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> 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
by mojomark 7y ago
> 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.
- jfoutz 7y agoThis 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.
- BurningFrog 7y agoJust 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.
- SECProto 7y agoHypothetical (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
- mcguire 7y agoBack 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 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?
- sjwright 7y ago
- thinkcontext 7y agoLazard'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-of-energy-version-120-vfinal.pdf https://www.lazard.com/media/450784/lazards-levelized-cost-o...