24-Hour Solar Energy: Molten Salt Makes It Possible | Hacker News Reader

24-Hour Solar Energy: Molten Salt Makes It Possible

insideclimatenews.org

240 pointspmoriarty121 comments

Peripherally related: molten salt thermal energy storage is also something the nuclear industry has been considering using to help improve load-following economics of nuclear in a heavily variable renewable world. The idea is the nuke would run 24/7 at constant power but the load of the plant would be swapped from the thermal storage tank (in the day while solar is providing all the electricity) to the grid. Meanwhile, the load of the solar thermal system would be turned off during the day and turn on at night. This effectively doubles the power capacity of the nuclear plant to help fill in the duck curve as the sun sets.

Doesn't help with seasonal renewable variability, but for day-to-day, it's pretty slick. The cool thing over TFA is that now it can work in many more geographic areas (e.g. where solar thermal doesn't make as much sense due to low intensity sunlight and there's more solar PV).

Conventional nukes aren't great at going to these temperatures so this is mostly a thing "advanced" reactor people talk about.

e.g.: https://inldigitallibrary.inl.gov/sites/sti/sti/6339782.pdf

Of course then there are molten salt cooled/fueled reactors, which is different from energy storage, making this topic even more confusing.

> Conventional nukes aren't great at going to these temperatures so this is mostly a thing "advanced" reactor people talk about.

Are the temperatures too high or too low?

Too low - water-cooled reactors are designed to bring the water in the secondary cooling system to just above the boiling point, because anything beyond that is wasted energy (the temperature of the steam doesn't really matter as far as driving turbines). So retrofitting a molten-salt system onto these reactors isn't very efficient and you would ideally want a new reactor design intended for that from the beginning.

It seems like a serious materials challenge problem to come up with a molten salt that has the right nuclear characteristics (neutron moderating, etc...) and is not horribly corrosive/flammable/etc... Especially if your usage model is to let the salts heat up to outrageously high temperatures during the day and then draw them down over night.

> (the temperature of the steam doesn't really matter as far as driving turbines)

This goes against everything I seem to remember from thermodynamics - superheated steam is exactly what is used for driving turbines, with saturated steam as the cold side outlet of the turbine. It's what makes district heating useful - there is still heat energy left in the saturated steam, too low grade for driving turbines, but still useful for heating apartments etc

Indeed, superheaters have been used since the early 1900s to dramatically increase the thermal efficiency of steam engines.

https://en.wikipedia.org/wiki/Superheater

Also, IIRC superheaters are especially important in turbine applications because water droplets damage the blades.

What's your turbine pressure? Steam at 700°F is apparently 3000psi, which is the highest temperature/pressure I can find.

Edit: Best Q/A thread I've seen recently: https://www.researchgate.net/post/At_what_temperature_water_...

"We need this value to be more specific numerical form to utilize in design of high temperature and high pressure steam boilers and turbines working at 300 bars."

advanced nuclear using a molten salt loop fro the buffer: https://usnc.com/MMR.html

LFTRs would have faster startup shutdown, and should be able to be built in smaller sizes so "banks" of reactors could be made active.

These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options for deployment. However, they are great for generating heat. And with heat you can trivially desalinate water. Since trees can be a nice carbon sink, I've often wondered if this type of scheme might make sense:

- Plant heliostat molten salt reactors in desert coastal areas (the concentrated solar kind)

- Use generated heat to desalinate water (e.g. Multi-stage flash distillation)

- Use desalinated water to provide irrigation

- Plant (potentially GMO'ed) trees and other bootstrapping organisms to "green" the desert

- Rinse repeat.

The net effect is that you can potentially turn large swaths of desert into forests, with minimal external energy requirements (and potentially build an agricultural community around them, more or less self contained in terms of water/energy)

Something like this? https://www.sundropfarms.com/facilities/

Yep! but then with fewer greenhouses so it has more of a https://en.wikipedia.org/wiki/Desert_greening effect

Coastal areas (even desert ones) are often plagued by clouds, and clouds are a big problem for concentrated solar. This doesn't make your idea bad but it's an obstacle.

Edit: Now that I think more about it, who cares if the heat is less reliable if all you're doing is distilling water? I need to take off my electric generation hat sometimes.

