Rooftop Solar in AZ: Actually helping the grid

[BackwoodsEE]

One case where PV solar actually makes sense, economically and societally, is on rooftops in Arizona when it's hot out (nine months of the year) and the grid is struggling to keep up with the demand from all those AC compressors humming away (much of the summer). This summer, power records were broken from the heat and Phoenix's sprawling population: http://www.azcentral.com/story/money...ona/416536001/

And rooftop solar actually made a difference! As an electrician friend of mine who lives there put it, they now have all these mini power plants all over town. The good news is that they produce power when it's needed most, for once.

The peak demand would have been slightly higher were it not for rooftop solar, which reduces a homeowner's draw on the power grid while the sun is shining. Solar customers also send power to the grid when they are not using it all from their panels, reducing what the utilities generate.

The bad news is that the AC units are still on as the sun moves west and then sets. The Phoenix asphalt-and-concrete heat island needs massive cooling all evening long in the summer. And all those compressors heat the surroundings even as they try to cool off the home interiors. So, the utilities are seeing demand shifting.

As more rooftop solar is installed, the peak demand for Arizona utilities gets later in the day, when power from those panels drops off.

"In 2012, the average peak for the months of June through August typically occurred around 4:30 p.m.," APS spokeswoman Annie DeGraw said. "In 2016, our average peak during the summer months occurred around 5:15 p.m. While we will not have the average peak time for 2017 until the fall, we believe that the peak will continue to migrate to later in the day."

The shift means utilities need more power sources that can pick up the demand quickly as solar drops off at night, she said.

[max2k]

One case where PV solar actually makes sense, economically and societally, is on rooftops in Arizona when it's hot out (nine months of the year) and the grid is struggling to keep up with the demand from all those AC compressors humming away (much of the summer). This summer, power records were broken from the heat and Phoenix's sprawling population: http://www.azcentral.com/story/money...ona/416536001/

And rooftop solar actually made a difference! As an electrician friend of mine who lives there put it, they now have all these mini power plants all over town. The good news is that they produce power when it's needed most, for once.



The bad news is that the AC units are still on as the sun moves west and then sets. The Phoenix asphalt-and-concrete heat island needs massive cooling all evening long in the summer. And all those compressors heat the surroundings even as they try to cool off the home interiors. So, the utilities are seeing demand shifting.

why they would need more power sources one more time? I understand Sun is out but those loads existed without PV in place. If anything they should see decrease in absolute peak. The fact that its remaining part shifted later should not make it worse for them.

[SunEagle]

why they would need more power sources one more time? I understand Sun is out but those loads existed without PV in place. If anything they should see decrease in absolute peak. The fact that its remaining part shifted later should not make it worse for them.

The problem is since the power is now coming from the solar installations the POCO generating plants are sitting idle or on a low burn. Starting them up in the evening when the sun is no longer out makes it much more expensive to run then just having them run all day at an output that is efficient.

Starting and stopping none RE power generation is much more expensive then just running them continuously all day long.

[max2k]

The problem is since the power is now coming from the solar installations the POCO generating plants are sitting idle or on a low burn. Starting them up in the evening when the sun is no longer out makes it much more expensive to run then just having them run all day at an output that is efficient.

Starting and stopping RE power generation is much more expensive then just running them continuously all day long.

I see what you're saying but the actual pre- and current graphs would help: I think what happened is the max shifted later and became lower so the POCOs actually can shut down some of their generation facilities and run the rest continuously, just like they did to accommodate previous mid day peak. If the shape of that curve changed a lot then yes, they might have a problem. My point is their load was Sun dependent and vary variable before PV due to thermostats turning on more AC during day and somehow that was not a problem.

[J.P.M.]

The problem is since the power is now coming from the solar installations the POCO generating plants are sitting idle or on a low burn. Starting them up in the evening when the sun is no longer out makes it much more expensive to run then just having them run all day at an output that is efficient.

Starting and stopping RE power generation is much more expensive then just running them continuously all day long.

Hence a place where energy storage may find a home.

[jflorey2]

]Starting and stopping RE power generation is much more expensive then just running them continuously all day long.

I think you meant "starting and stopping conventional power generation is much more expensive." Which I agree with in the case of coal and nuclear; however, modern combined cycle gas plants and hydro plants are quite easy to throttle. (And of course solar and wind are very easy to throttle.)

[SunEagle]

I think you meant "starting and stopping conventional power generation is much more expensive." Which I agree with in the case of coal and nuclear; however, modern combined cycle gas plants and hydro plants are quite easy to throttle. (And of course solar and wind are very easy to throttle.)

Yes that is what I meant. Thanks for catching my error.

