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Mike_hearn's comment was grey but was correct: phase following is indeed done through software in the inverter. Phase matching is still required, wherever the phase difference is not zero there is a deadweight loss of power as heat.

Currently the main driver of battery deployments is not so much energy price time arbitrage as "fast frequency fresponse": you can get paid for providing battery stabilization to the grid.

(for the UK not Spain: https://www.axle.energy/blog/frequency )

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Oh that is fascinating.

So if you have a smarter solar panel, or a smart battery, you can stabilize the grid. I’m assuming that all of the traditional software complexity things in distributed systems apply here: you want something a little bit smart, to gain efficiency benefits, but not too smart, to gain robustness benefits.

My intuition is that bringing the market into it at small timescales probably greatly increases the efficiency significantly but at the cost of robustness (California learned this “the hard way” with Enron)

> Phase matching is still required, wherever the phase difference is not zero there is a deadweight loss of power as heat

If the electronic controller is “ahead of” (leading) the grid, then that heat would come from the solar plant; if it is “behind” (following) then that heat comes from the grid. Is that right? And likely, solar plants opted for the simplest thing, which is to always follow, that way they never need to worry about managing the heat or stability or any of it.

I wonder if the simplest thing would be for large solar plants to just have a gigantic flywheel on site that could be brought up via diesel generators at night…

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Most solar and wind plants follow the inertial lead of the thermal plants. They can't synchronize without enough thermal generation being online. Supposedly there are efforts to change that, I don't know enough about grid engineering to say how far along that might be in Spain.
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> But with solar, how is the synchronization provided? In like a giant buck? Or in software somehow? Does the phase shift matter as much as in the electromechanical systems?

If you mean how does solar detect phase and synchronize to the grid: https://en.wikipedia.org/wiki/Phase-locked_loop

If you mean how does solar act to reinforce the grid: search for terms like "grid forming inverter vs. grid following inverter" though not all generators are the same in terms of how much resilience they add to the grid, esp. w.r.t. the inertia they do or do not add. See e.g. https://www.greentechmedia.com/squared/dispatches-from-the-g...

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Harder mostly, See the frequency is set by huge rotating masses in the form of generators, and when the supply and demand is matched the frequency and voltage are stable, when demand dramatically increases it pulls the frequency and voltage down, which is effectively slowing the generators down as load / magnetic drag increases with current drawn. Having large inertial masses spinning actually helps smooth out frequency changes. whilst large solar farms can and do syncronise with the grid, they are reactive and do not add the same smoothing effect as humungous spinning masses.

Low Grid frequency & voltage can cause an increase in current & heating of transmission lines and conductors and can damage the expensive things, this is why these systems trip out automatically at low frequency or low voltage, and why load shedding is necessary

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> Harder mostly, See the frequency is set by huge rotating masses in the form of generators

I'm not saying you're wrong, but this isn't obviously correct to me.

Since solar going to a grid is completely dependent upon electronic DC->AC conversion, I would expect that it could follow a lot greater frequency deviation for a lot longer than a mechanical system that will literally rip itself apart on desync.

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the person you replied to is mostly wrong.

The real reason that small scale solar PV is grid following (i.e. it depends on an external voltage and frequency reference) is that this ensures power line safety during a power outage. That's it.

An inverter can be programmed to start in the absence of an external reference and it can operate at a wide range of frequencies.

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About 10 years ago I had a chance to work in the Utilities vertical for a power producer. I asked the same question: how is the frequency set and the answer was that the biggest power plant sets the frequency because they can produce a lot power and any other smaller generator would not be powerful enough to change the frequency.
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Sure, the smaller plant gets pulled into the larger plant's inertia.

However, DC-AC converters don't have an inherent inertia. They can follow almost any frequency and phase within reason. Certainly a DC-AC converter should be able to respond way faster than any frequency/phase changes that a mechanical system can generate.

In theory, they should be able to set themselves to be ever so slightly closer to ideal so that the amount of power they have to sink is limited but are still exerting a very slight force to bring the grid back into compliance rather than continuing to add load which propagates the collapse.

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I'd say a little harder to negligible now, but potentially way easier in the future.

The main difficulty is that the software of grid-following inverters tend to make them trip out very suddenly if the grid parameters get too far out of spec (they will only follow the grid so far), but once the grid is good they basically instantly synchronise.

But all large solar farms are likely to be mandated to switch from grid following to grid forming inverters eventually which will make them beneficial for grid security because they will help provide 'virtual intertia' that looks exactly the same to the rest of the grid as spinning mass does.

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