Yeah it does limit it a bit, and if the goal is really to plant trees, then eventually it will be somewhat self defeating as forests cool the air and will generate clouds. On the other hand, desalination doesn't require extremely high temperatures, so it also kinda depends on the heat capacity of the molten salt. It probably also doesn't really have to be 24/7/365. But that's I guess a numbers game, so obviously it has to be modeled first.

If you're displacing groundwater based desert agriculture, that's one thing, but it's worth keeping in mind that in general, desert != wasteland. Deserts are fragile ecosystems with many rare and specialized plants and animals.

Absolutely, but then again (almost) everything is a fragile ecosystem. And if man-made climate change is real (I'm inclined to believe that), then it's less of an absolute and more of a trade-off ... a tricky one certainly, but already we're seeing deserts expand (https://en.wikipedia.org/wiki/Desertification) and there are efforts to prevent it (https://en.wikipedia.org/wiki/Great_Green_Wall) so it could potentially be another tool.

For sure, I just don't think we should gloss over the nature of such ecosystems, since many people really don't know.

Deserts are fragile ecosystems with many rare and specialized plants and animals.

Climate change may push the temperature of some of those deserts too high, wiping out the specialized plants and animals that live there. Perhaps we could use a solar installation to provide shade in areas that are getting too hot.

I'm well aware, just wanted to point out a fact about an underappreciated ecosystem. I feel the same way when people complain about swamps.

Hmmm we have multiple CSP plants in southern Spain, I wonder if we could do that, because it has been predicted that Spain will desertify with coming climate changes.

My issue is what do we do with the byproducts of desalination? If I did understand it there's no really use for that, and I've seen that other countries just dump it into the water, which is a big no no for local ecosystems (and I guess for oceans ph levels if this becomes widespread).

Straight up dumping it in the ocean is generally considered bad. The standard trick is to wash/mix the brine with fresh ocean water to reduce the concentration of salt before dumping it back. Another interesting byproduct that is often overlooked are the metals and minerals. Things like lithium (and even gold) are relatively abundant in sea water and could be recovered from the brine (at the cost of complexity of course).

That looks like a large scale operation. CSP is struggling to compete in Spain with PV, but I can see it happening with companies like Acciona or some other spanish utility behemoths.

Gold is not abundant in seawater: ~10 parts per trillion by mass.

The infrastructure to get the salt water to the desert and then to distribute the fresh water to the trees will also be a challenge.

There are other challenges that you might not have considered, like sand dunes ruining your progress.

China has been working to turn some of it deserts into forests with pretty good success.

For the sand dunes issue, they’ve come up with a webbed system that’s fairly easy to deploy. The material is cheap and it’s easy for unskilled labor to deploy.

Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure.

Lots of videos on the desert projects, just search for “china desert to forest”.

Here’s one of them https://youtu.be/7Nur35fnjDA

In the US Southwest there is the Salton Sea which is an already artificial saline reservoir. Just pipe more ocean into it and use that as the salt water source.

> Putting aside the horrible human rights issues with China, it’s amazing to see what they’re doing with infrastructure.

Mussolini got the trains running on time, and China has hundreds of thousands of Uyghur and Muslim people locked away in concentration camps.

Do you consider what side of history you're on when you "put aside" such behavior?

1) This is not a constructive comment. Author did not minimize PRC's conduct, or justify it. Rather he negated it from the equation. If PRC's de-desertification strategies were reliant on the prison camps, or in any way contingent, you might have a point.

2) There is no right side of history; there is only what gets remembered and how that memory is portrayed. Consider that America is quite accurately describes as a White Nationalist government for the duration of WWII. One could then frame the war as Nazis and Imperialists being defeated by Communards and White Nationalists with the assistance of Colonizers.

The role of the US in WWII is always grossly exaggerated.

WWII was a slugfest between two totalitarian regimes, Germany and USSR, conducted using troops that were, in the majority, neither Russian nor German, but slaves of one and then the other, and then, typically, executed.

The Western front was a sideshow. Stalin could easily have rolled over all of Europe, but stopped short for reasons known only to him.

There's the old saying: WW2 was won with British intelligence, American steel, and Russian blood.

To be fair, the Soviets are directly responsible for arming the Third Reich. They created the monster and then they had to put it down. People always forget the cross border training and massive amount of raw and finished goods transfered from Russia to Germany.

