Introduction

In the east of the territory of India lies the state called Arunachal Pradesh and in the farthest corner in the west of India lies the state called Gujarat. The western corner has a longitude of 68°07′ and the eastern corner has a longitude of 97°25′. This covers a spread of more than 29° which is 1/12th of the earth’s perimeter [2]. So, time difference between western and eastern corners of India is theoretically calculated as 1/12th of 24 h i.e. 2 h.

So, for practical reasons, the territory of India may be divided into different time zones where the farthest corners from east to west shall have a time difference of 2 h.

The current Indian Standard Time (IST) is based on a longitude of 82.5°(GMT + 5:30). The Planning Commission of India has consistently acknowledged in its Integrated Energy Policy documents the necessity of two time zones for energy savings [3, 4]. Several leading Institutes of India has carried out research in daylight savings time (DST) and multiple time zones. The National Institute of Advanced Studies (Indian Institute of Science Campus, Bangalore) has recommended the advancement of IST by half an hour (GMT + 6:00) and have estimated a benefit of Rs. 1,000 crore per annum. This is achieved by reducing the evening energy consumption with more daylight. This approach has the significant drawback that it does not reduce the peak demand. However, it clearly establishes that there will be lower electricity consumption due to lighting as there will be more daylight during the evenings [2]. But a major policy decision like advancing the clock calls for much higher benefits. Several other studies have been also carried out in India since 1990 by National Physical Laboratory (NPL) and The Energy and Resources Institute (TERI) to estimate the probable impact of various time-based measures for energy savings. Most significant are the detailed studies undertaken by TERI in 1988 [5] and 2011 [6]. The 1988 study by TERI was undertaken on behalf of the Government of India’s Advisory Board on Energy and revealed only limited energy savings potential. The recommendations did not warrant a major policy decision. The study was unique in the sense that unlike the previous studies which only focused on DST, it also explored the reduction in peak load [5]. A further reinvestigation study was undertaken by TERI in 2011 where it went one step further by creating a third scenario to propose two time zones (GMT + 6:00 and GMT + 5:00) based on the load dispatch regions of India. The estimated results are surprising as it projected a net loss of energy. This study was carried out in great depth and established that the prospect of DST and advancement of clock has a very little potential compared to the risks [6]. It is also well established by several research work that the tropical countries near the Ecuador cannot expect significant benefits from DST or advancement of clock [1, 7].

In the present communication two observations have been made from the study made by TERI in 2011.

  1. 1.

    For proposing time zones, we may not limit ourselves to geography of Regional Load Dispatch Centres (RLDCs) but also explore the geography based on State Load Dispatch Centres (SLDCs), as each state is a governing Centre and may maintain its own timings.

  2. 2.

    The electricity demand of Eastern Region and North Eastern Region (time zone 1, GMT + 6:00 as proposed by TERI) is roughly about 10 % of the national demand and has different peak demand and off-peak demand timings from northern region, southern region and western region (time zone 2, GMT + 5:00 as proposed by TERI). This has resulted in negative energy savings in Scenario 3 proposed by TERI [6].

Due to administrative reasons, there are certain advantages of having a uniform time across the territory of India which may outweigh the practical difficulty of continued daylight during the late hours of a day or dark hours in the morning. In spite of these advantages, USA has four time zone divisions across its contiguous territory and makes considerable savings in energy by optimum use of the daylight across the different time zones. One of the problems of implementing such time zones across India is that the geographical landmass is not uniformly distributed from east to west like USA and the savings in energy in terms of daylight may not be significant.

Objective

Over the past ten years, the peak demand for electrical power in India has grown more than 100 % (from 60,000 MW in the year 2000 to 1,26,000 MW in 2010) [8–10]. There is a case for examination of the peak demand and the distribution of demand for electrical power of the various states in the territory of India to check if the peak demands across different time zones can be spread which will reduce the overall peak demand.

