5 ms·

I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost

by ilyt 3y ago

JadeNB 3y ago
> I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost You can—and it's usually safe to, in the translation from actual researchers to PR departments—ceertainly doubt the viability of this claim, but the whole article is devoted to at least explicitly claiming that they're aware of the obvious problems, and can overcome them: > … the efforts to collect energy from falling raindrops have faced a technical hurdle that has made the concept inefficient and impractical. … as one might expect, the amount of power per raindrop is incredibly small. … > Now, a team of researchers says they have found a design and configuration that greatly reduces the coupling capacitance issue and one they claim could make energy-harvesting rain panels a practical reality. One key seems to be that, although you're obviously meant to think of rooftop panels, it seems more to be about large-scale installations: > “The peak power output of the bridge array generators is nearly 5 times higher than that of the conventional large-area raindrop energy with the same size, reaching 200 watts per square meter,” Li explained, “which fully shows its advantages in large-area raindrop energy harvesting.” (I do notice on re-reading that it says "… may lead to the development of rooftop, power-generating rain panels", but (1) one can freely claim that anything may lead to something else, and (2) one can claim that anything may lead to anything else, so I prefer to go by quotes from the researchers themselves.)
- Retric 3y ago
  Raindrops fall at 10m/s or less. The absolutely rainiest place on earth revives 12 meters of rain per year. A 1x1x12 meter block of water weighs 12,000kg going 10m/s it has KE = 1/2 M * V^2 = 6 * 10 ^ 5j. 200 watts per meter is 200j/second… So your hypothetical 200 watts per square meter at 100% efficiency assuming spherical cow types of ideal conditions could possibly provide that power for 50 minutes per year under ideal circumstances or average 0.02w/m2 over a year. And average roughly 0.002w/m2 in extremely rainy though not world record setting locations. Now, you ignore the kinetic energy in rainfall and try and harvest the potential energy when it lands at a high altitude, allowing a large collection area and large differences in altitude. But we call those things dams.
- ilyt 3y ago
  Right, so why they are bothering ? The technical limit is known and it is making it barely acceptable if it was free (because you still need to have dedicated inverter channel for the power conversion as characteristics are much different than what solar panels generate). And if it wasn't free or near-free it's competing with putting one more panel or adding one more battery to the system. Or... just big, cheap funnel that is feeding water generator Sure you lose some of the velocity but it is so much simpler system Like, generating energy from tiny movements have its niches (like sensors powered by piezoelectrics from vibrations of machine they monitor), but using it for raindrops just feels like a waste of time, most areas don't even get enough rain for that to matter. Now if they figured out to do it to airflow with few moving parts, that would be more interesting.
- feoren 3y ago
  Peak output doesn't matter: you cannot get more energy out of rain than rain has. You could build a turbine that can theoretically generate 10MW at its max speed, but if it's being pushed by ants, who cares what its max theoretical output is? Look at the top comment of this thread. Even at 100% efficiency, there is nowhere near 200 W/m^2 of energy to possibly extract from rain. Four orders of magnitude less.
willcipriano 3y ago
In the UK it would probably look a lot better, rainforests as well.
- konschubert 3y ago
  A factor 3 doesn’t compensate a factor 1000
  - willcipriano 3y ago
    There is a sort of reverse time value of money[0] but for energy. When it's raining, it's often cloudy so solar isn't as efficient and the cost of energy goes up. Things like this become more attractive under certain conditions and I could see a use as the technology is improved and commercialized. Energy is never going to be a single technology, we will probably end up with dozens of sources in the end. https://en.m.wikipedia.org/wiki/Time_value_of_money https://en.m.wikipedia.org/wiki/Time_value_of_money
    - stephen_g 3y ago
      It's good to think outside the box, but unfortunately the theoretical amount of energy available (that others have calculated in the comments here) just make it a non-starter. For comparison, even on the rainiest day I've measured in the last year from my 6.6 kW photovoltaic array on my house, I made 8 kWh of energy (on a good summer's day I get around 40 kWh), with the lowest output across most of the day being 450W (less at sunrise and sunset obviously). Other have posted calculations of the maximum energy that can be expected to be collected from raindrops, and from those calculations, I doubt that with a raindrop capture device as large as my PV array you could make 8 kWh in a month.
    - Brusco_RF 3y ago
      Even the most optimistic reading has these "rain panels" well under 1W/m^2. For comparison, peak solar irradiance is something like 1400W/m^2. This webpage has already burned more energy than that panel will ever produce.
    - 3y ago
kevinlinxc 3y ago
200W/m^2 is what it says at the end right? Regardless, the tech will improve and get cheaper and this will be a nice sell for countries with less sun. Maybe eventually we could get hybrid panels powers by Sun or rain?
- angry_moose 3y ago
  Then their math is off by nearly 4 orders of magnitude somewhere (see other comments in the the thread). "Technology improvements" can't get around the fundamental limit in the amount of energy available to harvest. Edit: Oh, that's horribly misleading. They seem to be reporting the theoretical maximum output of this harvesting technology - e.g., how much energy could be recovered if they started blasting the panel with a firehose. The amount available in rain is on the order of .2-.4 W/m^2. At that rate you'd never recover the amount of energy as was used to produce the panel.
- jacquesm 3y ago
  200 mW at best... seriously, this is bunk.

