<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>samatman</author><text>&amp;gt; &lt;i&gt;It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels. They still use leaded gas!&lt;/i&gt;&lt;p&gt;It&amp;#x27;s important to qualify this: jet fuel contains no lead, and constitutes the vast majority of commercial aviation, and hence of emissions.&lt;p&gt;Jet fuel itself is kerosene, with some additives that aren&amp;#x27;t superb in raw form, but nothing so durable in the environment as lead.&lt;p&gt;A sibling comment does a fine job of explaining why avgas still contains lead, and to be sure, a plan to phase that out except where absolutely necessary would be welcome.</text><parent_chain><item><author>PaulHoule</author><text>It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels.  They still use leaded gas!&lt;p&gt;It seems you would try methane before you try hydrogen:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;energynews.us&amp;#x2F;2013&amp;#x2F;08&amp;#x2F;26&amp;#x2F;midwest&amp;#x2F;could-natural-gas-fuel-commercial-flights-of-the-future&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;energynews.us&amp;#x2F;2013&amp;#x2F;08&amp;#x2F;26&amp;#x2F;midwest&amp;#x2F;could-natural-gas-f...&lt;/a&gt;&lt;p&gt;Petroleum-based liquid fuels contain mixed entity hydrocarbons that match a specification;  if you have the perfect feedstock and markets for the fractions you don&amp;#x27;t use this is cheap.  Worst-case you have to synthesize them with Fischer-Tropsch chemistry&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fischer%E2%80%93Tropsch_process&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fischer%E2%80%93Tropsch_proces...&lt;/a&gt;&lt;p&gt;which is such a PITA (normally a chem E would be delighted that you can use iron as a catalyst,  but it works so poorly that a desperate search of the other 91 elements found just 2 that sorta-kinda work)&lt;p&gt;The issue there is you are sticking C&amp;#x27;s onto the end of a chain and you have to deal with a network of reactions that produce products you couldn&amp;#x27;t care less for,  such as petroleum jelly that gums up your catalyst,  sticks up your downrisers,  etc.&lt;p&gt;Sustainable motor fuels tend to be single entities such as 1-butanol,  dimethyl ether,  etc.  You might need to blend something in for low temperature starting,  but it&amp;#x27;s possible for a single entity fuel to be synthesized with decent yield.&lt;p&gt;General av is seen as a backwater that is barely hanging on and couldn&amp;#x27;t possibly get the lead out.  The USAF has done biofuels trials,  but commercial av is spooked to try anything that could leave passengers up in the air.</text></item><item><author>jeffreyrogers</author><text>&amp;gt; In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.&lt;p&gt;I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation.&lt;p&gt;This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.</text></item><item><author>55873445216111</author><text>Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source.&lt;p&gt;Therefore the relevant comparison is between H2 fuel cells and Li ion batteries. Batteries have much higher full cycle efficiency (energy input -&amp;gt; storage -&amp;gt; energy output), but they are large and heavy. H2 can be stored in less volume and less weight, but it is less efficient. In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.</text></item></parent_chain></comment><story><title>Ask HN: Is hydrogen likely to be a major source of power in the next 10 years?</title><text>There has been hype around hydrogen fuel cells being a source of green power for decades, but the hype cycle is currently ramping up significantly. Hydrogen fuel cell stocks such as PLUG and FCEL have gone up 10x despite the lack of any significant new breakthrough technology and a history of loss making and value destruction.&lt;p&gt;Just today, Bank of America research released a 103 page &amp;quot;Hydrogen Primer&amp;quot; in which they predict that the hydrogen space will generate $2.5 trillion in direct revenues and $11 trillion of indirect infrastructure potential. They believe that a tipping point is coming soon because of the falling cost of renewable energy and electrolysers used to produce &amp;quot;green&amp;quot; hydrogen, as well as better efficiencies in fuel cells.&lt;p&gt;My question is for the experts in the crowd here, either based on engineering experience or on first principles and physics, does this seem likely to you? Why do we really need hydrogen? It seems we are getting to the point where wind power and particularly solar power are now cost effective. Once we have better batteries for storage, what problem do we have left that requires hydrogen to solve? Is this just a giant promotional bubble being pushed by Wall Street and unscrupulous companies trying to sell a dream? I may sound skeptical but I genuinely don&amp;#x27;t know and would like to hear from people with more expertise.