De-carbonising electricity generation

1. We'll need both wind and solar, plus hydro, tidal, small hydro, and wave power, and any legacy nuclear.   The reason we'll need both wind and solar is that the wind blows at night, when the sun isn't shining, and also that they are negatively correlated.  In summer in high latitudes, the wind drops off, but solar is surprisingly strong.  In winter, the sun in high latitudes is dim, but the winds tend to be strong.  Together, wind and solar can produce much less variable output than either on its own, except in the tropics.
2. We'll need 4 hours of storage.  4 hours will be enough to handle the morning and evening peaks in demand, and to do some short-term smoothing of the random fluctuations in wind, though geographically diversified wind farms will help with this.  But 4 hours will not be enough to take wind and solar to more than 90% of total generation.  We'll need long-term storage for that.
3. We'll have built-in generation overcapacity.  Remember, that wind and solar variability can mean not just too little generation but also too much.  Up to now, when it's potentially too much, the grid operators curtail output of wind and commercial solar farms.  They're also getting the ability to curtail output of rooftop solar too, in many locations.  In future, this output will not be lost but used to generate green hydrogen.
4.  Storing hydrogen is hard.  Its atoms are very small and easily escape through the interstices between larger atoms, meaning the using hydrogen for seasonal storage will be much less effective than using methane.  It also makes pipelines brittle.  Green methane can be made from hydrogen using the Sabatier method, with a small additional loss of energy.  Methane is already routinely stored for months with minimal losses; there are already methane (natural gas) grids in most mid- to high-latitude developed countries, where seasonal storage will be needed; gas peaking plants will not need to be retro-fitted to handle hydrogen; methane is much easier to store and transport than hydrogen; and it can be used for heating, though electric heat pumps may be cheaper and more efficient.
5. It's possible, though I am not convinced, that we will need some small percentage (10- 20%) of nuclear in the grid.  But we are a long way from 80% wind and solar penetration in most global grids--the most recent data have the global average at 10%.  Setting aside legacy nuclear, new nuclear, if it happens, will tend to be smaller plants, because the giants are just so expensive.  I've talked about SMRs, micro nuclear and the great potential for hydrogen-boron fusion reactors, but these are all at least 5 to 10 years away from them being successfully deployed.
6. Micro-hydro, tidal power, wave power and electricity generated from incinerating/gasifying rubbish will all be handy additions to the grid, because they  are uncorrelated with wind and solar.  Even waves, which are driven by wind, can be created by winds hundreds of kilometres away.

OK, how does the actual transition happen?

1. We could leave it to the market.  Wind and solar are much cheaper than new coal and gas, and comparable to existing coal and gas in most places on the globe.  As existing fossil fuel power stations age, they will be replaced by renewables plus storage.  This will take decades, however, so, since we want to substantially reduce emissions from power generations as quickly as possible, we'll need to give this process a nudge.
2. We could set targets for renewables.  Each utility/electricity producer will be required to achieve an annual/quarterly percentage from renewables, rising steadily over time, aiming for 100% within a decade.   Those utilities which exceed this target will earn carbon credits, those utilities which don't reach this target will have to buy credits.  This carbon penalty will encourage utilities to build out more wind and solar farms, as well as other renewable supply, including nuclear.
3. We could run a reverse auction where individual power stations would offer to close down for a fee.  Let's say a decline of 10% a year in emissions from electricity generation is required.  Each year, the government would offer a lump sum payment to the power stations which would close down, choosing those with the lowest offers until the total reaches 10% for that year.  Conditions could be applied to any deals: redundancy payments to workers; requiring the output of the power station to be replaced with new "firmed" output from renewables; making sure the new wind and solar farms are located close to the communities where coal power stations are ceasing to operate.

Source: Our World in Data

Most powerful tidal turbine ever starts generating

 

From The BBC

A tidal-powered turbine, which its makers say is the most powerful in the world, has started to generate electricity via the grid in Orkney. The Orbital O2 has the capacity to meet the annual electricity demand of 2,000 homes for the next 15 years.

In May, it was sailed out of Dundee, where it was assembled over 18 months.

The 680-tonne turbine is now anchored in the Fall of Warness where a subsea cable connects the 2MW offshore unit to the local onshore electricity network.

Orbital Marine Power said its first commercial turbine, which will be powered by the fast-flowing waters, is a "major milestone".

It is also providing power to an onshore electrolyser to generate green hydrogen.

The turbine's superstructure floats on the surface of the water, with rotors attached to its legs which extract energy from the passing tidal flow.

 

It is held on station by a four-point mooring system with each mooring chain having the strength to lift over 50 double decker buses.

Electricity is transferred from the turbine via a dynamic cable to the seabed and then through a static cable to the local onshore electricity network.

The company is now aiming to commercialise its technology in a move it says will deliver a jobs boost to coastal communities.

Mr Scott said: "We believe pioneering our vision in the UK can deliver on a broad spectrum of political initiatives across net zero, levelling up and building back better at the same time as demonstrating global leadership in the area of low-carbon innovation that is essential to creating a more sustainable future for the generations to come."

The construction of the O2 turbine was enabled by public lenders through the ethical investment platform, Abundance Investment.

It also received £3.4m from the Scottish government's Saltire Tidal Energy Challenge Fund.

Energy Secretary Michael Matheson said: "With our abundant natural resources, expertise and ambition, Scotland is ideally-placed to harness the enormous global market for marine energy whilst helping deliver a net-zero economy.

"The deployment of Orbital Marine Power's O2, the world's most powerful tidal turbine, is a proud moment for Scotland and a significant milestone in our journey to net zero."

On my calculations, this tidal generator will provide about 2% of Scotland's power, meaning that just 5 of these will provide 10% of Scotland's electricity.  Scotland uses roughly 10% of the UK's power, so 50 of these machines could provide 10% of the UK's electricity.   We can get to ±90% renewables in the grid, with around 4 hours of storage.   Larger percentages of wind and solar will require exponentially more storage, so the remaining 10% will need to come from more stable generation sources.  For now, that will likely be gas, but tidal power, wave power, and micro hydro, though each will be relatively small on their own, could fill the gap.  Tidal power is more expensive than wind because it is a relatively new technology.  But the question is: is it more expensive than the exponential jump in battery storage we'll need to get to 100% without it?  And is it more expensive than nuclear?