<story><title>Rain Panels: Harvesting the energy of falling raindrops</title><url>https://thedebrief.org/forget-solar-panels-here-come-rain-panels/</url></story><parent_chain><item><author>angry_moose</author><text>So 25mm&amp;#x2F;hour (1&amp;quot;) is a fairly heavy sustained rain. Terminal velocity of rain drops is on the order of 10 m&amp;#x2F;s. Volume of a rain drop is on the order of .5ml.&lt;p&gt;Total rainfall volume per m^2 is .025 m^3&amp;#x2F;hour. This is approximately 500,000 randrops&amp;#x2F;hour or about 14 drops&amp;#x2F;second. Each drop has 1&amp;#x2F;2 * m * V^2 = 25 mJ of energy.&lt;p&gt;So putting it all together, this is generating 25 mJ&amp;#x2F;drop * 14 drops&amp;#x2F;second = .35 W&amp;#x2F;m^2, and that&amp;#x27;s only when its raining. (Edit: and this is assuming 100% conversion efficiency, which....no. Don&amp;#x27;t know anything about this technology, but probably cut that number in half again).&lt;p&gt;Sounds a lot like Solar Freakin Roadways.&lt;p&gt;Edit: Just a sidenote; back in college the best course I took was billed as a &amp;quot;Renewable Energy&amp;quot; but was really just a weekly set of unit conversion problems like this that proved how absolutely stupid most energy proposals are.&lt;p&gt;We did focus a fair amount on real technologies like Wind and Solar (and analyzing the shortcomings like storage, which haven gotten better since ~2009). The professor took a lot of joy in shooting down ideas like this though.</text></item></parent_chain><comment><author>dojomouse</author><text>Love you for this! I had exactly the same “solar freaking roadways” thought, although at least that idea qualified by basic theoretical analysis of available energy and area for harvesting and conversion efficiency. It was an obviously terrible idea for other reasons :-) yet it still got a prototype…&lt;p&gt;I wasn’t sure about the droplet analysis so took your same numbers (25mm&amp;#x2F;h, 10m&amp;#x2F;s) and just worked out aggregate mass: 25mm over 1m^2 = 0.025m^3 = 25kg&lt;p&gt;0.5mv^2 =&amp;gt; 1250J&amp;#x2F;h… so looks like we agree.&lt;p&gt;And to add a simple economic analysis of why this is such a dead-end idea:&lt;p&gt;Mawsynram, in India, is apparently the rainiest city in the world with roughly 10,000mm of annual rainfall - 10x the global average.&lt;p&gt;A given rain energy harvesting panel, deployed there, would generate 500,000J&amp;#x2F;yr… or 0.138kWh. That’s significantly less than what a typical rooftop 1m2 solar panel would generate in an &lt;i&gt;hour&lt;/i&gt; on a sunny day. 0.138kwh is worth around 1.3cents at 10c&amp;#x2F;kWh.&lt;p&gt;A big roof might get you $1-$2&amp;#x2F;year. You couldn’t pay to clean your roof for that. You couldn’t even pay someone to answer an email enquiry about the install costs for your system for that. This solution would have to be VASTLY cheaper than &lt;i&gt;paint&lt;/i&gt; to stand a chance of being viable.&lt;p&gt;There is a reason our existing systems to collect power from rainfall rely on vast existing landscapes and aggregation mechanisms (rivers) to concentrate the rainfall for us.&lt;p&gt;It is - in my view - a dead idea.</text></comment>
<story><title>Rain Panels: Harvesting the energy of falling raindrops</title><url>https://thedebrief.org/forget-solar-panels-here-come-rain-panels/</url></story><parent_chain><item><author>angry_moose</author><text>So 25mm&amp;#x2F;hour (1&amp;quot;) is a fairly heavy sustained rain. Terminal velocity of rain drops is on the order of 10 m&amp;#x2F;s. Volume of a rain drop is on the order of .5ml.&lt;p&gt;Total rainfall volume per m^2 is .025 m^3&amp;#x2F;hour. This is approximately 500,000 randrops&amp;#x2F;hour or about 14 drops&amp;#x2F;second. Each drop has 1&amp;#x2F;2 * m * V^2 = 25 mJ of energy.&lt;p&gt;So putting it all together, this is generating 25 mJ&amp;#x2F;drop * 14 drops&amp;#x2F;second = .35 W&amp;#x2F;m^2, and that&amp;#x27;s only when its raining. (Edit: and this is assuming 100% conversion efficiency, which....no. Don&amp;#x27;t know anything about this technology, but probably cut that number in half again).&lt;p&gt;Sounds a lot like Solar Freakin Roadways.&lt;p&gt;Edit: Just a sidenote; back in college the best course I took was billed as a &amp;quot;Renewable Energy&amp;quot; but was really just a weekly set of unit conversion problems like this that proved how absolutely stupid most energy proposals are.&lt;p&gt;We did focus a fair amount on real technologies like Wind and Solar (and analyzing the shortcomings like storage, which haven gotten better since ~2009). The professor took a lot of joy in shooting down ideas like this though.</text></item></parent_chain><comment><author>geph2021</author><text>I&amp;#x27;m wondering if the charge generated by a rain drop could be from its static charge, rather than kinetic energy conversion?&lt;p&gt;Clearly storm systems can accumulate a large charge differential with the ground (i.e. lightning), but I don&amp;#x27;t know if that&amp;#x27;s the principle behind rain drop charge harvesting.   Cursory googling[1] tells me electrostatic charge may be the source?&lt;p&gt;1 - &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;onlinelibrary.wiley.com&amp;#x2F;doi&amp;#x2F;abs&amp;#x2F;10.1002&amp;#x2F;smll.202301568&quot; rel=&quot;nofollow noreferrer&quot;&gt;https:&amp;#x2F;&amp;#x2F;onlinelibrary.wiley.com&amp;#x2F;doi&amp;#x2F;abs&amp;#x2F;10.1002&amp;#x2F;smll.2023015...&lt;/a&gt;</text></comment>