Sure, but those battery backed solar plants usually only have 2-4 hours worth of storage. They're not actually producing full output throughout the night.

The cost of batteries would skyrocket if countries actually tried to provision 12 hours of battery storage. Because the US alone uses 500 GWh of electricity each hour. This is greater than the global battery production figures in 2022 [1].

1. https://www.spglobal.com/mobility/en/research-analysis/growt...

You’re calculating that storage number as if the solar power plant would have produced power for 24 hours.

To simplify if you have 8 hours of power and you store 1/2 of it you need 4h of storage. So our hypothetical 4GW solar power plant produces 2GW for 8 hours and 1 GW for 16. That already batter fits the demand curve than steady state output.

However things get better if you instead consider real world demand and the actual production of solar panels being spread across the entire day a 4 hour of storage is close to perfect. Except, the real world isn’t a hypothetical 100% solar grid so 2h ends up working fine in most areas.

Again, the demand curve is the opposite of what you claim: peak production happens during the night, at around 9 pm, not during the day. You'd need to supply more energy during periods of non-production, not less. You can't get away with 50% output at night, unless you have some other energy source picking up the slack. And remember, during the winter you're getting less than 12 hours of sunlight, maybe even less than that if you consider that cloud cover eliminates 75-90% of solar power output.

These factors do depend on geography. Hotter climates do see more energy use during the day to power A/C. But on the flip side, colder climates see even more energy demand during the night to heat homes. And unfortunately this also coincides when solar is producing the least amount of energy due to fewer sunlight hours, axial tilt, and more cloud cover.

There are niches solar can carve out: Las Vegas and Australia have loads of empty space, clear weather, and hydroelectricity that can fill in periods of non-production. But nuclear power is a much more flexible solution. All you really need is water to cool the reactor, and 80% of the population lives within a hundred miles of the coastline (you just need water, not fresh water).

Energy use for heating can be quite easily reduced just by insulating houses (and installing more efficient heating equipment such as heat pumps).

Do we have any idea what the cause of that 9pm spike is? That seems like a bizarre time to be the peak to me (I can't work out what the primary energy users would be at that time).

Replacing gas heating with heat pumps is going to increase, not reduce, electricity use.

Replacing gas heating with solar thermal is even cheaper and doesn’t. Electric heat pumps are viable when electricity is cheap or demand is low and you want AC, the more they drive up electric costs the more alternatives become viable.

Net effect you tend to see them in areas where there’s a surplus of winter electricity which also tends to be places with minimal demand for heating like Virginia rather than Mane. 46% in South Carolina, 42% in North Carolina, 30% in Virginia etc: https://www.statista.com/statistics/1327164/share-of-househo...

Solar thermal heating is not going to produce much energy in the winter when there's fewer hours of sunlight and more hours of cloud coverage - which just so happens to coincide with places that would need heating during the winter. Solar thermal performance is worse with diffuse light (read: overcast days) than PV solar, in fact that's a big part of why it was largely abandoned in the 2000s.

The main advantage of solar thermal is it’s really cheap so you can just scale collection to cover winter heating. That’s why adoption is so high in China even relatively far north. As to the US, the cost savings just isn’t that appealing for most people. It’s frankly ugly, complicated, and has minimal payoff at current prices.* Passive solar design can have significant benefits while looking much nicer. But if you’re increasing the cost of electricity or gas then suddenly it’s looking significantly more attractive.

* Except of course when people want to heat a pool, that takes crazy amounts of energy.

“Israel became the world leader in the use of solar energy per capita with 85% of households using solar thermal systems (3% of the primary national energy consumption)” https://en.wikipedia.org/wiki/Solar_water_heating

As per your link, solar thermal water heating is very variable depending on geography:

> The amount of heat delivered by a solar water heating system depends primarily on the amount of heat delivered by the sun at a particular place (insolation). In the tropics insolation can be relatively high, e.g. 7 kWh/m2 per day, versus e.g., 3.2 kWh/m2 per day in temperate areas.

Because of this, many solar thermal systems are supplemented by convention heaters.

> In winter, the percentage of your hot water heated by the sun drops to as low as 10-20%—as you might expect with short days and weak sun in December. That’s why practically every solar water installed in the US will be connected to a backup conventional water heater to ensure that your hot water needs continue to be met even in January.

https://www.aspessolarproducts.com/solar-water-heater/how-do...

