Technology

An end to power cuts

Print edition : April 03, 2015

In Gudalur, Nilgiris district, one of the 20 houses that are part of the pilot project for providing 24×7 access to electricity. Photo: Special Arrangement

Appliances at the Electrical Engineering Department of IIT Madras run on direct current.

Figure 1: Solar photovoltaic gives direct current which has to be converted to alternating current to power the loads. A battery stores only DC and requires an AC-DC converter for charging and a DC-AC converter for discharging.

Figure 2: Schematic of IIT-M off-grid home deployment. The system has two output lines: a main solar DC line and an emergency output line. When the grid has long blackouts and there is no significant solar output as well, the main line is cut off below a certain depth of discharge of the battery. Then, the emergency DC line, which can power a couple of devices, can be used for long hours even when the battery is low.

Figure 3: The grid supplies power on two lines. The existing AC line supplies unlimited power, but is cut off during brown-out. The new DC line supplies limited power, but stays on during both normal and brown-out states.​

The brown-out technology has undergone extensive testing and trials at IIT-M, and was validated successfully at Madhuranthakam near Chennai in December 2014. As many as 281 homes were covered and they remained lit even when the rest of the area had extended power cuts.

Researchers at IIT Madras come up with an innovative solution to link decentralised solar-based DC power to grid-based AC power which has the potential to provide 24×7 access to electricity in homes and put an an end to power cuts.

IF you happen to visit the Electrical Engineering Department at the Indian Institute of Technology Madras you will be surprised to find that the electrical appliances in the rooms of the department operate on direct current (DC), and not alternating current (AC), which is the standard the world over for power transmission and usage, both industrial and domestic. It is an innovation using solar power, which has been conceptualised and executed by two professors from the department, Ashok Jhunjhunwala and Bhaskar Ramamurthi, who is also the Director of IIT-M. This has been done in a few other departments and in some of the hostels of the institute as well.

By linking the concept of decentralised solar-based DC power to the grid-based AC power, a team of institute researchers from IIT-M, led by Jhunjhunwala and Ramamurthi, has come up with an innovative solution that has the potential to provide 24×7 access to electricity to all homes. This could be a game changer in a country where about 60-70 million homes still do not have access to electricity at all and large parts of the rest suffer daily power cuts ranging from a few hours to 10-12 hours.Those who are familiar with the work of the duo over the past decade and a half know that they are basically experts in communication engineering, and not in power engineering at all, and would seem to be somewhat unlikely people to come up with such a revolutionary solution.

And 24×7 access would seem like an unbelievable dream. During the late 1990s, the two developed the Wireless in Local Loop (WLL) technology for wider telecom access in developing countries through their corDECT solution, which is now widely deployed in India and 15 other countries. In fact, at the IIT-M, Jhunjhunwala heads the Telematics and Computer Network Group (TeNet), which has nothing to do with solar power or other power engineering solutions.

So how did they get into this? “About two years back,” Jhunjhunwala said in his address at the recently held annual meeting of the Indian Academy of Sciences in Chennai, “when there were serious power cuts in Chennai, lasting anywhere from two hours to 12-14 hours, we were all getting fed up. Bhaskar and I felt that something must be done about it. So we started working on it. A colleague said solar power was the solution. We started looking at solar power to see what could be done. Solar power projects are being implemented in State after State with all kinds of subsidies. But we were amazed and aghast at how poor and inefficient the whole thing was. How nobody had applied any thought. Everything comes from outside the country; just plug it in without even applying your mind to it. Sometimes they work and sometimes they don’t.”

Energy efficiency

The IIT-M technology sprung from the realisation that AC supply for basic domestic and commercial power needs, rather than DC, is a highly inefficient way of using energy in the present times. Historically, AC has come to be the worldwide choice for using electricity because it allows for an increase or decrease of voltage using transformers, and this makes it possible to haul large amounts of power over long distances with cheap infrastructure and with minimum energy loss owing to thermal heating. Accordingly, most of the industrial and domestic electric appliances, such as fans, lights and water pumps, run on AC.

