Grids are tricky, because the electric socket is kind of a leaky abstraction for heavy plant machinery in turbines of thermal plants, load balancing, synchronisation, and a gazillion other things I really don't understand.
Is a grid built on renewables and batteries somehow more resilient? Solid state things tend to be less fiddly, hence my question.
I remember reading at one point in the past that renewables were actually worse for the grid due to less predictable power generation or something, but that was a long time ago, certainly pre-battery storage.
I'll give a somewhat simpler answer than Filligree has. The problem with renewable energy sources is that they are typically both highly variable and not dispatchable (i.e., controllable). The former leads to supply peaks that can exceed transmission capacity or supply lows that require compensating generation elsewhere. The latter means that energy generation can easily be increased or decreased as required, which is of course very helpful for grid management. Dispatchable generation can be increased if supply requires it, or multiple dispatchable generators can be 'redispatched' to relieve congestion in a part of the power grid (by rebalancing generation). Power from renewable sources can be decreased through curtailment, but that wastes the generated energy.
The "problem" with renewables is that they are not dispatch-able, meaning you will never be 100% sure that tomorrow or a week for now there will be sun or wind in a specific region. On the other hand, a nuclear or a coal powered plant, know months in advance if they will be available for peak load or not.
Yes, if it is sunny or windy, they can be scaled in minutes, but only if conditions are met. The inverse is true for nuclear/coal - they cannot be scaled up & down in minutes.
Yeah, hence I mention batteries specifically in my question. I guess a renewable grid will need a lot of batteries. And presumably these are highly dispatchable?
> Is a grid built on renewables and batteries somehow more resilient?
So this is a complicated subject in itself, and a full answer won't fit inside this textbox. Some bullet points:
- Grid stability is maintained by batteries, but not literally. The "batteries" in question are typically rotating generators, i.e. turbines, wind, literally anything where you have an electrical coupling to a lot of physical inertia. That's what keeps the grid running second-to-second; while a power plant might pretend it's outputting a constant 4MW, it actually shifts noticeably from moment to moment. The kinetic energy of the generator helps balance that out.
- Going up from the sub-second range, an overload of the generator obviously would cause the shaft to slow down, dropping the frequency and causing brownouts. Brownouts are bad and can damage the grid, so typically breakers will disconnect if it falls below 49Hz; a 2% drop.
- Baseload plants can't cope with this, as they take multiple minutes to spool up. Minimum; for something like a coal power plant, where you have to shove in additional coal and wait for it to catch fire, it's going quite a few minutes. This is what defines 'baseload'.
- Peaker power plants can increase (or decrease) their mechanical power production in a matter of seconds. These days that typically means gas turbines, though hydroelectric power is even better, and nuclear power could be used for peaker plants -- but isn't; most nuclear reactor designs outside of the navy is a baseload design. France does have some load-following designs, and we need more of those.
- Wind turbines can't increase their output, flat out, but they can decrease it (by feathering, or by using brakes). This is good enough, except this would turn them into 'peaker plants' that can't help with peaks. If we had enough wind turbines to cover 100% of the load then we'd technically be fine, but economically speaking that doesn't work; they'd be at less than 10% power most of the time.
- Wind turbines have rotating shafts, but a lot of the time they produce DC power, linked through inverters, which removes that benefit and makes them act like solar panels in effect. However, this is a purely economic issue; they can trivially be upgraded to support grid stability if the pricing scheme will pay for it.
- Solar panels are worse: They have no inertia! There is no rotating shaft there to cover sub-second usage spikes. That's where complaints about 'renewables causing reduction of grid stability' come from, along with issues like domestic solar needing to backfeed power through distribution lines and transformers that aren't necessarily designed for that.
- But batteries can absolutely help. The kinetic energy of a rotating turbine isn't actually that big; it's not that expensive to pair a solar panel with a battery to build a grid-forming system that acts the same way a kinetic power plant would.
For wind turbines, solar, and batteries, the frequency stability is doable through controlling frequency from inverters.
Some wind turbines are also internally a hybrid design that can dynamically adjust the frequency difference angle both for minimal losses in production, but also to provide frequency shifting and even artificial demand (i.e. essentially using wind power as brake)
The inertia provided by synchronous generators was in essence a natural benefit to the grid that we never appreciated previously. But now with more renewables it’s now something we have to consider and design for. Running a grid on 100% non synchronous requires a bit more effort!
It almost sounds like running a large motor/generator with a large flywheel on it, just for the purposes of frequency stabilization and flattening load spikes, may be a good idea in a large solar installation. The downside is the mass and the bulk, and the cost of copper. The upside is zero reaction time.
Is a grid built on renewables and batteries somehow more resilient? Solid state things tend to be less fiddly, hence my question.
I remember reading at one point in the past that renewables were actually worse for the grid due to less predictable power generation or something, but that was a long time ago, certainly pre-battery storage.