That is said, but without both British intelligence and American steel, the result would be largely the same. And the blood wasn't mostly Russian, although it was sent into combat by Russians.

Maybe the British intelligence and American steel bought western Europe. Or maybe the success of the Manhattan project -- which Stalin was kept briefed on, in detail, by his spies -- gave him pause.

I should add that a very, very large fraction of the Soviet blood that was spilled was done by Russians. Stalin killed maybe 10-15 million before formal hostilities began, including every educated person in the east half of Poland, before 1941. (The Germans killed them in "their" half at the same time.) A large fraction of that number weren't Russian, but maybe more than half were.

You could say that killing 15 million people seems pretty hostile, but that's not how historians count. Anyway the US and Britain weren't evidently bothered by it.

The US accounted for significant portions of the USSRs vehicle fleet as well as provisioning. The USSR fought Germany, but the US defeated Germany. It wasn't fair; war never is.

The US sent 400,000 trucks, 350,000 tons of explosives, 3m tons of petroleum, 4.5m tons of food, 3000 ship engines, and 2000 locomotives in through Iran, and corresponding amounts of other supplies. But Russia had already pushed Germany much of the way out by the time the stuff arrived in any volume.

For all that, it added only 20% to their own production, food possibly excepted. Russia made a point of acknowledging the food, and the trucks were maintained for long afterward.

Mussolini did not get the trains running on time. Rather, he had the people complaining about them not running on time shot. There's a difference.

Perhaps it's subtle.

> The infrastructure to get the salt water to the desert and then to distribute the fresh water to the trees will also be a challenge.

The proposal was for "desert coastal areas".

Doesn't matter. Has been done the other way around already, so it could be reversed.

[1] https://en.wikipedia.org/wiki/Great_Man-Made_River

Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts?

Obviously having more arable or at least livable land is useful to human society, but I generally assume that messing with any large scale climates or biomes has adverse effects. I'm not yet aware of what that would be for deserts though. I suppose they have fairly high albedo, unlike most land formations that can exist in lower latitudes.

(To be clear my own views aren't necessarily so utilitarian and I like deserts. Just curious about a rational geoengineering civilization might do.)

>Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts?

Getting rid of deserts could actually be quite bad for other ecosystems. The Amazon is fertilized by the Sahara for example https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...

That's incredible. I assumed arrogantly it was mostly inert silica, not phosphorous.

Yeah the earth is a very complex system. When YC came out and proposed the idea of proposed turning the Sahara into a bunch of algae ponds [1] I cringed. First the plan requires more power than we currently produce just to pump all the water but then you would drastically reduce how much gets blown over to the Amazon AND you would suddenly introduce a tremendous amount of moisture to the atmosphere which would almost certainly change global weather patterns.

All of that moisture could cause a considerable increase in rainfall for somewhere (presumably the Amazon, I don't know anything about weather modelling though and am just guessing) which could be catastrophic for life there and even result in tremendous economic losses.

Even relatively small scale geoengineering like damns can have profound negative impacts on ecosystems with some being very predictable and some being completely wildcard. We know the Sahara fertilizes the Amazon but what level does it effect marine life by feeding stuff at the bottom of the food chain (plankton for example) and what would removing that mineral/nutrient source do to the food chain, would it increase rains (and cloud cover) over that area of ocean that might change temperatures subtly enough to make an impact on currents, etc. We're at the point now as a species where we have the power of gods but can't begin to understand the implications of what we are capable of doing.

[1] http://carbon.ycombinator.com/desert-flooding/

We know the Sahara was green, not too long ago. What do we know about the Amazonas from that time? Was it barren because it lacked the input? Was it agricultural land, worked by long overgrown cities by some sunken civilization? I've read about that somewhere, where LIDAR found signs of that, similar to what the Aztecs had.

Some deserts are quite natural. It doesn't matter what you do to them short of knocking down the mountains upwind of them, they're going to be deserts.

Some are not.

I consult my mental image of deserts and I observe that the Sahara is almost devoid of life, whereas the deserts of the American Southwest are rich and diverse despite their lack of substantial rainfall. (The latter I've also visited and spent some time in. I've never been to the Sahara to know if that's correct.) If my mental image is accurate, fixing the unnatural, almost entirely uninhabited desert would be nothing but a win. "Fixing" the natural kind would be relatively destructive of an existing ecosystem.

