Until this year, Nova Scotia Power’s residential customers were restricted to two tariffs: the Domestic Service Tariff, used by most residential customers, and the Time-of-Day Tariff, reserved for households using electric thermal storage.
Two new tariffs, Time-of-Use and Critical-Peak Price, are now available, reflecting an evolution in the demand-side and supply-side of the electricity system, respectively.
Time-of-Use Tariff
The Time-of-Use tariff (ToU) has three per-kilowatt/hour prices determined by when the electricity is consumed.
From 1 April to 31 October, the cost of electricity is 11.719 cents/kWh (about 5.8 cents less than the Domestic Service tariff). In the winter months (1 November to 31 March), the tariff has two different rates, depending on the time of day, as shown in the following table.
ToU winter pricing (cents/kWh)
| On peak | Off peak | On peak | Off peak |
| 7am to 11am | 11am to 5pm | 5pm to 9pm | 9pm to 7am |
| 32.120 | 16.931 | 32.120 | 16.931 |
The cost of electricity during the eight on-peak hours (32.120 cents/kWh) is almost twice that of the 16 off-peak hours (16.931 cents/kWh). The off-peak charge is less than the Domestic Service tariff. Weekends and holidays are charged the off-peak rate.
By having an extremely high on-peak tariff, customers with electric vehicles will be encouraged to charge their vehicles during the off-peak hours, thereby reducing the volume of electricity NSP needs to generate during the peak. The very low cost during the non-winter months coincides with the driving season, another inducement for EV owners to switch to this tariff.
Critical-Peak Price Tariff
The cost of electricity using the Critical-Peak Price (CPP) tariff, like the ToU tariff, varies by season and time of consumption.
During the non-winter months (1 April to 31 October), the rate is 14.290 cents/kWh, regardless of when the electricity is used.
Throughout the winter months (1 November to 31 March), there are two different rates depending on whether NSP has announced that a critical-peak event will start at a specific time and run for four hours (critical peak events are always four-hours long and announced by 4pm the day before they take effect). There can be a maximum of 18 critical peak events during the winter months.
During non-critical peak-event times, the tariff is 14.29 cents/kWh. However, during critical peak-events, the tariff is 142.256 cents/kWh, about 10 times greater.
A critical-peak event can be called at any time, weekdays and weekends. Holidays are excluded.
NSP’s generation mix is undergoing radical changes, with a push for an ever-increasing use of renewable sources of electricity, notably wind and solar. These renewables are variable, meaning they might not be available when they are needed, such as during the peak hours. When that occurs, NSP will need to turn to more expensive sources, such as natural gas or imported electricity.
Reducing electricity costs
Neither the ToU or the CPP would at first appear to offer any chance of reducing the cost of electricity to the customer. This is not necessarily true as the following chart shows.
A Domestic Service Tariff customer would pay $2,336 to consume 12 MWh in 2024.
The cost to a CPP tariff customer would depend on the volume of electricity consumed during the four-hour critical event. Consuming two-kWhs for each critical-event hour (CEH) costs $2,129. If consumption could be brought to zero, the cost would be $1,945.
The ToU cost depends on two factors: the volume consumed during the non-winter months and the percentage of the peak consumed during the winter months. For example, if a customer could split the load evenly between summer and winter (S50%:W50%) and limit consumption to 40% of the peak, the cost would be $2,043. Bringing consumption to zero would see a cost of $1,933.
Reducing the cost
Both the critical-peak price and the time-of-use tariffs offer customers a means of reducing their energy costs by shifting their electricity consumption during certain periods of the day. How this is done depends on the resources available to the customer.
The customer could attempt to reduce demand from the peak times to the non-peak times. This can involve explicitly delaying the use of energy-intensive electrical services (such as water heaters or some appliances) from peak to non-peak hours. This might be easier said than done because in some situations it may not be possible, such as cooking a morning or evening meal.
The other type of customer who could benefit would be one with their own “behind-the-meter” source of electricity.
An increasingly common approach in parts of the United States and Mexico is for customers to store electricity in batteries, charged from their own solar panels, or during the non-peak hours for use during the peak hours. For example, for CPP customers, any time before a four-hour critical-peak event, or ToU customers, during the sixteen hours of off-peak tariff.
Cui bono?
Some customers will benefit greatly from these tariffs.
However, most, including those on low- or moderate-incomes, will not.
Other tariffs are needed, such as the inverted block tariff, which I first proposed to the UARB in 2004 and revised with new data in 2022.
Larry Hughes is a professor in the Department of Electrical and Computer Engineering at Dalhousie University.
The work in this report was not funded by the federal or provincial governments or any other organization.
I don’t see how this will help those who currently heat with electricity, but not with a thermal storage device that would allow you to shift your major electricity consumption to a low tariff time.
Rather than tie people into contracts etc, could you not just offer a reduced rate off peak hours. Been done in Ontario for several years at least a decade, not new concept!
In fairness to NSP, increase peak hours rates very slightly to all consumers commercial and residential, to encourage behavior switch. Therefore, be more cost effective and efficient for all, why not try?
Very interesting article and research summary. They are not going to make this easy to sort out and I bet most will not switch to any of the new options.
The Ontario system is much better, easier to understand and use for the average household. One example is the off peak hour starts at 7pm not 9pm. Start the dishwasher and laundry. There is no winter summer rate. Does it cost more to generate electricity in the winter than the summer, I would think not. NSP has designed a seemingly good plan to show the government it’s “trying to meet customer demands for lower rates”. It is deliberately confusing, difficult to apply and even harder to understand for the average consumer who would have no choice but to live their lives according to a ridiculous timetable from NSP. To me this means NSP will make more money under the guise of helping it’s customers. I am sure more bonuses will now be in order for the overpaid executives. This to me just proves the old adage that ” BS baffles brains”. I have read Mr. Hughes article twice and am still confused and perplexed, am I alone?