UPDATE: Upon further investigation this argument doesn't carry for most countries because the amount of space required is a constraining factor more than price. It may still be true for countries like Australia.

Last year I changed my mind about nuclear power. This is a position held by a lot of smart contrarian people, and I think we need to update. 

Is this important? I don't think this is as important as many other issues effective altruists focus on. That said, I think paying about as much attention to this as you pay to any other popular political issue seems about right.

Epistemic Status: Check the comments to see if I made any obvious mistakes.

Why was I pro nuclear? Nuclear power can provide cheap reliable electricity without contributing much to climate change. It's not as unsafe as most people feel it is. This made it seem like the ideal solution, if only we could rally the political will. I’m not trying to convince anyone here, but my reasons for supporting are probably similar to others.

What’s changed? In short, renewables are getting cheaper, and are now cheaper than Nuclear. Combined with the fact that rallying support for nuclear would be much harder than for renewables, I think we should update towards supporting renewables. 

Source: Our World in Data

What to do? I'm roughly just going to vote for renewables and against non-renewables. I don't think nuclear is bad, but I am happy to accept the "anti-nuclear pro-renewables" package. I'd love to hear any other concrete suggestions about what to do in the comments.

(A version of this was cross-posted on my blog).

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Cost is one factor, but nuclear also has other advantages such as land use, amount of raw material required (to make the renewables and lithium etc. for battery storage), and benefits for power grid.

It's nice that renewables is getting cheaper, and I'd definitely like to see more renewables in the mix, but my ideal long term scenario is a mix of nuclear, renewables and battery. I'm weakly open to a small amount of gas being used for power generation in the long term in some cases.

I think my (updated based on the comments so far) conclusion is the same as yours!

It seems a little misleading to compare costs in this way. Pro-nuclear people generally don't think we should build more plants with the current cost structure: they think we should reform the current regulatory system (e.g. get rid of ALARA), which would make it much cheaper, and then we should build more. Additionally, they generally oppose closing existing nuclear plants, which are much cheaper to keep running than to build new ones due to the high fixed costs.

I think the main reason that nuclear power is so expensive is that it is subject to extremely strict safety standards that go beyond the regulations imposed on other energy sources, including fossil fuels. Many of these regulations are actually unnecessary to keep people safe; governments should repeal them and reform their regulatory frameworks to achieve the desired tradeoff between cost and safety. There are also advanced nuclear technologies that seem to reduce costs while improving safety, such as certain small modular reactor designs. Maybe with these regulatory and technological advances, nuclear will look more affordable.

This isn't my area, but I thought renewables were hard to get enough consistent power supply from in a lot of places. Was this not an issue? Or has this been solved? Also, land use may be too high.

Some pessimistic takes I've come across previously (one links to the other), possibly biased: https://www.bloomberg.com/graphics/2021-energy-land-use-economy/ https://michaelshellenberger.substack.com/p/finally-they-admit-renewables-are

I wrote a series of posts on the feasibility of an all-solar grid last year, here (it links to two prior posts).

Overall my tentative conclusion was:

  • It's economically feasible to go all solar without firm generation, at least in places at the latitude of the US (further north it becomes impossible, you'd need to import power).
  • The price of the land required for all-solar production seems very small.
  • However, the absolute amount of land required is nonetheless quite large. In the US building enough solar to supply all energy needs through a cloudy winter would be something like 8% of land; in Japan 30%+.
  • I expect this to be a serious political obstacle even if it's not an economic obstacle. (Though in extreme cases like Japan it may also become an economic obstacle since you have to move to increasingly marginal + expensive land.)
  • So in practice I expect most countries to need alternatives to solar for winter generation, at least in places at the latitude of the US  (closer to the equator it  becomes easier).
  • If you have alternatives for winter generation (or long-term storage), the land requirements fall by something like 3-5x. Winter vs summer isn't nearly as big a deal for total costs as for land use (since so much of the all-in cost is batteries and other infrastructure) (ETA: don't see where that 3-5x number came from, might be right but take this bullet with a grain of salt. I do think it's a big factor but maybe not that big?)
  • It seems like all-solar is mostly economically and technically feasible, though in addition to lots of land it requires modest further improvements in battery prices, maintaining back-up natural gas to use once a decade (which is relatively cheap), and building long-distance transmission (which is again affordable but likely to be prohibitively difficult politically).