(Then you get into the question of "how do you valuate and compare two different ecosystems?". I've thrown that gauntlet a couple of times and I don't think I've even seen anyone engage with that question properly in a non-knee-jerk way. The heuristics people have been taught to use about environmentalism do not admit of that question even existing.)

Also note that some deserts are variable, and human activity can tip the balance [1].

especially considering the global carbon balance, it seems that tipping some parts of the desert back to forest would be a net plus. Humans are already doing massive uncontrolled experiments with bad results, it may help some to do some deliberate experiments with good foundations with the goal of creating good results?

[1] https://www.smithsonianmag.com/science-nature/what-really-tu...

Humans have been creating deserts for thousands of years, by denuding forests. Grow trees there again, and the forests will bring their own water, after a time.

Petra used to be forest. So did much of the North American southwest.

If we wait long enough, the planet is going to get rid of the desert.

> For several hundred thousand years, the Sahara has alternated between desert and savanna grassland in a 20,000 year cycle[8] caused by the precession of the Earth's axis as it rotates around the Sun, which changes the location of the North African Monsoon. The area is next expected to become green in about 15,000 years (17,000 AD).

I've read multiple times that the dust from the sahara makes it over the atlantic and works as fertilizer for the amazonian rain forests. That is relatively new knowledge, since about a decade or so. Has been featured in nature documentations also. What is not known is how much dependence there is on this input. Whereas i'm asking myself what about the other sand deserts then, like the Namib, or Gobi?

> These types of systems are generally not competitive with PV for electricity, since they require a lot of concentrated solar energy thus limiting the options for deployment.

> However, they are great for generating heat. And with heat you can trivially desalinate water.

Not trying to be a PITA, but to your first point, suggest you provide a citation if you're going to make a sweeping claim. I'm actually interested in this claim.

To your second point, while desalination at scale isn't 'rocket science', it isn't exactly trivial. Having designed and worked on desalination plants for commercial ships, yes, you can buy an off the shelf evaporator. However, you still need to carefully design the heat supply system and pressure regulation.

Also, you have to carefully manage the highly corrosive brine discharge. When I say corrosive, I mean this stuff is NASTY. At sea, it's a little easier, because you are constantly moving can kust discharge it overboard (although the environmental impacts are becoming increasingly apparent, so I'm not sure that direct discharge option will last much longer). However, you still need thick/expensive corrosion resistant brine discharge line piping/valves/etc. (or you will be replacing pipe often). Ashore, you need to manage to transport the brine away and somehow dilute it to a point where it's non-toxic.

You also have to carefully manage scaling inside of the evaporator, and I'm telling you this scaling is not something you can just brush off. This stuff is like a mollusk she'll coating on all of your internally heat transfer surfaces. If you can remove it with a chisel and hammer and not damage your system, you're a better person than I.

I'm not saying it's not doable, there are land-based desalination plants all over the place. I'm just saying it's not as simple as running some heating coils in a tub of water and collecting the evaporated water.

This is a fascinating comment.

In a municipal environment, would standard remediation of sewer water be good enough to dilute the brine? It seems like you could get something close to a closed loop. Obviously some water would be lost to evaporation, but in a city a lot of water comes out of the tap, over dishes or people or laundry, and then right back down the drain. It's not drinkable anymore, but we've got lots of tools to make it reasonably cleanish enough to put in a river. Would using that gray water to dilute brine alleviate some of that pain?

I'm not remotely an expert in this area, just spitballing here. But you clearly have some experience. I'm curious if closing the loop might be enough to make such a system workable.

Just to clarify, the brine is just concentrated sea water, that's left over after evaporating as much pure water as possible?

It seems weird that that could damage ocean life in any substantial way. I imagine i gets diluted back to "regular strength" fairly quick. At least if we're talking about the open seas.