Again batteries smooth over instantaneous demand.

If you really want to model things you need to consider the vast drop off between midnight and 5 am in which that steady state I talked about would be wasted. Batteries don’t really care about when the peak is just the total demand minus power production. And again steady state like nuclear looks terrible by comparison.

Running summer numbers you see an extension in the number of hours the panels are producing which then reduced the gap you need to fill with batteries. Winter sees the reverse as average output drops but conversely batteries are storing a higher percentage of total energy produced. Sizing is further adjusted based on expectations for daily output not hypothetical maximums.

Which of those is more critical depends on local conditions but the grid is always sized for absolute worst case not the average one. There’s lots of micro optimization such as aiming panels East or West to shift production, local hydropower and wind resources etc etc.

None of which is that important compared to the overall effect I was describing where batteries are sized to the daily output not the peak output. The important number is the cost which is running 60$/MWh vs the daily demand not whatsoever the nameplate numbers people love to talk about to make projects seem more important.

And yet again: batteries are not available at a scale where they can even remotely smooth over demand. Even just provisioning 1 hour of storage for the USA requires 500 GWh of storage. A steady state like nuclear works just fine for the grid: it's only a problem for intermittent sources that are made redundant by a source of decarbonized energy that works 24/7. The disparity between peak and trough energy demand is not that great: it's typically 20-30%.

Pointing to one specific project is not relevant: we can't replicate this project to the point where demand is fulfilled because that would require an order of magnitude more batteries than are produced.

We don’t need batteries on that scale any time soon. Let’s project out 25 years and we might need 3-5 hours of 100% grid electricity storage nationwide depending on your assumptions but that’s about it. It’s not like hydroelectricity is going away anytime soon and that’s extremely flexible not just in terms of time of day but also days of the week, and wind doesn’t care when the sun is shining, and solar can shift east to west to cover more of peak evening demand on the east coast and peak etc etc. We can quibble about the numbers but it’s just not important.

As to storage we’re talking 4h * 500 GWh +/- whatever that’s only 2,000 GWh ish, but the specifics aren’t important. By comparison we’re talking a nearly 100% EV cars so 75 kWh per car * 282 million, that’s ~ 21,150 GWh. Those numbers are so huge we could bump things to 16 hours of electricity and it’s still fairly trivial by comparison. Build enough generation and storage could actually be even lower, it’s just a cost tradeoff and renewables are really cheap. (Edit: There’s been a lot of research into it and there’s plenty of raw materials for a 100% EV transition and on this timescale ramping battery manufacturing isn’t an issue.)

Also, that 30% number is wildly incorrect. Even just over a week the CA demand is expected to go from a low of 24,867 to a high of 42,007 in a single day, but you can’t design a grid for a single day. https://www.caiso.com/TodaysOutlook/Pages/default.aspx#secti... Things look similar nationally, we don’t have enough interconnects to really smooth things out and even if you did the daily variation is quite significant.

However, the actual disparity between peak annual demand and minimal annual is vastly higher and you can’t smooth it out. That delta is why idling a grid of mostly nuclear power would be so wildly expensive. Without France style exporting and importing from non nuclear countries cost go insane. The only way it’s even vaguely viable in the US is with similarly vast amounts of storage. But at that point adding just a little cheap solar + wind saves money, and that keeps being true as you use less and less nuclear.

TLDR; Cost effective mostly nuclear grid needs even more storage due to capacity factor issues when you can’t follow France’s model of importing and exporting a large fraction of your power to non nuclear countries.

And on the flip side, some energy markets like New England see a minimal variation in energy demand throughout the day, less than 10%.

Provision enough generation to satisfy peak demand and spend the excess power doing things like carbon dioxide sequestration or desalination in places with limited drinking water. Too much energy is a vastly easier problem to solve than too little. And the great thing about nuclear is that it's no more expensive to run at 100% capacity than 50%.

That sounds great until you consider the opposite.

The issue with nuclear is it costs twice as much per kWh at 50% capacity than it does 100% capacity. Nuclear is expensive at 90% capacity factor, it’s insane at 45% capacity factor.

Further, daily demand isn’t that problematic. It’s really seasonal demand that kills people’s dreams of scaling nuclear power. Over 24 hours going from a 100% high down to 50% low might average say 70-80% depending on specifics. But if 1/2 the year you never get over 80% capacity, and you also need to curtail on nights and weekends year round, and take the plant offline for weeks to refuel etc, then things look much worse.