But, with the advent of power electronics, this basic disadvantage of DC no longer exists. More importantly, all electronic devices that one uses today, such as LED/LCD (light-emitting diode/liquid crystal display) TV, laptops, LED lamps and mobile phones/chargers, all run on low-voltage DC. But homes and offices are still powered by AC. So to use them, the AC supply is converted to DC using converters, adapters or chargers, which are often built into appliances. But the efficiency of conversion of these interfaces is poor, ranging anywhere from 25 to 50 per cent, says Jhunjhunwala.

Solar power, particularly what is generated through photovoltaics (PV), produces DC power and the batteries used to store solar power also deliver only DC. With the increasing move towards decentralised solar power using rooftop PV panels, DC-based appliances, such as refrigerators, air conditioners, washing machines and fans, using brushless DC (BLDC) motors have begun to appear in the market. However, the basic electric supply grid infrastructure continues to be AC-based. Therefore, the use of DC-based appliances in grid-connected homes, even if they are augmented with rooftop solar power, becomes difficult because the load is AC-based. DC power from solar panels has to be converted to AC and synchronised with the grid and be reconverted to DC to run the connected load. So DC/AC and AC/DC conversion becomes necessary at different stages even when we use solar DC power. If we add a battery, which is usually the case as solar power fluctuates greatly, this conversion is once again required for charging and discharging the battery because the battery stores and delivers only DC.

Each conversion, according to Jhunjhunwala, causes a loss of 10-15 per cent of power. So when solar power with battery is used, there is a loss of about 30-45 per cent. Figure 1, for example, illustrates how, in a typical situation with solar power utilisation, AC↔DC conversion inefficiencie↔s add up to result in a huge net loss of energy. Even in off-grid homes (OGH) with rooftop solar power, the problem remains the same because electronic devices such as LED lamps, laptops and mobile chargers although they run on DC are designed to be plugged into AC sockets and other grid supply interfaces. So, at the electronic device end, there is a further loss because this AC/DC conversion is once again required.

“This must change and home-load must move towards DC if energy consumption has to be brought down,” points out Jhunjhunwala. For example, while a 72 watt AC fan at the lowest speed will consume about 60 W of power, an equivalent 30 W BLDC fan consumes only 9 W. Similarly, LED lamps are twice as efficient as CFLs for a given light output. While a standard 1.2 m CFL consumes about 36 W, an equivalent LED lamp consumes only about 15W. LED lamps can be dimmed as per requirement, which further reduces power consumption. According to him, the cost of the appliances themselves will not differ too much if DC becomes the norm and the appliances are produced in large volumes. “Use of DC-powered energy-efficient devices will bring down the consumption by 50 per cent,” he adds. Solar power can be used directly to drive the DC load or to charge the battery whose DC power can then drive the load.

The IIT-M experience

And this is what has basically been done within the IIT-M campus in order to demonstrate the use of solar DC electricity directly to power lights, fans and other electronic devices. The solar-powered DC electricity supply system (Figure 2) developed by IIT-M has a rooftop PV panel, supplemented by a battery, which is designed to have 48 V +/− 3V output that feeds a local DC grid operating at that voltage. A 48 V line inside the house/building powers the DC devices and appliances. All AC↔DC conversions are thus eliminated in this system. Obviously, this can be replicated in a straightforward manner in OGHs with decentralised rooftop solar power.

Two Kolkata-based scientists, Parthasarathi Majumdar of the Ramakrishna Mission Vivekananda University and Sekhar Banerjee, an independent researcher, have also been working along similar lines to use solar power to drive home appliances and devices at low voltage DC. Their particular innovation is in replacing the battery with a solar-charged supercapacitor, also known as Electrochemical or Electric Double Layer Capacitors (EDLC), which are more efficient and can go through a far greater number of charge-discharge cycles than conventional batteries. Using a bank of such capacitors, they have even designed and built models of supercapacitor-driven railcar, cyclerickshaw and ferry. However, the duo is seriously constrained by lack of resources to conduct large-scale trials or widen the scope of their development. “On our part, not having access to well-equipped research laboratories confines us to making low-end prototype models,” they wrote in a recent paper describing their work.