Hypothetical (impossibly efficient) desalinator for consideration, turns 101L seawater into 100L potable water and 1L brine effluent. If you diluted the brine with another 100L of seawater, the diluted effluent would have twice the salinity of natural seawater. Dilute that 1L of effluent with 1000L and it would still be 10% above background (3.8% salinity, rather than 3.5%), which I think would affect sea life in the discharge area. Would have to dilute it with 10,000 litres to get it back down to 1% of background level (3.53% instead of 3.5%). I'm sure some saltwater aquarium people would have comments here :)

More mixing and dilution will happen after discharge, which would likely make it not a big deal for moving brine source. But a land based desalinator would need a very detailed impact assessment to prove it wouldn't have an impact on marine life at the discharge site

Back in the '80s, Grant Callin wrote a couple of pretty decent hard science fiction novels. In one, the aliens had a magic quantum mechanical technology that enabled flying cars and such, but generated very large amounts of heat as a side effect. (A Lion on Tharthee, https://archive.org/details/lionontharthee0000call)

"What do you do with the heat?"

"We store it temporarily on the vehicles and then radiate it into the ocean."

"Doesn't that cause an ecological problem?"

"Hah! That's the joke! We could do this for hundreds of thousands of years before we raised the ocean temperature 0.1 degree."

My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good?

If you disperse it into an ocean current, you’d have much of the mixing done for you.

(How that would affect the ocean current, given that they’re thermally driven, is less clear and unlikely to be good.)

> My question: How do you distribute gigawatts of energy uniformly through the ocean? Or are you simply boiling a bay somewhere and calling it good?

Assuming this is your question, and not a continuation of the quote: thermal energy is definitely a concern. It could be solved with dilution, like other pollutants.

In the particular case we're discussing, of using heat from a nuclear power plant to desalinate water: Every thermal power plant already creates waste thermal heat. They exhaust this heat either through evaporation (the stereotypical hyperboloid cooling tower of a nuclear power plant) or discharge into a body of water (thermal plants around me do this). The latter is definitely a sticking point in gaining modern environmental approval.

Why in the world would you concentrate seawater to 100:1, and then dilute it, instead of just reducing it to 2:1? If it is a matter of heat efficiency, surely a long heat exchanger can recover it all on the way back to the sea, absorbing it into the incoming water.

It was a hypothetical to illustrate how much dilution is needed to get effleunt close to background level salinity. It isn't even possible to extract that much fresh, since seawater is 3.5% salt. I was not talking about heat at all.

To illustrate: the effluent dilution requirement in your case isn't actually much better. If you took in 100L of seawater, extracted 50L fresh, that leaves you with 50L brine at twice the background concentration. To get that effluent back to 1% above background, you have to dilute that 50L brine with 4950L of seawater.

Lazard's Levelized Cost of Energy Analysis for 2018 has utility scale PV at $36-$46/MWH vs solar thermal w/ storage at $98-$181. Haven't seen an estimate that attempts to add storage to the PV to make it more directly comparable to thermal + storage.

https://www.lazard.com/media/450784/lazards-levelized-cost-o...

You should check first that lowering the desert's albedo with trees is not worse than keeping the CO2 in the air.

These types of systems are generally not competitive with PV for electricity

You should tell that to the people who built at least a dozen of these plants in the American west, with more to come.

Right now there are at least four that I've seen in Nevada exporting electricity to California.

There is a good map on the wiki of Concentrated Solar [1] showing the Direct Normal Irradiation. The US West coast is in somewhat of a unique position (as is Australia, South Africa, and a couple of others I suppose): high density population centers in areas with a lot of solar radiation. In those areas it might very well be the best method available (dunno, could be). Transporting electricity at distance is non-trivial however. Plans to put these installations in the Sahara and transport it to Europe via high-voltage DC lines have pretty much gone nowhere (https://en.wikipedia.org/wiki/Desertec). So non-competitive was more a reference to the constraints that it imposes, but I could've been clearer for sure.

[1]: https://upload.wikimedia.org/wikipedia/commons/c/c7/Global_M...

This would only lead to a constant shift in total CO2 emissions because there is only so much space you can utilize. When a plant dies it releases the CO2 back to the atmosphere. For the money, you can likely get higher CO2 abatement (i.e. close a coal fired power plant and replace it with renewables subsidy).

In the first case, you save the CO2 roughly equivalent to the total weight of the plants. In the pther case, you save x tonnes of CO2 every year.

True, but planting trees as a method for carbon sequestering is not a novel idea, and currently seems one of the better short-term options. Long term it's not that great for the reason you mentioned, and there is quite a lot of debate about it going on right now.

https://science.sciencemag.org/content/365/6448/76

https://www.nature.com/articles/d41586-019-00122-z

for two more or less competing views.

