Time of Day Tariff

What Is ToD Tariff?

Time of Day (ToD) tariff is an electricity pricing structure where the per-kWh rate varies according to the time when electricity is consumed. DISCOMs divide the 24-hour cycle into multiple time blocks, typically two to four, and apply different tariffs to each block. Peak hours, when electricity demand is highest and generation most expensive, carry the highest tariff. Off-peak hours, typically late night when demand is lowest, carry the lowest tariff. Normal or standard hours fall between these extremes.

The fundamental principle behind ToD pricing is cost-reflective tariff design. Electricity cannot be stored economically at grid scale, so supply must match demand in real time. During peak evening hours, when residential lighting, cooking, and cooling overlap with residual commercial and industrial load, the grid must dispatch expensive peaking power plants or purchase power at high spot market rates. During off-peak night hours, base load plants run below capacity and surplus power is available at lower marginal cost. ToD tariffs communicate these cost differences to consumers, creating price signals that encourage demand shifting and reduce the need for costly peak capacity.

ToD has been applied to HT industrial consumers in India for decades, particularly in states with advanced metering infrastructure. The Electricity (Rights of Consumers) Rules 2020 accelerated ToD adoption by mandating time-of-day metering for HT consumers and consumers with connected load above 10 kW by April 2024. State implementation has proceeded at varying speeds, with some states already having mature ToD frameworks and others in early rollout phases.

For solar energy systems, ToD has profound implications. Solar photovoltaic generation peaks between 10 AM and 2 PM, producing maximum output during what is typically the normal-tariff block in most ToD structures. This means solar offsets grid consumption at normal rates, not peak rates. The economic gap between normal-tariff solar value and peak-tariff grid cost represents an opportunity that battery storage can capture. A solar-plus-battery system charges the battery during normal-rate daytime hours and discharges during peak evening hours, effectively arbitraging the ToD differential.

Why ToD Tariff Matters

ToD tariffs matter because they fundamentally change how commercial and industrial consumers should think about electricity costs, solar system design, and energy storage economics. Under flat tariffs, the value of solar is straightforward: every kWh generated offsets a kWh purchased at the single flat rate. Under ToD, the value of solar depends on when it is generated, and the value of storage depends on the spread between charge-time and discharge-time tariffs.

For HT industrial consumers, ToD can shift annual electricity costs by lakhs of rupees depending on consumption patterns. A facility running single-shift daytime operations consumes primarily during normal-tariff hours, experiencing modest ToD impact. A facility running continuous three-shift operations with significant evening activity faces higher exposure. Conversely, facilities that can shift energy-intensive processes to off-peak night hours realise substantial savings.

The solar industry must adapt system designs to ToD realities. Solar-only systems generate during normal-tariff hours and cannot directly offset peak-tariff consumption. This does not reduce solar’s value, but it does mean that the full economic potential of a site requires storage to capture peak-hour value. For a commercial consumer paying Rs 8 per kWh normal and Rs 12 per kWh peak, solar offsets the Rs 8 rate during daytime. Adding a battery allows the same solar energy to displace the Rs 12 rate during evening peak, increasing the effective value per kWh by 50%.

Battery storage economics improve dramatically under ToD regimes. Without ToD, battery payback depends primarily on backup value, net metering optimisation, and demand charge reduction. With ToD, batteries generate daily arbitrage value by buying low (charging during normal or off-peak) and selling high (discharging during peak). For a 100 kWh battery cycling once daily with a Rs 4 per kWh peak-to-normal spread, the annual ToD arbitrage value alone is Rs 1.46 lakh (100 kWh × Rs 4 × 365 days). This value stream, combined with solar integration benefits, can reduce battery payback from 12-15 years to 8-10 years. Correct battery bank sizing is essential to actually capture this arbitrage window; QBits Energy’s hybrid solar battery sizing guide covers the calculation in detail.

Heaven Green Energy, Gujarat’s #1 ranked PM Surya Ghar installer, models ToD impacts in every commercial and industrial solar proposal. Our analysis for Gujarat DISCOMs (UGVCL, MGVCL, PGVCL, DGVCL) shows that C&I consumers with significant evening load can improve project IRR by 2 to 3 percentage points by adding appropriately sized battery storage to capture ToD differentials.

How ToD Tariff Works

The ToD tariff mechanism operates through a structured time-block billing process. Understanding each step helps consumers model costs and identify optimisation opportunities.