</text></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>ohazi</author><text>&amp;gt; General av is seen as a backwater that is barely hanging on and couldn&amp;#x27;t possibly get the lead out.&lt;p&gt;The issue is infrastructure. Modern engines run fine on unleaded fuel, but the little airstrips in the middle of nowhere all have 100LL and&amp;#x2F;or jet fuel, so that&amp;#x27;s what pilots use.&lt;p&gt;I know a few pilots who are &lt;i&gt;prefer&lt;/i&gt; to use unleaded in their Rotax engines to prevent spark plug fouling, and they have to jump through some pretty ridiculous hoops to get gas, while their buddies just fill up with whatever is on the field.</text><parent_chain><item><author>PaulHoule</author><text>It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels.  They still use leaded gas!&lt;p&gt;It seems you would try methane before you try hydrogen:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;energynews.us&amp;#x2F;2013&amp;#x2F;08&amp;#x2F;26&amp;#x2F;midwest&amp;#x2F;could-natural-gas-fuel-commercial-flights-of-the-future&amp;#x2F;&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;energynews.us&amp;#x2F;2013&amp;#x2F;08&amp;#x2F;26&amp;#x2F;midwest&amp;#x2F;could-natural-gas-f...&lt;/a&gt;&lt;p&gt;Petroleum-based liquid fuels contain mixed entity hydrocarbons that match a specification;  if you have the perfect feedstock and markets for the fractions you don&amp;#x27;t use this is cheap.  Worst-case you have to synthesize them with Fischer-Tropsch chemistry&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fischer%E2%80%93Tropsch_process&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Fischer%E2%80%93Tropsch_proces...&lt;/a&gt;&lt;p&gt;which is such a PITA (normally a chem E would be delighted that you can use iron as a catalyst,  but it works so poorly that a desperate search of the other 91 elements found just 2 that sorta-kinda work)&lt;p&gt;The issue there is you are sticking C&amp;#x27;s onto the end of a chain and you have to deal with a network of reactions that produce products you couldn&amp;#x27;t care less for,  such as petroleum jelly that gums up your catalyst,  sticks up your downrisers,  etc.&lt;p&gt;Sustainable motor fuels tend to be single entities such as 1-butanol,  dimethyl ether,  etc.  You might need to blend something in for low temperature starting,  but it&amp;#x27;s possible for a single entity fuel to be synthesized with decent yield.&lt;p&gt;General av is seen as a backwater that is barely hanging on and couldn&amp;#x27;t possibly get the lead out.  The USAF has done biofuels trials,  but commercial av is spooked to try anything that could leave passengers up in the air.</text></item><item><author>jeffreyrogers</author><text>&amp;gt; In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.&lt;p&gt;I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation.&lt;p&gt;This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.</text></item><item><author>55873445216111</author><text>Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source.&lt;p&gt;Therefore the relevant comparison is between H2 fuel cells and Li ion batteries. Batteries have much higher full cycle efficiency (energy input -&amp;gt; storage -&amp;gt; energy output), but they are large and heavy. H2 can be stored in less volume and less weight, but it is less efficient. In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.</text></item></parent_chain></comment><story><title>Ask HN: Is hydrogen likely to be a major source of power in the next 10 years?</title><text>There has been hype around hydrogen fuel cells being a source of green power for decades, but the hype cycle is currently ramping up significantly. Hydrogen fuel cell stocks such as PLUG and FCEL have gone up 10x despite the lack of any significant new breakthrough technology and a history of loss making and value destruction.&lt;p&gt;Just today, Bank of America research released a 103 page &amp;quot;Hydrogen Primer&amp;quot; in which they predict that the hydrogen space will generate $2.5 trillion in direct revenues and $11 trillion of indirect infrastructure potential. They believe that a tipping point is coming soon because of the falling cost of renewable energy and electrolysers used to produce &amp;quot;green&amp;quot; hydrogen, as well as better efficiencies in fuel cells.&lt;p&gt;My question is for the experts in the crowd here, either based on engineering experience or on first principles and physics, does this seem likely to you? Why do we really need hydrogen? It seems we are getting to the point where wind power and particularly solar power are now cost effective. Once we have better batteries for storage, what problem do we have left that requires hydrogen to solve? Is this just a giant promotional bubble being pushed by Wall Street and unscrupulous companies trying to sell a dream? I may sound skeptical but I genuinely don&amp;#x27;t know and would like to hear from people with more expertise.</text></story>