Direct Mechanical Hydropower

In most “developed” countries, electrical power is relatively cheap, widely available, of high capacity, and reliable. This is not the case in many other parts of the world – where low power, expensive and unreliable supplies are the norm.

I see some people here have talked about using gasoline engines, or even human pedal-power, to get around this problem. However, in many countries thare has been a very long history of using small scale water power for tasks such as grinding corn. The power requirement of a small mill is probably of the same order of magnitude as that required by the Precious Plastic shredder.

Read this aricle about the advantages of using direct hydropower. Maybe it could be an alternative source of mechanical shredding power where you live.

Back to Basics: Direct Hydropower



Of course Google has a dedicated patent search engine…

Should have known…


Well, I guess I found the Haystack.

Now to find the pointy stuff…


Any tips on where to best ‘patent mine’?

The Eurpean Patent Office Espacenet search facility is still pretty good. And they also have a beta version of a new search interface available, which should eventually replace the old one.

Each of the various national patent office websites seem to have their own search facility too.

And, of course, there is always Google Patents – which even seems to search Russian stuff.

@frogfall thank you for running the numbers to confirm what many have suspected……

Eindhoven just doesn’t get enough rain

if it is an exturder i think my first one i used 24 watts. at 1 inch diameter .5″ radius and 19 rpm. so like 16 Newtons or like 3.6 lbs.

Me personally i would not use the calculation of power as a calculation end. I would look at force. 5.46 tonnes is plenty of Weight aka Force to shredd plasic. you can shredd plastic with a 1/4 inch blade with like 180lb depending on the moment arm you use to turn shredder (3 feet). This all depends if you are talking about powering a shredder or a extruder. the shredder powered by roof water would be very interesting.

I have not seen this machine, but it indeed looks like something I might build 🙂

Although I would use some fitness device for the pump action and I would invert it to 12/24V

Stay in shape AND power the health food machines 🙂

(a sprouter only uses about 10W, 0W if you gravity feed the sprinklers)


These kind of machines are also great educational tools in these ‘plug and play’ times. Physics and Chemistry have almost become synonymous to ‘magic’…


Any tips on where to best ‘patent mine’?






Have you seen this Human Powerplant project? It was touring around the Netherlands in 2017.
Some of this looks more like an art project than an engineering one. Storing pumped energy by compressing air can be a bit less efficient than using gravity, and small electrical dynamos are notoriously inefficient, but it is still interesting.

As you say, it depends what you want to use the energy for.

And no, I’ve not dug through the patents on this subject (yet) – although I’ve done a lot of patent searching in the past (some of it was part of my job).

Exactly, or the are abandoned because they don’t fit the specific purpose.


Like here (for me).

Okay, using roof-rainwater for energy may not make much sense, but there’s always art ( like Strandbeest does with windpower) or a way to power a slow flowing Duckweed greywater filtration system for a 2 meter sprouting tower linked to a garden irrigation system (first thing that springs to mind, there might be other applications 🙂 )
I especially like the bike2pump idea to store energy in gravity.


Did you happen to already do the ‘Bureaucratic Exploring’ in the Patent caves?

Might also be of interest to the PP-community, though a seperate database might be needed for all the information (not a problem to create one).

Yeah, pumping five and a half tonnes of water up 10m by pedalling for an hour does sound excessive. I guess the idea is just counter-intuitive – which is why it is aways important to do the calculations.

Pulling a vacuum in a ground level “discharge tank” would add a bit to the potential energy of the system, but would add complexity.

Unfortunately, a lot of “energy harvesting” proposals seem to result in designs for equipment that would take far more energy to build and maintain than they would ever gather in “ambient energy”.  But I don’t know which side of the equation a “roof hydro” system would fall without more details of the exact system.

Interestingly, a typical problem with a lot of “innovation” is that ideas often get abandoned before anyone actually proves whether they would work or not.  So the same speculative ideas get re-invented again and again.  The patent records are full of proposals for systems that wouldn’t work in practice – but have been accepted by the examiners. And because the ideas already exist on paper, it discourages anyone else to “go the extra mile” to see if the device would work, becuase they couldn’t then get a monopoly on it.