I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost

by ilyt 3y ago

I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost

> I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost You can—and it's usually safe to, in the translation from actual researchers to PR departments—ceertainly doubt the viability of this claim, but the whole article is devoted to at least explicitly claiming that they're aware of the obvious problems, and can overcome them: > … the efforts to collect energy from falling raindrops have faced a technical hurdle that has made the concept inefficient and impractical. … as one might expect, the amount of power per raindrop is incredibly small. … > Now, a team of researchers says they have found a design and configuration that greatly reduces the coupling capacitance issue and one they claim could make energy-harvesting rain panels a practical reality. One key seems to be that, although you're obviously meant to think of rooftop panels, it seems more to be about large-scale installations: > “The peak power output of the bridge array generators is nearly 5 times higher than that of the conventional large-area raindrop energy with the same size, reaching 200 watts per square meter,” Li explained, “which fully shows its advantages in large-area raindrop energy harvesting.” (I do notice on re-reading that it says "… may lead to the development of rooftop, power-generating rain panels", but (1) one can freely claim that anything may lead to something else, and (2) one can claim that anything may lead to anything else, so I prefer to go by quotes from the researchers themselves.)

Retric 3y ago
Raindrops fall at 10m/s or less. The absolutely rainiest place on earth revives 12 meters of rain per year. A 1x1x12 meter block of water weighs 12,000kg going 10m/s it has KE = 1/2 M * V^2 = 6 * 10 ^ 5j. 200 watts per meter is 200j/second… So your hypothetical 200 watts per square meter at 100% efficiency assuming spherical cow types of ideal conditions could possibly provide that power for 50 minutes per year under ideal circumstances or average 0.02w/m2 over a year. And average roughly 0.002w/m2 in extremely rainy though not world record setting locations. Now, you ignore the kinetic energy in rainfall and try and harvest the potential energy when it lands at a high altitude, allowing a large collection area and large differences in altitude. But we call those things dams.
ilyt 3y ago
Right, so why they are bothering ? The technical limit is known and it is making it barely acceptable if it was free (because you still need to have dedicated inverter channel for the power conversion as characteristics are much different than what solar panels generate). And if it wasn't free or near-free it's competing with putting one more panel or adding one more battery to the system. Or... just big, cheap funnel that is feeding water generator Sure you lose some of the velocity but it is so much simpler system Like, generating energy from tiny movements have its niches (like sensors powered by piezoelectrics from vibrations of machine they monitor), but using it for raindrops just feels like a waste of time, most areas don't even get enough rain for that to matter. Now if they figured out to do it to airflow with few moving parts, that would be more interesting.
feoren 3y ago
Peak output doesn't matter: you cannot get more energy out of rain than rain has. You could build a turbine that can theoretically generate 10MW at its max speed, but if it's being pushed by ants, who cares what its max theoretical output is? Look at the top comment of this thread. Even at 100% efficiency, there is nowhere near 200 W/m^2 of energy to possibly extract from rain. Four orders of magnitude less.

willcipriano 3y ago

In the UK it would probably look a lot better, rainforests as well.

konschubert 3y ago
A factor 3 doesn’t compensate a factor 1000
- willcipriano 3y ago
  There is a sort of reverse time value of money[0] but for energy. When it's raining, it's often cloudy so solar isn't as efficient and the cost of energy goes up. Things like this become more attractive under certain conditions and I could see a use as the technology is improved and commercialized. Energy is never going to be a single technology, we will probably end up with dozens of sources in the end. https://en.m.wikipedia.org/wiki/Time_value_of_money https://en.m.wikipedia.org/wiki/Time_value_of_money
  - stephen_g 3y ago
    It's good to think outside the box, but unfortunately the theoretical amount of energy available (that others have calculated in the comments here) just make it a non-starter. For comparison, even on the rainiest day I've measured in the last year from my 6.6 kW photovoltaic array on my house, I made 8 kWh of energy (on a good summer's day I get around 40 kWh), with the lowest output across most of the day being 450W (less at sunrise and sunset obviously). Other have posted calculations of the maximum energy that can be expected to be collected from raindrops, and from those calculations, I doubt that with a raindrop capture device as large as my PV array you could make 8 kWh in a month.
  - Brusco_RF 3y ago
    Even the most optimistic reading has these "rain panels" well under 1W/m^2. For comparison, peak solar irradiance is something like 1400W/m^2. This webpage has already burned more energy than that panel will ever produce.
  - 3y ago

kevinlinxc 3y ago

200W/m^2 is what it says at the end right? Regardless, the tech will improve and get cheaper and this will be a nice sell for countries with less sun. Maybe eventually we could get hybrid panels powers by Sun or rain?

angry_moose 3y ago
Then their math is off by nearly 4 orders of magnitude somewhere (see other comments in the the thread). "Technology improvements" can't get around the fundamental limit in the amount of energy available to harvest. Edit: Oh, that's horribly misleading. They seem to be reporting the theoretical maximum output of this harvesting technology - e.g., how much energy could be recovered if they started blasting the panel with a firehose. The amount available in rain is on the order of .2-.4 W/m^2. At that rate you'd never recover the amount of energy as was used to produce the panel.
jacquesm 3y ago
200 mW at best... seriously, this is bunk.