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A Tower of Molten Salt Will Deliver Solar Power After Sunset (ieee.org)
schwit1 sends this report from IEEE Spectrum: Solar power projects intended to turn solar heat into steam to generate electricity have struggled to compete amid tumbling prices for solar energy from solid-state photovoltaic (PV) panels. But the first commercial-scale implementation of an innovative solar thermal design could turn the tide. Engineered from the ground up to store some of its solar energy, the 110-megawatt plant is nearing completion in the Crescent Dunes near Tonopah, Nev. It aims to simultaneously produce the cheapest solar thermal power and to dispatch that power for up to 10 hours after the setting sun has idled photovoltaics. ... [The system] heats a molten mixture of nitrate salts that can be stored in insulated tanks and withdrawn on demand to run the plant’s steam generators and turbine when electricity is most valuable. ... Eliminating the heat exchange between oil and salts trims energy storage losses from about 7 percent to just 2 percent. The tower also heats its molten salt to 566 degrees C, whereas oil-based plants top out at 400 degrees C.
Actually, it depends on the time of year. Demand is only highest (peaks) in the daylight hours during the summer, when air conditioning load is at its highest. During the spring and fall, when the temperatures are moderate, it's not uncommon that the peak is in the evening with lighting load (really lights + TV + commercial resteraunt use). In winter, it's definitely evening peaks with higher overnights with electric heating load. So, from a wholesale power perspective, you only need to cover that 7pm to 9pm period before load drops off (bedtimes) to smooth pricing.
They are providing power to Vegas which has the highest power usage in the evening up to midnight according to the article.
Why do you need to smooth pricing? By allowing prices to rise and fall throughout the day in response to supply and demand, you don't need to add supply between the time the sun goes down and the time people go to bed at night.
In other words, you can treat it as an economics problem and save your customers a lot of money on power plants and fuel. This is why the world is switching from flat rate pricing to time-of-use pricing.
The goal isn't to smooth pricing...it's to smooth the peaks and valleys of demand.
The grid has to be built for peak, not average...in other words, if 5% of the time, the total load of a utility's customer base is 4.5 gigawatts, then they have to be able to provide 4.5 gigawatts, even though 95% of the time the demand is half that, at most.
Ideally, power demand would be flat and constant...the same amount, all the time. Steam plants experience metal fatigue when they throttle up and down, and this is already a major problem with most utilities now. It's also way harder to regulate an efficient burn at multiple rates...which in turn, means it's harder to regulate emissions, which leads to limits on capacity if they exceed emissions of certain sorts (and, just to make it fun, those standards have just been tightened...a LOT). Those are both a big deal: too much leaking in the heat exchange coils in the boiler, and the whole plant has to come offline. Even getting close to the limit on emissions for a period, and the plant comes offline to avoid overshooting it...the plant goes into reserve mode, needed only for emergencies. And this, in turn, increases the impact of the peaks/valleys situation on the rest of the utility. And what I just described assumes 100% controllable, fuel-based generation (nuclear, petroleum, coal, gas). Now, these peaks are predictable (and predicted...there's a whole industry around the metrics and predictive load management involved), but it still poses a challenge. The steeper the walls of the peak, the faster and harder you have to spin up the generators, and the greater the stress, as well.
Renewable energy is great, except that it throws another wrench into the works. Let's say you're getting a lot of your power from solar...but then clouds move in. Effectively, for your non-renewable generation, you've just introduced a peak because it has to throttle up to take up the slack. So you end up with lots of peaks of various sizes, instead of the one or two big peaks per day. And even worse, these peaks aren't predictable.
If, however, your solar generation capacity includes a way to continue generating power after the clouds roll in, you've done two things. One, if the cloud layer is short-lived, you're able to simply disregard it and life goes on. Two, if it isn't, then you've bought more time to spin up capacity more slowly...which means less stress on the boilers, and also more options to choose from. Maybe you fire up a CT peaker, which has less trouble with variable load but takes 20-30 minutes to come online, for example. But ultimately, what you've done is taken one of the biggest problems with renewable generation and dramatically reduced it.
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Molten salt is terrible for electricity storage.
Thermal energy capacity: 0.13 kWh/kg
Electrical conversion efficiency: 25% at best
Electrical storage capacity: 0.03 kWh/kg
Amount of mass to store 12 kWH (one household overnight): 400 kg
Amount of mass to power a large city overnight (1 million households): 1 Empire State Building
Sodium-sulfur battery electrical storage capacity: 0.5 kWh/kg
Charge/discharge efficiency: 80%
Useful storage capacity: 0.4 kWh/kg
Amount of mass to store 12 kWh (one household overnight): 30 kg
Amount of mass to power a large city overnight (1 million households): 1 large submarine
Both systems use cheap, common materials, both systems are proven reliable over decades, but you get about 10 times as much energy storage when you use chemistry.
