Demand Response in the Residential Setting

[SageBrush]

This article attempted to identify opportunities for smart meter enabled appliance throttling to avoid overloads in the transformer network. The focus was on the last transformer before a home, and I was surprised to read that 3-7 homes are on a 25 kVA transformer. Presuming I am not too far off in calling that a 25 kW maximum load, I'm surprised that transformers are not blowing up left and right. Five AC units across say a five home network pulling at the same time would do it ;-)

Let alone a Tesla added to the mix.

How is this resolved, or do I understand the entire issue wrong ?

 

[miimura]

I believe that transformer kVA ratings are continuous. Therefore, you could expect it to deliver several times its rating for short periods of time. Short being durations like 10-15 minutes of central air conditioners running.

 

[mspohr]

This article attempted to identify opportunities for smart meter enabled appliance throttling to avoid overloads in the transformer network. The focus was on the last transformer before a home, and I was surprised to read that 3-7 homes are on a 25 kVA transformer. Presuming I am not too far off in calling that a 25 kW maximum load, I'm surprised that transformers are not blowing up left and right. Five AC units across say a five home network pulling at the same time would do it ;-)

Let alone a Tesla added to the mix.

How is this resolved, or do I understand the entire issue wrong ?

My 25kW transformer has 7 houses on it. If I have Tesla charging, hot tub, spare room electrical heat and electric dryer running, I can pretty much max out 20 kW.
When I built my new garage/spare room addition last year, I talked to the power company about this situation and they weren't worried. They said I could buy my own transformer for $10k if I wanted but they wouldn't upgrade the transformer. So far, it hasn't blown up and I'm not worried since I let them know the situation and it's their problem if it blows up.
I think their equipment is very conservatively rated and able to tolerate larger loads.

 

[mknox]

Utilities size transformers based on the diversified loads of the homes connected. Most home loads are not continuous. Electric heat, stoves, water heaters and air conditioners cycle on and off and the chances are that not everyone's appliances will all be on at the same time up and down the street. This does present utilities with a bit of a conundrum after extended outages known as "cold load pickup" whereby everyone's heat or a/c does come on at the same time when power is restored. What utilities do in this case is go around and pull the meters (cutting power) to about half of the houses on a transformer, let the others settle back into cycling situations, then plug the meters back in at the previously disconnected homes.

EVs present a whole different situation. They don't cycle on and off as they charge like pretty much every other residential load does. Utilities will have to look at a combination of capital upgrades and "smart" charging solutions that schedule all of the EVs on a particular transformer such that they are not all charging at the same time.

 

[mspohr]

Here's my power load for one day.

The 4 kW spikes are my hot tub heater cycling. A few of the broader and taller spikes are electric heat and dryer. The 8 kW 4 hour load is my car charging. At peak, I'm drawing about 12 kW from my shared 25 kW transformer. (Blue line is temperature inside garage)
I don't have TOU since I have solar panels and my local utility (in it's wisdom... or avarice) doesn't allow TOU with solar so I don't feel any need to schedule charging overnight.

 

[Ampster]

my local utility (in it's wisdom... or avarice) doesn't allow TOU with solar so I don't feel any need to schedule charging overnight.

TOU rates are coming in January 2019 per the CPUC. I am pretty sure SCE, PG &E and SDG & E all have TOU rates per NEM 1.0. right now. Maybe if you are with a Municipal Utility you may be exempt.

 

[mspohr]

TOU rates are coming in January 2019 per the CPUC. I am pretty sure SCE, PG &E and SDG & E all have TOU rates per NEM 1.0. right now. Maybe if you are with a Municipal Utility you may be exempt.

That would help price my generation appropriately.
my utility is Liberty, a small electric company that serves the area around Lake Tahoe and to the north.