The temptation is to say batteries to the rescue, but then you’re directly competing with solar on price per kWh. It’s really hard to make things work without natural gas to pick up the slack.

Again, you exaggerate the fluctuations in energy demand. This is a good primer on the hourly and seasonal fluctuations of electricity demand: https://www.eia.gov/todayinenergy/detail.php?id=42915

Even in the summer in Texas, where we experience the largest demand fluctuations, minimum demand is around 60% that of peak demand. And this is indeed a good use case for rooftop solar, especially since it can be used to power A/C in the same building on which its mounted - I never said we should have zero solar power, just that it's infeasible to use for the primary source of electricity. Rooftop solar is indeed a good way to mitigate A/C power draw. But outside of summer peak and minimum power draw is only about 20% difference, and again the peak power is at night.

I don't doubt that nuclear power is expensive. But at least is feasible to build. "Feasible but expensive" is much better than "not feasible regardless of cost". Intermittent sources are only feasible in a grid backed by fossil fuel and hydroelectric sources that can flexibly respond to solar and wind's variation. Once you enter the realm of a predominantly renewable grid, this changes drastically. Storage at a scale anywhere close to what's required to smooth the intermittency of renewables is not even feasible regardless of cost. No amount of money is going to provision the amount of storage required to smooth out the daily fluctuations of solar, let among the seasonal variations of both solar and wind. Overproduction and HVDC connections only take you so far unless you're going to cross the Atlantic (which is also of dubious feasibility). Even just a few hours of storage is well outside of reach. Don't be misled by a handful of battery stations in the MWh scale: actually trying to providing 2 TWh of storage would cause prices to skyrocket because production cannot remotely fulfill that level of demand. Not to mention it'd kill electric vehicle adoption.

This is why most proposals for a primarily renewable grid involve a novel storage system. Will hydrogen, or compressed air, or giant flywheels deliver the required scale? Maybe, in the same vein that maybe deep-drilled geothermal power will deliver cheap decarbonized energy. Those are unknown factors in that one cannot assume will work out. Would you consider it a reasonable plan to assume deep-drilled geothermal will solve decarbonization? After, Iceland has used geothermal for decades, and we have lots of experience drilling for oil? This is how we ought to regard things like hydrogen electricity storage or ammonia: they're in the realm of possibility not feasibility.

Again, it's not a question of cost it's a question of what's even possible without an engineering breakthrough. Maybe we'll figure out a way to build storage at grid scale. And maybe we'll figure out geographically independent geothermal power. But both of those are things not presently within our technical capabilities.

> ...and take the plant offline for weeks to refuel etc, then things look much worse.

Nuclear has historically had the highest capacity factor of all generation sources [2]. This hasn't been an issue with existing generation sources with even more downtime, so why would it be an issue with nuclear?

1. https://www.deegesolar.co.uk/do_solar_panels_work_in_the_win...!

2. https://www.eia.gov/tools/glossary/index.php?id=Capacity_fac....

This is the Australia energy market price and demand dashboard[1].

Note the two peaks: 1 happens at 7am. There's very little solar at 7am even though the sun is up, but demand is at a maximum. The other happens at around 6pm - when people get home. There's also very little solar at 6pm (sun sets at 5pm in Winter, during the day it's longer).

Also note the demand fall off in the evening: that's a very lopsided peak, because people stay at home (whereas in the morning they turn on the kettle, then leave). But also note the absolute magnitudes: at the minimum, which is about 4am, demand last night bottomed at about 6,800MW. The peak was 9,800MW. So even the "low demand" was 2/3rds of peak demand, and it took 8 hours to get there. Most of the night, consumption was a lot higher.

But it gets worse: before you're going to recover any real capacity from your solar, the largest demand of the day is about to happen in 3 hours, with the sun just barely over the horizon.

[1] https://aemo.com.au/en/energy-systems/electricity/national-e...

The better you model this the better the number look. First demand falls off a cliff from midnight to 5 am, a steady state nighttime rate will be extremely wasteful but batteries can shift demand to these peaks just fine. Remember 100% of their output is offsetting battery demand which is significant even just at 9AM or 6PM.

Also, your not actually getting 100% solar output over the day. Batteries that could store 50% of your hypothetical maximum are well over half of your expected average output especially in winter when these peaks are most pronounced.