Data Collection

The demand for all the states and union territories have been shown separately except the following:

  1. 1.

    Sikkim

  2. 2.

    Andaman and Nicobar

  3. 3.

    Lakshadweep

The reason for excluding Andaman and Nicobar and Lakshadweep is that they are not connected to the National Grid. The Data for Sikkim is not separately shown and is clubbed with that of West Bengal. As Sikkim and West Bengal are in the same geographical region, it is appropriate to assume that they will fall in the same time zone.

As Damodar Valley Corporation (DVC) has separate, but overlapping jurisdiction with state of West Bengal and state of Jharkhand, there is a system constraint that DVC, West Bengal and Jharkhand should be in the same time zone division. As the data for state of Sikkim is not shown separately, it should also be in the same time zone as the State of West Bengal. There is no practical issue in having Sikkim, West Bengal, Jharkhand and DVC in the same time zone based on their geographical locations.

The peak demand for all states are available from the websites mentioned in [8, 11–16]. The minimum (off-peak) demand for all states and union territories are also available except those in western region. The hourly demand figures are not available from the websites but the following factual data are available:

  • The monthly load duration curve for entire country is available in the monthly report from the website of the national load dispatch centre since April 2012 [16].

  • The time and value for peak demand and the time and value for minimum (off-peak) demand for each region is available from the daily report of all RLDCs since July 2012 [11–15].

  • The regional peak demand period is between 18:00 h and 20:00 h across all seasons. The occurrence time of peak demand varies across seasons for NRLDC, ERLDC and SRLDC. For NERLDC and WRLDC, it is same across all seasons.

  • The regional off-peak demand occurs at 08:00 h for NERLDC, at 14:00 h for ERLDC and at 03:00 h for all other RLDCs across all seasons. This occurrence time for all RLDCs is same for all seasons.

Lemma 1

The period of peak demand may be construed to occur between 17:30 h and 20:30 h which is for 3 h during the day of 24 h for all states in the RLDC where the peak demand occurrence is at 19:00 h. It may be proportionately adjusted for other RLDCs around the respective peak demand occurrence time.

Proof

This is available from daily reports [11–15] and monthly report [16].

Lemma 2

The period of off-peak demand may be construed to occur between 06:30 h and 09:30 h for NERLDC, between 12:30 h and 15:30 h for ERLDC and between 01:30 h and 04:30 h for all other RLDCs.

Proof

This is available from daily reports [11–15] and monthly report [16].

Lemma 3

During the period between off-peak demand to peak demand, the rate of rise in demand shall be uniform and between peak demand to off-peak demand, the rate of fall in demand shall be uniform. The specific variations in a State between peak and off-peak periods shall be ignored.

Proof

This is available from The National Load Duration Curve in Monthly Reports [16].

In absence of hourly demand figures during the day except during peak and off-peak hours, the hourly demand figures are constructed based on earlier Lemmas. Based on the construction methodology, the hourly values shall be in conformity with the national load duration curve.

A load duration data (Table 1) is prepared from the monthly load duration curves from April 2012 to October 2013 [16]. It is to be noted that the load duration curve for January 2013 is not available.

Table 1 Load duration data for percentage of time during a month it stays above a certain load in GW (Indian Power Grid)
Full size table

The rate of rise or fall of the load demand during peak period and off-peak period in the load duration curve is half of the actual rate of rise or fall of the load demand during peak period and off-peak period if there is only one peak and off-peak during the 24 h of a day. For all the infrastructural facilities in the world, it is seen in general that there are at least two peak demand periods and one off-peak demand period during a 24 h day. It is same for electricity demand. This can be verified from the load curves of the State of Punjab, Delhi and Eastern Region presented in Fig. 1. For the state of Punjab, there are three peaks. For Delhi, there are two peaks and for eastern region as a whole, there are two peaks. For two peaks, the rate of rise or fall of the load demand during peak period shall be four times the slope of the peak period in load duration curve, as the load will have to both rise and fall four times during these periods.