1. Time block definition: The state SERC defines time blocks in the tariff order. A typical three-block structure divides the day as follows:

   • Off-peak (night): 10:00 PM to 6:00 AM, tariff multiplier 0.8x to 0.9x
   • Normal (day): 6:00 AM to 6:00 PM, tariff multiplier 1.0x (reference rate)
   • Peak (evening): 6:00 PM to 10:00 PM, tariff multiplier 1.2x to 1.5x

2. Meter registration: Time-of-day capable meters or smart meters record kWh consumption separately for each time block. The meter maintains separate registers that accumulate consumption during each defined period.

3. Tariff application: The DISCOM billing system applies the appropriate per-kWh tariff to consumption in each block. Energy charges are calculated as:

   Energy Charge = (Off-peak kWh × Off-peak Rate) + (Normal kWh × Normal Rate) + (Peak kWh × Peak Rate)

4. Demand charge treatment: Some states apply time-differentiated demand charges; others apply a flat demand charge regardless of when peak demand occurs. The specific treatment is defined in the SERC tariff order.

5. Net metering adjustment (if applicable): For solar consumers with net metering, exported solar energy may be credited at different rates depending on the time block of export. Three common approaches exist:

   • Aggregate 1:1: Total monthly export nets against total monthly import regardless of time block. Simplest and most favourable for solar consumers.
   • Time-block 1:1: Export during a given block credits against import during the same block. Limited cross-block credit.
   • Conversion factor: Export during off-peak yields fewer kWh credit for peak imports. For example, 100 kWh exported off-peak may yield only 70 to 80 kWh withdrawable at peak.

Consider a practical example: A commercial building in Ahmedabad with normal-tariff energy charge of Rs 8.50 per kWh consumes 10,000 kWh monthly, split as 2,000 kWh off-peak, 6,000 kWh normal, and 2,000 kWh peak. With multipliers of 0.85x off-peak, 1.0x normal, and 1.35x peak:

• Off-peak: 2,000 × Rs 7.23 = Rs 14,460
• Normal: 6,000 × Rs 8.50 = Rs 51,000
• Peak: 2,000 × Rs 11.48 = Rs 22,960
• Total ToD bill: Rs 88,420

Under a flat tariff at Rs 8.50, the bill would be Rs 85,000. The ToD premium is Rs 3,420 (4%). However, if consumption shifts to 1,000 kWh off-peak, 5,000 kWh normal, and 4,000 kWh peak, the ToD bill rises to Rs 97,380, a 14.6% increase over flat tariff. Conversely, shifting 1,000 kWh from peak to off-peak reduces the bill to Rs 79,460, a 6.5% saving versus flat tariff.

Visual Explanation

Real-World Example

A pharmaceutical manufacturing facility in Vadodara, Gujarat, operates on an HT connection with 2,000 kVA contract demand. The facility runs two shifts: 8:00 AM to 4:00 PM and 4:00 PM to midnight. The second shift overlaps with evening peak hours (6:00 PM to 10:00 PM), creating significant ToD exposure.

Before solar installation, the facility’s monthly consumption was 180,000 kWh, with 40% occurring during peak hours due to the second shift. Under Gujarat’s ToD structure with peak at 1.3x normal, the energy bill carried a substantial peak-hour premium. The facility management approached Heaven Green Energy for a solar solution that addressed both daytime generation and peak-hour consumption.

We designed a 750 kW rooftop solar system paired with a 250 kWh LFP battery energy storage system. The solar system generates approximately 3,000 kWh daily during normal-tariff hours, offsetting daytime grid consumption. The battery charges from excess solar during midday and from grid during off-peak night hours at 0.85x normal rate.

During evening peak hours, the battery discharges at 100 kW for 2.5 hours, displacing 250 kWh of peak-tariff grid consumption daily. At a peak-to-normal differential of Rs 3.50 per kWh, the daily ToD arbitrage value is Rs 875. Over 300 operational days annually, this equals Rs 2.62 lakh in ToD value alone.

The solar system saves Rs 8.50 per kWh on 90,000 kWh annually (Rs 7.65 lakh). The battery adds Rs 2.62 lakh in ToD arbitrage plus Rs 1.8 lakh in demand charge reduction through peak shaving. Combined annual savings exceed Rs 12 lakh. The total system cost of Rs 85 lakh (solar plus battery) achieves payback in 7 years, compared to 9 years for solar alone without storage.

