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Should "Rain Power" be added to our topic list?
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kenneal - lagger
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PostPosted: Fri Mar 23, 2018 3:45 pm    Post subject: Should "Rain Power" be added to our topic list? Reply with quote

This could be ideal for our climate.
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PS_RalphW



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PostPosted: Fri Mar 23, 2018 4:08 pm    Post subject: Reply with quote

Come back when they have a production model that harvests 10% more energy than a solar panel the same area, for the same price as a solar panel. This is just a research project, with no numbers in it at all.
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adam2
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PostPosted: Fri Mar 23, 2018 5:51 pm    Post subject: Reply with quote

I am very doubtful indeed. I do not believe that useful power can be produced by rain falling on a surface.
If a lot of rain falls over a large area, and can be collected at high level, and passed through a turbine at a lower level then power can be produced. It is called hydroelectric power and is a mature technology.

But rainfall on a surface, I cant see where significant energy would come from.
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woodburner



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PostPosted: Fri Mar 23, 2018 10:45 pm    Post subject: Reply with quote

Laughing Laughing Laughing They have published too early, 1st of April is next Sunday. Laughing
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BritDownUnder



Joined: 21 Sep 2011
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PostPosted: Sat Mar 24, 2018 1:47 am    Post subject: Reply with quote

adam2 wrote:
I am very doubtful indeed. I do not believe that useful power can be produced by rain falling on a surface.
If a lot of rain falls over a large area, and can be collected at high level, and passed through a turbine at a lower level then power can be produced. It is called hydroelectric power and is a mature technology.

But rainfall on a surface, I cant see where significant energy would come from.

I presume it collects the kinetic energy of raindrops that is turned into frictional energy.

Assume 100% energy conversion.

Annual rainfall in 'most' populated parts of the UK is 800mm. Therefore in one square metre 0.8 x 1 x 1 cubic metres of rain falls annually. This weighs 800 kg. Terminal velocity of a falling object is approx 125 mph (or 55m/sec in new money).

Hence annual kinetic energy harvested is 1/2 x mass x velocity^2
Doing the calcs in metric to give energy in Joules.
= 0.5 x 800 x 55 x 55 = 1,210,000 Joules

1kWh = 3,600,000 Joules

Therefore you will harvest annually about 1/3 kWh per metre squared of panel.

Verdict.... a gimmick.

Disclaimer. Another person please check my maths.
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Lurkalot



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PostPosted: Sat Mar 24, 2018 2:25 pm    Post subject: Reply with quote

I'm not going to question your figures but did wonder how much wind would affect those figures. Would drizzle have anywhere the potential energy of driving rain and is snowfall included in those 800mm average figures?
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woodburner



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PostPosted: Sun Mar 25, 2018 1:48 am    Post subject: Reply with quote

BritDownUnder, when have you ever been hit by a raindrop doing 125mph? It is fairly uncomfortable holding your hand out of a car window at 70 in he rain.

I would get no electricity if it was raining that fast as I woud stay in doors. Please buy some shares in the company to ensur it goes bankrupt. Better buy some in Monsanto and a few other big names too. Wink
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BritDownUnder



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PostPosted: Sun Mar 25, 2018 3:44 am    Post subject: Reply with quote

woodburner wrote:
BritDownUnder, when have you ever been hit by a raindrop doing 125mph? It is fairly uncomfortable holding your hand out of a car window at 70 in he rain.

I would get no electricity if it was raining that fast as I woud stay in doors. Please buy some shares in the company to ensur it goes bankrupt. Better buy some in Monsanto and a few other big names too. Wink


I have not been hit by such a fast raindrop. From memory a falling human body will fall at 125mph (that's where I got the number from) and I am merely indicate a 'best' case scenario with terminal velocity raindrops on a back of the envelope calculation which shows that even the best case scenario will provide little useful energy. I would suspect that 'actual' terminal velocity depends on things such as object density, aerodynamic shape, deformity and the like and a raindrop will have a lower terminal velocity lower than a lead ball, for example. From what I understand the latest guided bombs have a 'terminal' velocity close to mach 1 if dropped under the right circumstances.
If the terminal velocity was nearly halved to 70mph as you seem to indicate is a more accurate number, and from your anecdote you are probably closer to the truth than I was, then the kinetic energy will drop to a quarter of the previous value.

I think we can happily say that this is a gimmick unless some other form of energy conversion is in process.
Putting on my boring maths hat again, let's assume that the falling raindrop collects static charge (of what polarity I have no idea) during its descent from the heavens.
Assume:
The mass of water falls from a cloud formation one mile up so its potential energy is converted to static charge.
Potential energy = mass x g x height where g is the acceleration due to gravity.

We now have
Energy = 800 x 9.8 x 1760 = 1,400,000 Joules (approx)
pretty much the same as the last calculation but gives you an interesting fact that the raindrop could never go much faster than 125mph anyway and probably a lot less due to frictional heating on its way down.

