mitch672
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Re: PV Solar now cheaper than Nuclear

Tue Sep 28, 2010 6:55 pm

garygid wrote:I suspect that PV Inverters (DC to Grid AC) should automatically scale back production of AV if the Grid Voltage rises "too" high, right?


I don't think that's possble, unless they "shunt" some of the power to "load banks", or shutdown some of the array strings by removing the inverter load from them (which is wastefull). If there was excess energy (not likely to happen), it could/should be used to "pump" water uphill for storage (a form of battery).
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garygid
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Re: PV Solar now cheaper than Nuclear

Tue Sep 28, 2010 7:23 pm

The Inverter can decide how much current to draw from the solar panels, and thus control how much AC current (and thus power) it feeds back "into" the Grid.
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evnow
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Re: PV Solar now cheaper than Nuclear

Tue Sep 28, 2010 7:30 pm

garygid wrote:The Inverter can decide how much current to draw from the solar panels, and thus control how much AC current (and thus power) it feeds back "into" the Grid.


Even so, that would just reduce use of renewable energy - not store that energy for later use.
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Re: PV Solar now cheaper than Nuclear

Tue Sep 28, 2010 7:36 pm

garygid wrote:The Inverter can decide how much current to draw from the solar panels, and thus control how much AC current (and thus power) it feeds back "into" the Grid.
IIRC, to the inverter, the "Grid" is really the transformer on the pole followed by the substation transformer. Both are extremely low impedance relative to the inverter, so the inverter can always adjust the voltage and sync the phase to just feed power into the "Grid", assuming the house does not present a larger load.

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Re: PV Solar now cheaper than Nuclear

Tue Sep 28, 2010 10:42 pm

While it's possible to design an inverter to regulate the amount of AC power it produces from PV panels, the only situation that I've seen this done is in off-grid setups to avoid overcharging batteries.

I believe that some SMA inverters will look at the AC frequency and adjust output based on that.

http://www.sma.de/en/products/knowledge ... agers.html

For example, some can be configured to reduce output if the grid frequency rises above 60Hz - this typically indicates an oversupply of power on the grid.

Of course, this isn't optimal - in general wind/solar generation is throttled only as a last resort as it has the lowest running cost - everything else typically will cost more so it's more cost effective to throttle down any fuel burning plants first.

It will take some time for enough renewable generation to show up on the grid to incur frequent throttling - when that happens expect demand for storage devices to take off. At that point it won't take long for smart-grid EVs to show up - in aggregate there will be a ton of battery capacity available if they are plugged in.
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Yodrak
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Re: PV Solar now cheaper than Nuclear

Tue Oct 05, 2010 2:20 pm

Hmmmm, I don't see why. The automatic control systems and human operators who manage the grid control frequency within tight limits, but they are often playing 'catch up' in one direction or another. Frequency will often run low for extended periods of time during daytime peak low periods, and then will intentionally be run high overnight to compensate.

Also, from the system operators point of view, residential PV output is not generation, which they control to manage frequency and voltage. It's negative load that fluctuates like all other load, and what the operators see and have to contend with is the total load on the system net of any residential PV.

Certainly you wouldn't want residential PV generation to cut back just because system frequency went above 60 Hz.

garygid wrote:I suspect that PV Inverters (DC to Grid AC) should automatically scale back production of AV if the Grid Voltage rises "too" high, right?



Wind generation is already being throttled at times in some places, because it is the last resort in localized situations where it is the wind output that is overloading the lines and there simply are no fossil units that could be curtailed to relieve the overloads. Transmission systems are designed to meet (in most places) summer peak loads, when maximum generation is required, with lesser attention paid to winter peak loads and summer 'shoulder' peaks. They are not designed with consideration given to minimum load periods, which is when wind generation tends to generating the best.

Also, the best places for wind generation tend to be places where there is not much existing generation, transmission, or load. So again, in certain places and at certain times, even though there may not be much wind capacity in comparison to total system capacity, there is more wind generation than can be used and no non-wind generation to back down. It's not a big problem yet, but it is happening and will only happen more often in more places as wind capacity becomes a larger piece of the generation mix.

In the upper midwest, the need to back down wind generation is already happening enough that the regional transmission operator is preparing proposals to submit to the Fededral Energy Regulatory Commission to make wind generation automatically dispatchable, under the control of the system operators, so that wind farms can be easily backed down when system conditions call for it.

drees wrote:While it's possible to design an inverter to regulate the amount of AC power it produces from PV panels, the only situation that I've seen this done is in off-grid setups to avoid overcharging batteries.

I believe that some SMA inverters will look at the AC frequency and adjust output based on that.

http://www.sma.de/en/products/knowledge ... agers.html

For example, some can be configured to reduce output if the grid frequency rises above 60Hz - this typically indicates an oversupply of power on the grid.

Of course, this isn't optimal - in general wind/solar generation is throttled only as a last resort as it has the lowest running cost - everything else typically will cost more so it's more cost effective to throttle down any fuel burning plants first.

It will take some time for enough renewable generation to show up on the grid to incur frequent throttling - when that happens expect demand for storage devices to take off. At that point it won't take long for smart-grid EVs to show up - in aggregate there will be a ton of battery capacity available if they are plugged in.
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garygid
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Re: PV Solar now cheaper than Nuclear

Tue Oct 05, 2010 7:37 pm

Grid frequency is controlled, and high or low frequency, by itself, does not mean over or under generation. That is usually observed as over or under VOLTAGE in the system.
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c1987
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Re: PV Solar now cheaper than Nuclear

Mon Oct 25, 2010 2:40 pm

This should help the CA power mix a bit when completed. I know of another solar plant and a wind turbine plant going
in near the central coast. It will be interesting to watch the power mix get greener.

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drees
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Re: PV Solar now cheaper than Nuclear

Mon Oct 25, 2010 3:11 pm

c1987 wrote:This should help the CA power mix a bit when completed. I know of another solar plant and a wind turbine plant going
in near the central coast. It will be interesting to watch the power mix get greener.

Yep, and you can watch it (in near real time) here:
http://www.caiso.com/outlook/SystemStatus.html

They include real time wind power and yesterday's renewable power charts. I'm hoping they also include real time solar power as some of these new big solar plants come on line.

I still have to wonder how much rooftop solar isn't included on those charts...
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Re: PV Solar now cheaper than Nuclear

Thu Oct 28, 2010 11:09 pm

Nuclear powered Leaf? Worse than renewable, better than coal?

I found this article on Thorium in Popular Mechanics when I went to read their article on the Leaf. Supposedly the reason we use uranium today is the 1950's need to produce plutonium for nuclear weapons. Thorium is 3-4x more plentiful, produces 200x more energy per ton, produces much less radioactive waste, and is useless for making weapons. Instead of waste that has to be safely stored for 10,000 years, waste from thorium reactions would be dangerous for "only" 600-700 years. It sounds much better. Good enough? I don't know.

http://www.popularmechanics.com/science/energy/next-generation/the-truth-about-thorium-and-nuclear-power?click=pp
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