H F Posted September 10, 2019 Share Posted September 10, 2019 We have a pond (about a quarter of an acre) that gets fed from numerous small streams and subterraneous sources, and the water feed is decent from autumn to spring especially when we get lots of rain. At the bottom of the pond, there is an overflow that has been concreted and this allow excess water to spill over into another stream that takes the water down the valley. This overflow gushes from autumn to spring. Based on this, I was wondering whether hydroelectric would be an option - it would obviously be on a very small (micro) scale, but was wondering whether we could generate 1-2kW (24/7) to help the ASHP over the winter months when the days are shorter and the solar PV isn't operating at maximum levels. Was wondering what an installation like this would entail, and would be need inverters and other expensive kit? Link to comment Share on other sites More sharing options...
SteamyTea Posted September 10, 2019 Share Posted September 10, 2019 (edited) You need to look at pico hydro systems. If you want to help run your ASHP, then you will need an approved inverter, and notify your DNO about the new installation. Be easier to run it direct into a resistance heater though. The bigger you can get the drop from the pond to the generator the better. Let gravity do the work. May be worth you getting this book. https://www.amazon.co.uk/Renewable-Energy-Power-Sustainable-Future/dp/0199261784 Edited September 10, 2019 by SteamyTea Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 10, 2019 Share Posted September 10, 2019 There's a local group who have done just that. A very welcoming bunch they are too: regularly hold Open Days. Right next to the M6, Lancaster North. Worth a trip ? Link to comment Share on other sites More sharing options...
ProDave Posted September 10, 2019 Share Posted September 10, 2019 The key thing is how much fall can you get? You need to capture water (in the pond or one of the streams feeding it) and pipe that to somewhere lower where it is released through a turbine. So the key issue is how much fall can you achieve on your own land? We have a burn through the garden but the fall is too small to do anything useful, I think I calculated I could generate somewhere between 50 and 100W. Something I might play with as a bit of fun some time but not as a sensible viable energy source. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 10, 2019 Share Posted September 10, 2019 Power = Head x Flow x Gravity Link to comment Share on other sites More sharing options...
Jeremy Harris Posted September 10, 2019 Share Posted September 10, 2019 1 hour ago, Home Farm said: We have a pond (about a quarter of an acre) that gets fed from numerous small streams and subterraneous sources, and the water feed is decent from autumn to spring especially when we get lots of rain. At the bottom of the pond, there is an overflow that has been concreted and this allow excess water to spill over into another stream that takes the water down the valley. This overflow gushes from autumn to spring. Based on this, I was wondering whether hydroelectric would be an option - it would obviously be on a very small (micro) scale, but was wondering whether we could generate 1-2kW (24/7) to help the ASHP over the winter months when the days are shorter and the solar PV isn't operating at maximum levels. Was wondering what an installation like this would entail, and would be need inverters and other expensive kit? As @SteamyTea has mentioned, the potential power is easy to work out. To that basic equation you need to factor in the Betz limit and efficiency, so in reality you would be lucky to get more than about 30% to 40% of the potential power from the water flow for a practical low head turbine, I think. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 10, 2019 Share Posted September 10, 2019 (edited) Good old wikipedia has loads on turbines. https://en.wikipedia.org/wiki/Water_turbine 5 minutes ago, JSHarris said: you need to factor in the Betz limit Don't think this applies as, they just refer to it as turbine efficiency. Think it is do do with the uncompressability of water. Though agree that with small water turbines, the efficiency is rubbish. Edited September 10, 2019 by SteamyTea Link to comment Share on other sites More sharing options...
joe90 Posted September 10, 2019 Share Posted September 10, 2019 I remember Dick Strawbridge years ago built a water wheel with gearbox and old alternator to generate 12v for his lighting, was a fun project. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 10, 2019 Share Posted September 10, 2019 (edited) Some people modify central heating water pumps. Never seen one being used, just read about them. But if you have an old washing machine: Edited September 10, 2019 by SteamyTea Link to comment Share on other sites More sharing options...