It was interesting to me that "political feasibility" and "economic feasibility" seemed to come apart so strongly in this case.

Not sure if all of that is right, but overall it significantly changed my sense of the economics and real obstacles to renewable power.

It’s economically feasible to go all solar without firm generation, at least in places at the latitude of the US (further north it becomes impossible, you’d need to import power).

How much does this depend on the costs of solar+storage continuing to fall? (In one of your FB posts you wrote "Given 10-20 years and moderate progress on solar+storage I think it probably makes sense to use solar power for everything other than space heating") Because I believe since you wrote the FB posts, these prices have been going up instead. See this or this.

Covering 8% of the US or 30% of Japan (eventually 8-30% of all land on Earth?) with solar panels would take a huge amount of raw materials, and mining has obvious diseconomies at this kind of scale (costs increase as the lowest cost mineral deposits are used up), so it seems premature to conclude "economically feasible" without some investigation into this aspect of the problem.

This does require prices going down. I think prices in many domains have gone up (a lot) over the last few years, so it doesn't seem like a lot of evidence about technological progress for solar panels. (Though some people might take it as a warning shot for long-running decay that would interfere with a wide variety of optimistic projections from the past.)

I think it's not clear whether non-technological factors get cheaper or more expensive at larger scales. Seems to me like "expected cost is below current electricity costs" is a reasonable guess, but ">75% chance of being economically feasible" is not.

My current understanding is that there are plenty of the relevant minerals (and in many cases there is a lot of flexibility about exactly what to use), and so this seems unlikely to be a major driver of cost over the very long term even if short-term supply is relatively inelastic. (Wasn't this the conclusion last time we had a thread on this?)

Thanks, it looks like you've put a lot of effort into summarising this information (it actually looks better and higher effort than my original post, oop). 

I wrote a series of posts on the feasibility of an all-solar grid last year, here (it links to two prior posts).

Is there a non-FB version of these posts?

No, sorry. Here's a copy-paste though.

Yet another post about solar! This time about land use.

— TL;DR

Suppose that you handle low solar generation winter by just building 3-6x more panels than you need in summer and wasting all the extra power.

1. The price of the required land is about 0.1 cents per kWh (2% of current electricity prices).

2. Despite the cost being low, the absolute amounts of land used are quite large. Replacing all US energy requires 8% of our land, for Japan 30%. This seems reasonably likely to be a political obstacle.

I’m not too confident in any of these numbers, corrections welcome.

— Background

I’ve been wondering about the price of an all-solar grid without any novel storage or firm generation. In my first post I proposed having enough batteries for 1-2 days, and said that buying that many batteries seemed affordable (https://www.facebook.com/paulfchristiano/posts/10226561810329293). In the second I argued that emergency natural gas you never actually use looked like it was totally affordable (https://www.facebook.com/paulfchristiano/posts/10226568532377340).

A potential drawback of the all solar plan is that you *massively* overbuild panels so that you have enough generation in the winter months. This isn’t too expensive because most of your capital cost was storage anyway. But it does mean you use a boatload of land. I wanted to understand that better. See the TL;DR above for my conclusions.

After this post, I think the biggest unresolved question for me is how variable cloud cover is during the winter—I know that large solar installations are pretty consistent at the scale of months (and can fall back to emergency natural gas in the rare cases where they aren’t). But is it the case that e.g. there is frequently a bad 4-day stretch in January where the average solar generation across Japan is significantly reduced?

My second biggest question is about the feasibility and cost of large-scale transmission, both to smooth out that kind of short-term variability and to supply power further north.

— A note on location

The feasibility of this depends a ton on where you are. I’m going to start by talking about the largest US solar farms in the southwest. I believe the situation gets about 2x worse if you move to the US northeast or northern Europe.

If you go further north it gets even more miserable---wintertime solar is much more sensitive to latitude than summer solar. I'd guess that people in the US northeast should already be importing power from sunnier places, to say nothing of Canada. I don’t know how politically realistic that is. If you didn’t have backup natural gas it sounds insane, but if everyone is just building backup natural gas anyway I think it might be OK.