Fig. 1
figure 1

Load curves of the state of Punjab, Delhi [14] and eastern region [18]

Full size image

Lemma 4

Hourly demand data for all states and union territories can be constructed based on the factual data of national load duration curve (Fig. 2), the peak demand with its time and the off-peak demand with its time [11–15].

Fig. 2
figure 2

National load duration curve for October 2013 (Indian Power Grid) [17]

Full size image

Proof

  • Let the following points of GW demand in the monthly load duration curve be defined as

  • P A  = Peak load demand (0 % of time)

  • P B  = Load demand for start of peak period (25 % of time), 6 h for 2 peaks

  • P C  = Load demand for start of off-peak period (87.5 % of time), 3 h

  • P D  = Off-peak load demand (100 % of time)

  • Hourly rate of rise or fall of the load demand in percentage during peak period (u) = 4 × (P A − P B ) × 100/(6 × P B )

  • Hourly Rate of rise or fall of the load demand in percentage during off-peak period (v) = 2 × (P C − P D ) × 100/(3 × P D )

  • Peak period value multiplier after an hour = 1 + u/100

  • Off-peak period value multiplier after an hour = 1 + v/100

  • Peak period value multiplier after 1.5 h (x) = 1 + u × 1.5/100

  • Off-peak period value multiplier after 1.5 h (y) = 1 + v × 1.5/100.

Based on these calculations from the load duration data table (Table 1) from April 2012 to October 2013, a rate of rise/fall of load demand during peak/off-peak/normal hours (Table 2) is prepared. However, the data for January 2013 is not available.

Table 2 Rate of rise/fall of load demand during peak/off-peak/normal hours table (Indian Power Grid)
Full size table

As it is desired to estimate the hourly peak values from the day’s peak demand and off-peak demand for every state, the following terms are defined SP A  = Peak load demand of a state on a particular date, MW; SP D  = Off-peak load demand of a state on a particular date, MW; Hourly incremental load demand of the State in MW during the period from off-peak demand to peak demand is given by (SP A /x − SP D  × y)/(number of hours between end of off-peak period and start of peak period); Hourly incremental load demand of the state in MW during the period from peak demand to off-peak demand is expressed as (SP A /x − SP D  × y)/(number of hours between end of peak period and start of off-peak period).

The earlier construction methodology is applied for hourly peak and off-peak demand values of all states [11–16] for 11th October, 2013. The peak demand figures, the constructed hourly demands and the overall peak demand can be seen from Table 3. The overall peak demand is 1,25,228 MW on 11th October, 2013 which occurred at 20:00 h.

Table 3 Constructed hourly peak demand of states and union territories on 11th October, 2013
Full size table

Analysis

With the assumption that the peak demand occurs at a particular time of day based on uniform official working hours, the official working hours will get shifted due to creation of separate time zone divisions and the peak demand of various states shall be spread over different times. As the geographical distance between the eastern and western corners of India limits the time difference to a maximum of 2 h, the maximum number of time zones is restricted to three. There are several options in grouping the states in different time zones. They are as follows: States may be grouped in three different time zones

  1. 1.

    Based on their distance from the farthest eastern corner of the territory of India;

  2. 2.

    According to load dispatch region;

  3. 3.

    With equitable distribution of aggregate peak demand across contiguous geography.

Lemma 5

The maximum reduction in peak saving in distribution of a single peak to multiple peaks is obtained when the values of the multiple peaks are equal and numbers of peaks are more.

Proof

  • Let the single peak value be P and the multiple peak values be P X , P Y , P Z .

  • So, P = P X +P Y +P Z , and P K  = P X  = P Y  = P Z  = P/3.

