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Comment by GlennS | Hacker News Reader

While it's clear that nuclear is uneconomical now and in the near future, it's still not quite clear to me if we can do without it.

Solar and wind are great, cheap options right now, and they've really outperformed what people expected over the past few years. Is there enough potential capacity of solar + wind + hydro to meet total future demand though? Are we going to run out of land and coast first?

If we're going to reduce our carbon emissions enough by 2050, we need to electrify heating, industry and transport. That's going to increase electricity demand by a lot.

Carbon capture and storage is pretty clearly dead. Tidal lagoons seem like they're also just too expensive. Neither fusion nor alternative fission technologies will be up and running in time to make much difference to the 2050 target for 80% reduction from 1990 levels (UK specific).

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Is there really a concern about running out of land/coast for power generation? I feel like there is a lot of space left.

The bigger issue to me seems to be the move from production we can control to production on nature's schedule. Nuclear plants can "just" "throw another rod in" and generate power as needed.

The promise there appears to be a distributed approach. Getting people installing batteries in homes as standard could make it so buying electricity when it's being produced rather than when you need it is the norm. The economics incentivise this and hopefully the tech is getting there. Combine that with the likely move to everyone having an electric car (read: giant battery) sat on their drive doing the same thing half the time, and maybe that problem is being solved.

I don’t think nuclear power is that on demand, can you really just throw a rod in when starting and stopping the plant is so expensive?

You can regulate a nuclear plant between ~50% and 100% output in a matter of minutes by adjusting the control rods.

That's very limited compared to most other options, but obviously much better than solar or wind.

And far worse than batteries

Batteries, like hydro reservoirs, can be charged from inflexible energy sources when they have surplus output. It really isn’t fair to compare them to energy sources as they can smooth over the inflexible ones.

Since they are direct substitutes it seems reasonable to compare them to me.

Again, batteries make sense with inflexible energy production methods. So if you want to use that coal more effectively, get a bunch of batteries or a lake up a hill to pump into.

Not at practical capacities. We're talking about a pair of 1.6GW reactors, so the control rods can adjust total generation by 1.6GW in a matter of minutes. How many batteries would it take to supply 1.6GW for a reasonable amount of time (let's say 24 hours)? How much would that cost?

100mw output of batteries costs $38m, so 16 of those costs $0.6b, 3% of the cost of Hinckley C, even assuming no more overruns.

Ok that only gives you 1 hour of charge, but your requirement was changing in minutes. These batteries respond to load change in milliseconds.

> 100mw output of batteries costs $38m, so 16 of those costs $0.6b, 3% of the cost of Hinckley C, even assuming no more overruns.

So 24 hours' worth would cost 72% of the cost of Hinkley C, and that's not including any amount of power generation. Looks like wind/solar + enough batteries to timeshift their output to match consumption would end up costing more.

> Ok that only gives you 1 hour of charge, but your requirement was changing in minutes. These batteries respond to load change in milliseconds.

The ability to change quickly is only part of the problem; if you want to run the country on wind or solar then you need to be able to handle several overcast or calm days in a row.

> if you want to run the country on wind or solar then you need to be able to handle several overcast or calm days in a row.

On a country scale yes, but not on a continental scale. Although in the case of solar, you probably just want to have peak output twice the size you’d expect for naive insolation, and it looks like it’ll be cheap enough soon enough for that to be economical.

No, you can't. I spent 22 years as a operations nuclear plant supervisor and I can tell you this can't be done. Two to four mw/min power increase, depending on several factors, is the norm. Power follows steam demand is an old saw in the industry. You slowly open the turbine valves and dilute the coolant in the reactor to keep things in balance. Control rods are kept fully withdrawn at all times at power.

So the nuclear reaction has constant power output, you just throw the energy you don't want away by using coolant instead of turning the turbines? That sounds.. inefficient.

My quotes were intended to show I didn't really think it was that easy, but compared to making the wind blow or the sun shine, it's "easy".

Is there enough potential capacity of solar + wind + hydro to meet total future demand though?

Yes. And very easily too. ANU did a study in Australia and found pump hydro could cover 100% of the supply needs while only using a small fraction of available sites. Australia is a very flat country so I'd imagine it is even easier in most countries.

See http://www.anu.edu.au/news/all-news/anu-finds-22000-potentia...

Australia is also very large and very low population. Less than 2/3rds the population of California but about 18 times the area.

That shouldn't really matter. It was something like 1% (?) of the available sites to make Australia 100% renewable. So in the US it might be 15% - except that the US has a lot more mountains and a lot more water near population centers.

We could provide the world's total energy needs by covering a small portion of the Sahara desert with solar. We are not running out of land anytime soon.

There is also a practical limit where wind energy takes too much energy out of weather systems, affecting climate, but that point is also far beyond the current world energy usage.

We're not running out of renewable energy anytime soon.

A single hurricane produces about 200 times the global energy use per year. We're not able to extract power from the atmosphere to make a dent.

>We could provide the world's total energy needs by covering a small portion of the Sahara desert with solar.

The Sahara desert is extremely sandy, and extremely windy, which makes it a pretty terrible, or at least prohibitively-expensive place to build a solar farm.

It is also extremely complicated and extremely expensive to transmit large amounts of power over long distances, particularly across national borders (everyone's on a different AC standard), particularly across many national borders.

It's not really that complicated or that expensive to move power over long distances via HVDC interconnects.

China has many overland HVDC links, some thousands of km long and with huge capacities, to move renewable energy from inland areas to the coast.

The UK and Iceland are considering an undersea HVDC interconnector more than 1000 km long.

The distance between potential solar array sites in the northern Sahara and the electrical grids in Southern Europe are considerably less than this.

> The UK and Iceland are considering an undersea HVDC interconnector more than 1000 km long.

At an estimated cost of about 3 billion, for less than 1/3 the capacity of this power station.

Icelink's estimated cost is about £2.4b, which would be shared by both sides.

Hinkley C's construction cost is £20.3b, and the cost to UK consumers over the plant's lifetime exceeds £50b.

Wind at say 1GW in 200 square miles (dogged bank figures)

Total sea area therefore is 1 million gw or 1,000tw, or 24ktwh/ day

Need 200k twh for global energy usage, with 30% to spare

Wind loading of average 25%, you need to cover less than 10% of the sea area to produce enough evergy to replace every form of power on the planet - not just electricity.

10% of the sea is absolutely huge though.

On land, it's the area of Russia, Canada and the US, completely covered with wind farms.

That's for the entire global energy production (and then some), including transport, heating, industry, not just electricity.

10% of land is set aside for agriculture, which is about 1/3 of 10% of water, but gives an indication. That's an area far larger than the entire US (including Alaska). We use a lot of space.

But you wouldn't produce your entire output from wind. In a desert you get about 2kwh per day from solar per square metre, or 2gwh per square km, or 100,000 SQkm of land for solar.

That's under half the size of Arizona's desert, or 1% of Sahara.

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