Pretty soon we won't even need all these parts. If Metal-Organic Frameworks (MOF) take off like these reports describe, we'll be able to irrigate deserts passively.

https://www.youtube.com/watch?v=XPSYzLZ7xKU

https://www.sciencemag.org/news/2019/09/crystalline-nets-har...

Sadly, the South Australian plant fell over financially: https://premier.sa.gov.au/news/statement-regarding-solarrese...

https://www.abc.net.au/news/2019-04-05/solar-thermal-plant-w...

Given that the company website is refusing connections, I think it's likely dead, which is sad too.

Acciona also sold its assets in Australia to some other companies. It seems that CSP is no easy business. There are still a few in Spain though.

CSP was very competitive 10 years ago before the bottom fell out of the solar panel market. Solar panels and batteries are now so ridiculously cheap that it's kind of silly not to just use battery backed PV solar.

I went and did a simple cost analysis and CSP is a dead end. A selling point is that it can store energy as molten salt. But when you run the numbers it's cheaper to heat the salt with PV solar energy.

The problem is PV silicon wafers have gotten so cheap that rest of the systems costs are dominating. The difference in costs between a mirror and a PV panel isn't large. Then add the mechanicals to focus the mirror and the mirror costs more.

Concentrated solar (thermal or PV) has not kept up with ordinary unconcentrated PV. And it doesn't work with diffused sunlight, which the latter collects just fine.

Would it make sense to use ordinary PV cells and use that energy to heat molten salt to use during the night? Or are there too many efficiency losses there?

There's a variety of storage ideas that just use any excess electricity e.g. Google X's Malta

https://www.maltainc.com/our-solution

There's various prototypes in testing but at least for short term storage I think lithium batteries continual price drop is leading the pack.

Unfortunately lithium is becoming increasingly difficult to obtain at scale. If graphite becomes commercially viable, that might be a good step up since Carbon is freaking everywhere.

Lithium reserves are more than 100x annual global production. Estimate lithium resources are something like 600x annual global production. There is no shortage of lithium, although there are temporary bottlenecks as capacity ramps up.

You could use a molten salt nuclear reactor to heat the molten salt and use the heat when you need it. Terrestrial Energy will produce such plants commercially in the next 10 years.

I've always wondered why "normal" unconcentrated PV system didn't at least have at least a couple mirrors put up around them to direct more photons onto the panels. It always seemed like a cheap way to get a bit more efficiency out of a system.

While we're at it, I also don't understand why solar hot water heaters aren't more of a thing as the efficiency gains are tremendous against using grid or gas power for heating.

We don't concentrate light in the normal PV systems because mirrors aren't cheaper enough when compared to the panels. Things used to be different, then PV got cheap.

Solar water heaters are also much more expensive than they first seem. Houses with pools usually have them, but if you don't own a pool it's normally better to put your money in a more flexible PV.

Houses with pools should use the waste heat from their air conditioning system to heat their pool.

Unfortunately, the system requires an HVAV technician, an electrician, and a plumber to install.

I’m also not sure how many HVAC techs are familiar with installing something like that.

Seems like a great energy saver though.

Here’sa video from This Old House on installing one of the systems. https://youtu.be/J7fB8ul9dZw

That is presuming you want to heat the pool rather than evaporative cooling the building to save on electricity.

That is presuming they live in an area that evaporative cooling isn't suited for.

It's mostly maintenance. Best concentrating mirror systems are Fresnel reflectors and they need meticulous cleaning, then there's a problem with heat dissipation for PV solar.

I understand it's now cheaper to heat water with a heat pump (or even a resistive heater) driven by PV, rather than by directly absorbing sunlight as heat.

When I run the numbers that's what I get. Also I think the Passive House nutters are starting to freak out because solar panels + heat pumps cost less than the extra insulation required by passive house regulations. Especially true because insulation quickly runs into diminishing returns.

How much insulation determine Passive House needs versus air-tightness? Isn't the latter also a metric that needs to be hit to get PH certification? Which of the two should be focused on (either by individuals doing a reno, or legislators updating code)?

I think not having gross leaks is a good thing, besides losing energy, leaks often carry moist air where you don't want it.

