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Off peak power demand


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#1 Capt Worley PE

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Posted 13 March 2012 - 12:32 PM

Generally, what is the percent differnce in demand load between peak and off peak load?

I know there's really not a general answer, as there are a lot of variables, but give me what you can.

#2 Wolverine

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Posted 13 March 2012 - 01:12 PM

A load profile is cyclical and highly variable based on region, temperature, season, etc. etc. (mostly region and temperature).

In the south in the summer the load profile is roughly a bell curve peaking at about 5pm. Sun comes up, the earth warms, AC comes on, load is up, 5pm everybody goes home

In the winter, it's a little more complicated, as load comes up in the morning, dips a little during the day, then blips up again around late day, then 5pm everybody goes home.

Spring and Fall? Forget a description - it looks like a wet piece of spaghetti thrown on the wall

So the Summer peak/profile is not the Winter peak/profile and Spring and Fall are something completely different. And for some regions, the winter is the peak and summer is the low load period. So to say there are a lot of variables is indeed a vast understatement.

But for a broad, broad, broad generalization using the South as an example (for discussion purposes only and with all appropriate "unless-its-not" caveats in place), one could say that the baseload (5AM) is roughly 60% of the peak (5PM) on a day where there's a big swing.

Keep in mind that if a couple of clouds blow over, the base/peak ratio gets much tighter.

I have no idea what the Winter profile in a cold northern state looks like. Summer looks like this I think ------------------------------------

#3 Master slacker

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Posted 13 March 2012 - 01:27 PM

Earlier this month (and this is a BROAD generalization using one day and one base-loaded set of turbines), one of our plants produced 739 MW from 7 AM to 5:20 PM. It produced 618 MW until 5 AM the next morning. Meh

#4 Capt Worley PE

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Posted 13 March 2012 - 02:06 PM

I was just wondering if there was enough slack in nightime capacity to support much of a population of plug-in electric cars recharging during nightime off-peak. I believe it takes 16kW-hrs to fully charge a Volt.

#5 Master slacker

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Posted 13 March 2012 - 02:37 PM

Our plants (a chemical facility with power plants, not strictly a power producer) has the capability to produce over 1500 MW, but are curtailed to the grid. I have no idea how the nuke facilities in the area operate.

#6 mudpuppy

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Posted 13 March 2012 - 05:42 PM

I have no idea what the Winter profile in a cold northern state looks like. Summer looks like this I think ------------------------------------


MI's summer load profile sounds identical to what you described for the South, but then we DO have air conditioning load around here, just a smaller magnitude. Definitely not a flat line, so we must not be a "cold" northern state. :P

I would be interested in seeing Florida's winter load profile, considering they set their peak demand in the middle of winter. I remember a couple years ago when then were interrupting load in the winter and schools were closing due to it "only" being 60 degrees inside (which is where I keep my thermostat set at home). I'm guessing they peak around 5 am and drop off when the sun comes up?

#7 Wolverine

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Posted 13 March 2012 - 07:05 PM

When I was a kid we used to spend summer in upstate New York. When it got hot, I asked why they didn't turn the air-conditioning on. They just looked at me funny. (actually it was more like "Why don't ya'll turn the air-condishnin' on?" Maybe that's why they were looking at me funny).

I've seen more houses up there in my adulthood that have what I would call a normal dual system, not just heat. Back then, no AC.

I'd be interested to see some different region load profiles too. What is the delta for a hot day in MI? What does the cold weather profile look like?

#8 engineergurl

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Posted 13 March 2012 - 07:08 PM

we had a stucco house in upstate ny growing up... during the summer, the windows got opened at night an right before the sun came up, Dad would run around shutting windows and blinds... by the afternoon, we were all hanging out in the basement waiting for the sun to go down so the upstairs would cool off again... here in Alabama, I couldn't live without my air...

#9 snickerd3

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Posted 13 March 2012 - 07:21 PM

we had a stucco house in upstate ny growing up... during the summer, the windows got opened at night an right before the sun came up, Dad would run around shutting windows and blinds... by the afternoon, we were all hanging out in the basement waiting for the sun to go down so the upstairs would cool off again... here in Alabama, I couldn't live without my air...


Ceiling and box fans growing up in chicago area. On occassion a single window AC unit was put on to cool the bedroom area. lots of hangin out in the basement and simply playing outside in the heat...we weren't wimpy kids back then. The water bill was just a little higher those months from running in the sprinkler.

My parents didn't get central AC until I was away at college.

#10 engineergurl

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Posted 13 March 2012 - 07:27 PM

my parents still don't have central AC

#11 jregieng

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Posted 13 March 2012 - 11:10 PM

What is this peak load that you speak of?

#12 Capt Worley PE

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Posted 14 March 2012 - 11:57 AM

here in Alabama, I couldn't live without my air...


You can get used to almost anything. Grew up with a partial AC house, but spent most time in the non-AC section (or with AC off--money doesn't grow on trees, you know). You get used to dressing for the heat and 'layin' useless' on the porch when it was stifling heat and humidity. Then again, the house was built pre-1940 and was designed for souther heat: tall ceilings, few windows compared to today, large porches and overhangs, oriented to avoid afternoon sun exposure, and trees planed for summer shade.

A lot of energy could be saved if we still built them this way.

#13 Master slacker

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Posted 14 March 2012 - 12:02 PM

here in Alabama, I couldn't live without my air...


We did without power for two weeks back in 2008 with hurricane Gustav (?). The heat was fine, but the heat with humidity was very uncomfortable when sitting on the sofa.

#14 engineergurl

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Posted 14 March 2012 - 12:14 PM

thinking about it, back in Aug 2007 when I was in North Carolina the heat pump broke and I didn't have the money to fix it for about three weeks, I had a lot of fans going, windows opened at night and I survived. I guess when you don't have much choice in the matter, you just deal with it... but I still love being able to set the thermostat to 70 and walk into the house on a 100 degree day...

#15 Master slacker

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Posted 14 March 2012 - 12:52 PM

^^^ That reminds me of my sophomore year at school. I lived in the old Pentagon barracks at LSU, which had no A/C... ever... until a couple of years ago. Anywho, we were on the first floor, had two LARGE windows, two box fans, and a live oak shading our building. I can't say that I was ever uncomfortable in that dorm even when the temperature reached 100. I miss college. :(




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