Hacker News Reader

Comment by bennofs | Hacker News Reader

> Imagine the massive spinning generators as a big mass that slow down just a little bit when you switch on a light and then that generator has to add more steam (or open hydro valve or whatever).

I have always wondered, would that still hold true if the grid was fully solar-based? There would be no rotating mass in that case.

View on HN

Yes, although a significant issue with that is there is no spinning mass to "borrow" inertia from, so while modern inverters at solar sites are good at shaping output phases, they have very little capability to absorb significant frequency deviations.

Grid scale battery systems are often used for voltage or frequency stability as opposed to deep discharging as generation offsets, although that will change eventually if batteries get better enough or really cheap LNG stops being a thing.

Yes indeed, inverter based generators (solar and batteries) don't have any inertia. But as long as the grid is still AC the frequency will be the same and the inverters would need to compensate internally. Especially with solar where a cloud going over a solar farm can easily knock off a few MW in seconds the volatility of the grid will increase and need for storage (batteries, hydro, etc) alongside Demand Side Response is getting much bigger.

It does hold true for some systems. Wind turbine generator controls can provide virtual inertia over very short time scales (a second or few) by exchanging energy with the turbine rotor. You can also provide primary frequency reserve in the negative direction (load step-off) using exactly the same ramp control that steam plants use. Typical ramp rate is 100% of rated power for a 5% change in frequency.

However, in order to provide primary frequency reserve in the other direction, you do need additional local storage. You don't need very much. Just 10% of rated power for 15 minutes gets you to very deep renewable penetration.

The trouble isn't with the technology, its with the economics. Once you set a sufficiently high price for frequency support and primary frequency reserve, suppliers will show up.

Reply on news.ycombinator.com