— Efficiency of solar

I looked up the Topaz solar farm (info taken from wikipedia: https://en.wikipedia.org/wiki/Topaz_Solar_Farm).

Setting aside its first year while panels were still be installed, its worst month was December of 2016 were it generated about 57 million kWh.

The “overbuild panels” plan requires us to build enough panels that we’d be OK even in the deepest winter. If we pessimistically assume that all of the excess power is completely wasted, that means you get about 684 million kWh per year.

The site area is 7.3 square miles. So in total we are getting about 94 million kWh per square mile per year. (Or 145 thousand kWh per acre).

I got almost identical numbers for McCoy solar installation.

I think you could push the numbers somewhat higher, perhaps a factor of 2, by economizing more on land (check out that picture of Topaz solar farm from space, tons of room to improve density), improving panel efficiency (once panel costs are no longer a major expense you can focus on efficiency rather than price), and focusing on winter generation. When I did this calculation on paper I got numbers 2-4 higher than the practical ones.

I’m going to just round the number up to 100 million kWh to make things simple. In reality you’d probably increase density above this but may also be pushed to use worse sites, so this seems fine for the headline figures.

— How much land is needed in the US?

In 2020 the US used about 100 quadrillion BTUs of power (mostly oil and natural gas), a bit less than 3e13 kWh: https://www.eia.gov/energyexplained/us-energy-facts.

If we pretend it was always midwinter, this would require 300,000 square miles. This is about 8% of all the land in the US.

To help understand what this means, this site gives us the total breakdown of US land. I don’t trust it totally but I think it’s roughly right. https://www.visualcapitalist.com/america-land-use/

* 842,000 square miles of forest

* 750,000 square miles of shrub

* 530,000 square miles of farmland

* 530,000 square miles of grassland (I assume this breakdown was just made up?)

* 400,000 square miles of other nature

* 63,000 square miles of cities

— How expensive is that land?

Suppose that we put solar farms on cropland. The cost of 1 acre of farmland in the US is about $3000. Renting an acre of unirrigated land is about $140/year. (https://www.nass.usda.gov/.../land-values-cash-rents.pdf)

Pasture is quite a lot cheaper than that, and you’d only have to use ~50% of the US pasture to put in all this solar. So I think $140/acre/year is pretty conservative.

Above we estimated that an acre generated 145,000 kWh per year.

So even if you are renting farmland, and *throwing away all power above the amount generated in midwinter*, the price is only a tenth of a cent per kWh. That’s about 50x lower than the current price of power. So it won’t be a large part of the price until you are dropping electricity costs by 10x or more.

— What about Japan?

Japan uses about 386 million tons of oil equivalent per year, or 4.5e12 kWh. By the same calculation that would require about 45,000 square miles. (I think Japan has fewer good solar sites than the southwest US, so they’ll be leaning more on the hope that you can squeeze more density out of installations).

The area of Japan is about 145,000 square miles. So this is about 30% of the total area. Right now in Japan I believe essentially all of this would have to come from clearing forest. The cost of clearing that land isn’t significant (and it’s not any more expensive than cropland), but I expect people would be unhappy about losing 1/3 of their forest.

— Other thoughts

These proposals involving wasting 65-85% of all the generation. If you are able to use more electricity on summer days, that helps a lot, as discussed in previous posts. The most obvious way this happens is if you can synthesize fuel, and energy costs of synthesis are dominant rather than capital costs. That would be a game-changer for the all-solar grid (as well as removing the need to electrify all your cars and planes).

I’ve ignored increasing energy usage. That seems kind of reasonable because I’ve discussed the US and Japan, two countries with relatively high energy use that has been declining in recent years. But big increases in energy use would change the picture.

In the long run it does seem like floating solar over the ocean could be quite important. But I have no idea how to think about the costs for that, and especially energy transport.

Depending on the design of your panels, putting down this many could change significantly heat the earth just by absorbing sunlight. This is on the same order of magnitude as the heat generated by running appliances (e.g. the heat generated by the engine of your car and the friction of your wheels against pavement), but if your panel is 20% efficient then I think it probably ends up about 2-3x bigger. I don’t normally think about e.g. space heaters contributing to global warming by literally heating up the house. It does seem like a consideration but I’d like to better understand how it compares.