The problem that most people don't understand is the cost of having a gas plant just sitting there for most of the day not doing anything and then starting it up when it is needed at night can cost a lot of money. It isn't as simple as starting up a small gas generator by yanking on a pull cord. It takes time, people and money to start one up. Even having them sit at low throttle is more costly then running them at optimum speed. The POCO will justify passing on the extras cost for that type of action which means higher electric costs.

Hydro may be able to be throttled but you are forgetting the problem they had in CA back when there was a drought. Little water in the pond made it hard to get the hydro up to full speed. And even if there was water available putting more down stream could cause high water levels and floods. Throttling hydro has it's limits

[jflorey2]

Hydro may be able to be throttled but you are forgetting the problem they had in CA back when there was a drought. Little water in the pond made it hard to get the hydro up to full speed. And even if there was water available putting more down stream could cause high water levels and floods. Throttling hydro has it's limits

Yes - however since throttling is fast and incurs no efficiency penalty, solar (and wind, and other intermittent renewables) has the immediate benefit of saving water during times of drought.

[SunEagle]

Yes - however since throttling is fast and incurs no efficiency penalty, solar (and wind, and other intermittent renewables) has the immediate benefit of saving water during times of drought.

That is a possibility but there is not enough hydro to support the entire US and during drought times it can't support what it was designed for.

Sorry. While I understand you want to look at the bright side of RE, I believe I have a more practical understanding about the reality of power generation and the ups and downs of keeping the lights on.

I have been in the electrical and power industry for over 40 years and while the grid may be changing you still need a based power source that can run 24/7/365. It will take decades to get RE to become a major power source for the US and there still is the chance that someone will be in the dark if they rely totally on RE.

[J.P.M.]

Yes - however since throttling is fast and incurs no efficiency penalty, solar (and wind, and other intermittent renewables) has the immediate benefit of saving water during times of drought.

Maybe a little but not entirely tongue in cheek:

Since a lot of common hydro can and does work at least partially by virtue of storing energy and/or raising a mass for later recovery and use (the Niagara Power Projectson both sides of the river being two good examples), maybe taking the water out of the process and using something else as the weight would be possible. I fully appreciate, maybe more than most, what the lowered efficiencies mostly from the increased friction would cause, and that pumped hydro can be very efficient. But, rocks are about as available as water and gravity has the same effect on both. Maybe the cost of the inefficiencies produced by changing the nature of the material mass used could be justified by some lowered acquisition and operating costs from fewer/smaller plants that have greater than the needed response time. I've noticed lots of rocks near desert PV plants.

[jflorey2]

Since a lot of common hydro can and does work at least partially by virtue of storing energy and/or raising a mass for later recovery and use (the Niagara Power Projectson both sides of the river being two good examples), maybe taking the water out of the process and using something else as the weight would be possible. I fully appreciate, maybe more than most, what the lowered efficiencies mostly from the increased friction would cause, and that pumped hydro can be very efficient. But, rocks are about as available as water and gravity has the same effect on both. Maybe the cost of the inefficiencies produced by changing the nature of the material mass used could be justified by some lowered acquisition and operating costs from fewer/smaller plants that have greater than the needed response time. I've noticed lots of rocks near desert PV plants.

At least one company wants to use trains on mountains. Trains come with massive motor/generators (a diesel locomotive's traction motors can output ~5 megawatts) and hopper cars full of rocks are as cheap as it gets.

[jflorey2]

That is a possibility but there is not enough hydro to support the entire US and during drought times it can't support what it was designed for.

Of course. It's a good solution for New England, Las Vegas and the Pacific Northwest, but it certainly won't work everywhere.

[max2k]

Maybe a little but not entirely tongue in cheek:

Since a lot of common hydro can and does work at least partially by virtue of storing energy and/or raising a mass for later recovery and use (the Niagara Power Projectson both sides of the river being two good examples), maybe taking the water out of the process and using something else as the weight would be possible. I fully appreciate, maybe more than most, what the lowered efficiencies mostly from the increased friction would cause, and that pumped hydro can be very efficient. But, rocks are about as available as water and gravity has the same effect on both. Maybe the cost of the inefficiencies produced by changing the nature of the material mass used could be justified by some lowered acquisition and operating costs from fewer/smaller plants that have greater than the needed response time. I've noticed lots of rocks near desert PV plants.

1kg of anything lifted 10m has potential energy of 0.028 Wh compare to lead acid battery of 30-40 Wh/kg

[max2k]

At least one company wants to use trains on mountains. Trains come with massive motor/generators (a diesel locomotive's traction motors can output ~5 megawatts) and hopper cars full of rocks are as cheap as it gets.

and a roundtrip efficiency of the process would be what, 50%? At least they'd warm up the area pretty well . Good thing you don't need to load/unload those rocks.

[SunEagle]

and a roundtrip efficiency of the process would be what, 50%? At least they'd warm up the area pretty well . Good thing you don't need to load/unload those rocks.

Except when you need to perform maintenance on those rail cars.