For example, multiple households in Bhanu Enclave near Yapral have installed solar panels and solar water heating systems. 

Also read:

• Guide to installing a rooftop solar plant in Bengaluru
• How to get a rooftop solar power connection for your Chennai home
• Soon, a green city in each Indian state
• Bengaluru apartments rush to install rooftop solar panels ahead of likely policy change

Other useful links

• Solar Calculator
• Solar Energy on-Grid Application Form 
• Application Form for connectivity with the Grid and sale of electricity from the Roof- top Solar Photo Voltaic System 
• Solar Energy Application Status
• https://tsredco.telangana.gov.in/GetregStatus.aspx
• List of empanelled suppliers of 1-500KWp grid-connected rooftop solar PV power plants for FY 2020-21