@frogfall, the calculations are correct, it’s just that I have trouble getting my head around the fact that I theoretically should be able to ‘pump’ 5.46 tonnes of water to a hight of 10 meters (well okay, let’s say 9.8 meters) by riding my bike for an hour 🙂


I know the Netherlands ain’t El Hierro, but using water to store energy against gravity (okay, rain may just be a drop in the ocean) should be interesting everywhere, even in the ‘flat(her)lands’.

Or (queue music) “If I can make it here, we can make it everywhere”!


If I used my bike to create a vacuum/suction to pump water (using air pressure) to my (okay, 8m) roof, would this result in more than 149 Watt-Hours of energy?


Maybe we are getting off topic.

You’re original arguments obliterate these little thoughts, but I think of them as science fair projects: Small scale PoC’s can lead to large scale implementations (like on El Hierro).

If you want to re-check my numbers, you are welcome.  Engineering calculations have been a large part of my profession for 40 years  – but errors can always creep in 😉

If you compare the sitation to a hilly region, like the one where I live, then (historically) hydropower was very common.  Water-powered textile mills were built all along the local valley – as this account, from 1841, of only a couple of the local neighborhoods shows.

In the production of these articles a very considerable power from water and steam is employed — there being in motion, in the two townships of Golcar and Longwood, twelve water wheels, of the united power of one hundred and seventy horses, and three steam engines, equal to the exertion of fifty-seven horses.

That is an average of 14 horsepower (10.5 kW) per wheel – and each one was expected to power a small factory.  The steam engines were 1.3x as powerful, and gradually steam largely displaced water power in the area.

Interestingly, a (now derelict) mill near me (mentioned in this thread) installed a water turbine in 1920 – utilising a larger vertical fall of the river Colne than had previously been possible for thier old waterwheel. There is a recent photograph below (taken by some unrban explorers).  The turbine produced 85 horsepower  (63kW) which was a useful amount of power – but when you consider that it is about the same as available from a typical small (1.4 litre), normally aspirated, petrol car engine – then you can see why the relative capital cost of the earthworks, ducting, and turbine is now seen as excessive.  However, if fossil fuel prices rise considerably, or people actually decide to stop burning coal/oil/gas to prevent a global catastophe, then the relative economics would certainly change.

But please, don’t give up your dream of using the power from rainwater captured by roofs.  As you say, @donald , there can be applications for micro power sources – and using static pressure from the head of water, for actuation, is always a possibility.

Multiplied by 7 million houses x 12 months 😉


Not gonna redo the numbers (they seem a bit off), but yes, not a lot of energy, but enough to trigger sensors or maybe some mechanical filtration action (opening/closing valves etc.) or plain and simple ‘water management’ as when it rains, it pours (we have had a couple days these last years we got 70mm in a quarter of an hour(!) and more are expected).

Not giving up on the dream just yet 😉







Let’s add a few numbers to the “rooftop rainpower” idea… 😉

If we assume a building that is 10m wide by 10m deep by 10m high, then the roof rain collecting area is 100m2.
The total average rainfall for Eindhoven for the month of May is 54.6 mm per square metre, or 54.6 litres per square metre.
Assuming all of the rain is capured and stored at roof height, then there is 5.46 tonnes of water up there (54.6kg x 100 / 1000) by the end of the month.
This has a potential energy of 535.6 kiloJoules (5.46t x 10m x 9.81m/s2), which sounds a lot. However 1kJ only equals 0.0002778 kWh, so the maximum potential energy available (assuming an impossible 100% conversion efficiency) is 0.1488 kWh, or appoximately 149 Watt-Hours.
This is the same energy as is available from an adult human being pedalling a bicycle for one hour.

I guess this is why the Netherlands is famous for its windmills, and not its watermills 😉

As it rains a lot in the Netherlands (and England 😉 ), me and a friend have often wondered how to harness the power of gravity, as the water flows down from the roof to the ground anyway, no matter how many stops it makes along the way.


We might not have mountains, but dam(n) do we have a lot of liters (=kilos) of water coming down from the sky…

You might almost say (rain)water is our ‘oil’.


Using mechanics to filter the water for in-house use would be the first thing that comes to mind, but whatever other uses could there be for an ‘only happy when it rains’ gravity fed system?



I prefer thermal-solar power, the most efficient form of power conversion to either electrical or mechanical.