Interesting Approach to Hydrokinetics
A reader asked for my comment on this technology: turbines installed inside of municipal water pipes that converts some of that hydrokinetic energy into electricity.
First, let’s start with the most obvious: this doesn’t apply to water that is flowing because it was pushed along by a pump. This device slows down the velocity of the water, and would therefore cause the pump to work harder to compensate for it. So we need to confine ourselves to gravity-fed pipes.
How much available energy is there in such pipes in the typical municipal system? I don’t know, but I doubt it’s worth the (extreme) capital costs of cutting open and retrofitting large numbers of pipes. Even omitting the O&M (operations and maintenance) costs of the system, I can’t imagine that the LCOE (levelized cost of energy) of such an approach would be at all attractive.
This, IMO, comes under the heading: “not theoretically impossible, but not too practical.”
Maybe Anchorage Alaska could considered dear this since most if not all of their municipal water supply comes from glacial melt water presumably sourced at a much higher altitude than the near sea level of most of the city. I agree that maintenance could swallow much of the savings in electrical generation cost. Then the E.P.A. Studies and lawsuits by enterprising lawyers would give any city government pause before considering this option.
At one time, a similar approach was used with gas. To reduce the pressure of gas they ran it through little turbines which produced somewhat useful power. I don’t remember where I read about that, but the article was about the opening of a new store in the late 19th century. I seem to recall that the turbines were used for pencil sharpeners, winding string, etc. Not very useful, but interesting.
At one time, elevators were powered by water pressure from city water systems. Instead of using hydraulic cylinders powered by oil pressurized by electric pumps, the lifting cylinders used water pressure from the water mains. In Minneapolis, the Soo Line Railroad building used elevators powered by water pressure. Apparently they were common through the 1940s but there couldn’t be many left. Here is an interesting article about water powered elevators:
http://www.nydailynews.com/archives/money/lifting-ride-water-powered-elevator-article-1.822421
So, city water pressure has been used for power in the past.
Hydro concepts like this are in common use the world over and have been for many decades.
They can also be very efficient systems as they tap into the one “free” force available for system design engineers to exploit “gravity” which when applied to flowing water provides for kinetic energy to be transformed; and in this case in point, motivate a turbine to generate usable electricity.
Although a simple to understand concept when initially laid out on the energy systems designers drawing board, like all things in practice, closer examination exposes the complications that then need to be overcome particularly when trying to exploit gravity efficiently and integrating this concept with a downstream pressurised pumped head system.
There are two categories of “pipe type” water flow systems:
[1] Pressurised full pipe systems which are characterised by a motor driven pump pressurising a water main, with customer take off points for normal consumer consumption. These systems are the standard ones that are used for distributing potable water in communities.
[2] Open head systems which we often see alongside rivers or streams and also known as “run of river” type systems. These use a single pipe running alongside a river [and fed from the river] for some distance to create sufficient head to motivate a turbine to produce electricity at the downstream point of efflux. These systems are only useful for exploiting potential energy and generating energy, not for distributing water.
Of the two categories described the best one for energy systems designers to work with is Open Head [2]. Only one source of energy input is used to motivate the turbine, water acted on by gravity.
This is the most efficient energy transformation scenario a system designer will ever encounter. If the right location can be found and accessed, the two key system components are provided by nature at zero cost; water plus gravity. It doesn’t get any better than that for designing with.
The Lucid system at Portland is most likely then an Open Head system [2] fed from an elevated reservoir or dam through a short Lucid Energy Pipe, which effectively emulates the “run of river” principle, and can be therefore very efficient, particularly if the discharge is “open” into an intermediate smaller reservoir for example, which might then feed a traditional pump pressurised water main.
The key efficiency metric for hydro power systems designers to be able to fully exploit water under gravity [kinetic energy] opportunities, is that the water discharge is not constrained and able to be exhausted to atmosphere [open pipe].
In the right topographical circumstances, the Lucid Energy Pipes like those in Portland can be a very efficient technology with excellent LCOE attributes and also easily become “semi intelligent” devices used for water quality sensing and evaluation, and real time feed-back/feed-forward control stations for chemical dosing pumps such as fluoride and chlorine etc.
We will be seeing more great innovation from Lucid in the future for sure.
Lawrence Coomber