This case illustrates how ToD structures make battery storage economically viable for industrial consumers who would otherwise find standalone battery payback too long. The ToD differential transforms storage from a backup luxury into a revenue-generating asset.

Technical Specifications / Benchmarks

Benefits / Advantages

• Cost-reflective pricing: ToD tariffs align consumer costs with actual grid generation and delivery costs, promoting economic efficiency.
• Peak demand reduction: Price signals encourage consumers to shift load away from peak hours, reducing the need for expensive peaking capacity.
• Grid stability improvement: Smoothed demand profiles reduce ramping requirements for thermal plants and improve grid frequency stability.
• Battery storage economics: ToD differentials create a revenue stream for battery storage through arbitrage, improving payback periods.
• Solar-plus-storage synergy: ToD makes pairing solar with batteries economically attractive, accelerating clean energy adoption.
• Consumer empowerment: Consumers who can shift consumption to off-peak hours realise direct bill savings, rewarding flexible operations.
• Reduced cross-subsidies: Cost-reflective tariffs reduce the need for cross-subsidies between consumer categories, improving DISCOM financial health.
• Smart meter justification: ToD provides a clear use case for smart meter investment, supporting India’s smart grid modernisation.
• Renewable integration support: Flexible demand facilitated by ToD pricing helps integrate variable renewable generation by shifting demand to match supply.
• Transparency: Time-block billing makes consumption patterns visible, enabling targeted energy efficiency measures.

Limitations / Drawbacks

• Bill complexity: ToD bills are more complex than flat-rate bills, requiring consumers to understand time blocks and consumption patterns.
• Limited consumer flexibility: Residential and some commercial consumers cannot easily shift essential consumption (cooking, lighting) to off-peak hours.
• Implementation cost: Smart meter rollout for ToD billing requires significant capital investment by DISCOMs, which may be passed to consumers.
• Regulatory variation: Time blocks and multipliers vary by state, creating complexity for multi-state businesses and solar developers.
• Solar-only limitation: Solar generates during normal-tariff hours and cannot directly offset peak consumption without storage.
• Net metering complexity: Time-block net metering creates administrative complexity and potential disputes over credit valuation.
• Initial bill shock: Consumers with peak-heavy consumption patterns may see bill increases when ToD is first implemented.
• Meter reliability: Time-of-day meters must maintain accurate timekeeping; clock drift can cause billing errors.
• Limited off-peak value for some: Facilities that already operate continuously (24/7) have limited ability to shift load to off-peak.
• Policy uncertainty: ToD block definitions and multipliers may change with each SERC tariff order, creating planning uncertainty.

Comparison Section

Applications

• Industrial peak shaving: Manufacturing facilities with evening shifts use battery storage charged by daytime solar to displace peak-tariff grid consumption during second and third shifts.
• Commercial building optimisation: Offices and malls with HVAC systems pre-cool buildings during normal-tariff hours and reduce chiller operation during peak hours, using thermal mass as passive storage.
• Solar-plus-residential storage: Homes with ToD tariffs charge batteries from rooftop solar during daytime and power evening loads from battery, avoiding peak rates for lighting, cooling, and appliances.
• Electric vehicle charging: EV fleet operators schedule charging during off-peak hours, taking advantage of 0.8x to 0.9x rates. Bidirectional EV chargers can also discharge during peak hours for vehicle-to-grid revenue.
• Data centre load management: Data centres with flexible compute workloads shift non-critical processing to off-peak hours, reducing both energy costs and cooling load during peak periods.
• Cold storage and refrigeration: Thermal energy storage in chilled water or ice banks allows refrigeration plants to run primarily during normal and off-peak hours.
• Water pumping and treatment: Municipal and agricultural pumping operations scheduled for off-peak hours benefit from lower tariffs while reducing peak grid stress.
• Solar EPC proposal modelling: Solar developers like Heaven Green Energy incorporate ToD analysis into C&I proposals, demonstrating storage value through quantified arbitrage savings.

Industry Standards & Regulations

ToD tariffs in India are governed by the Electricity Act 2003 framework, with specific implementation driven by the Electricity (Rights of Consumers) Rules 2020. Rule 14 of these rules mandates that every distribution licensee shall provide time-of-day meters to consumers with connected load above 10 kW and all HT consumers. The rules further require that tariffs progressively reflect the time-varying cost of supply.