I'm much more dubious about ultra high levels of insulation and trying to completely seal the envelope.

A combination of unconcentrated PV with a heat pump is stellar though, gives you upwards of 3 kWh of heat for every kWh of energy you put in.

Google's Malta is doing that, iirc

"The Crescent Dunes Solar Energy Project .. substantially missed its intended power production over its four-year lifespan by only achieving about 20% of its capacity on an annual basis"

https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr...

This is pretty old technology. Right now it's cheaper to build normal PV and rely on e.g. gas peakers. Eventually we'll want to deploy this, unless batteries become a lot cheaper.

Old? It's not really been properly widely deployed yet and is still in the falling cost phase.

It is very much a Big Engineering thing though, unlike PV which can be deployed at the level of individual calculators.

Not old as the wheel of course, but the first commercial installation happened a decade ago. It's not like it's some kind of experimental stuff that was discovered only recently.

A large part of the cost of concentrated solar thermal is from mature components like turbines and generators and heat exchangers. These are not going to get much cheaper, at least anytime soon.

Coal/gas was cheaper than solar/wind (in certain areas) until it wasn't.

We have to build these plants to get the experience to make them cheaper.

And just comparing cost v fossil fuels is kind of missing the point. We have to move off carbon sooner rather than later. Fine, compare it the various battery technologies and nuclear, but comparing it to the thing we're moving away from, for good reason seems overly dismissive, and not particularly helpful.

I think you misread my comment. I'm comparing it to normal photovoltaics without overnight storage.

I understood you to be comparing photovoltaics + night time gas v photovoltaics + molten salt night time storage?

That seems the most reasonable scenario?

I'm kind of hoping that wind power covers most nighttime demand eventually. Right now we have so little renewable generation in most grids that just adding the cheapest option without caring about storage at all seems best.

Wind is useful, but not really as base load. There are long lulls sometimes, more than a week. You could run gas peakers but then you haven't fixed anything...

Fixing wind lulls requires continent-wide network of wind farms with corresponding grid. Computations suggest best case even 100 GW across Europe. That is nothing compared to demand.

(Un)fortunately we have nuclear as a base load option. And fusion as research program. Potentially space solar including space mirrors too.

You can use power-to-gas technology together with the existing infrastructure for strategic gas reserves to store enough renewable energy to run your gas plants during windstill winters. Maybe that's cheaper than nuclear power. It's probably easier to do politically.

So you're saying we should concentrate on (cheap) photovoltaics before moving onto expensive storage? Agreed although we do need to be thinking about storage, so we have technologies ready to go when the photovoltaics are built out.

Speaking from a UK perspective, renewables now account for about a third of electricity production, so that's well on the way in certain scenarios to be thinking about storage. The UK is lucky in that most of this is wind which tends to coincide with peak demand, if it were solar generation, night time and evening could start being a problem.

Okay. Gas peakers are not a sustainable alternative to renewables, so we're going to need solutions that cost more.

Or you could deploy base load nuclear and use solar PV as peakers, with some load optimisation for big daytime spenders depending on insolation.

Solar PV plus solar thermal, while seductive, competes for space and deployment.

Nuclear is also much more expensive than solar, takes a long time to construct (so it's another "big infrastructure" project), and it's heavily regulated. Most countries demonstrably do not want to deal with it. Not to mention, nuclear isn't actually "sustainable" either, it just doesn't cause global warming.

I suggest we keep building normal PV and wind power until balancing the grid actually becomes a problem and then switch to more expensive technology. Gas peakers can actually be sustainable if you feed them with gas from power-to-gas plants btw. That's a convenient but expensive way for storing large amounts of power.

That's not remotely practical and you know it. Let's not pretend that burning gas is a sustainable approach to power generation, regardless of how it's generated. I also don't really understand how you think we're going to suddenly flip a switch when "balancing the grid becomes a problem" if there are no alternative plant designs that people have actually constructed in large enough quantities to learn how to do it cheaply. In practice, if new nations onboarding with solar energy also add gas plants, we use more gas faster and contribute more to global warming. To me, it's pretty indefensible not to look at alternatives because they're more expensive.

Accusing someone of secretly agreeing with your point of view despite pretending to believe the opposite does not amount to assuming good faith. Do you think you could rephrase your comment in a less insulting way?

