I don’t know much about solar tech, it sounds simple but how easy is this to do on a big scale? - eg does having an open circuit damage the panels if they are illuminated?
No, you just turn them off. It's a big photodiode.
However, what's quite common is that renewable energy is not sold at the spot price but instead at a "strike price" agreed at time of construction, which gives the stability to finance the project. So asking a plant to turn off their grid input will invoke a penalty clause for "curtailment". This is more common with wind turbines.
And I assume you can have open circuits on generators (from nuclear or other) -- there'd be somewhat less inductive drag on the generator, but I assume that's not a requirement for operation, esp. at low power. (Though I assume you don't want to short/shunt all your power unless you really want to heat something up...)
Seems like you could at least be doing inertial storage by pumping water uphill or lifting huge cement blocks so you can harvest that potential energy later.
Opening the circuits on a steam turbine without reducing the incoming flow of steam is a bad idea: the 'inductive drag' on the generator is where a large fraction of energy is leaving the system! If you don't do anything the turbine will destroy itself fairly quickly. The next thing you can do is route the steam past the turbine, which will effectively waste some of the thermal energy through the condensors. However in most nuclear power plants these condensers aren't designed to take the full energy output of the reactor, so if you remove all the load from the system you'll need to reduce the reactor's power output, which is not a fast operation to reverse (fossil fuel based power stations will generally be able to react faster in this case).
But long and short is if you interrupt the power going out from a nuclear power station it will not be producing useful power for a while! (it won't damage anything but it'll take some time to get it back up to normal operation).
Generating electricity creates mechanical load on the generators that in turns allows to discharge the energy in generated high pressure steam.
At some point you hit a case where you can't go lower without shutting down completely, and that involves all parts of the system - just spinning up or down a steam turbine can be a harrowing moment as depending on the whole setup there could be an RPM range where the harmonic oscillation might destroy the whole thing (as my grandfather, who was working as engineer on steam turbines for electricity generation, described it: "we would slowly spin the turbine to the critical RPM range, then open the throttle to cross the critical range in as short time as possible, then do slow and steady to the rated RPM")
Well you can't just magically do nothing with all that energy, it's not something I know a lot about, but I assume the risks (i.e. reasons you cannot open circuit) include arcing across contacts, and excess heat build-up.