State Electricity Regulatory Commissions (SERCs) issue tariff orders that define specific time blocks, tariff multipliers, and consumer categories subject to ToD. These orders are typically issued annually and may be revised in multi-year tariff determinations. Consumers must reference the latest applicable tariff order for their DISCOM.

Metering standards ensure accurate time-block measurement. IS 16444 specifies requirements for smart meters, including time-of-day registration capabilities. Class 0.5S or 1.0S accuracy is required for billing meters. Time synchronisation via GPS or network time protocol ensures accurate block transitions.

The Central Electricity Authority (CEA) provides technical standards for meter installation, communication, and data management under the Smart Grid programme. State-level smart meter rollout programmes, often funded through RDSS (Revamped Distribution Sector Scheme), are accelerating ToD-capable meter deployment.

India-Specific Context

India’s ToD implementation landscape varies significantly across states, reflecting differences in DISCOM financial health, metering infrastructure, and regulatory priorities. Gujarat, through GUVNL and its four DISCOMs (UGVCL, MGVCL, PGVCL, DGVCL), has implemented ToD for HT and large LT consumers with clear time blocks and moderate peak multipliers. The state’s relatively strong DISCOM finances have supported smart meter investment, enabling accurate ToD billing. For the DISCOM-specific net metering paperwork that determines how ToD export credits are applied, see Heaven Designs’ UGVCL solar net metering guide.

Maharashtra and Tamil Nadu have the longest history of ToD tariffs for industrial consumers, dating back over a decade. These states have mature frameworks with well-defined blocks and higher peak multipliers that create stronger price signals. Karnataka and Andhra Pradesh followed with their own implementations.

The Electricity (Rights of Consumers) Rules 2020 accelerated national ToD adoption, but implementation timelines vary. States with active smart meter rollouts under RDSS are progressing faster. The target is universal ToD for all consumers above 10 kW and eventual extension to residential consumers as smart meter penetration increases.

For PM Surya Ghar beneficiaries, ToD is currently irrelevant for most residential installations on flat tariffs. However, as smart meters reach residential consumers, ToD will create new opportunities for solar-plus-storage configurations. A 5 kW residential solar system with a 5 kWh battery could shift evening peak consumption to stored solar, delivering savings beyond what solar alone achieves.

Heaven Green Energy monitors SERC tariff orders across Gujarat and neighbouring states to ensure our solar proposals reflect current ToD structures. Our engineering team models consumption profiles against time blocks to optimise battery sizing for ToD arbitrage value, not just backup duration.

Future Trends

The future of ToD tariffs in India points toward finer granularity, broader consumer coverage, and deeper integration with distributed energy resources. Hourly or half-hourly pricing, rather than broad two- to four-hour blocks, will provide more precise price signals and enable sophisticated demand response.

Real-time pricing linked to Indian Energy Exchange (IEX) day-ahead and real-time market rates is emerging for large consumers with advanced metering. This creates direct exposure to wholesale price volatility, which batteries and flexible loads can exploit for arbitrage.

Virtual power plants (VPPs) aggregating thousands of residential solar-plus-battery systems will participate in demand response programmes, collectively shifting load during peak hours. ToD tariffs provide the economic foundation for VPP participation by ensuring that individual consumers benefit from load shifting.

Dynamic pricing apps and smart home energy management systems will automate load shifting based on ToD signals. Water heaters, EV chargers, air conditioners, and pool pumps will automatically schedule operation during low-price periods, reducing manual intervention.

Seasonal ToD variations will become more pronounced as climate change intensifies summer cooling demand. Some states may introduce super-peak blocks during extreme heat events, with multipliers exceeding 2.0x, creating even stronger incentives for storage and demand flexibility.

The integration of ToD with carbon pricing mechanisms is a longer-term possibility. Peak-hour generation often relies on more carbon-intensive peaking plants. Time-varying carbon intensity signals, combined with ToD pricing, could further incentivise clean dispatch from batteries and solar.