I got the idea for power-to-gas as energy storage from Prof. Quaschning, who is a leading figure in Germany's Scientists for Future movement and an expert for energy systems, so I assumed as a layman that it is in fact at least somewhat practical. I'm open to hearing refutations though.

There is one of these on the Nevada-California border outside of Las Vegas. I know they have had issues with the plant, such as the valley it's located gets foggy, which lowers the output. What's bad is the concentrated sun rays have been killing birds from what I've heard. Not sure of any easy way to dissuade birds from coming near it. It does look really cool off Interstate 15.

It would be pretty ironic if we got to the point of too cheap to meter with renewable based electricity.

I realise that this is unlikely to happen but given the way prices are falling ...

The price of energy is definitely trending to free in Australia due to renewables —- just not for every hour of the day, yet.

It’s not that electricity will be free when we get there, it’s just that consumers will stop paying for volume (how much energy did you use) and start paying for capacity / maximum demand (how much generation and network infrastructure was required to serve you).

Or consumer will have to buy it at hourly market rate, and the price will swing and consumer will have to constantly watch a meter.

Why do you think Smart Meters are being pushed?

> too cheap to meter

I like to joke that electricity is already too cheap to meter; just look at all the free places to plug in a phone or laptop!

IMO: Energy will never be "too cheap to meter," because someone will always come up with a way to consume lots of cheap energy.

cryptocurrency mining comes to mind...

In fact there are situations where companies get paid to consume electricity because it is very difficult to store large amounts of it.

> IMO: Energy will never be "too cheap to meter," because someone will always come up with a way to consume lots of cheap energy.

Jevons paradox:

> Economists have observed that consumers tend to travel more when their cars are more fuel efficient, causing a 'rebound' in the demand for fuel.[10] An increase in the efficiency with which a resource (e.g. fuel) is used, causes a decrease in the cost of using that resource when measured in terms of what it can achieve (e.g. travel). Generally speaking, a decrease in the cost (or price) of a good or service will increase the quantity demanded (the law of demand). With a lower cost for travel, consumers will travel more, increasing the demand for fuel. This increase in demand is known as the rebound effect, and it may or may not be large enough to offset the original drop in fuel use from the increased efficiency. The Jevons paradox occurs when the rebound effect is greater than 100%, exceeding the original efficiency gains.[5]

* https://en.wikipedia.org/wiki/Jevons_paradox

Any reason we cannot melt the salt the conventional way while using excess electricity from renewables?

You mean melting the salt using electricity with excess capacity?

I'm not an expert but I'm guessing we don't do this because the process of converting heat back to electricity is pretty inefficient. I think I saw someone say you only capture 1/3rd of the energy when you do that.

However, if you're already starting with heat and need to convert it to electricity, you can just store it for later conversion.

Engineering-wise, no. It's just a question of conversion efficiency and cost. Use electricity to heat up a thermal store (molten salt), pull power from the thermal store via generator. But how much does it cost, relative to any number of other storage mechanisms that do basically the same thing - but particularly batteries?

The article mentions that the solar plant produces 110MW, which I presume is the thermal energy captured. On average converting thermal to electric is about 1/3 efficient so this two-mile-wide field of mirrors, all of which require electric motors, maintenance, and regular cleaning for actual operation, will produce maybe 40MW of electricity? How many megawatts would be generated if all of those mirrors had PV panels installed instead?

I would think produces in this sense is the electrical output of the facility.

In the daytime - probably more.

In the nighttime - zero.

that is one of the primary points of the system; You can generate molten salt when the sun is out, and genereate the electricity via a steam turbine whenever you want.

This gives you the possibility to use this technology as a buffer.

Perhaps a hybrid system would be the best compromise: use PV panels to capture electricity, but keep some salt molten using a combination of electrical heating and solar energy redirected off the panels' protective coatings, then at night you can supplement your batteries with the far longer lasting molten salt.

> 110MW, which I presume is the thermal energy captured

That would be deceptive advertising. 110 MW is the "nameplate capacity" which is basically its maximum sustainable generation capability. Its storage capacity is specified straight-forwardly as 1,100 MWh (electric)

[1] https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Pr...

Missing [2018] tag

Reply on news.ycombinator.com