  • And the amount of peak saving shall be = P − P K

  • If, P′ X , P′ Y , P′ Z are not equal and say, P′ X  > P′ Y , P′ Z

  • So, P′ X  > P K and the amount of peak saving shall be = P − P′ X

Hence P − P′ X  < P − P K and the maximum peak savings will be P − P K and this occurs when the distributed multiple peak values are equal. If the distribution is among two peaks, P′ K  = P/2. So, P − P′ K  < P − P K and reduction in peak value is more if the number of peak values for distribution are more. As a consequence, from the earlier three groupings third option with three time zones for distribution of peak value will be the best to meet our objective.

Since our purpose is to spread the peak demand of the states to different hours of the day, the best strategy shall be to adopt option 3 from earlier. These groupings have been shown in Fig. 3 and Table 4. The groupings have been achieved by preparing a precedence table where each state will have one or more entries to specify its immediate adjacent state towards the west. The columns and rows of Table 4 have been prepared starting with ‘Arunachal Pradesh’ and precisely following the entries in the precedence table. This strategy has shuffled states across load dispatch regions but achieved equitable distribution of aggregate peak demand in the three time zones (Fig. 3). While grouping the states, the contiguity of the states in a time zone has been almost achieved by following the precedence table.

Fig. 3
figure 3

Equitable distribution of aggregate peak demand in the three time zones

Full size image
Table 4 Grouping of states with equitable distribution of aggregate peak demand in the three time zones
Full size table

The hourly demand figures from Table 3 need to be recast with a view to the three time zones. Before this, the time zones need to be selected. The present IST is GMT + 5:30 h. This time standard may be considered for our central time zone (Time Zone 2) and the three time zones may be selected as follows:

Time Zone 1: GMT + 6:30 h

Time Zone 2: GMT + 5:30 h

Time Zone 3: GMT + 4:30 h

The earlier time zone divisions maintain a difference of 2 h only which is in line with the distance covered by the territory of India from east to west with respect to the perimeter distance of the earth surface. The earlier is expected to result in energy savings in time zone 1 due to additional daylight hours in the evenings. It is also expected to result in energy loss in time zone 3 due to reduced daylight hours in the evenings. As the aggregate peak demand in these time zones are nearly equal, the overall daylight savings effect shall be near zero.

The recast hourly demand figures for the states and union territories with groupings under the three time zones are given in Table 4. This has changed the overall peak demand to 1,18,426 MW. This gives a reduction of peak demand of 6,802 MW. The representation of the time zones in the map of India is presented in Fig. 4.

Fig. 4
figure 4

Proposed time zones for reducing peak demand in Indian Power Grid

Full size image

The 24 h load curves for October 11, 2013 with and without time zones is presented in Fig. 5. The Load Curves clearly establish that there is a curve flattening effect due to the introduction of three time zones. Apart from peak demand savings, this has also the effect of raising the demand during the off-peak demand period. This is expected to eliminate the problem of high frequency and high voltage during off-peak hours and improve System Stability [18, 19].

Fig. 5
figure 5

Load curve for Indian Power Grid on October 11, 2013

Full size image

The results for the entire available dataset (July 2012–October 2013) [8, 11–16] is presented in Table 5. The Peak Demand savings ranges from 3,034 to 6,865 MW across all seasons. The average peak demand savings is 5,094 MW across all seasons.

Table 5 Peak demand savings in available dataset July 2012 to October 2013
Full size table

The peak demand savings are relatively low in summer months due to air-conditioners and electric fan loads which does not vary with time. Day light savings also reduces the lighting load in evening hours. From the sector-wise power consumption pattern presented in Table 6, it is seen that the share of domestic consumption is going up [20, 21].

Table 6 Sector-wise  % power consumption in past 20 years
Full size table

There is scope for further investigation into the pattern of sector-wise hourly consumption for possible measures in peak savings in specific sectors. An attempt was made in this regard by different authors [17, 22]. This problem is complex in nature and may be explored with emerging smart grid tools and techniques. The present paper leaves such investigation outside its scope.

