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TBC with Two Peak TOU periods

Darwin

Member
Jan 12, 2018
75
96
Phoenix, Az
This is a bit esoteric, but just trying to understand how they may calculate some of these usage numbers since I'm not installed yet (scheduled for a couple weeks from now). For example, do you happen to know if SRP uses rigid on the hour, and half-hour periods (2pm, 2:30pm, 3pm, etc) for their calculations, or would they shift their calculation in the scenario where I use my ac for a solid, but only for 30 minutes (say at a 3kWhr run rate), but insure it straddles two 30 minutes periods, thus only running 15 minutes during each period. Does SRP then shift and say that I used 3kWhrs from 2:15-2:45 (for peak and 30 minute period usage calculations) and charge me as such, or would they see it as 1.5kWhrs from 2-2:30, and 1.5kWhrs from 2:30-3pm? I'm simplifying here, assuming I use no other power than the AC just for the entire hour from 2-3pm.

Yes, SRP uses rigid, on the hour and half hour (2pm, 2:30pm, 3pm, etc) periods for their demand calcs. So if you're going to run your AC for 30 minutes, you ideally want to straddle two 1/2 hour periods - starting it 15 minutes into a demand period and ending it 15 minutes into the next period. This is precisely the concept behind how the thermostat management portion of my SmartThings Demand app is able to minimize demand, although it's not necessarily strict about when to stop and start your AC. It's more focused on letting your thermostat do it's thing and only intervenes when necessary to meet your demand goal preference. Of course, with a Powerwall that all becomes much less critical and only comes into play if your PW max kW output is exceeded or the battery is exhausted.

I'm also assuming, what ever I actually use in net actual during a 30 minute period, they then double it to come up with a "hourly kWh" peak and such usage number for charging me, but for the given 30 minute period.

Yes, I think you have it, but I'll clarify on the net usage part just in case.

You can approximate your 30-minute demand kW number by doubling your 30 minute kWh energy usage number, but this isn't exactly correct. If don't have solar and you're not currently exporting, this number should be pretty accurate, but if you do export to the grid, your 30-minute demand will always be at best equal to and quite possibly much larger than this. If you calculate net hourly energy for 30 minutes when it's consumption (not export) and then double it (and then drop the h in the units!), then you should have an accurate number, but to me, it's kind of a round-about calculation (and you would need a net energy meter that only considers usage, not export).

It's subtle (and probably in the category of 'who cares' for most people), but since demand is a power measurement (measured in kW, not energy measured in kWh) there's technically no net energy involved in the calculation and there is no doubling to do. The actual calculation simply continually determines the (integrated) average of the (positive only) value of your real-time kW power consumption, and at the end of your demand interval (30 minutes in SRP's case), that's the resultant demand number.
 
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  • Informative
Reactions: JayClark

JayClark

Member
Aug 6, 2019
224
181
Arizona
Yes, SRP uses rigid, on the hour and half hour (2pm, 2:30pm, 3pm, etc) periods for their demand calcs. So if you're going to run your AC for 30 minutes, you ideally want to straddle two 1/2 hour periods - starting it 15 minutes into a demand period and ending it 15 minutes into the next period. This is precisely the concept behind how the thermostat management portion of my SmartThings Demand app is able to minimize demand, although it's not necessarily strict about when to stop and start your AC. It's more focused on letting your thermostat do it's thing and only intervenes when necessary to meet your demand goal preference. Of course, with a Powerwall that all becomes much less critical and only comes into play if your PW max kW output is exceeded or the battery is exhausted.



Yes, I think you have it, but I'll clarify on the net usage part just in case.

You can approximate your 30-minute demand kW number by doubling your 30 minute kWh energy usage number, but this isn't exactly correct. If don't have solar and you're not currently exporting, this number should be pretty accurate, but if you do export to the grid, your 30-minute demand will always be at best equal to and quite possibly much larger than this. If you calculate net hourly energy for 30 minutes when it's consumption (not export) and then double it (and then drop the h in the units!), then you should have an accurate number, but to me, it's kind of a round-about calculation (and you would need a net energy meter that only considers usage, not export).

It's subtle (and probably in the category of 'who cares' for most people), but since demand is a power measurement (measured in kW, not energy measured in kWh) there's technically no net energy involved in the calculation and there is no doubling to do. The actual calculation simply continually determines the (integrated) average of the (positive only) value of your real-time kW power consumption, and at the end of your demand interval (30 minutes in SRP's case), that's the resultant demand number.

Ok, that's very helpful, kind of what I thought but with some nuances in relation to generation & usage that I hadn't thought through all the way. Right now my AEON is on the Grid side of everything, and I may put it back there after all the installations are done, and maybe add one to two more AEON monitors to measure at different points.... just because. I like the detail I can get from those things - but maybe not needed with your app once the PW & Solar is installed.
 

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