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Solar and batteries have some challenges about maintaining frequency and syncrhonization. When using spinning magnets (wind/steam turbines) the frequency is rel

by rocqua 4y ago

Solar and batteries have some challenges about maintaining frequency and syncrhonization. When using spinning magnets (wind/steam turbines) the frequency is related to power draw. As demand spikes, the generators get slowed down. Effectively the rotational inertia works a bit like a buffer. Balancing the grid is hence a matter of 'maintaining frequency'. Which makes the frequency very stable. Solar and batteries are inherently DC. They have converters that take a reference AC signal, and output their energy synchronized to that reference. Incidentally, this makes it difficult to run your house off solar during a black-out, because you lack the reference. Even in smarter converters that don't need a reference to match the frequency, they still need a reference to synchronize the phase. When we move to more batteries and solar for generation, that will put more strain on the spinning-based generation for short-term fluctuations. Less spinning mass means less buffer. At some point, any flaws in behavior of DC converters might start dominating. If they happen to resonate with each other, we might see some weird things.

jeffrallen 4y ago
It is categorically untrue that "it is hard to run your house off solar". Thousands of sailboats, and country houses around the world do just that. It is true that if you insist on making the cutover from inverter derived AC to grid AC without an interruption, you will need some subtle circuitry that can automatically "glide" the inverter into synchrony with the grid before cutting over. I don't know if Tesla, Bluetti, and EcoFlow devices do this, or just make a step-change in the phase and frequency of the output. That would be an interesting investigation, maybe Matthias Wander can do it?
- rocqua 4y ago
  From what I remember the main problem is code requirements around being able to go from 'isolated' back to being connected to the grid. If you are out of phase when the grid gets back, it gets damaging. So it is difficult to get an approved system that can do it.
Panzer04 4y ago
I feel like the bigger issue would be lack of feedback, since presumably an inverter can maintain perfect frequency under any load right up until it can supply Lo more power; I suppose voltage measurement might become more relevant than frequency in such cases (or perhaps inverters are programmed to lag a bit under load, though that seems needlessly artificial)
- rocqua 4y ago
  A perfect frequency can be kept easily, but it wouldn't remain synchronized with the rest of the grid. You could try to drag the grid to a perfect frequency by lagging or leading the pattern. But that feels like it wouldn't work.
rcxdude 4y ago
It's pretty easy to get inverters attached to a battery to act like "virtual inertia", in fact this kind of service to the grid is an area where they massively outcompete traditional turbines (providing far better frequency stability for lower cost). This concern is a complete non-issue if you have even a small fraction of the storage that a renewable grid needs.
- rocqua 4y ago
  That works for stabilizing power levels. It doesn't do much for stabilizing the frequency of the grid.
  - rcxdude 4y ago
    It does both (while there's still spinning generators on the grid, those are exactly the same thing because of how the generators work. When there aren't any on the grid, they are in principle seperate, but the inverters will still use the frequency as a signalling mechanism, since it's a very robust means of controlling a system as large and complex as a grid).
Fabricio20 4y ago
I wonder if at some point, with solar and batteries on most houses, we'll make the switch to DC power inside the house. Maybe with some low voltage wiring (lights and such) and high voltage wiring circuits (other appliances). This way we avoid the loss of converting from DC to AC and remove most of these issues entirely. Sure, a lot of appliances wouldn't work in DC power, specially appliances that have motors in them, so for those we can have the DC to AC unit. Same thing for generating power back into the grid, just have one of these converters strapped to our house output/input.
bombcar 4y ago
It would seem that the frequency and synchronization could be solved by referencing both to the atomic clock, which is a time signal available most anywhere and via methods that are not grid dependent. Perhaps it is not accurate enough.
- rocqua 4y ago
  The problem isn't accuracy. It's not generally important to hold perfect frequency. The importance is in coordination. If the grid frequency lags a little bit, then other plants should also lag, to prevent being out of phase.

by rocqua 4y ago

jeffrallen 4y ago

It is categorically untrue that "it is hard to run your house off solar". Thousands of sailboats, and country houses around the world do just that. It is true that if you insist on making the cutover from inverter derived AC to grid AC without an interruption, you will need some subtle circuitry that can automatically "glide" the inverter into synchrony with the grid before cutting over. I don't know if Tesla, Bluetti, and EcoFlow devices do this, or just make a step-change in the phase and frequency of the output. That would be an interesting investigation, maybe Matthias Wander can do it?

rocqua 4y ago
From what I remember the main problem is code requirements around being able to go from 'isolated' back to being connected to the grid. If you are out of phase when the grid gets back, it gets damaging. So it is difficult to get an approved system that can do it.

Panzer04 4y ago

I feel like the bigger issue would be lack of feedback, since presumably an inverter can maintain perfect frequency under any load right up until it can supply Lo more power; I suppose voltage measurement might become more relevant than frequency in such cases (or perhaps inverters are programmed to lag a bit under load, though that seems needlessly artificial)

rocqua 4y ago
A perfect frequency can be kept easily, but it wouldn't remain synchronized with the rest of the grid. You could try to drag the grid to a perfect frequency by lagging or leading the pattern. But that feels like it wouldn't work.

rcxdude 4y ago

It's pretty easy to get inverters attached to a battery to act like "virtual inertia", in fact this kind of service to the grid is an area where they massively outcompete traditional turbines (providing far better frequency stability for lower cost). This concern is a complete non-issue if you have even a small fraction of the storage that a renewable grid needs.

rocqua 4y ago
That works for stabilizing power levels. It doesn't do much for stabilizing the frequency of the grid.
- rcxdude 4y ago
  It does both (while there's still spinning generators on the grid, those are exactly the same thing because of how the generators work. When there aren't any on the grid, they are in principle seperate, but the inverters will still use the frequency as a signalling mechanism, since it's a very robust means of controlling a system as large and complex as a grid).

Fabricio20 4y ago

I wonder if at some point, with solar and batteries on most houses, we'll make the switch to DC power inside the house. Maybe with some low voltage wiring (lights and such) and high voltage wiring circuits (other appliances). This way we avoid the loss of converting from DC to AC and remove most of these issues entirely. Sure, a lot of appliances wouldn't work in DC power, specially appliances that have motors in them, so for those we can have the DC to AC unit. Same thing for generating power back into the grid, just have one of these converters strapped to our house output/input.

bombcar 4y ago

It would seem that the frequency and synchronization could be solved by referencing both to the atomic clock, which is a time signal available most anywhere and via methods that are not grid dependent. Perhaps it is not accurate enough.

rocqua 4y ago
The problem isn't accuracy. It's not generally important to hold perfect frequency. The importance is in coordination. If the grid frequency lags a little bit, then other plants should also lag, to prevent being out of phase.