Diesel Fuel

[FulmenParticipant @fulmen]

All useful energy has value, this has always been true. So, no free energy ever, not even if one could make it for free.

[Kiwi Bloke]

On Kiwi Bloke Said:

On Robert Atkinson 2 Said:

No we could not. The current design of the UK grid (and most others) relies on a certain level of mechanical generation for stability. This is literally mechanical inertia. Historically it was provided by the rotating generators. Now they are having to add huge flywheels with attached motor generators.
It’s not just renewables that need this. The high voltage DC links used for international power transfer also need them.

This is another area where nuclear power (especally small distributed generation like Small Modular Reactors if they ever happen) has an advantage as they use rotating generators.

… can you explain why stability of the grid requires (temporary) mechanical energy storage? Clearly, there are lots of rotating generators in service, and use can be made of their rotational energy, but is mechanical storage a necessity? Wouldn’t battery storage (assuming the batteries are practicable and affordable) also work? If so, solar farms, for example, with massive batteries, would seem (to this layman) to provide advantages regarding grid stability.

Mainly to balance supply and demand.  Both vary slowly, suffer occasional violent outages, and have to cover many peaks and troughs in between. Get it wrong and the lights go out, and electricity costs more.

• Domestic demand tends to fall during the day, rise after dark until bedtime, then drop until we get up and suddenly turn lights, heating, kettles, showers etc on.    Industry and commerce  tend to consume more power during working hours than at night or weekends.   Several other cycles in play, like winter and Summer.
• Supply varies too: on a clear day solar is dirt cheap compared with fossil fuels, but depends on the weather, and drops to zero during the night.  A nuclear leak will shut a reactor down in seconds, causing gigawatts to disappear.  Accidents,  system failures, distribution faults and human error all cause crunches.

Elaborate control systems and engineering are applied to prevent brown-outs, cuts and over-provision.  Over provision is a serious problem when cost matters, and it always does!

The supply system applies different technology to meet various circumstances, and they overlap:

• the average level below which demand never falls was historically met by slow-to-change generating plant like coal and nuclear.  Both have significant disadvantages.
• gas turbines excel at covering demand that’s changing slowly over hours rather than minutes, and, for time being, natural gas is cheap.  Some are engineered to power up within about 5 minutes, which is useful.   Unfortunately natural gas is not sustainable in the long run.
• Renewables are cheaper, safer, low CO2 and pollution, sustainable and independent.   But much harder to match supply to demand. Though feeding renewable power into the grid reduces money, wear, and pollution by allowing gas turbines to be switched off, renewables can’t guarantee 24×7 availability.  Some form of storage is needed.
• Storage is also required to cover short-term peaks and troughs – fast events, typically lasting less than 10 minutes.  The grid is a grid, arranged so that a broken power line is bypassed by switching in an alternative route, but, even though this is semi-automatic, it can take several minutes to restore order.  During that time supply and demand are unbalanced, and bad things happen unless it’s managed!  Several options:
  • Inertial energy in generators will cover a few tens of seconds, maybe!
  • Inertial energy supplied by a giant flywheel is common.  How much cover depends on the size of the wheel.
  • More recently, “virtual inertia” has gained ground.  They’re particularly good for renewables that don’t spin big generators, like solar!  A useful alternative to flywheels because they provide more control, but it’s not that one is better than the other. Horses for courses.
    • Usually provided by giant batteries and inverters.  UK has about 10GWh of batteries installed, with a further 14GWh in construction.  The plan is to have 90GWh.   Batteries react in the 50 to 100mS range, so worst case within 5 cycles at 50Hz.  Batteries are also good for ‘black start’ cover, that is what happens when several power sources go down and have to restart at the same time – they have to synchronise with the same 50Hz source, usually another power station.  But which one depends on what went wrong, and who is ready to go first, and…
    • Less common, compressed Air, and pumping water to a height.
    • Super-Capacitors too: their advantage is speed rather than capacity, covering fast events less than 50mS, and I’m not aware fast-glitches are a big problem,
    • In development, chemical energy for turbines: Hydrogen, Ammonia, Hydrazine, all of which can be made with surplus renewable electricity.

Flywheels and the various forms of virtual inertia are not intended to power the grid for very long!  They flatten peaks and troughs, which is good for consumers and suppliers.  Apart from preventing brown-outs, they reduce wear and tear on the machines.  Generators and turbines are jolted every time demand fluctuates rapidly.  Batteries and flywheels absorb the shock, reducing maintenance, and increasing mechanical reliability and service life.

Power is managed in other ways too.  One, very common technique is to reduce the energy delivered to consumers by altering the frequency.  Look closely and the mains is not held exactly at 50Hz.  Another is to change patterns of consumption by altering the tariff: not a new idea, Economy 7 encouraged us to burn electricity at night to soak up coal-powered over-production.  (Coal generators work best at full capacity, not on a throttle)  Tariffs apply to wholesale electricity too – it’s bewildering.  Also possible to disconnect customers by district, or category.

Modern engineering and how it’s exploited are far from simple.   Diesel and electricity are intertwined.  Much more to diesel that filling up on a forecourt, and much more to electricity than plugging in a lathe.  Which reminds me, I have to make something!

Dave

 

[Author]

Posts