If clearing forests or pasture, it seems important not to release all that carbon into the atmosphere. My guess would have been that most of this land would be at rough equilibrium and so this isn’t going to have a CO2 effect (assuming you don’t burn the biomass or let it rot), but I’d be interested to know, and am not sure if that’s feasible.

And here's the initial post (which seems a bit less reasonable, since I'd spent less time learning about what was going on):

Given current trends in technology and policy, solar panels seem like the easiest way to make clean electricity (and soon the easiest way to make energy at all). I’m interested in thinking/learning about what a 100% solar grid would look like.

Here are my own guesses.

(I could easily imagine this being totally wrong because I’m a layperson who has only spent a little while looking into this. I’m not going to have “I think caveats” in front of *every* sentence but you should imagine them there.)

Overall I was surprised by how economical all-solar seems. Given 10-20 years and moderate progress on solar+storage I think it probably makes sense to use solar power for everything other than space heating, for which it seems like we should probably just continue to use natural gas. I was surprised by how serious and isolated a problem space heating seemed to be.

Other forms of power like nuclear or fusion might be even better, but it feels like all-solar will still be cheaper and easier than the status quo and won’t require any fossil fuels at all. Issues with storage would create big fluctuations in the price of electricity, which would change the way we use and think about electricity but would not change the basic cost-benefit analysis.

ETA: feels like the main problem is if there's variability in how dark winters are and some of them are quite dark. This is related to the heating issue, but might be a big problem even for non-heating needs.

1. Night vs day

It looks like the costs of overnight energy storage will eventually dominate the costs of solar, but still be low enough to easily beat out other power sources.

For example, the cost of a Tesla powerwall like $400/kWH; they can be cycled 5000 times under warranty. If you did that every night for 15 years it’s a total cost of $0.08/kWH stored. The cost of battery storage has fallen by a factor of 3 over the last 5 years and seems likely to continue to fall, and I expect utility-scale prices to also fall to keep up roughly with batteries.

Here are some cost projections of $400/kWH in 2020 falling to $200/kWH in 2030: https://www.nrel.gov/docs/fy20osti/75385.pdf. Here is a description of historical costs that finds them falling from $2150/kWH to $625/kWH in 2018: https://www.eia.gov/todayinenergy/detail.php?id=45596. Overall it looks to me like the $200/kWH looks pretty realistic

(ETA: I now think that forecast is probably pretty conservative and $100/kWH or less is more likely. But the rest of the post doesn't depend on such aggressive estimates, except for the part where I talk about heating.)

The efficiency of storage is 90%+ which is high enough to not matter much compared to the cost of storage, especially as solar prices fall.

Current electricity prices are around $0.10/kWH. So at $0.08/kWH solar couldn’t be quite competitive, but another factor of 2-4 could easily do it (especially if other costs of solar continue to fall to negligible levels at their current very rapid clip). I haven’t seen anyone projecting batter prices to plateau before hitting those levels.

Overall the trends on storage are worse than on panels themselves; it’s already the biggest cost of an all-solar grid and I think it would just become totally dominant. But they still seem low enough to make it work.

Storage is a lot cheaper if you are using some of your electricity directly from panels (as under the status quo) and need to store <100% of your power. You’d only need 100% in the worst case where all solar power arrives in a burst at noon, and the real world isn’t going to be quite that bad.

I could easily imagine cutting this down to only needing to store 50-75% of electricity, which cuts the cost with current technologies to $0.04-0.06/kWH. I think cutting costs in this way would be important in practice, but given that we’re only talking about a factor of 2 it’s not going to make a big difference unless battery costs plateau in the next few years.

Meaningful amounts of solar are only available for ~1/3 of a day (depending on latitude) so if you just used energy constantly and wasted nearly half of the solar power you’d need like 66% storage (depending a lot on latitude and season). Today we have a *lot* of appliances that use electricity a small fraction of their life and that you can run when electricity is cheap; and also most of our needs are when humans are awake and the sun is up. But if you switch to using electricity for more applications and if we industrialize further (as I’d expect) then this will get less possible. Amongst the things that can be shifted, you might as well put them at the peak hours around noon, which helps cut peak losses. (For things like cars and computers with batteries, you can either think of these as flexible appliances or as further reasons.)