Common Mistakes & Misconceptions

• Treating ToD as just another tariff: ToD is a dynamic pricing structure that creates active optimisation opportunities. Consumers who passively continue existing consumption patterns miss significant savings potential.
• Ignoring ToD when planning solar: Solar-only systems generate during normal-tariff hours and do not capture peak-hour value. Storage must be modelled to realise full ToD benefits.
• Underestimating storage value under ToD: Many consumers dismiss battery storage as too expensive without quantifying ToD arbitrage value. In states with 1.4x peak multipliers, storage payback improves by 3 to 5 years.
• Mismatching net metering structure with ToD: Some states reduce solar export credit value during off-peak hours. Consumers should verify their state’s net metering rules before sizing storage for arbitrage.
• Not modelling consumption by time block: Average monthly consumption alone reveals nothing about ToD exposure. Hourly load profiles are essential for accurate ToD bill modelling.
• Assuming ToD blocks are fixed: SERCs revise time blocks and multipliers in annual tariff orders. Long-term solar-plus-storage economics should include sensitivity analysis for tariff changes.
• Overlooking demand charge interaction: Some states apply time-differentiated demand charges in addition to energy charges. Peak demand occurring during peak hours may carry higher per-kVA rates.
• Confusing ToD with seasonal tariffs: Seasonal tariffs vary rates by month (summer vs winter). ToD varies by time of day. Some states apply both, creating two-dimensional rate variation.
• Expecting immediate residential ToD: While the Rules 2020 mandate eventual residential ToD, smart meter rollout timelines mean most residential consumers remain on flat tariffs through 2026-2027.
• Neglecting battery degradation in arbitrage calculations: Battery capacity degrades over time, reducing available arbitrage energy. Long-term ToD value projections should include conservative degradation assumptions.

Key Takeaways

• ToD tariff varies electricity rates by time of day, with peak evening hours typically 1.2x to 1.5x normal daytime rates and off-peak night hours 0.8x to 0.9x.
• The Electricity (Rights of Consumers) Rules 2020 mandates ToD for HT and 10 kW-plus consumers, with phased state-level implementation ongoing.
• Solar generates during normal-tariff daytime hours and offsets grid consumption at normal rates; it does not directly capture peak-hour value without storage.
• Battery storage paired with solar enables ToD arbitrage by charging during normal/off-peak hours and discharging during peak hours, capturing the tariff differential.
• A 100 kWh battery with Rs 4 per kWh peak-to-normal spread generates Rs 1.46 lakh annually in ToD arbitrage value alone.
• Gujarat, Maharashtra, Karnataka, and Tamil Nadu have mature ToD frameworks; other states are in various stages of implementation.
• Net metering interactions with ToD vary by state; some states credit exports at time-block rates while others use aggregate 1:1 netting.
• Consumers should model hourly consumption profiles against ToD blocks to quantify exposure and identify load-shifting opportunities.
• APFC panels and efficient motor systems reduce baseline consumption, amplifying the proportional impact of ToD optimisation.
• Future trends include finer granularity (half-hourly pricing), real-time market linkage, and virtual power plant aggregation of distributed storage.

Related Glossary Terms

• Sanctioned Load
• Contract Demand
• HT vs LT Connection
• DISCOM
• Net Metering
• Battery Energy Storage System
• LFP Battery
• Hybrid Inverter
• Maximum Demand Penalty
• Feed-in Tariff
• Trivector Meter
• ABT Meter
• Battery Cycle Life
• Banking Electricity

Related Resources

• PM Surya Ghar Complete Guide
• Net Metering in India
• Lithium vs Lead Acid Batteries
• Home Solar System Size Guide
• 3kW vs 5kW vs 10kW Home Solar
• Commercial Solar Solutions
• Industrial Solar Solutions
• Solar Savings Calculator
• Solar Inverters
• Solar Insulates You From Tariff Hikes

Sources & References

• Electricity (Rights of Consumers) Rules 2020, Ministry of Power, Government of India
• Central Electricity Authority (CEA) Smart Meter Guidelines and Standards
• Gujarat Urja Vikas Nigam Limited (GUVNL) Tariff Order 2024-25
• Maharashtra State Electricity Distribution Company (MSEDCL) ToD Tariff Orders
• Karnataka Electricity Regulatory Commission (KERC) Tariff Orders
• Tamil Nadu Generation and Distribution Corporation (TANGEDCO) Tariff Schedule
• IS 16444: Smart Meter Standard for Time-of-Day Metering
• Electricity Act 2003, Section 61 and Section 62 (Tariff Determination)
• National Smart Grid Mission Implementation Reports, Ministry of Power
• MNRE Grid-Connected Rooftop Solar Programme Guidelines
• Heaven Green Energy project modelling database (C&I installations, Gujarat, 2020-2026)