ToD tariffs, smart meters and what changes for solar

For years Indian homes paid the same rate for a unit at noon and at 9 pm. That is changing. Smart meters are being installed across the country, and with them come time-of-day (ToD) tariffs that make electricity cheaper in the middle of the day, when solar floods the grid, and dearer in the evening peak. For rooftop solar this is both a challenge (exports at noon may be worth less) and an opportunity (moving loads to the day and, eventually, batteries).

The rules

The Electricity (Rights of Consumers) Amendment Rules, 2023 made ToD tariffs the norm:

• Commercial and industrial consumers with maximum demand above 10 kW: from 1 April 2024.
• Most other consumers (except agriculture): from 1 April 2025 at the latest.
• For consumers with smart meters, ToD applies from the time the smart meter is installed.
• Solar hours (eight hours a day, set by the SERC) must be charged at least 20% below the normal rate; peak hours at least 1.2 times normal for C&I and 1.1 times for other consumers, and the peak period may not be longer than the solar hours. ToD rates apply to the energy charge only. Each SERC sets the exact windows and percentages in its tariff order; in practice few states charge households a peak premium yet (October 2026).

The same amendment also eased the rules on sanctioned-load penalties for smart-meter customers. Check your state's tariff order for the exact ToD design and the date it applies to each category (check the current notification).

Smart meters

Under the Revamped Distribution Sector Scheme (RDSS), DISCOMs are replacing old meters with smart prepaid meters. A smart meter:

• records energy in short intervals (typically 15 or 30 minutes) and sends it to the DISCOM daily,
• can be read and, in prepaid mode, recharged through an app,
• in a net-metered connection, records import and export separately for each interval, so the DISCOM knows exactly how much was exported in solar hours and imported in peak hours,
• can be disconnected and reconnected remotely.

Smart meters are specified to IS 16444. For installers the practical effects are: the customer's hourly data becomes available (very useful for sizing), and ToD settlement becomes possible.

What ToD does to net metering

It depends on how your SERC settles net-metered energy under ToD. Two broad approaches exist:

• Unit netting across the day or month: exports and imports are netted in units, whatever the hour, and only the net units are priced. Solar keeps nearly its full value.
• Block-wise netting: exports in a ToD block offset imports in the same block first, and any leftover is valued at that block's rate (or carried forward within the block). Chhattisgarh, for example, uses a monthly ToD-block adjustment. Here, noon exports are worth only the solar-hour rate, while evening imports cost the peak rate.

Worked example: a 5 kW home

Daily figures (simplified): - Solar: 20 kWh, all in solar hours - Consumption: 20 kWh: 8 in solar hours, 6 in the peak, 6 in normal hours - Rates: normal ₹7.00, solar hours ₹5.60 (20% below), peak ₹7.70 (10% above)

No solar: 8 × 5.60 + 6 × 7.70 + 6 × 7.00 = 44.80 + 46.20 + 42.00 = ₹133.00 a day

Solar with unit netting: exports 12 kWh, imports 12 kWh: net zero units, energy charge ₹0. Saving ₹133.

Solar with block-wise value netting: - Solar block: 20 generated − 8 used = 12 exported, credited at ₹5.60 = ₹67.20 - Peak imports: 6 × 7.70 = ₹46.20; normal imports 6 × 7.00 = ₹42.00 - Net: 88.20 − 67.20 = ₹21.00 a day, about ₹7,665 a year. Saving ₹112 a day instead of ₹133.

The same system saves about 16% less. Your payback model must use the settlement method that actually applies.

Moving loads into solar hours

Now the family shifts 4 kWh a day into the solar hours: water heating, washing machine, the water pump and pre-cooling the bedroom AC in the late afternoon (2 kWh from the peak and 2 kWh from normal hours).

• Solar block: 20 − 12 = 8 exported, credited ₹44.80
• Peak: 4 × 7.70 = ₹30.80; normal: 4 × 7.00 = ₹28.00
• Net: 58.80 − 44.80 = ₹14.00 a day

Load shifting recovers ₹7 a day, about ₹2,550 a year, at almost no cost. It also helps the grid, which is the purpose of ToD.

Advice for customers on ToD

• Run flexible loads between about 10 am and 3 pm: pumps, washing machines, dishwashers, geysers (with a timer), irons, EV charging if the car is home.
• Pre-cool: run the AC harder in the late afternoon and set it a degree or two higher in the peak.
• Use timers and smart plugs: cheap and effective.
• Commercial customers: shift processes into the solar window and review the contract demand; ToD peak premiums for C&I can be larger.
• Batteries: as spreads widen, the case improves. Run the numbers with module 7, lesson 4.

Key points

• ToD tariffs apply to C&I (above 10 kW) from April 2024 and most other consumers from April 2025, immediately for smart-meter customers; SERCs set windows and rates.
• Smart meters record import and export by interval, enabling ToD settlement and giving useful hourly data.
• Under block-wise netting, noon exports are worth the cheaper solar-hour rate while evening imports cost the peak rate, reducing savings.
• Shifting flexible loads into solar hours recovers much of that loss at little cost.
• Model each customer with the settlement method and rates in the current tariff order.

Check yourself

1. From when must ToD apply to a residential customer who gets a smart meter?
2. A home exports 10 kWh in solar hours (₹5.60) and imports 10 kWh in the peak (₹8.00). Under block-wise value netting, what is the daily energy charge?
3. Name three household loads that can be moved into solar hours.