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 )

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.

> 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...

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

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.