The IIT-M technology demonstrator actually goes a step further. In situations where grid supply is available, the system can supplement the grid by providing backup DC electricity from the solar-powered battery. The grid supply AC power is converted to DC at 48 volts (using an AC/DC converter) to match the solar DC and integrated with the grid. A subsystem called OGH-controller, an IIT-patented device, integrates the 48 V DC power from the PV panel, the battery and the grid (where available) in such a way that dependence on the battery is minimised. The technology, therefore, can be used both for OGH situations and for near-OGH (limited access with extended power cuts of 12-14 hours a day) situations. The OGH-controller also enables metering of the DC power consumption.

The system (Figure 2) has two output lines: a main 48 V line and an emergency output line. When the grid has long blackouts and there is no significant solar output as well because of cloudy or rainy conditions, the main line is cut off below a certain level of depth of discharge (DOD) of the battery. The emergency line, which can power a couple of devices, say a light and a fan, can be used for long hours even when the battery is low. The OGH deployment, say with a 125 W solar panel and a 200-500 watt-hours (Wh) battery, in each house will include an LED tubelight, an LED bulb, one BLDC fan, one remote to operate the fan and the tubelight, one socket and one mobile charger. The solution (with 100 Wh) is designed to operate a BLDC fan at full speed, the tubelight and the bulb for about 10 hrs on a normal day and using up only 50 per cent of the battery power (50 per cent DOD). At reduced speed and reduced brightness of the lamps, the power can last longer. Once the battery is low, the emergency line takes over, which can last for about 24 hours.

The IIT-M has, in association with a couple of manufacturers, developed the DC lights, fans, remotes, chargers, sockets and solar panels required for the OGH solution. According to Jhunjhunwala, specifications for these, including the operating standards for these 48V DC appliances (which are being evolved), will be made public and any manufacturer will be eligible, in a tender, to supply these products.

Besides the IIT-M campus, this technology has been implemented on a pilot basis in Gudalur in the Nilgiris (20 houses), and installations are ongoing in Irakum island in Nellore, Andhra Pradesh, Dampada in Odisha, Hanskali in West Bengal and a police station and an ayurveda hospital in Chennai. Actually, the OGH installation in Gudalur is based on a cluster homes model. In this, one OGH system is deployed in a cluster of two to four homes and the main components, which drive the cluster, are deployed in one of the houses. The biggest challenge in this deployment was installing the system in the kuccha tribal homes. The other challenge was teaching the tribal people to use a remote to operate the LED tubelight.

Power for all

There are about 250 million houses in India. If you install a 500 W (0.5 kW) solar panel (measuring about 5 m) in every home, with insolation (exposure to sun’s rays) of about 1,500 hours a year, the total power generated will be about 190 (250 million x 0.5 kW x 1,500) GW a year, which is roughly the annual domestic power consumption. “Decentralised solar [with DC-driven appliances and devices] can thus make a huge difference. It has the potential to free the grid from all domestic demand,” says Jhunjhunwala. If the above DC power system is implemented widely, it will help bring down the overall energy consumption in the country greatly.

The IIT-M group hopes to extend it to cover as many as 100,000 off-grid/near-off-grid homes in different parts of the country. To be able to achieve this target, government support is necessary and the institute has offered this innovative solution to the Ministry of Power, the Ministry of New and Renewable Energy (MNRE) and the Rural Electrification Corporation (REC).

Of course, there is a cost involved to implement, run and maintain these DC systems. According to rough estimates by IIT-M, at the pilot stage (100,000 homes) of implementation, cost per home is about Rs.20,000-30,000 (including five-year maintenance) depending on the terrain, kind of houses and density. For 100,000 homes, the total cost works out to about Rs.300 crore. This, they hope, will be met through a mix of government (MNRE) subsidies routed through the institute, funding from State governments and other government bodies, private donors and corporate social responsibility (CSR) schemes.

No more blackouts

Although IIT-M’s OGH/near-OGH system does provide uninterrupted DC (UDC) power by providing a low-level battery backup in situations where grid connectivity exists, it does not really solve the basic problem that the two professors set out to tackle, namely getting rid of blackouts. “This also does not create a pull factor for solar power,” Jhunjhunwala adds. According to him, it was a former Secretary of Power who pointed out that what they had done went only halfway. “We needed something more innovative to address the blackout issue and at the same time provide the necessary technology push for decentralised solar power and energy-efficient DC appliances.”