Thorium fission can scale.
Thorium (specifically Th-232) doesn't fission. It has to be bred up into U-233 by absorbing a neutron which can then fission by being hit by another neutron releasing energy. Fission of U-233 releases an average of about 2.2 neutrons to carry out further breeding and fission. This breeding-fission process is a bit knife-edge compared to regular PWRs, BWRs and other uranium-fuelled reactors where only one neutron is required to fission a U-235 nucleus and produce 2+ more.
What recent developments in "thorium fission" can you point us at? There's a lot of Powerpoint presentations and glossy brochures being waved around by folks looking to make a buck from research funding and subsidies but no-one is bending metal and pouring concrete right now on anything based on thorium as a primary source of nuclear energy. There ARE some experiments with thorium going on; PWR-style fuel pellets with thorium mixed in with uranium and plutonium are being exposed in a test reactor in Norway at the moment and there's an experimental Chinese pebble-bed reactor which can use some thorium in the fuel pebbles but that's about it.
As for modularity, it's not a new thing in regular uranium reactors -- see the units used in submarines, icebreakers and large aircraft carriers for the past fifty years and more as a worked example. The Russians are building a "power barge" carrying a ship reactor to produce about 40MW of electricity for coastal communities in Siberia and the Chinese are pouring concrete on a commercial modular power reactor (about 105MWe) but it's going to be a pebble-bed design fuelled entirely by uranium and plutonium to begin with. It might use a small amount of thorium in the future but that's a long way off and its commercial viability is still to be proven. Previous attempts to commercialise pebble-bed reactors capable of using some thorium such as the German THTR-300 were not a success.
Thorium (specifically Th-232) doesn't fission.
I am well aware of that but using "thorium fission" as a shorthand for "thorium cycle fission" seems common enough that I thought it would not need explanation. I assumed that people that knew what LFTR was would know what I meant and everyone else could search on "thorium fission" in Google, Wikipedia, or wherever and figure it out by clicking on the first link that shows up.
This breeding-fission process is a bit knife-edge compared to regular PWRs, BWRs and other uranium-fuelled reactors where only one neutron is required to fission a U-235 nucleus and produce 2+ more.
A lot of nuclear engineers seem to disagree with you. There are several techniques to make thorium cycle viable, the most popular are molten salt variations. Molten salt allows poisons that would normally accumulate in solid fuel to boil out. Iodine and xenon are the biggest concerns and those simply cannot remain in solution for long, and there are techniques to speed the removal from the core adding efficiency.
What recent developments in "thorium fission" can you point us at?
Here's a good place to start:
https://www.youtube.com/user/g...
There's a lot of Powerpoint presentations and glossy brochures being waved around by folks looking to make a buck from research funding and subsidies but no-one is bending metal and pouring concrete right now on anything based on thorium as a primary source of nuclear energy.
I believe that China and India would disagree with you. Right now in the USA and Canada thorium fission is being held up by regulators that don't know what to do with thorium yet. I suspect we'll see a boom in LFTR and DMSR shortly after China demonstrates their first MSR. It used to be that the USA was first in technology, now we race to be second place.
Previous attempts to commercialise pebble-bed reactors capable of using some thorium such as the German THTR-300 were not a success.
Let's see, steam turbines, helium cooled core, small manufactured fuel pebbles, and a one off design. What could possibly go wrong? Water creeping into the helium coolant. Pebbled fuel breaking in the reactor and getting lodged in piping. Difficulty in sourcing fuel. Not a high point of thorium as a fuel.
LFTR uses molten salt as coolant and fuel carrier, any leaking between them does cause contamination but it will not stop operation. Leaks can be repaired and operation resumed. There is no water cooling to create concerns over flash boiling, corrosion of metals, or contamination of fuel. LFTR does not require "manufacture" of the fuel, it's a stable salt with very low chemical and nuclear reactivity. Once melted it can be simply poured into the core. Waste products are removed as part of normal operation, they won't accumulate to levels that would cause massive release if there is a catastrophic failure. Any kind of large failure would be limited to destruction of the core, it can't "blow it's top" like water cooled and solid fuel reactors of the past.
This design was tested and operating fifty years ago. However, because we've learned a lot in the last fifty years in material science, manufacturing, and so forth that design would not be considered viable today. What it does do is show the physics work and if we can only get the DOE to get their assess off their thumbs then maybe we can see thorium as a fuel before another fifty years pass.
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> The problem today is that solar costs three times what it needs to cost to be competitive.
Read this article and say that solar is still 3x competitive range:
http://www.pv-tech.org/news/buffett_projects_record_low_cost_is_part_of_pricing_trend_says_first_solar
Same company as the original story, by the way, NV Energy.