Jeremy Harris Posted September 10, 2019 Share Posted September 10, 2019 11 minutes ago, SteamyTea said: Good old wikipedia has loads on turbines. https://en.wikipedia.org/wiki/Water_turbine Don't think this applies as, they just refer to it as turbine efficiency. Think it is do do with the uncompressability of water. Though agree that with small water turbines, the efficiency is rubbish. Air is also incompressible at sub-sonic velocities, so both air and water behave in a similar way as far as turbines are concerned (apart from the differences in density and viscosity). The logical test is to consider the limiting case for a turbine that extracts 100% of the potential energy from the flow. The implication of this is that there is zero outflow from the turbine, as the turbine would be absorbing all the flow without it ending up anywhere. Clearly this cannot happen (you can't just magic away a mass of anything, at least not under practical, earth-condition, conditions), so therefore efficiency can never reach 100% and there must be some finite limit. Betz defined this for air (not water) but the same principle of their being a finite limit applies to any machine operating in a fluid flow. Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 40 minutes ago, AnonymousBosch said: There's a local group who have done just that. A very welcoming bunch they are too: regularly hold Open Days. Right next to the M6, Lancaster North. Worth a trip ? Will look into this - thanks for the pointer - could be worth a trip for sure. 1 Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 44 minutes ago, SteamyTea said: You need to look at pico hydro systems. If you want to help run your ASHP, then you will need an approved inverter, and notify your DNO about the new installation. No problems with informing our DNO - we've had to do that for our solar PV and ASHP. Would we still need to inform them if we're producing tiny amounts of power? I can't imagine us producing vast amounts of electricity. I may actually contact the guys that installed out ASHP to get a quote and see how much the kit will cost. Will also check out the book. Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 37 minutes ago, ProDave said: We have a burn through the garden but the fall is too small to do anything useful, The drop from our pond "exit" to the stream below will be between .50-.75m - so not huge. I will go down to the pond later and do measurements and then get around the calculations. Thanks for all the assistance and pointers. As always, it's massively appreciated. Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 On a semi-related note, are there RHI grants for hydro? Link to comment Share on other sites More sharing options...
ProDave Posted September 10, 2019 Share Posted September 10, 2019 2 minutes ago, Home Farm said: No problems with informing our DNO - we've had to do that for our solar PV and ASHP. Would we still need to inform them if we're producing tiny amounts of power? I can't imagine us producing vast amounts of electricity. I may actually contact the guys that installed out ASHP to get a quote and see how much the kit will cost. Will also check out the book. The trouble is, the DNO will just sum together all your generation power and assume at some point it is possible for all that to be exported. And it the total exceeds 16A per phase, you will need prior permission to connect it, and may need a network upgrade to do so. Even if, in the real world, very little of it actually gets exported. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted September 10, 2019 Share Posted September 10, 2019 Worth looking at Paul Camelli's blog: https://lifeattheendoftheroad.wordpress.com He has a small hydro system, that generates a few hundred watts. He laid a few hundred metres of pipe from a small loch down to his turbine house and spent a fair bit of time getting the system running OK, but as he's off grid it's a very useful way to help keep his batteries topped up. Link to comment Share on other sites More sharing options...