The question that the IIT-M team asked was, instead of a mere back-up of a solar power battery at the consumer end, which at best can light up one bulb or a fan, can one do something at the grid supply or sub-station end? The idea that the IIT-M group subsequently came up with, if implemented on a large scale, can get rid of blackouts and has the potential to be a game changer in the power scenario in the country. Of course, besides technology push, a policy push is also required to achieve the cherished goal. Hopefully, appropriate policy support will also be forthcoming to enable implementation of the idea on a countrywide scale.

So what is this breakthrough idea? The grid supply as it is today functions in an either/or mode: the grid is designed to carry either full power (normal, 100 per cent) or zero power (load-shedding/blackout, 0 per cent). The IIT-M technology involves the introduction of a new low-level AC power line (say at 10 per cent) and supply a minimum amount of DC power at 48 V to all homes 24×7 on the existing grid. Some tweaking at the substation will obviously be needed, which, according to Jhunjhunwala, will involve minimal changes in the grid at no great cost. This is called the “brown-out” mode.

At the substation, there will be two lines emerging from the distribution transformer, the usual 230 V line and a 90 V line. During the brown-out, only the latter would remain open. At the consumer end, the 90 V supply line is converted to a 48 V DC line by an AC/DC converter, which would then be similar to the earlier OGH situation. While the main 230 V AC line is cut off during this mode, the low power 48 V DC line remains “ON” all the time (Figure 3). Having two grid supply lines is not unfamiliar as most homes have separate lines for 5 amp and 15 A. This would be similar. This low-level limited power, according to the team, is small enough to be made available at all times, even in the worst power crisis situation.

What if consumers draw arbitrary amounts of power from this line resulting in a grid collapse? The main line should cut off automatically and instantaneously within a millisecond leaving the other line open, points out Jhunjhunwala. This issue of how to engineer this instantaneous cut-off bothered both Jhunjhunwala and Ramamurthi for a few months before they came up with an innovative solution.

Innovative solution

When a blackout happens, there is a rapid drop in the voltage at the substation end. So when the voltage drops from 230 V by a factor 2.5 (90V), the system should signal a brown-out and cut off the main line. Through a GPRS (General Packet Radio Service) mobile network system, the substation instantly signals to the home cluster the occurrence of the brown-out. The main line is cut-off and only the 10 per cent capacity line feeding DC power remains, from which the power you can draw is limited by design. “The idea of drop in voltage to do the normal-to-brown-out signalling was the Eureka moment for us,” Jhunjhunwala said. One may also ask whether 10 per cent power is sufficient for a household to function. Actually, a brown-out situation is quite like the OGH case, only that the DC supply is coming from the grid itself instead of a solar panel or a storage battery. Since one is using highly energy-efficient DC devices, as in the OGH case, a good number of household appliances can be operated.

According to Jhunjhunwala, the 48 UDC line, providing 100 W power per home, can support three lights, two fans (or one fan and one LED TV) and one mobile charger. And in case someone wants more, solar PV, with a battery support if needed, can be added. A 500 W solar PV can support five fans, three lights, two TVs, multiple mobile chargers and a laptop charger. For metering the DC consumption, an Uninterrupted DC Power Module (UDPM), which forms part of the installation, is used. It is done through a wireless system based on Bluetooth technology. Consumption data are transferred to an android mobile phone connected to the meter box via Bluetooth.

This brown-out technology has undergone extensive testing and trials at IIT-M and has also been successfully validated at Madhuranthakam near Chennai during December 2014. As many as 281 homes were covered, and this cluster in the neighbourhood remains lit even when the rest of the area has extended power cuts. According to Jhunjhunwala, the neighbouring areas, too, have taken an interest and would like the model replicated there. Brown-out technology installations are also ongoing in Telangana (Moinabad) Kerala (Thiruvanathapuram) and Odisha.

While large-scale deployment of the brown-out technology may not take off immediately as it involves government investment and perhaps some policy and regulatory issues, uninterrupted DC supply through the OGH/near-OGH technology, which does have a potential to bring down the electricity supply-demand gap significantly, can take off if there is requisite support from government agencies, including standardising of DC appliances and their efficiency rating by the Bureau of Energy Efficiency (BEE) and even grant of fiscal incentives to enable manufacturers to get into DC appliance production on a large scale.

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