Electric / hybrid aircraft propulsion (NOT cars)

I recall someone needed an explanation of my term “steam cycle”, which is what it was called in the 1970s. I found a good one here.

The LA Times article highlights a long existing and well known problem with connecting Solar and Wind to an otherwise gas fired power grid: it requires that you maintain spinning reserve in existing conventional power plants, meaning that due to startup/shutdown issues gas fired plants run anyway, but at reduced power. That in turn means that in order to meet renewable goals on paper for local (in this case California) consumption you end up paying to make gas fired power and then paying others to take it. Arizona residents are the recipients of the gift and are laughing all the way to the bank: their utility company is paid to consume gas fired electricity that can used to power their state (including any electric aircraft!)… just so it stays ‘off the books’ in California where the natural gas is actually paid for and burned

achimha wrote:

A temporary problem Silvaire and not a reason against

It’s indeed the classical grid problem. Wind and solar lack one fundamental thing, the ability to produce on demand. It’s only half of the coin, they only collect energy, they are incapable of producing power (energy delivery on demand). The solution is to store energy somehow. The way it is going now, is distributed battery storage. It’s still a bit expensive, but sooner than we know, solar power combined with batteries will become as everyday in every house as light bulbs are today. For more industrial energy requirements, other solutions are coming also.

LeSving, I think there is a fundamental comprehension mistake. Solar & Wind do not “collect” energy – they transform one form of energy into another. Just like a coal or CCGT transform stored chemical energy into electrical energy.

Wind and Solar very much have the capacity to “produce on demand” – I think the word you’re looking for is “convert” – as a matter of fact they can be turned on and off even faster than a peak load CCGT powerplant. You just need enough of them out there to meet peak demand, and enough grid capacity. Solid electrolyte batteries & hydro storage should take care once and for all of the “what of the wind doesn’t blow at night or what if the moon stops causing tides” issues.

Shorrick is right. Local variations in sunshine and wind strength do even out over a larger area, so if you have a say pan-european smart grid capable of routing say overproduction in say a windy Denmark to a cloudy/overcast area in Spain where solar isn’t producing as necessary and do the inverse on another day where no wind is blowing in Denmark but the sun shines all over Spain, then you have a solution to the unpredictable output from renewables.

Shorrick_Mk2 wrote:

LeSving, I think there is a fundamental comprehension mistake. Solar & Wind do not “collect” energy

I disagree. I know what you mean, and you are not wrong, only it’s not the usual usage in the energy business.

In the energy business we use the terms power and energy. I know they have SI definitions, but power means energy on demand, ie the grid needs power to maintain frequency and voltage when the production is smaller than the consumption. It’s a grid stabilizing thing, not a consumption thing. Energy means everything else that is not power, the steady flux of energy for consumption. All energy and power is “electric” and have no real meaning outside the electrical grid. Energy for thermal plants is produced (fossil or nuclear fuel). Energy for hydropower is collected and stored (dams). Energy for solar and wind are neither. They aren’t producers of electricity, they are collectors. They cannot produce energy nor power on their own. They cannot serve the grid alone. The grid is 3 phase AC, and for it to work, both active and reactive power is “needed”, it’s an intrinsic part of the grid, the distribution of AC electric power and energy. If there are no suppliers of reactive power, the grid will collapse. Solar being solid state DC produce zero reactive power. It is utterly incapable of serving the grid, but combined with batteries and clever power electronics they say it is possible (I’m not sure if someone actually has made it work, but when distributed (solar and battery), it will have very little negative effect on the grid, because the net flux of energy is almost negligible to from a house.

Today when thinking solar power, we automatically think PV cells. For larger plants, this does not seem to be the best option though. Concentrated solar power using the sun to heat up water for a steam turbine, seems to be a cheaper and simpler way to serve the grid for large scale production.

Shorrick_Mk2 wrote:

You just need enough of them out there to meet peak demand, and enough grid capacity

The problem here is that it would be like having an aircraft with 100 engines, and a requirement that if 99 engines are broken, the aircraft must be able to fly one 1. It would be ridiculously expensive and inefficient.

Your energy business might be different than the rest of the energy business that uses SI definitions… but grid balancing has nothing to do with power <> consumption.

W regards to your engine analogy – how “expensive and efficient” is it to have CCGTs stand by to pick up load spikes and provide “reactive power”? It’s exactly the same thing.

For solar being “utterly incapable of serving the grid” it certainly seems to work so well that utilities lobby against feed-in tariffs…

I assume the megawatts of electricity from wind generators will lead to a lowering of atmospheric temperature. Air has a low energy capacity compared to water. Or has conservation of energy now been disproved?
Tidal energy seems the obvious choice for Scotland, with hundreds of narrows in sea lochs and between islands, and tides are predictable, but that’s not been the politicians choice.