Verdict... still a gimmick

On another note. I am open to each and all share tips but consciously investing in the hope of some company actually going bankrupt will be a new one for me. Unconsciously investing giving much the same result seems to happen quite a lot to me. At least I missed Toys are Us!
I will investigate Monsanto though. At this still early stage of our civilizational collapse there are probably still irrational acts that humanity can do that will kick the can down the road a bit further and will make a profit for some, including temporarily increasing crop yields beyond sustainable land carrying capacity. Monsanto's business in a nutshell.
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woodburner



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PostPosted: Sun Mar 25, 2018 8:52 am    Post subject: Reply with quote

BritDownUnder, I did not suggest 70mph was a more accurate speed for a raindrop, I said it was uncomfortable sticking your hand out of the window at 70mph.

speed of raindrops

This gives a rough speed for a drop of light rain around 5m/s or about 12mph.

Power output is therefore around 0.3Wh for the year.

“Gimmick” doesn’t even come close.
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Little John



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PostPosted: Sun Mar 25, 2018 12:44 pm    Post subject: Reply with quote

If I remember my physics correctly, air resistance rises the smaller the object. The reason being, the ratio of surface area to volume rises the smaller the object. and surface area is what generate air resistance.

Eg.

----------------------------------------------------------

A cube of 10cm*10cm*10cm

Surface area = 600 square centimetres

Volume = 1,000 cubic centimetres

Ratio = 3:5

---------------------------------------------------------

A cube of 5cm*5cm*5cm

Surface area = 150 square centimetres

Volume = 125 cubic centimetres

Ratio = 6:5

--------------------------------------------------------

The air resistance of a raindrop, relative to its volume, will be massive which, in turn, will mean the time it would take to reach terminal velocity will be huge. Meaning, in practice, by the time it hits the ground, it will be nowhere near terminal velocity.

And none of the above takes into account things like wind, which could reduce its velocity still further.
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vtsnowedin



Joined: 07 Jan 2011
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PostPosted: Sun Mar 25, 2018 1:05 pm    Post subject: Reply with quote

Little John wrote:
If I remember my physics correctly, air resistance rises the smaller the object. The reason being, the ratio of surface area to volume rises the smaller the object. and surface area is what generate air resistance.

Eg.

----------------------------------------------------------

A cube of 10cm*10cm*10cm

Surface area = 600 square centimetres

Volume = 1,000 cubic centimetres

Ratio = 3:5

---------------------------------------------------------

A cube of 5cm*5cm*5cm

Surface area = 150 square centimetres

Volume = 125 cubic centimetres

Ratio = 6:5

--------------------------------------------------------

The air resistance of a raindrop, relative to its volume, will be massive which, in turn, will mean the time it would take to reach terminal velocity will be huge. Meaning, in practice, by the time it hits the ground, it will be nowhere near terminal velocity.

And none of the above takes into account things like wind, which could reduce its velocity still further.
Only the area of the face moving forward or down in this case counts against air resistance. That is why bullets are pointed and long. A water droplet gets it's tear drop shape from air resistance pulling water molecules from the edges of the drop back where they form a tapered tail in the resistance shadow of the droplet.
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adam2
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PostPosted: Sun Mar 25, 2018 1:10 pm    Post subject: Reply with quote

According to Wikipedia, rain drops fall at speeds from about 7MPH up to about 20MPH, depending on size. Nothing like the 125MPH suggested earlier.

Anyone who has used a motorcycle, open top car, or vintage open cockpit aeroplane will confirm that rain drops striking the face at say 60MPH are most unpleasant and might be dangerous, goggles or helmets are often used as protection. No such precautions are needed against naturally falling rain.

I think that the whole idea is nonsense.
At the very most, the extra power produced would be a tiny fraction of the PV production. Making the PV array just 1% bigger would make more sense.
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clv101
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PostPosted: Sun Mar 25, 2018 1:55 pm    Post subject: Reply with quote

vtsnowedin wrote:
Only the area of the face moving forward or down in this case counts against air resistance. That is why bullets are pointed and long. A water droplet gets it's tear drop shape from air resistance pulling water molecules from the edges of the drop back where they form a tapered tail in the resistance shadow of the droplet.

Rain drops aren't 'tear drop' shaped. More burger buns, wider than they are tall. And the bigger the drop the more exaggerated this ratio become. This feature is used by dual-polarized weather radar for classification where they compare the reflection on the horizontal and vertical axis.
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woodburner



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PostPosted: Sun Mar 25, 2018 2:49 pm    Post subject: Reply with quote

Little John wrote:
If I remember my physics correctly, air resistance rises the smaller the object.

<snip>

The air resistance of a raindrop, relative to its volume, will be massive which, in turn, will mean the time it would take to reach terminal velocity will be huge. Meaning, in practice, by the time it hits the ground, it will be nowhere near terminal velocity.

And none of the above takes into account things like wind, which could reduce its velocity still further.


Raindrops reach their terminal velocity quickly. Once the resistance force reaches the force due to gravity and its mass, that’s it, terminal velocity.
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kenneal - lagger
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PostPosted: Sun Mar 25, 2018 4:48 pm    Post subject: Reply with quote

All very interesting but according to the article the mechanism for the collection of energy is -
Quote:
as it rolls down (the panel), the friction creates a static charge.


so it's the collection of electrical energy in addition to that from the sun.

I have no idea how this would work but if any one can enlighten me I would be grateful.
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