That’s a complicated mess of considerations. 50-75% is a rough guess for how much you’d have to store but I’m not at all confident.

Eventually it will be unrealistic to amortize battery costs over 15 years. That said, 30 year interest rates are currently 1% and I think time horizons are changing pretty slowly, so I expect this trend to be much slower than changes in storage costs.

2. Winter vs summer

My impression is that solar panels give like 33% less power in winter than summer (obviously depending a ton on latitude, but that’s a typical value for populated places). Storing energy across seasons seems completely impractical.

That sounds like a lot but even in the worst case it only increases the cost of solar power by 50%, since you can just build 50% more panels. That doesn’t seem like enough overhead to make a fundamental difference.

Most importantly, this doesn’t increase the number of batteries you need. You will have enough batteries to store power in the winter, and then in the summer you will have a ton of extra production that you can't store and so use in some low-value way. So if batteries are the dominant cost, you don’t even care.

I think this is the main answer, and the rest of this section is gravy. But as in the last section, the “gravy” could still cut costs by 10% or more, so I think people will care a lot about it and it will change the way we relate to electricity. So also interesting to talk about.

Here are some guesses about what you could scale up in the summer:

* You can run some machines only during the summer, e.g. if the main cost of your computer was the cost of running it (rather than capital costs) then you might as well scale down your datacenters in the winter. Of course, you probably wanted to move that kind of machine towards the equator anyway where electricity prices would be lower.

* You could imagine literally migrating your machines to wherever the power is cheap (e.g. moving your datacenter to the other hemisphere for the winter). This sounds a bit crazy but I wouldn’t be at all surprised if it works for a non-negligible % of energy. Perhaps the simplest case would be moving vehicles and having people travel more during their summer.

* There are lots of small tweaks on the margin, e.g. using 10% more energy during the summer than you would if electricity was constant-price and using 10% less energy during the winter. You can do everything a bit slower and more efficient when it gets colder.

These things are interesting to think about—I like the image of a civilization that hums to life during the summer days—but it doesn’t seem like it changes the calculation for feasibility of solar at all. You could just totally ignore all of this and pay a small premium, from 0% (if batteries dominate anyway) to +50%. Some of these changes would happen from the most cost-conscious customers.

3. Other fluctuation and peaking power

In addition to winter/summer and night/day there is also some variability from weather day-to-day. My impression is that this is a smaller deal than the other two factors and doesn’t change the calculus much for a few reasons:

* As discussed in the last section, you probably want to have too many panels anyway and be bottlenecked by storage. In that case, variability in weather doesn’t matter much since you have too much capacity most days.

* It only really potentially matters in the winter months with already-low light, where you may fall short on total production (and not even be able to charge batteries).

* But once you are talking about a small fraction of the year, it’s pretty cheap for some people to just turn off the power (e.g. scaling down my datacenter) from time to time. If I’m doing that for 5% of the year it effectively increases capital costs by 5%, which is only really a problem if electricity costs are a tiny fraction of my net expenses. And there only have to be a few industries that can do that. So we only have a problem if the all-solar grid is serving every industry exceptionally well (in which case the absolute size of my problem is quite small).

There are also fluctuations in demand. In general having variable demand seems like it’s probably good, since by passing on costs appropriately you can shift demand to times when power is available. But big exogenous changes could cause trouble. This seems to be by far most troubling at the scale of days rather than hours (since you have a ton of batteries to handle within-day variability).

I think most people can avoid huge fluctuations in demand most of the time---there just aren’t that many things that bounce around from day to day where I have very little control over when they happen. The big exception I know about is climate control—people want to use a lot more power for AC during hot days and for heating during cold days (if we move away from natural gas for heating).

AC isn’t a problem, because it happens during hot summer days when you have tons of extra power anyway. So that brings us to...