Conclusion

It is seen that with figures of savings in peak demand, the maximum demand across all seasons using a single time zone is 135,640 MW and the maximum demand across all seasons using three time zones is 131,785 MW. The overall National Peak Demand can be reduced at least by 3,855 MW. It may be seen with a view that the domestic demand is not time dependent and it may not shift with shift of time zone. As domestic demand is approximately 25 % of overall demand, the reduction in overall National Peak Demand is cut down to 2,891 MW. As the Peak Demand is estimated to grow by 50 % during the twelfth 5 years plan, the peak savings is expected to increase by 50 % to 4,337 MW at the end of twelfth plan period, i.e. in the year 2017 [20, 25]. The requirement of generation capacity for a load demand of 4,337 MW is 50 % more i.e. 6,505 MW [20, 21]. So, the savings in Peak Demand will result in reduction of additional generation capacity by 6,505 MW. Based on the latest estimates by US Energy Information Administration (April 2013) [23, 24]. Capital Expenditure for creation of every 1 MW in coal-fired generation capacity (excluding transmission) is US$3.5 million i.e. approximately Rs. 20 Crore/MW. Therefore, reduction in additional generation capacity by creation of time zones is 6,505 MW and expected savings in capital expenditure in the next 5-year plan period is Rs. 1,30,100 Crore.

In addition to savings in capital expenditure, this strategy will improve the utilization of the existing generating stations and increase their plant load factor. There is also savings in fixed operation and maintenance cost which would be required for the additional generation capacity.

Substantial savings are also expected in operation cost. The average peak demand savings may be cut down by 25 % to consider the domestic demand factor and a peak demand savings of 3,820 MW on an average across all seasons is arrived. It may be fairly estimated that on a daily basis, 4,000 MW unit capacity will not be required to be fired. Based on the latest estimates by US Energy Information Administration (April 2013) [23, 24], the operating cost for generating 1 MWh is estimated to be US$50/MWh i.e. Rs. 3,000/MWh. For 1 h of additional peak load of 4,000 MW, the additional coal-fired units will have to operate for at least 4 h. Whereas the peak demand is flattened and energy consumption is met by spinning units, the additional units will consume fuel for additional 3 h every day.

So, daily savings in operation cost due to reduction of peak generation by 4,000 MW is Rs. 3.6 Crore

In a year, the estimated savings in operating costs is Rs. 365 × 3.6 Crore = Rs. 1,314 Crore.

To conclude, a comparative assessment of the various suggested schemes is made and presented in Table 7.

Table 7 Comparative assessment of suggested schemes
Full size table

The costs associated with implementation of the earlier time zones must not be neglected. There will be both one-time and recurring expenses for publicity, advertisements, time tables, mandatory hoardings in the State borders where time zone changeover occurs. This is estimated to be within a total of Rs. 100 crore for the next 5 years.

The major expenses for time zone divisions shall be for the equipment of NPL for the standard time and frequency systems. The changes required in the transmitter-end equipment may be incorporated with little time and cost but the receiver-end equipment are widely spread across India and are almost countless. The time and cost required for the changes in the receiver-end equipment can be estimated only by the concerned authorities. However, this is only a one-time expenditure and will not be repeated in the future 5-year plan periods. This one-time expenditure may be fairly estimated to be within Rs. 100 crore.

The earlier estimation shows that against the savings in capital expenditure of Rs. 1,30,100 crore, the expenses shall be limited to Rs. 200 crore over a 5 years time period. Whereas the expenditure is one-time only, the national savings and benefits will be perpetual. In addition, it has also been explained that there will be daily savings of Rs. 3.6 crore in recurring expenditure of operation and maintenance necessary for operating additional Power Generation of 4,000 MW on an average. In the premises, it is expected that the implementation of time zone division shall result in substantial savings in both capital and recurring expenditure. The benefits of the proposed scheme shall be best availed in the integrated national power grid operation proposed in 2014.