ProDave Posted September 10, 2019 Share Posted September 10, 2019 2 minutes ago, Home Farm said: The drop from our pond "exit" to the stream below will be between .50-.75m - so not huge. I will go down to the pond later and do measurements and then get around the calculations. Thanks for all the assistance and pointers. As always, it's massively appreciated. That is the sort of drop I would be able to achieve. At that low drop you are probably looking at an overshot water wheel rather than a turbine. Design it right and it could be a nice garden ornament as well. Because it's hard to capture our gently falling burn I will probably at some point experiment with an undershot wheel. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 10, 2019 Share Posted September 10, 2019 4 minutes ago, Home Farm said: Will look into this - thanks for the pointer - could be worth a trip for sure. The Queen has a turbine at Windsor. https://www.bbc.co.uk/news/uk-england-berkshire-16276225 Not sure how far it is up to that hippy housing development, but lets us say it is 600 miles round trip. If your car does 50 MPG, then that is 12 gallons of fuel, 55 lt. A litre of gasoline has around 9.5 kWh of energy, so that will be around 520 kWh. To offset that with electrical energy from a turbine, it would have to produce 60W of power for a year. After that, your are quids in. 1 Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 8 minutes ago, JSHarris said: Worth looking at Paul Camelli's blog: https://lifeattheendoftheroad.wordpress.com He has a small hydro system, that generates a few hundred watts. He laid a few hundred metres of pipe from a small loch down to his turbine house and spent a fair bit of time getting the system running OK, but as he's off grid it's a very useful way to help keep his batteries topped up. Brill. Will look at his blog tonight, and I may reach put to him too. Link to comment Share on other sites More sharing options...
H F Posted September 10, 2019 Author Share Posted September 10, 2019 9 minutes ago, ProDave said: Because it's hard to capture our gently falling burn I will probably at some point experiment with an undershot wheel. Will look into undershot wheels this afternoon. Link to comment Share on other sites More sharing options...
Ed Davies Posted September 10, 2019 Share Posted September 10, 2019 1 hour ago, JSHarris said: you need to factor in the Betz limit Not for a turbine operating in duct. If the Betz limit applied pumped storage systems wouldn't be able to achieve 80% round-trip efficiency. https://energymag.net/round-trip-efficiency/ Link to comment Share on other sites More sharing options...
Jeremy Harris Posted September 10, 2019 Share Posted September 10, 2019 19 minutes ago, Ed Davies said: Not for a turbine operating in duct. If the Betz limit applied pumped storage systems wouldn't be able to achieve 80% round-trip efficiency. https://energymag.net/round-trip-efficiency/ Yes, I shouldn't have suggested Betz, as Betz set the limit specifically for air, but there is equally a limit for any other incompressible fluid flowing through a turbine. Has to be, as the limiting case for 100% efficiency implies zero outflow, and that clearly cannot ever be achieved with a real system. The fact that there will always be energy in the outflow water means that mechanical efficiency can never be 100%, without accounting for electrical efficiency. Any home-brew micro hydro system is likely to be significantly less efficient than a large scale system, too, partly because the losses don't scale linearly with size, I suspect. Link to comment Share on other sites More sharing options...
jamieled Posted September 10, 2019 Share Posted September 10, 2019 2 hours ago, Home Farm said: On a semi-related note, are there RHI grants for hydro? The equivalent for hydro was the feed in tariff. However, it doesn't exist now. Have a look at the powerspouts as they are relatively straightforward plug and play type systems. I am thinking of sticking one on our burn. They do low head versions ( a pelton will be fine for us as we have a big drop). However, the lower the drop the more flow most turbines need. Even if they're not suitable for your situation you should be able to pick up a lot of useful info from the website. Having worked on a few similar schemes I'd say don't underestimate the work involved in all the other bits such as getting a good intake and pipeline. Link to comment Share on other sites More sharing options...
joe90 Posted September 10, 2019 Share Posted September 10, 2019 On the subject of efficiency (but hoping not to divert this thread), with Dick Strawbridge and his over shot wheel the inefficiency came mainly from the gearbox , something like 100:1, lots of gears and an inefficiency in every one. I thought at the time that a chain drive would be a lot more efficient?. I would love to have a water source that I could generate from . Link to comment Share on other sites More sharing options...
A_L Posted September 10, 2019 Share Posted September 10, 2019 The theoretical output in Watts is mass per second (in kg, effectively litres/sec for water) x gravity (9.81m/s2) x head (in metres). The electrical efficiency of hydro at the kW scale is about 50% for good turbines. So with a 0.5m head you would need around 400litres/sec of flow for a 1kW output. Link to comment Share on other sites More sharing options...
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