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Inertia is stored energy. To emulate an energy storage, you need to be able to get energy from "somewhere". That's just physics. Plus, it works both ways: If th

Inertia is stored energy. To emulate an energy storage, you need to be able to get energy from "somewhere". That's just physics. Plus, it works both ways: If there is excess power, you also need to dissipate power from the grid. But an individual solar inverter fluctuates wildly, and has no significant amount of energy stored (e.g. in capacitors). It also has no place to put power (okay, you can put it in the PV panels to produce heat, but they won't like that during a hot summer day). That's why they are using batteries to emulate inertia: They are energy storage, and thus can act like inertia. Both putting energy into the system and "removing" it. The power industry is slow moving, so we're only seeing it now. (Not an EE, but I think the reasoning is sound. Proper EEs feel free to teach me)

rstuart4133 2y ago
> It also has no place to put power (okay, you can put it in the PV panels to produce heat, but they won't like that during a hot summer day). Actually solar can vary it's output fairly easily. The inverters are constantly monitoring the voltage from the panels, and rasing or lowering their impedance to extract the maximum energy from them. It is trivial for them to deliberately extract less power by varying that impedance, and that's exactly what happens with solar battery chargers. They have to match what the battery can accept. But from the grid's viewpoint though it would be a pointless additional complexity. The contribution from each household is so small they can achieve the same effect by shutting on and off an entire household, or more likely a suburb. To put it another way they are saying they want to power off solar to ensure grid stability. But at the times you might want to power off solar there is excess capacity. Yes it's not stored, but it's just there, waiting to be turned on or not. Keeping the grid locked to phase is much harder. The inertia of spinning iron does it automagically for a short while, without any complex control systems or fancy programming. They each pull the others into sync. But if the grid falls apart the magic is gone, and it the grid has to be brought up one generator at a time somehow manually syncing each one. That's hard enough when there are 100's of coal fired plants around the country, but can you imagine what it would be like if there are a millions of solar powered homes all trying to have their say in what the phase should be. Maybe this has something to do with that, or maybe not. I'm not a power EE. Interest factoid: most solar + battery setups will not power the house from the battery if they lose grid supply. The reason is the inverter refuses to switch while it doesn't have a grid to sync phase with. If was switched on and then the grid came up at a different phase a lot of smoke would result. You can get setups that will work while there is no grid, it's just that unless you specifically ask for it you may not get it.

rstuart4133 2y ago

> It also has no place to put power (okay, you can put it in the PV panels to produce heat, but they won't like that during a hot summer day). Actually solar can vary it's output fairly easily. The inverters are constantly monitoring the voltage from the panels, and rasing or lowering their impedance to extract the maximum energy from them. It is trivial for them to deliberately extract less power by varying that impedance, and that's exactly what happens with solar battery chargers. They have to match what the battery can accept. But from the grid's viewpoint though it would be a pointless additional complexity. The contribution from each household is so small they can achieve the same effect by shutting on and off an entire household, or more likely a suburb. To put it another way they are saying they want to power off solar to ensure grid stability. But at the times you might want to power off solar there is excess capacity. Yes it's not stored, but it's just there, waiting to be turned on or not. Keeping the grid locked to phase is much harder. The inertia of spinning iron does it automagically for a short while, without any complex control systems or fancy programming. They each pull the others into sync. But if the grid falls apart the magic is gone, and it the grid has to be brought up one generator at a time somehow manually syncing each one. That's hard enough when there are 100's of coal fired plants around the country, but can you imagine what it would be like if there are a millions of solar powered homes all trying to have their say in what the phase should be. Maybe this has something to do with that, or maybe not. I'm not a power EE. Interest factoid: most solar + battery setups will not power the house from the battery if they lose grid supply. The reason is the inverter refuses to switch while it doesn't have a grid to sync phase with. If was switched on and then the grid came up at a different phase a lot of smoke would result. You can get setups that will work while there is no grid, it's just that unless you specifically ask for it you may not get it.