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RAIN POWER (cont.)

Posted on 2025/04/23 by secret santa

“A system that creates electricity from rain could one day be added to rooftops”

CHARGE SEPARATION
https://newscientist.com/rain-clean-way-of-generating-electricity/
Rain could be a clean way of generating lots of electricity
by Chris Simms / 16 April 2025

“Water droplets falling through a tube have generated enough electricity to power 12 LED lights. Such an approach could one day be used in roof-based systems to harvest lots of clean power from rain. “Rain falls on Earth every day. All the energy is wasted due to the lack of a system to harvest rain energy,” says Siowling Soh at the National University of Singapore. Normally, when we generate electricity from water, we use the movement of lots of it to drive a turbine in a river, the sea or even in drinking water pipes. But water flowing over an electrically conductive surface can generate its own electrical charge through a process called charge separation.

This is driven by positively charged protons of the water molecules staying in the liquid and negatively charged electrons being donated to the surface, much as you can generate static electricity by rubbing a balloon on your hair. The phenomenon is usually an inefficient way of generating electricity because the electric charge is created only on the surface the water touches, and if you use micro or nanoscale channels to increase the surface area, you end up requiring more energy to pump the water into them than you get back out. Now, Soh and his colleagues have created a simple set-up that relies on gravity to move water down a vertical tube that is 32 centimetres tall with an inner diameter of 2 millimetres. Water flows out of the bottom of a container via a horizontal, stainless steel needle, then falls towards the tube below. As the rain-like water droplets collide at the top of the tube, they capture pockets of air, creating what is called a plug flow as they fall. This disjointed flow seems to help the electrical charges of the water molecules separate as they travel down the tube.

Wires at the top and bottom of the tube then harvest the generated electricity. In an experiment, one tube produced 440 microwatts. When the researchers used four tubes at once, they could power 12 LEDs for 20 seconds. “We can, for the first time, harvest the energy of rain, or other natural sources such as rivers or waterfalls, via charge separation at the solid-liquid interface,” says Soh. The amount of electricity generated might not seem particularly impressive, but Soh says the set-up converted more than 10 per cent of the energy of the water falling through the tubes into electricity, which is five orders of magnitude more electricity than obtained from water flowing through the tubes in a continuous stream. “Rain falls from a few kilometres up in the sky to earth, so there is a lot of room in three-dimensional space to harvest rain energy,” he says. This suggests that the system could be used to generate electricity from rain, perhaps on rooftops. “If it could be developed in a way that could be useful on a house-by-house basis, that could be a really useful thing,” says Shannon Ames at the Low Impact Hydropower Institute in Boston.”

Journal reference: ACS Central Science DOI : 10.1021/acscentsci.4c02110

“A miniature hydroelectric turbine that can generate electricity from water pipes”

LOW IMPACT HYDROPOWER
https://newscientist.com/microturbines-electricity-drinking-water-pipes/
Microturbines can generate electricity from drinking water pipes
by James Dinneen / 10 January 2024

“The excess pressure in water pipes can be used to spin miniature hydroelectric turbines, providing an underutilised source of clean energy. Some envision a distributed network of small turbines serving as a form of reliable storage to back up wind and solar power. “I think it is a very under-tapped resource,” says Shannon Ames at the Low Impact Hydropower Institute, an environmental non-profit based in Massachusetts. “The infrastructure is there; adding a turbine into the infrastructure makes a lot of sense.” This type of “in-conduit” hydropower already supplies around 530 megawatts of generation capacity in the US, according to a 2022 study by researchers at Oak Ridge National Laboratory in Tennessee.

If such systems were installed at all potential sites in the country, the study estimated this could provide at least 1.41 gigawatts of additional capacity – equivalent to around 450 onshore wind turbines – without requiring any large new infrastructure to be built. “Billions of miles of pressurised pipelines exist in the world,” says Gregg Semler at InPipe Energy, an Oregon-based company that has installed three such systems, including one that powers floodlights in a baseball stadium outside of Portland.

The company’s latest installation to a pipe carrying drinking water to people in the East Bay Municipal Utilities District (EBMUD) in California started generating power in November. The EBMUD system is expected to generate 130,000 kilowatt-hours of electricity per year, which will be used to power nearby water pumps. Any excess power will be sent to the grid, helping the utility move towards its target of carbon neutrality by 2030, says Christopher Tritto at EBMUD. The project is predicted to reduce the utility’s carbon dioxide emissions by about 6 tonnes each year.

Semler says a similar system will be installed in Aurora, Colorado, in April, and that InPipe is in discussions with the New York City government about ways to generate electricity from the nearly 4 billion litres of water that flow into the metropolis every day. Eventually, he envisions water utilities with networks of small systems working in concert as a form of hydropower storage backing up intermittent renewables. “If there was no sun, or there was no wind, water utilities could put more water through the pipes to produce more energy,” he says.

InPipe’s system serves the same function as a regular pressure valve, which dissipates the excess water pressure generated by gravity and pumps. Instead of simply releasing this pressure, however, InPipe’s technology uses it to generate electricity. In parallel to an existing valve, the system diverts piped water through a bypass, where it spins a hydroelectric turbine before returning it to the pipe. “We don’t change the flow of the water, but we take out pressure,” says Semler.

This is different from the approach taken by Semler’s previous company, Lucid Energy, which aimed to generate power by placing turbines directly within existing pipes. The company – which has since shuttered – installed one such system in Portland that is still generating power. But Semler says convincing water utilities to cut open their pipes and abandon existing pressure valves to generate electricity proved difficult.

Other hydropower companies, such as NLine Energy and Canyon Hydro, have developed similar in-conduit hydropower systems, and the idea has been around for at least two decades. But only a hundred or so have been installed, says Frank Zammataro at Rentricity, a New York City-based company that has installed more than 30 systems across the US. However, Zammataro thinks such systems could soon be adopted more widely. He says the industry is at an “inflection point” thanks to a new emphasis on cutting emissions, support for upgrading infrastructure and growing track record of in-conduit systems. “We’re not going to break your pipes,” he says.”

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