5 ms·

Something to take note of. Different types of energy production are useful for different roles. Nuclear tends to fall into the category of base load - it cost

Something to take note of. Different types of energy production are useful for different roles. Nuclear tends to fall into the category of base load - it costs (close enough to) just as much to run it at 5% capacity as at 100%. Most traditional fossil-fuel steam turbines (coal, oil) have spin-up times on the order of several hours to a day. As such, they tend to be used to compensate for longer-timescale variations, but cannot really cope with very short term spikes. There are fossil-fuel power stations with shorter lag times, but they tend to be relatively inefficient, and as such only get used for unexpected high loads. Hydro is really good in a lot of ways, at least where hydro power stations can be built. The biggest reason is that it can be adjusted on really short timescales. Read: minutes or less. Longer lag time for larger power stations - the biggest limitation tends to be preventing cavitation and water hammer. Solar and wind are both extremely variable, and unpredictably so (you can predict, but there is enough inaccuracy in the predictions that you cannot trust them). As such, they are practically useless without at least one of power storage, fast-responding power generation, or fast-acting power usage cuts when necessary. (Read: hydro or paying aluminum smelters to only run in the back shifts. (First thing that came to mind)) As there is no efficient and decently long-lasting power storage at grid scales (Vanadium-redox batteries are good, but have issues. Molten-salt storage leaks heat quickly. Etc.), effectively: you can forget about solar and wind for grid-scale power without hydro. Nuclear power for everything is a waste unless society changes. And good luck with that.

dredmorbius 12y ago
Quite. Hydro, hydro pumped storage, tidal impounds (essentially low-head but large-area reservoirs), and geothermal (wet field) are all highly dispatchable. Solar thermal is expensive but among its benefits it has is a built-in storage capability. For most present plants that's only a few hours, but several days worth of banked heat might be viable. There are a number of storage options, of which the prospect of synfuels, in particular seawater-based Fischer-Tropsch fuel synthesis, which as been studied by Brookhaven National Labs, MIT, and the US Naval Research Lab for over 50 years, looks fairly promising. It starts with hydrogen electrolysis, to which CO2 is added, sourced from seawater. Outputs are analogs of present day diesel, gasoline, natural gas, or other hydrocarbons. Most of the energy cost is in the electrolysis. Net energy return in terms of fuel is about 50-60%, round-trip net of generation would be fairly low (~20%), but the energy storage is very long-term stable, and dense by weight or volume (for liquids). We've got a lot of experience burning hydrocarbons, and these are carbon-neutral (the source CO2 comes from the present biosphere). http://www.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ http://www.reddit.com/r/dredmorbius/comments/28nqoz/electric... http://www.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ http://www.reddit.com/r/dredmorbius/comments/22k71x/us_navy_... There's also work by some (including a recent video by Amory Lovins) suggesting that there are relatively modest requirements for dispatchable generation, though I suspect those are a tad optimistic. http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/8272/Is-Storage-Necessary-for-Renewable-Energy.aspx?ENGCOM= http://www.engineering.com/ElectronicsDesign/ElectronicsDesi... https://www.youtube.com/watch?v=MsgrahFln0s https://www.youtube.com/watch?v=MsgrahFln0s
- TheLoneWolfling 12y ago
  Dispatchable. That's the term. Thanks. The thing is, by the time you talk about the design lifetime power output of wind in particular, and couple in the 20% figure you quote for the round trip, one has to wonder if it is worth it. It's a lot of metal (and in particular the "weirder" metals - rare-earths and the like) to smelt and move around to get a relatively small amount of power. And the increased power losses due to having to put them where the wind is. And the power cost of building the storage capability. Synfuels are indeed interesting, for bunches of reasons, chief among them that they are the most power-dense storage solution we've got. Personally, it's about the best option for personal vehicles. Yeah, electric vehicles are neat, but they suffer from short ranges and long recharge times, as well as using bunches of relatively rare elements (and elements that are mined using techniques that are abysmal in environmental terms).
  - dredmorbius 12y ago
    There are a few people who've done calculations of the EROEI (energy returned on energy input) of various renewable energy technologies, most notably the guy who came up with the term, Charles A.S. Hall. I've had a few discussions with him on this. Wind power has a modestly high EROEI, around 18. For solar PV, his numbers are far lower -- around 2.6. The problem comes in when you account for whether there's a minimum EROEI necessary to sustain an advanced civilization, and just what that might be. Hall's view is that it's around 6-10, after which you pretty much fall off a cliff -- you've got to get a sufficient return on your energy investment to make other economic activity possible. For the synfuel path I discussed, the point is that there are a few things for which having hydrocarbons (liquid or gas) is really, really useful, and as I've noted elsewhere in this discussion, there's simply not enough net biological productivity ("photosynthetic ceiling" to use Jared Diamond's term, or HANNP, human appropriation of net primary productivity, another formulation) to provide fuels in the quantities humans are presently accustomed to -- some of the acreage requirement estimates get stunningly large and rapidly: http://www.reddit.com/r/dredmorbius/comments/2cvap7/the_intractable_problem_of_biomass_for_fuels_is/ http://www.reddit.com/r/dredmorbius/comments/2cvap7/the_intr... In particular (the table on that page is a bit prettier than it will appear here on HN): Crop Yield (gal/acre-yr) Acres required (millions) soybeans 50 5,670 canola 100 2,835 canola 300 945 algae 1000 283 algae (high est) 10,000 28 Note that total arable land in the US is about 410 million acres, and total land area of the US is 2.4 billion acres. You'd have to overplant the US twice to get enough fuel-from-crops via soybeans. Note that "rare earths" aren't actually all that rare, though there are plenty of minerals which are limited in abundance: http://www.reddit.com/r/dredmorbius/comments/267901/global_resources_stock_check_bbc_june_2012/ http://www.reddit.com/r/dredmorbius/comments/267901/global_r... As for synfuels: since you're converting surplus generating capacity, your marginal energy cost is nil. Even assuming you're building capacity specific to the need, what you're trading is a non-storable, non-mobile, non-dispatchable form of energy for one which has all of those properties. That can be a good trade. The fact that it's a drop-in replacement for the existing energy system is an added bonus. Will it work? I really don't know, though the answer to that question's been occupying me for some time.

