Most cities probably often end up wasting energy without even knowing it. Water flows downhill through large pipes under heavy pressure. Before it finally reaches your faucet, the pressure has to drop. In most cases, valves will simply release the excess pressure. However, Portland, Oregon, found a way to use it instead. According to a project case study published by Lucid Energy, the company that built the system, the Portland Water Bureau installed four 42-inch turbines in a drinking water pipe. By January 2015, they were producing electricity while water flowed to the homes all the time, just as it did before.
A pipe that was already working hard
Water providers install pressure-reducing valves (PRVs) at several points throughout the water distribution network. The valves are meant to reduce pressure to prevent damage to smaller pipes downstream. However, in the process, energy is wasted, which can actually be utilized. Portland installed its turbines just upstream of one such PRV located below Powell Butte Reservoir of the city. The installation let the system do double duty: harvesting energy that the valve would otherwise have wasted, while also easing the pressure load on the valve itself and extending its working life. The turbines are NSF/ANSI Standard 61 certified, which means that there were no effects on water quality and distribution.
Four turbines, no slowdown
Each turbine resembles a large metal ball rather than a normal propeller. It is made of stainless steel and composite material and has blades inside. The case study showed that the four units were spaced at an average of four pipe widths along the pipeline. Together, they pull some 20 psi of pressure from the water flowing through. That is the pressure that the old valve used to waste. Portland didn’t have to build anything new outside the pipe because the turbines sit inside the existing line. The pipe still performs its original task. Now it just has a second job.