4. Heating

Heating during cold periods seems like a big problem. As far as I can see it's the biggest single problem with an all-solar grid (with all-electric heating)

Unfortunately, I think heating is a giant use of energy (at least in the US). Right now I think it’s almost half of home energy use, mostly natural gas, and I’d guess something like 10-20% of total energy use in the US.

It's also the worst possible case for solar. It’s seasonal, which is already bad, and then there is huge variation in how cold it actually gets. And it’s really bad if you aren’t able to keep things heated during a cold snap. In practice you should just stop other uses of electricity when it gets cold. But with an all-solar grid you aren’t going to be putting many energy-intensive activities in places with cold winters, so you may have less cheap slop than you wanted and blackouts from cold could be quite expensive (even if you literally aren't having people freeze in their homes).

Here are some options:

* Use peaking power plants basically just for heating. It’s crazy to me to imagine the world where this is the *only* reason you actually need peaking power plants. I suspect you don’t want to do this.

* Use natural gas to heat homes. This is appealing because it’s what we currently do so doesn’t require big changes, it’s pretty clean, and you don’t need to maintain a bunch of peaking power plants with significant efficiency losses in transit. I think the main cost is maintaining infrastructure for delivering natural gas.

* Do something creative or develop new technologies. In some sense heating is an incredibly “easy” problem, since anything you do with electricity will generate heat. The problem is just getting it where you want to go. You could move more electricity-consuming appliances into homes/offices you want to heat, or do cogeneration with data centers, or something else crazy.

Here are some reasons the heating cost may not be so bad, so that you may be able to just eat the costs (for any of the above proposals).

* If we are doing a lot of electricity-intensive industry then space heating may be a much smaller fraction of costs. Honestly, I think this whole discussion is mostly relevant if we want to scale up electricity use quite a lot, but I don’t expect to scale up space heating in the same way. So I think it would be reasonable to keep meeting our heating needs in a primitive way while scaling up an all-solar grid for our increasing energy needs.

* You could massively improve insulation over the status quo if heating costs were actually a big deal. Right now heating is a huge fraction of energy but a much smaller fraction of costs. Under an all-solar grid the energy for heating would be by far the most expensive energy, and so incentives to save on heat would be much larger.

* We could generally move to hotter places. They get more appealing as AC gets cheaper / heating is more expensive, and I’m told global warming will make everywhere a bit hotter.

* We could probably modestly improve the energy efficiency of heating by using heat pumps Unfortunately it’s kind of hard to improve efficiency in any other way. And heat pumps are pretty scary since they don’t work when it gets really cold.

Overall my guess is that you should just leave natural gas infrastructure in place, especially in cold places, and use solar for everything else.

Digging into this a bit, I may have gotten the original argument for nuclear wrong - it does seem like some countries would struggle to source their energy from renewables due to space constraints (arguably, less of a problem in Australia). 

"I’m not even sure it’s physically possible with 100% renewables... if you were to try and just replace oil in a country like Korea or Japan, so a densely populated country without huge amounts of spare land, you have to take up a significant proportion of the entire nation with solar panels... In the UK... if you want to replace our oil consumption, you’d have to cover over one and a half times the size of Wales with solar just for oil; never mind about decarbonizing the electricity grid and all the rest of it." - Mark Lynas on the 80,000 hours podcast

Thanks, I've found this helpful (if a little embarrassing)! 

Not here to weigh in on the pro/anti nuclear arguments.

I just wanted to thank you for posting and engaging with the forum about your thoughts! I think that this style of post is one of the most useful because it leads to a better understanding for all involved. 

Thank you! I really appreciate the encouragement! 

I think it’s a mistake to favour one technology over another. Ultimately, there will always be lots we don’t know about the future path of either technology.

If we are lobbying for changing energy policy then we should focus on ensuring externalities (CO2 emissions, air pollution, and waste) are priced in, that intermittency costs are priced in correctly, that badly-designed (e.g. based on misconceptions around risk) regulations don’t increase the costs of a given source, and that each energy source can compete on its own merits without undue favouritism.

That said, I think that chart you shared gives us reason to be unsatisfied with the status quo around nuclear. It should be getting cheaper but for whatever reason we aren’t building enough to benefit from Wright’s law.

I'm all for pricing in carbon and sensible policy that regulates in proportion to our best estimate of the risk!