This article represents two letters written by Mr. Robert M. Gershey to NSP Inc. about their Time-of-Use Rate and the corporation's response.

Letter to Theresa Anthony at NSPI, 28 October 1998


You will recall our telephone conversation that took place earlier this day. This letter summarizes the main points that I wished to convey during that conversation. that NSPC, with consent of the Public Utilities Board, offers special Time-of-Use rates to customers who purchase Electric Thermal Storage home heating units. To make you aware that the energy use pattern characteristic of the Electric Thermal Storage units is comparable to that of houses built on the principle of passive solar heat collection [see SNS Newsletter VOL 5(1)]. Many such houses exist in Nova Scotia and are promoted by a local non-profit organization, Solar Nova Scotia. the similarities between the two energy use patterns suggest that the benefits of Time-of-Use rates be extended to all NSPC customers who exhibit such an energy use pattern including, but not necessarily limited to, owners of houses having passive solar design elements. we suggest that an initial step to implementing such a program would be to install in selected homes, upon request, time-sensitive electric meters to evaluate their suitability to your program.

I would be pleased if you would review this information and forward it to the appropriate personnel within your organization. Specifically, it would be useful to determine how best to facilitate the process of extending the scope of your Time-of-Use rate program to all who might benefit from it.

Thank you for your attention to this matter.

Letter from Michelle Gillard, Market Manager, NSPI, 9 November 1998


I am writing in response to your letter of Oct. 28th to Thesea Anthony, which was forwarded to me. Your letter suggested that passive solar heating systems may be a suitable application for the Time of Use rate structure, and provided some information on solar heating for consideration.

I would like to thank you for taking the time to express your interest in our program, and for the information you provided. I shall attempt to address your inquiry and provide you some additional information on extending the rate to other applications.

The NS Utilities and Review Board (UARB) introduced the Time of Use (TOU) rate in a decision rendered March 4, 1996. Recognizing that load-shifting technologies were necessary to achieve the benefits of a TOU rate, the UARB required Nova Scotia Power Inc. (NSPI) to develop, introduce and promote Electric Thermal Storage (ETS). The UARB also recognized that there may be other technologies that would realize benefits from a TOU rate structure.

NSPI has been focused on developing and implementing a successful ETS pilot program over the past two years. It is now evident that this technology works very well with the TOU rate. One of the reasons for the success is the ability to program this equipment to operate primarily during off-peak hours. ETS operated 80% off peak, with a 96% satisfaction level with the comfort level of the heat. This allows maximum benefits to be realized while still ensuring the heating requirements for the home are met.

NSPI is now investigating other applications suited to the TOU rate structure. The UARB is currently considering our request to test the TOU rate with in-floor radiant heating systems. Several customers have requested consideration of TOU for this system, and a couple of customers (in addition to yourself) have requested the same consideration be given to passive solar heating. In an attempt to get an initial assessment of solar heat, one of the test sites identified has solar heating as well as in-floor radiant.

We hope to have UARB approval for this testing by the end of November, and the test period will be for six months. The reason for the test phase is to ensure that the heat source can be controlled to operate effectively with the TOU rate; that is, provide adequate heat for the home while realizing some benefits from the rate.

For example, a preliminary look at the data you provided (on the kilowatt hour consumption) would indicate that, for this 36 hours period, it would have been to your detriment to be on the TOU rate structure. I penciled into your graph [not included here ] the on-peak, mid-peak and off-peak timeframes of the TOU rate for January with the costs per kWh for each timeframe. While I can't quantify the amounts without numerical data, there appears to be significant kWh consumption during the on-peak and mid-peak periods, and minimal consumption during off-peak (at least on Day 1). The customer benefits by shifting usage to off-peak when rates are half price, so the ability to benefit from the rate is directly proportionate to the customer's ability to shift us age. In your example, it is evident that costs for this consumption pattern would in fact be higher with the TOU rate than with the standard rate.

In summary, NSPI realizes that there may be other applications for TOU, as does the UARB, and we are working toward making the rate available to as many customers as possible. NSPI hopes to test in-floor radiant heating starting in December, and solar heat w ill be represented in the sample to get a preliminary indication of its suitability for TOU. The test results should be available by June 1999, and they will determine our next course of action. I will contact you in June 1999 to provide a status update.

If you have any additional questions or comments, please don't hesitate to contact me.

Letter from Michelle Gillard, Market Manager, NSPI, 9 November 1998


Thank you for the letter that you sent in response to my letter of 28 October to Theresa Anthony. I am pleased to hear that NSPI is investigating the expansion of the TOU rate structure to a variety of domestic use applications, including passive solar heating.

You recall that I included some data from my solar home to support the idea and the TOU rate structure would be appropriate for the usage pattern exhibited. On page two of your letter you come to the opposite conclusion, but this is because you have misinterpreted the data (which fault I will accept as mine for not clearly presenting the same).

Please allow me to clarify this matter. The graph included in my previous letter shows all of the energy purchased from NSPI was in the off-peak rate area (between 0000-0600 17 Jan). The balance of the energy described by that curve was completely solar-derived. No energy was purchased from NSPI during the On Peak or Mid Peak times.

The data for the next 12 hours (0600 17 Jan - 1800 17 Jan) were included to show that during that overcast period there was no benefit from solar gain (not surprisingly). I have integrated the peak areas from the chart and present them in the table below [not included here].

These data clearly show that passive solar heating is perfectly suited for the TOU rate structure. Because this solar benefit will only accrue on sunny days, the overall savings will be less than with an ETS unit controlled by a timer. The net benefit will be reduced by the proportion of the installation's heat generated by electricity to that obtained by passive solar collection. This value is typically 0.5 to 0.4 for solar heated homes in Nova Scotia. Thus the TOU rate structure would be cost effective for such installations.

I would be pleased to further discuss any aspect of this matter with you. I would also be pleased to take part in your test program, perhaps simply by the expedient of installing a TOU rate meter on my passive solar home.

Thank you for your careful consideration of previous letter. It is my hope that the present clarification will be of use to you in evaluating the potential expansion of the TOU rate structure program.