dredmorbius 12y ago

Quite. Hydro, hydro pumped storage, tidal impounds (essentially low-head but large-area reservoirs), and geothermal (wet field) are all highly dispatchable. Solar thermal is expensive but among its benefits it has is a built-in storage capability. For most present plants that's only a few hours, but several days worth of banked heat might be viable. There are a number of storage options, of which the prospect of synfuels, in particular seawater-based Fischer-Tropsch fuel synthesis, which as been studied by Brookhaven National Labs, MIT, and the US Naval Research Lab for over 50 years, looks fairly promising. It starts with hydrogen electrolysis, to which CO2 is added, sourced from seawater. Outputs are analogs of present day diesel, gasoline, natural gas, or other hydrocarbons. Most of the energy cost is in the electrolysis. Net energy return in terms of fuel is about 50-60%, round-trip net of generation would be fairly low (~20%), but the energy storage is very long-term stable, and dense by weight or volume (for liquids). We've got a lot of experience burning hydrocarbons, and these are carbon-neutral (the source CO2 comes from the present biosphere). http://www.reddit.com/r/dredmorbius/comments/28nqoz/electrical_fuel_synthesis_from_seawater_older/ http://www.reddit.com/r/dredmorbius/comments/28nqoz/electric... http://www.reddit.com/r/dredmorbius/comments/22k71x/us_navy_electricitytofuel_synthesis_papers_and/ http://www.reddit.com/r/dredmorbius/comments/22k71x/us_navy_... There's also work by some (including a recent video by Amory Lovins) suggesting that there are relatively modest requirements for dispatchable generation, though I suspect those are a tad optimistic. http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/8272/Is-Storage-Necessary-for-Renewable-Energy.aspx?ENGCOM= http://www.engineering.com/ElectronicsDesign/ElectronicsDesi... https://www.youtube.com/watch?v=MsgrahFln0s https://www.youtube.com/watch?v=MsgrahFln0s

TheLoneWolfling 12y ago
Dispatchable. That's the term. Thanks. The thing is, by the time you talk about the design lifetime power output of wind in particular, and couple in the 20% figure you quote for the round trip, one has to wonder if it is worth it. It's a lot of metal (and in particular the "weirder" metals - rare-earths and the like) to smelt and move around to get a relatively small amount of power. And the increased power losses due to having to put them where the wind is. And the power cost of building the storage capability. Synfuels are indeed interesting, for bunches of reasons, chief among them that they are the most power-dense storage solution we've got. Personally, it's about the best option for personal vehicles. Yeah, electric vehicles are neat, but they suffer from short ranges and long recharge times, as well as using bunches of relatively rare elements (and elements that are mined using techniques that are abysmal in environmental terms).
- dredmorbius 12y ago
  There are a few people who've done calculations of the EROEI (energy returned on energy input) of various renewable energy technologies, most notably the guy who came up with the term, Charles A.S. Hall. I've had a few discussions with him on this. Wind power has a modestly high EROEI, around 18. For solar PV, his numbers are far lower -- around 2.6. The problem comes in when you account for whether there's a minimum EROEI necessary to sustain an advanced civilization, and just what that might be. Hall's view is that it's around 6-10, after which you pretty much fall off a cliff -- you've got to get a sufficient return on your energy investment to make other economic activity possible. For the synfuel path I discussed, the point is that there are a few things for which having hydrocarbons (liquid or gas) is really, really useful, and as I've noted elsewhere in this discussion, there's simply not enough net biological productivity ("photosynthetic ceiling" to use Jared Diamond's term, or HANNP, human appropriation of net primary productivity, another formulation) to provide fuels in the quantities humans are presently accustomed to -- some of the acreage requirement estimates get stunningly large and rapidly: http://www.reddit.com/r/dredmorbius/comments/2cvap7/the_intractable_problem_of_biomass_for_fuels_is/ http://www.reddit.com/r/dredmorbius/comments/2cvap7/the_intr... In particular (the table on that page is a bit prettier than it will appear here on HN): Crop Yield (gal/acre-yr) Acres required (millions) soybeans 50 5,670 canola 100 2,835 canola 300 945 algae 1000 283 algae (high est) 10,000 28 Note that total arable land in the US is about 410 million acres, and total land area of the US is 2.4 billion acres. You'd have to overplant the US twice to get enough fuel-from-crops via soybeans. Note that "rare earths" aren't actually all that rare, though there are plenty of minerals which are limited in abundance: http://www.reddit.com/r/dredmorbius/comments/267901/global_resources_stock_check_bbc_june_2012/ http://www.reddit.com/r/dredmorbius/comments/267901/global_r... As for synfuels: since you're converting surplus generating capacity, your marginal energy cost is nil. Even assuming you're building capacity specific to the need, what you're trading is a non-storable, non-mobile, non-dispatchable form of energy for one which has all of those properties. That can be a good trade. The fact that it's a drop-in replacement for the existing energy system is an added bonus. Will it work? I really don't know, though the answer to that question's been occupying me for some time.