SAM thinks it's Monday - Time-of-Use Tariff confusion

Hello,

I'm modelling a Photovoltaic, Commercial system and want to model the Time of Use Tariff. But have got confused as to how this can work given the number of inputs, so that the monthly $$ savings are calculated correctly.

If SAM assumes that the first day of the year is Monday how do you set up the Time of Use Tariffs so that SAM knows what day it really is so that the load data and the Tariff periods align correctly?

To give you an example my load data is for 2015 so it starts on a Thursday (only two days to the weekend woohoo!). But SAM assumes the 1 Jan 2015 is a Monday. My tariff has off-peak rate all weekend. By the third day in my Load data the off-peak rates for Saturday should kick in but SAM thinks it's Wednesday so assumes weekday tariff rate applies.

Can anyone explain how I can get the Load data and the Time-of-use tariff data to align so that the financial results are correct?

Hello,

Because SAM arbitrarily assumes that January 1 is a Monday, you'll have to make adjustments to your load data so that the weekdays and weekends match. I would only go to that effort if 1) your rate structure has different weekday and weekend rates, and 2) your load is significantly different on weekdays than weekends.

I would suggest shifting your load data so that the time series starts with the first Monday in January. For the last week of the year, you might just copy the data from days in the last complete week to fill out the data to the end of the year. (It turns out that December 31 is also a Monday.)

The reason SAM uses the approach that it does is that it was originally designed to work with typical year (TMY) data, where the actual day of week represented by the data is different for different months. Now that singe-year weather data is becoming more easily available, we may consider making it possible to define the day of week, or perhaps automatically determine it based on the data year.

Best regards,
Paul.

Hi Paul,

OK great thanks!

I think lining up the load to the weather data is less critical than the load to the tariff data. Defining the first day of the week sounds like a great solution.

Cheers,

Andrew

I was struggling with this too, and realising that SAM expects Day 1 to be a Monday (and lining up the electricity data accordingly) helped cut down the error to around 3%. It's frustrating not to be able to get it exact though.

Russell

I ran into same problem, do you have to redefine the parameters every use?

Dear alshehri,

I don't understand your question. Can you clarify?

Best regards,
Paul.