So, I just finished a good chunk of the AC side wiring for my off-grid solar project. I'll post details of that elsewhere, but I moved the wiring for my HPWC in the process.
All of the wiring I used for my project is copper, and probably a gauge larger than needed. My sub-panel to HPWC run is 2 gauge copper, roughly 40 ft. The sub panel is fed from a 200A breaker through 3/0 gauge copper through a 200A transfer switch then over from the utility service panel. (The transfer switch will let me cut off the utility later...)
So anyway... I measured my voltage drops trying to figure out my resistive losses.
At the HPWC before starting a charge I was at 249V. It's only me and one other house on a rather large transformer currently, so, the good starting voltage is pretty normal. Only about 2kW of other loads on the 320A (400A) service.
Measuring the voltage at the HPWC and at my service panel, they were virtually identical under no load (within a couple tenths of a volt, within a reasonable margin of error).
After starting to charge at 80A, voltage at the car dash sagged to 237V, at the inside of the HPWC about 238-239V (I know the cable for the HPWC is less than ideal already so this was expected).
At my 200A sub panel where the HPWC is connected, 239-240V, and at my service panel 240V.
So, between the car and my service panel I have roughly a 3V drop. This comes out to only ~240W of heat radiating off of the 25' HPWC cable, 40' of 2 gauge from the HPWC to the sub panel, and ~30' of 3/0 between the sub panel and service panel. The majority of it being the charge cable itself. This is pretty good and shows that all of my connections are pretty solid on my wiring. After 90 minutes, confiming with my FLIR cam shows a pretty negligible temperature rise on that run. Virtually nothing on the 3/0, about a 20F rise on the 2 gauge, and the 100A breaker sitting at about 35F above room temp. All normal or better than normal.
So... we started with 249V.... that means there is a 9V drop between my service panel's mains and the transformer. 9V @ 80A is 720W of heat coming off of that wiring... and that wiring is on the utility's side of the meter, sans ~4 feet of it (a staight line on Google maps from my meter to the transformer is about 170').
So, lets say I charge for 3 hours (what I'm doing now since my HPWC was offline for a couple of days for my rewire job). Thats 3*720W = 2.16kWh in heat losses in the service conductors. 2.16kWh that the utility is paying for, not me, since it is on their side of the meter. The losses on my side of the meter are negligible. That is a 3-4% "toll" the utility is paying.
Granted, that comes out to about 1 kWh they lose for every 80 miles I drive, so it's not a whole lot. But I'm guessing if you added this up for every Model S owner the utility companies are probably losing a measurable amount of power here. For the average driver at 12000 miles per year, that's 150 kWh of heat losses on the utility side. Let's say there are 1,000 Model S in the state (out of the air figure)... that's 150 megawatt hours per year, or about $18,000 in electricity at the national average rate, in power that just heats wires between your house and the transformer.
Now I'm sure others have better or worse losses, but still... seems interesting to me and something that I bet utilities will eventually start taking into account. However, I bet the losses over X years are still less than the cost of using copper service entrance conductors over aluminum... so maybe not.
-wk
All of the wiring I used for my project is copper, and probably a gauge larger than needed. My sub-panel to HPWC run is 2 gauge copper, roughly 40 ft. The sub panel is fed from a 200A breaker through 3/0 gauge copper through a 200A transfer switch then over from the utility service panel. (The transfer switch will let me cut off the utility later...)
So anyway... I measured my voltage drops trying to figure out my resistive losses.
At the HPWC before starting a charge I was at 249V. It's only me and one other house on a rather large transformer currently, so, the good starting voltage is pretty normal. Only about 2kW of other loads on the 320A (400A) service.
Measuring the voltage at the HPWC and at my service panel, they were virtually identical under no load (within a couple tenths of a volt, within a reasonable margin of error).
After starting to charge at 80A, voltage at the car dash sagged to 237V, at the inside of the HPWC about 238-239V (I know the cable for the HPWC is less than ideal already so this was expected).
At my 200A sub panel where the HPWC is connected, 239-240V, and at my service panel 240V.
So, between the car and my service panel I have roughly a 3V drop. This comes out to only ~240W of heat radiating off of the 25' HPWC cable, 40' of 2 gauge from the HPWC to the sub panel, and ~30' of 3/0 between the sub panel and service panel. The majority of it being the charge cable itself. This is pretty good and shows that all of my connections are pretty solid on my wiring. After 90 minutes, confiming with my FLIR cam shows a pretty negligible temperature rise on that run. Virtually nothing on the 3/0, about a 20F rise on the 2 gauge, and the 100A breaker sitting at about 35F above room temp. All normal or better than normal.
So... we started with 249V.... that means there is a 9V drop between my service panel's mains and the transformer. 9V @ 80A is 720W of heat coming off of that wiring... and that wiring is on the utility's side of the meter, sans ~4 feet of it (a staight line on Google maps from my meter to the transformer is about 170').
So, lets say I charge for 3 hours (what I'm doing now since my HPWC was offline for a couple of days for my rewire job). Thats 3*720W = 2.16kWh in heat losses in the service conductors. 2.16kWh that the utility is paying for, not me, since it is on their side of the meter. The losses on my side of the meter are negligible. That is a 3-4% "toll" the utility is paying.
Granted, that comes out to about 1 kWh they lose for every 80 miles I drive, so it's not a whole lot. But I'm guessing if you added this up for every Model S owner the utility companies are probably losing a measurable amount of power here. For the average driver at 12000 miles per year, that's 150 kWh of heat losses on the utility side. Let's say there are 1,000 Model S in the state (out of the air figure)... that's 150 megawatt hours per year, or about $18,000 in electricity at the national average rate, in power that just heats wires between your house and the transformer.
Now I'm sure others have better or worse losses, but still... seems interesting to me and something that I bet utilities will eventually start taking into account. However, I bet the losses over X years are still less than the cost of using copper service entrance conductors over aluminum... so maybe not.
-wk
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