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First day in Europe. Windmills

James Lemon

James Lemon

Well-known member
Jerome Marot said:
Yes, particularly for solar panels which produce direct current. One of the major manufacturers of converters for the home market in Europe is based in the Netherlands, BTW (Victron Energy).



I don't understand what you mean by grid inertia. As to solar panels, they obviously cast shade and plants don't grow well in the shade. When panels are installed on the ground, depending on the kind of ground, grass may still grow under them and needs to be regularly trimmed. I have not seen gravel being installed under solar panels.
Click to expand...
"Historically, in the U.S. power grid, inertia from conventional fossil, nuclear, and hydropower generators was abundant—and thus taken for granted in the planning and operations of the system. But as the grid evolves with increasing penetrations of inverter-based resources—e.g., wind, solar photovoltaics (PV), and battery storage—that do not inherently provide inertia, questions have emerged about the need for inertia and its role in the future grid."

"If a coal plant is like a large cyclist with high inertia, a power converter is like a tiny exercise bike with basically no inertia at all, even if it supplies more electricity than the coal plant".

blogs.dal.ca

Reliability issues with renewable energy

blogs.dal.ca blogs.dal.ca
 
Jerome Marot

Jerome Marot

Well-known member
I see. What this "inertia" concept means is that power plants running essentially large alternators will lower their frequency under overload while electronic power converters will not and will switch off instead.
This is true, but this is by design. Power converters are designed to disconnect when the frequency is out of range as this is generally considered beneficial. While it was not in the specific case of Australia, I do not know.
Presumably, authorities may decide to change the regulations on power converters to allow for a revised behavior under heavy load if that is found to be beneficial. Or the grid can be redesigned with that problem in mind. It is not an unsolvable problem.
 
Doug Kerr

Doug Kerr

Well-known member
Greetings,

A gratuitous essay on this topic.

******

In each of the four distinct “power grids” serving the United States and Canada, most of the electrical power has traditionally come from turbines (steam, gas combustion, or water), driving synchronous alternators (generators). These all regulate their operation to deliver the appropriate quota of power into the grid while operating at such rotational speeds that the frequency of the grid is precisely as intended (60.0 Hz).

If a major power station on the grid unexpectedly has to suddenly stop operation, its contribution must now be picked up by the other participants. But the nature of turbine-driven alternators is such that they cannot do this “instantaneously”. The result is that, for a short period, the turbines/alternators a slow a bit, and thus the frequency of the grid will “dip”, not an ideal situation.

But mitigating the slow response of the turbine‑driven alternators is the fact that each one stores, in its spinning rotor, a substantial amount of energy in mechanical kinetic (“inertial”) form. This energy is inherently and immediately contributed to the grid (at every such power station) without any action on the part of the control systems. As a result, the “grid frequency dip” that might otherwise occur is greatly reduced.

But today a substantial part of the power generated in each of these grids comes from photovoltaic (solar) systems. These differ in two ways (with respect to the issue here) from traditional turbine-driven alternator systems. Firstly, they can almost instantaneously increase their output power (up to the maximum possible at the moment) when needed in the event of loss of capacity elsewhere. That is an advantage for such systems.

But they do not have an equivalent of the “inertial energy” held by traditional turbine-driven alternator systems. Thus they cannot quickly and briefly “punch above their weight” to cope with the dynamics of loss of another major source. That is a disadvantage for such systems.

Thus the planning of the configuration and management of power grids has be done under a new set of realities.

*****

An excellent paper on this matter is available here:

https://www.nrel.gov/docs/fy20osti/73856.pdf

Best regards,

Doug
 
Doug Kerr

Doug Kerr

Well-known member
As to power converters "shutting down" when loaded to beyond their capacity, this is of course a perfectly valid notion of itself, and certainly applies in various situations (I suspect it applies to inverter-type portable generators). But it does not play a role in the behavior of multiple generating facility power grids.

Suppose that in such a grid one small photovoltaic facility had a power converter that is limited in output to to, say 2 MW. (Let's not worry for the moment about whether that is continuous or for some short period). Suppose that at this moment the solar irradiation on the PV panel array is enough that it could indeed lead to that output.

The system is controlled so that it only will push (if it has the solar "soup" to do so) up to 2 MW into the grid. There is no way that it can be "overloaded" - there are perhaps 1000 other generating stations "rowing this boat". It in Marxian fashion, it delivers "what it can".

So that converter will never (at least from a load standpoint) be obligated to shut down to save its life.

Best regards,

Doug
 
Robert Watcher

Robert Watcher

Well-known member
British Countryside

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Doug Kerr

Doug Kerr

Well-known member
One of the many generating stations on the Western Interconnection grid ("Dos Palmas PV") is located at our home here in Alamogordo, N.M. It all the time feeds into the grid the power that can be developed from the maximum DC output of the photovoltaic panel array (based on the current solar irradiance) but never greater than 7.61 kW (the inverter is rated at 7.6 kW).

Then our home draws from the grid whatever it draws. The inverter actually knows nothing of this. (Metering for billing by the electrical energy utility company, the operator of the grid as it reaches us, is another matter altogether.)

If in fact the voltage of the grid falls above or below some limits, or if the frequency of the grid goes outside some limits (I have no idea what any of those are), the converter will shut down. The inverter doesn't wish to play in a game where the properties are greatly irregular.

Best regards,

Doug
 
Robert Watcher

Robert Watcher

Well-known member
A toned black and white of the old Ghent Post Office. I took 6 exposure variations in camera and ran them all through Affinity Photo HDR compositing. I then creatively processed the final result in Snapseed. All done on old iPad


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